Articles about shockwaves by CAVILUX customers

Shockwave

DLR, Germany

Authors: Klaus Hannemann, Jan Martinez Schramm, Sebastian Karl, Stuart J. Laurence
Title: “Enhancement of free flight force measurement technique for scramjet engine shock tunnel testing”
Published: 21st AIAA International Space Planes and Hypersonics Technologies Conference, International Space Planes and Hypersonic Systems and Technologies Conferences, (AIAA 2017-2235)
Application: Shockwave
Product: CAVILUX Smart

Authors: Stuart J. Laurence, Jan Martinez Schramm, Sebastian Karl and Klaus Hannemann
Title: “An experimental investigation of steady and unsteady combustion phenomena in the hyshot ii combustor”
Published: 17th AIAA International Space Planes and Hypersonic Systems and Technologies Conference 11 – 14 April 2011
Application: Shockwaves
Product: CAVILUX Smart

Authors: Stuart J. Laurence, Jan Martinez Schramm and Klaus Hannemann
Title: “Force and moment measurements on a free-flying capsule model in a high-enthalpy shock tunnel”
Published: 28th Aerodynamic Measurement Technology,Ground Testing, and Flight Testing Conference 25 – 28 June 2012
Application: Shockwaves
Product: CAVILUX Smart

Authors: Jan Martinez Schramm
Title: “Method of optical tracking to determine forces on free flying models in hypersonic flow”
Published: 10th Pacific Symposium on Flow Visualization and Image Processing Naples, Italy, 15-18 June, 2015
Application: Shockwaves
Product: CAVILUX Smart

Japan Aerospace Exploration Agency, Japan

Authors: H. Takayanagi, A. Lemal, S. Nomura and K. Fujita
Title: “Measurements of Carbon Dioxide Nonequilibrium Infrared Radiation in Shocked and Expanded Flows”
Published: Journal of Thermophysics and Heat Transfer, Volume 0, Issue 0
Application: Shockwave
Product: CAVILUX HF

Los Alamos National Laboratory, USA

Authors: M J Murphy and C E Johnson
Title: “Preliminary investigations of he performance characterization using swift”
Published: Journal of Physics: Conference Series 500 (2014) 142024
Application: Shockwaves
Product: SILUX

Military Unversity of Technology, Poland

Authors: Wojciech Napadáek
Title: “Laser percussive strengthening of the aluminum alloys”
Published: Journal of KONES Powertrain and Transport, Vol. 18, No. 1 2011
Application: Shockwaves
Product: CAVILUX HF

MIT – Massachusetts Institute of Technology, USA

Authors: D. Veysset, U. Gutierrez-Hernandez, L. Dresselhaus-Cooper, F. De Colle, S. Kooi, K. A. Nelson, P. A. Quinto-Su, T. Pezeril
Title: “Single-bubble and multi-bubble cavitation in water triggered by Laser-driven focusing shock waves”
Published: ARXIV
Application: Shockwave
Product: CAVILUX Smart

Nagoya University, Japan

Authors: Ducthuan Tran, Xie Chongfa, and Koichi Mori.
Title: “Experimental investigations of impulse generation and stabilization performance on spherical target irradiated by donut-mode beam”
Published: AIAA AVIATION Forum, (AIAA 2017-4160)
Application: Shockwave
Product: CAVILUX Smart

Authors: Ducthuan Tran, Xie Chongfa, and Koichi Mori
Title: “Experimental study of effect of ambient pressure to energy process of laser propulsion”
Published: AIAA AVIATION Forum, (AIAA 2017-4160)
Application: Shockwave
Product: CAVILUX Smart

Authors: Hoang Son Pham, Manabu Myokan, Takahiro Tamba, Akira Iwakawa, and Akihiro Sasoh.
Title: “Impacts of energy deposition on flow characteristics over an inlet”
Published: 47th AIAA Fluid Dynamics Conference, AIAA AVIATION Forum, (AIAA 2017-4305)
Application: Shockwave
Product: CAVILUX Smart

Authors: Hoang Son Pham, Tatsuro Shoda, Takahiro Tamba, Akira Iwakawa, and Akihiro Sasoh.
Title: “Impacts of laser energy deposition on flow instability over double-cone model”
Published: AIAA Journal, Vol. 55, No. 9 (2017), pp. 2992-3000.
Application: Shockwave
Product: CAVILUX Smart

Authors: Akira IWAKAWA, Tatsuro SHODA, Ryosuke MAJIMA, Son Hoang PHAM, Akihiro SASOH
Title: “Mach Number Effect on Supersonic Drag Reduction using Repetitive Laser Energy Depositions over a Blunt Body”
Published: TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, Nr. 60 (2017) 5 p. 303-311
Application: Shockwave
Product: CAVILUX Smart

Authors: Hoang Son Pham, Manabu Myokan, Takahiro Tamba, Akira Iwakawa and Akihiro Sasoh
Title: “Effects of Repetitive Laser Energy Deposition on Supersonic Duct Flows”
Published: AIAA Journal, Volume 56, Issue 2
Application: Shockwave
Product: CAVILUX Smart

Authors: DucThuan Tran, Akifumi Yogo, Hiroaki Nishimura, and Koichi Mori
Title: “Impulse and mass removal rate of aluminum target by nanosecond laser ablation in a wide range of ambient pressure”
Published: Journal of Applied Physics, Volume 122, Issue 23
Application: Shockwave
Product: CAVILUX Smart

Authors: Akira Iwakawa, Tatsuro Shoda, Hoang Son Pham, Takahiro Tamba and Akihiro Sasoh
Title: “Suppression of low-frequency shock oscillations over boundary layers by repetitive laser pulse energy deposition”
Published: AEROSPACE 2016, 3(2)
Application: Shockwaves
Product: CAVILUX Smart

Oxford University, UK

Authors: Phillip A. Anderson, M. R. Betney, H. W. Doyle, B. Tully, Y. Ventikos, N. A. Hawker, and Ronald A. Roy
Title: “Characterizing shock waves in hydrogel using high speed imaging and a fiber-optic probe hydrophone”
Published: Physics of Fluids, Volume 29, Issue 5, 10.1063/1.4982062
Application: Shockwaves
Product: CAVILUX Smart

Authors: MR Betney, PA Anderson, H Doyle, B Tully, NA Hawker, Y Ventikos
Title: “Numerical and experimental study of shock-driven cavity collapse”
Published: Journal of Physics: Conference Series 656 (2015)
Application: Shockwaves
Product: CAVILUX Smart

Saga University, Japan

Authors: Guang Zhang, Ik In Lee, Tokitada Hashimoto, Toshiaki Setoguchi, Heuy DongKima
Title: “Experimental studies on shock wave and particle dynamics in a needle-free drug delivery device”
Published: Journal of Drug Delivery Science and Technology
Volume 41, October 2017, Pages 390-400
Application: Shockwave
Product: CAVILUX HF

Stevens Institute of Technology, USA

Authors: Muhammad Mustafa, Matthew B. Hunt, Nick J. Parziale, Michael S. Smith, and Eric C. Marineau.
Title: “Two-dimensional krypton tagging velocimetry (ktv) investigation of shock wave/turbulent boundary-layer interaction”
Published: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2017-0025)
Application: Shockwave
Product: CAVILUX HF

Tohoku University, Japan

Authors: Shin Yoshizawa, Ryo Takagi, Shin-ichiro Umemura
Title: “Enhancement of high-intensity focused ultrasound heating by short-pulse generated cavitation”
Published: Applied Sciences 2017, 7(3), 288
Application: Shockwave
Product: CAVILUX Smart

Authors: Kai Suzuki, Ryosuke Iwasaki, Ryo Takagi, Shin Yoshizawa and Shin-ichiro Umemura
Title: “Simultaneous observation of cavitation bubbles generated in biological tissue by high-speed optical and acoustic imaging methods”
Published: Japanese Journal of Applied Physics, Volume 56, Number 7S1
Application: Shockwave
Product: CAVILUX Smart

Authors: Hiroki Imaeda, Mingyu Sun
Title: “Dynamic Characteristics of Underwater Objects after Shock Wave loading”
Published: 2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018-0579)
Application: Shockwave
Product: CAVILUX HF

Authors: Jun Yasuda, Takuya Miyashita, Shin Yoshizawa and Shin-ichiro Umemura
Title: “Effects of rose bengal on cavitation generation in gel phantom investigated using high-speed camera”
Published: 23 June 2014, The Japan Society of Applied Physics
Application: Shockwaves
Product: CAVILUX Smart

Tokyo University of Agriculture and Technology, Japan

Authors: Shota Yamamoto, Yoshiyuki Tagawa, Masaharu Kameda
Title: “The evolution of a shock wave pressure induced by a laser pulse in a liquid filled thin tube using the background-oriented schlieren technique”
Published: 17th International Symposium on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, 07-10 July, 2014
Application: Shockwaves
Product: CAVILUX Smart

Authors: Shota Yamamoto, Yoshiyuki Tagawa, Masaharu Kameda
Title: “Application of background-oriented schlieren (bos) technique to a laser-induced underwater shock wave”
Published: Experiments in Fluids, May 2015, 56:93
Application: Shockwaves
Product: CAVILUX Smart

Authors: Yoshiyuki Tagawa, Shota Yamamoto, Keisuke Hayasaka and Masaharu Kameda
Title: “On pressure impulse of a laser-induced underwater shock wave”
Published: Journal of Fluid Mechanics, Volume 808, Dec. 10th 2016, pp. 5 – 18
Application: Shockwaves
Product: CAVILUX Smart

Toyota Technological Institute – Department of Advanced Science and Technology, Japan

Authors: Taro Handa, Akira Urita
Title: “Experimental study of small supersonic circular jets actuated by a cavity”
Published: Experimental Thermal and Fluid Science, Volume 96, September 2018, Pages 419-429
Application: Shockwave
Product: CAVILUX Smart

University of Glasgow, UK

Authors: Kristoffer Johansen, Jae Hee Song, and Paul Prentice
Title: “Validity of the Keller-Miksis equation for ”non-stable” cavitation and the acoustic emissions generated”
Published: Researchgate
Application: Shockwave
Product: CAVILUX Smart

Authors: Kristoffer Johansen, Jae Hee Song, and Paul Prentice
Title: “Blind deconvolution of a hydrophone with a bubble-collapse shock wave”
Published: Researchgate
Application: Shockwave
Product: CAVILUX Smart

Authors: Kristoffer Johansen, Jae Hee Song, Paul Prentice
Title: “Performance characterisation of a passive cavitation detector optimised for subharmonic periodic shock waves from acoustic cavitation in MHz and sub-MHz ultrasound”
Published: Ultrasonics Sonochemistry Volume 43, May 2018, Pages 146-155
Application: Shockwave
Product: CAVILUX Smart

Authors: Phillip A. Anderson, Nicholas Hawker, Matthew Betney, Brett Tully, Yiannis Ventikos and Ronald A. Roy
Title: “Experimental characterisation of light emission during shock-driven cavity collapse”
Published: ICA 2013 Montral Proseedings, vol 19, 2013
Application: Shockwaves
Product: CAVILUX Smart

Authors: Jae Hee Song, Kristoffer Johansen, and Paul Prentice
Title: “Covert cavitation: spectral peak suppression in the acoustic emissions from spatially configured nucleations”
Published: The Journal of the Acoustical Society of America, Volume 141, Issue 3, 10.1121/1.4977236
Application: Shockwaves
Product: CAVILUX Smart

Authors: Kristoffer Johansen, Jae Hee Song, Keith Johnston, Paul Prentice
Title: “Deconvolution of acoustically detected bubble-collapse shock waves”
Published: Ultrasonics, Volume 73, January 2017, Pages 144-153
Application: Shockwaves
Product: CAVILUX Smart

Authors: Jae Hee Song, Kristoffer Johansen, and Paul Prentice
Title: “An analysis of the acoustic cavitation noise spectrum: the role of periodic shock waves”
Published: The Journal of the Acoustical Society of America 140, 2494 (2016)
Application: Shockwaves
Product: CAVILUX Smart

Authors: Kristoffer Johansen ; Jae Hee Song ; Paul Prentice
Title: “Characterising focused ultrasound via high speed shadowgraphic imaging at 10 million frames per second”
Published: 2016 IEEE International Ultrasonics Symposium (IUS), 18-21 Sept. 2016
Application: Shockwaves
Product: CAVILUX Smart

University of Maryland, College Park, USA

Authors: Richard E. Kennedy, Stuart J. Laurence, Michael S. Smith, and Eric C. Marineau
Title: “Hypersonic boundary-layer transition features from high-speed schlieren images”
Published: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2017-1683)
Application: Shockwave
Product: CAVILUX HF

Authors: S.J. Laurence, C.S. Butler, J. Martinez Schramm, K. Hannemann
Title: “Force and Moment Measurements on a Free-Flying Capsule in a Shock Tunnel”
Published: Journal of Spacecraft and Rockets, Ahead of Print : pp. 1-12
Application: Shockwave
Product: CAVILUX Smart

Authors: Jason R. Burr and Ken H. Yu
Title: “Detonation propagation in a linear channel with discrete injectors and side relief”
Published: 26th ICDERS July 30th – August 4th, 2017
Application: Shockwaves
Product: CAVILUX Smart

Authors: Camilo Aguilera, Amardip Ghosh, Kyung-Hoon Shin, Kenneth H. Yu
Title: “Dynamic pressure characterization of a dual-mode scramjet”
Published: 26th ICDERS July 30th – August 4th, 2017
Application: Shockwaves
Product: CAVILUX Smart

Authors: Joseph S. Jewell, Richard E. Kennedy, Stuart J. Laurence, and Roger L. Kimmel.
Title: “Transition on a Variable Bluntness 7-Degree Cone at High Reynolds Number”
Published: 018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018-1822)
Application: Shockwave
Product: CAVILUX HF

Authors: Jason R. Burr and Kenneth H. Yu.
Title: “Detonation Wave Propagation in Discretely Spaced Hydrocarbon Cross-Flow”
Published: AIAA SciTech Forum, (AIAA 2018-1420)
Application: Shockwave
Product: CAVILUX Smart

Authors: Richard E. Kennedy, Stuart J. Laurence, Michael S. Smith, and Eric C. Marineau
Title: “Visualization of the Second-Mode Instability on a Sharp Cone at Mach 14”
Published: 2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018-2083)
Application: Shockwave
Product: CAVILUX HF

University Paris Saclay, French

Authors: Sergey Stepanyan, Jun Hayashi, Sara Lovascio, Gabi D. Stancu, and Christophe O. Laux
Title: “Hydrodynamic effects induced by nanosecond sparks in air and air/fuel mixtures”
Published: 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2017-1581)
Application: Shockwave
Product: CAVILUX HF

University of Tokyo, Japan

Authors: Shinji Nakaya, Shingo Iseki, XiaoJing Gu, Yoshinari Kobayashi, Mitsuhiro Tsue
Title: “Flame kernel formation behaviors in close dual-point laser breakdown spark ignition for lean methane/air mixtures”
Published: Proceedings of the Combustion Institute, Volume 36, Issue 3, 2017, Pages 3441-3449
Application: Shockwave
Product: CAVILUX HF

 

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Articles about additive manufacturing by CAVILUX customers

Laser cladding

Dresden University of Technology, Germany

Authors: Johannes Trappa, Alexander M.Rubenchik, Gabe Guss, Manyalibo J.Matthews
Title: “In situ absorptivity measurements of metallic powders during laser powder-bed fusion additive manufacturing”
Published: Applied Materials Today, Volume 9, December 2017, Pages 341-349
Application: Additive Manufacturing
Product: CAVILUX HF

Lappeenranta University of Technology, Finland

Authors: Mehrnaz Modaresialam
Title: “Real-time monitoring of additive manufacturing
Published: Master Thesis, Lappeenranta University of Technology
Application: Additive Manufacturing
Product: CAVILUX HF

Lawrence Livermore National Laboratory, USA

Authors: Umberto Scipioni Bertoli, Gabe Guss, Sheldon Wu, Manyalibo J. Matthews, Julie M.Schoenung
Title: “In-situ characterization of laser-powder interaction and cooling rates through high-speed imaging of powder bed fusion additive manufacturing”
Published: Materials & Design, Volume 135, 5 December 2017, Pages 385-396
Application: Additive Manufacturing
Product: CAVILUX HF

Authors: M. J. Matthews
Title: “Physics of laser-assisted advanced manufacturing processes”
Published: Own publication
Application: Additive Manufacturing
Product: CAVILUX HF

Luleå University of Technology, Sweden

Authors: Jetro Pocorni, John Powell, Eckard Deichsel, Jan Frostevarg, Alexander F.H.Kaplan
Title: “Fibre laser cutting stainless steel: fluid dynamics and cut front morphology”
Published: Optics & Laser Technology, Volume 87, January 2017, Pages 87-93
Application: Additive Manufacturing
Product: CAVILUX HF

Authors: Ramiz S.M., Samarjy, Alexander F.H.Kaplan
Title: “Using laser cutting as a source of molten droplets for additive manufacturing: a new recycling technique”
Published: Materials & Design, Volume 125, 5 July 2017, Pages 76-84
Application: Additive Manufacturing
Product: CAVILUX HF

Stankin University, Russia

Authors: M. Doubenskaia, A. Domashenkov, I. Smurova
Title: “Study of the laser melting of pre-deposited intermetallic tial powder by comprehensive optical diagnostics”
Published: Surface and Coatings Technology, Volume 321, 15 July 2017, Pages 118-127
Application: Additive Manufacturing
Product: CAVILUX HF

University of Erlangen-Nuremberg, Germany

Authors: O. Hentschel, C. Scheitler, A. Fedorov
Title: “Experimental investigations of processing the high carbon cold-work tool steel 1.2358 by laser metal deposition for the additive manufacturing of cold forging tools”
Published: Journal of Laser Applications 29, 022307 (2017);
Application: Additive Manufacturing
Product: CAVILUX HF

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Measurements of hypersonic boundary-layer instabilities using a pulsed-laser schlieren technique

Author: Stuart Laurence, Department of Aerospace Engineering, University of Maryland, College Park

1 Introduction

When a hypersonic vehicle travels through the atmosphere, a boundary layer develops in the air close to the vehicle surface. Initially (close to the nose of the vehicle) this boundary layer is laminar, but typically will transition to turbulence at some point downstream. A turbulent boundary layer produces significantly larger heat flux and frictional drag at the vehicle surface than a laminar one, so to be able to accurately predict vehicle performance, knowledge of the laminar-to-turbulent transition process is important. There are a variety of boundary-layer instabilities whose growth and breakdown can lead to transition; for slender planar or axisymmetric bodies and small incidences, a key instability mechanism is the second or Mack mode, which can be thought of physically as acoustic waves that become trapped within the boundary layer. Second-mode waves typically exhibit very high frequencies – around 100 kHz or even higher – which makes their measurement very difficult with conventional techniques. Here I describe measurements of the second-mode instability using a schlieren system incorporating a CAVILUX pulsed-diode laser.

2 Experimental configuration

Experiments were performed at two hypersonic wind tunnels: the High Enthalpy Shock Tunnel Goettingen (HEG) of the German Aerospace Center (DLR), and Hypervelocity Tunnel 9 of the Arnold Engineering Development Center (AEDC) at White Oak, Maryland. HEG is capable of reproducing the extremely high flow velocities typical of atmospheric reentry (up to 7 km/s), though for very short test periods (~1 ms). In the present experiments, the flow velocity and density were 4.4 km/s and 0.0175 kg/m3. Tunnel 9, on the other hand, can produce high Mach numbers with longer test periods (around 1 s), but with lower flow velocities. In the present Tunnel 9 experiments, a variety of flow conditions were used, all having a Mach number of approximately 14 and a flow speed of 2 km/s.

In both cases the test article was a slender, 7° half-angle cone. The flow within the boundary layer over the cone was visualized using a conventional Z-fold schlieren arrangement, as shown in figure 1.

Figure 1: Z-fold schlieren visualization set-up used in the experiments described here.

Schlieren is a technique used to visualize flow features in compressible flows: a density gradient at some location in the imaging plane within the test section (in a direction normal to the knife edge placed in front of the camera) will result in a change in intensity at the corresponding location on the image taken by the imaging device (in this case a high-speed camera). In the HEG experiments the light source was a CAVILUX Smart pulsed-diode laser and the camera was a Vision Research Phantom v1210, recording at 200 kHz. The laser was run in ultra-high-speed mode, with a repeated 4-pulse pattern as shown in figure 2.

Figure 2: Laser pulse pattern used in the HEG experiments: Δt12 is 2 μs and Δt34 is 3 μs.

This pattern was necessary because the characteristic frequency of the second-mode disturbance in this case (~600 kHz) was significantly higher than the recording frequency, so closely spaced pulse pairs were used to unambiguously resolve the wave motion (further details to be provided shortly). In the Tunnel 9 experiments, a CAVILUX HF laser providing, uniformly spaced pulses at approximately 70 kHz, was used together with a Phantom v2512 camera. The laser pulse width in the two experiments varied between 20 ns and 50 ns; such short pulse widths were necessary to freeze the high-speed flow structures in images.

3 Results

The HEG experiments were particularly challenging because of the high flow velocity (meaning high second-mode frequencies) and low density (meaning weak intensity variations in the schlieren images). An example of a visualized second-mode wave packet, visible from its oblique “rope-like” structures close to the surface, is shown as it propagates within a sequence of schlieren images in figure 3. The propagation speed of the wave packet is constant – the apparently uneven motion is a result of the laser pulse pattern. By performing two-dimensional image correlations, it is possible to recover the propagation speed – in this case it is 3.8 km/s. The unequal spacing between the two pulse pairs in figure 2 avoids problems with aliasing in these correlations. By then taking the Fourier transform of rows of pixels parallel to the cone surface, wavenumber spectra can be constructed; these can subsequently be converted into frequency spectra using the propagation speed calculated earlier.

Figure 3: Sequence of reference-subtracted schlieren images showing the propagation of a second-mode wave packet (flow is left to right)

Plots of the averaged power spectral density (PSD) at three locations downstream are shown in the left plot of figure 4. Here we see a strong peak at approximately 600 kHz – this corresponds to the second-mode frequency at these conditions. The peak grows rapidly as we move downstream, showing strong amplification of the second mode. A more detailed picture of this growth is shown in the right plot of figure 4, which is a contour plot of the PSD versus distance downstream. Further details of these measurements can be found in Laurence et al. (2016).

Figure 4: (Left) Plots of the schlieren power spectral density (PSD) near the surface at three locations downstream (s is the distance along the cone from the nose); (right) contour plot of the PSD versus distance downstream.

An example of a propagating second-mode wave packet in one of the Tunnel 9 experiments is shown in figure 5. Again we see the characteristic “rope-like” structures, though now the disturbance energy appears to be less concentrated towards the cone surface than it was in the HEG experiments.

Figure 5: Propagation of a second-mode wave packet in a Tunnel 9 experiment

In the Tunnel 9 experiments, the schlieren system was calibrated by placing a long-focal-length lens in the imaging plane and recording images of it. This enabled a calibration curve relating image intensity to the density gradient to be established. From this calibration curve, one can then quantify the growth rate of the second-mode instability. A contour plot of the integrated growth rate, or N-factor, versus distance downstream and frequency is shown in figure 6.

Figure 6: Contour plot of N-factor versus distance downstream and frequency in Tunnel 9 experiment.

Again we see a strong second-mode contribution, but now at a much lower frequency of approximately 100 kHz. The decrease in this frequency moving downstream is associated with the thickening of the mean boundary layer. Such quantitative measurements are very important as they provide data against which numerical simulations and stability analysis computations can be compared. Further details of the Tunnel 9 experiments can be found in Kennedy et al. (2017).

4 Conclusions

The experiments described here demonstrate that it is possible to use high-speed schlieren techniques to perform quantitative measurements of extremely high-frequency instability waves in hypersonic boundary layers. The capabilities of CAVILUX pulsed-diode laser light sources proved instrumental in enabling these measurements.

5 References

Kennedy, R., Laurence, S., Smith, M., and Marineau, E. (2017), “Hypersonic Boundary-Layer Transition Features from High-Speed Schlieren Images”, 55th AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, AIAA Paper 2017-1683

Laurence S., Wagner, A., and Hannemann, K. (2016), “Experimental study of second-mode instability growth and breakdown in a hypersonic boundary layer using high-speed schlieren visualization”, Journal of Fluid Mechanics, vol. 797, pp. 471-503

About the author

Stuart Laurence (Ph.D) completed his graduate studies at the Graduate Aeronautical Laboratories, California Institute of Technology, in the area of hypersonic flows. He currently is Assistant Professor at the Department of Aerospace Engineering, University of Maryland, College Park

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Uni Glasgow studies focused ultrasound via high-speed shadowgraphy imaging

CavLab at the University of Glasgow is using CAVILUX Smart to study focused ultrasound via high-speed shadowgraphy imaging with up to 10 Million frames per second. The video below shows the development of a 1.1MHz ultrasound field created by a needle hydrophone. The video is captured at 5 Million fps.

Shockwaves are very fast phenomena that can be studied with ultra-high-speed imaging. However, the small size and high speed of the object can create motion blur in the images.  Cavitar’s laser illumination provides very short pulses that minimize the effect of motion blur while providing sufficient lighting for images taken at ultra-high-speed.

Original Article:
Kristoffer Johansen, Jae Hee Song, and Paul Prentice, CavLab, Cluster of Ultrasound Science, Technology and Engineering Research, University of Glasgow, UK, Characterising Focused Ultrasound via High Speed Shadowgraphic Imaging at 10 Million Frames Per Second, published at 2016 IEEE International Ultrasonics Symposium Proceedings

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An analysis of the acoustic cavitation noise spectrum: The role of periodic shock waves

This application note is a shortened version of the article “An analysis of the acoustic cavitation noise spectrum: The role of periodic shock waves” by Jae Hee Song, Kristoffer Johansen, and Paul Prentice, used under CC BY.

1 Introduction

Research on applications of acoustic cavitation is often reported in terms of the features within the spectrum of the emissions gathered during cavitation occurrence. There is, however, limited understanding as to the contribution of specific bubble activity to spectral features, beyond a binary interpretation of stable versus inertial cavitation. In this work, laser-nucleation is used to initiate cavitation within a few millimeters of the tip of a needle hydrophone, calibrated for magnitude and phase from 125 kHz to 20 MHz. The bubble activity, acoustically driven at f0¼ 692 kHz, is resolved with high-speed shadowgraphic imaging at 5 million frames per second. A synthetic spectrum is constructed from component signals based on the hydrophone data, deconvolved within the calibration bandwidth, in the time domain. Cross correlation coefficients between the experimental and synthetic spectra of 0.97 for the f0/2 and f0/3 regimes indicate that periodic shock waves and scattered driving field predominantly account for all spectral features, including the sub-harmonics and their over-harmonics, and harmonics of f0.

2 Experimental configuration

The experimental arrangement depicted in Fig. 1(a) is used to study cavitation in unprecedented detail, both optically and acoustically. High-intensity focused ultrasound (HIFU) is generated via a single element piezoceramic transducer (H-149, Sonic Concepts, Bothell, WA), connected to a power amplifier (2100L, Electronic and Innovation, Rochester, NY), and a waveform generator (DG4102, Rigol Technologies, Beijing, China). The HIFU transducer has a natural fundamental frequency at 200 kHz, however, for the current work it is driven at the third harmonic through an impedance matching network, such that f0 = 692 kHz for all results presented. This driving frequency is chosen so that acoustic cavitation emissions are well within the calibration bandwidth of the needle hydrophone (NH, 1.0 mm diameter, PVdF, Precision Acoustics, Dorchester, UK). A 20 mm central hole, through the body of the transducer, serves to mount the NH, aligned vertically along the HIFU axis, Fig. 1(a), with the tip located around the pre-focus -6 dB contour, ~3 mm from the focal point. We refer to this orientation as the “emission collection” position, Fig. 1(b). The NH is connected to an oscilloscope (MS07104A, Agilent Technologies, Lexington, MA).

Figure 1. Illustration of experimental setup: (a) cross-sectional side view, and (b) an axial scan of the HIFU focal region, with representations of the NH outlined for “emission collection”
position (solid black)

To precisely initiate cavitation activity relative to the NH tip, and in the HIFU focus, we employ the lasernucleation technique. A single 1.2 ± 0.1 mJ (instrument error according to manufacturer), 6–8 ns laser pulse (Nano S 130-10 frequency doubled Q-switched Nd:YAG, Litron Lasers, Rugby, UK), is passed through a long working distance microscope objective lens (50  0.42 NA Mitutoyo, Kawasaki, Japan), submerged in a sealed unit, mounted on an xyz manipulator (Velmex Motor, Bloomfield, NY), and pre-aligned to the HIFU focus, ~3 mm above the NH tip in situ. The laser pulse, triggered to be incident ~5 cycles into a 65-cycle burst of HIFU, generated the cavitation activity reported below. The transducer-NH configuration is housed within a custom-built chamber, measuring 420 x 438 x 220 mm3 and filled with degassed, deionized water. Two of the walls of the chamber are recessed, to allow the placement of imaging optics in proximity to the intended location of the cavitation, facilitating reasonably high spatial resolution imaging. High-speed shadowgraphic imaging of the resulting cavitation activity is undertaken orthogonally to the nucleating laser axis, through a Monozoom 7 lens system (Bausch & Lomb, Rochester, NY), at 5  million frames per second (HPVX2, Shimadzu, Kyoto, Japan), with synchronous 10 ns laser  pulses (CAVILUX Smart, Cavitar, Tampere, Finland) providing the illumination and effective temporal resolution, per frame. A delay generator (DG535, Stanford Research Systems, Sunnyvale, CA) provides electronic triggering to synchronize each of the instruments. The Q-switch of laser, which is detected by the NH, signifies laser pulse emission and cavitation nucleation, and is taken as t = 0 µs.

3 Results of high-speed imaging and needle hydronephone data

Figures 2(a)–2(c) represent high-speed imaging data captured for cavitation driven by a PPPAHIFU = 1.63 ± 0.12 MPa. The activity appears to consist of a single bubble, undergoing pseudo-spherical oscillation, with alternating strong collapses coincident to shock wave emission at f0=2, captured Fig. 2(b) at 8.25, 14.05, 17.05 µs and arrowed, Fig. 2(c), and intervening partial deflations. It is known that for shadowgraphic imaging of acoustic transients, the focal plane for best resolution of the pressure fluctuations is slightly removed from the plane within which the emitting bubble is located. For this reason, the bubble of Figs. 2(a) and 2(b) is slightly out of focus, and the bubble oscillation is not optimally resolved.

Figure 2. Images extracted from a high-speed sequence recorded at 5 mio fps, of cavitation activity in the f0/2 regime. (a) The whole field of view, depicting the NH tip position relative to the activity, with a shock wave (arrowed white) incident to it. (b) Selected images representing the cavitation oscillation dynamics, including three strong collapses, and coincident shock wave emission. The entire image sequence is available, in movie format, as supplementary material. (c) Radius-time curve based on a dark pixel counting algorithm, for the time interval under investigation. Diamond and squares indicate the specific images represented in (a) and (b), respectively.
Scale bar represents 250 µm.

Nonetheless, the data confirm the cavitation behavior reported previously, for a HIFU-cloud system in the f0=2 regime. Figure 2(c) represents the bubble radius variation with time, graphically, determined from the entire image sequence captured for this experiment. Figure 3(a) is the raw voltage signal collected by the NH in the emission collection position. A control experiment, for which the HIFU burst was generated, but no laser pulse incident to nucleate cavitation, is also represented. Subtraction of the control, and NH deconvolution within the calibration bandwidth generates Fig. 3. Figures 3(b) and 3(c) show the cavitation emission signal and the cavitation emission spectrum respectively. There is a propagation time from each shock wave is emitted by the cloud and imaged during by high-speed data acquisition, Fig. 2, and detection at the needle hydrophone, Fig. 3, of ~1.8–1.9 µs, depending on the precise timing of cloud collapse and shock wave emission. The propagation distance can be measured from Fig. 2(a) as ~2.7 mm; however, neither the location of the sensing element within the shaft of the NH, nor the properties of the intervening material, are known. An average propagation speed of ~1520 ms–1 can, however, be inferred from the high-speed imaging of periodic shockwave propagation, and a short period of supersonic propagation may be assumed.

Figure 3. (a) Raw NH data recorded during the cavitation activity of Fig. 2 (blue solid) and control exposure for an equivalent HIFU burst (red dot), without cavitation nucleation. The inset zoom around 19.0 µs, reveals a detected shock wave in the raw data, also arrowed for the rest of the trace. (b) Control subtracted and NH-deconvolved data, revealing the signal emitted by the cavitation captured in the high-speed imaging of Fig. 2.
(c) The cavitation spectrum obtained via Fourier transformation of (b).

4 Further studies by Glasgow University using CAVILUX

Deconvolution of acoustically detected bubble-collapse shock waves, Kristoffer Johansen, Jae Hee Song, Keith Johnston, Paul Prentice; Ultrasonics, Volume 73, January 2017, Pages 144–153.

Characterising focused ultrasound via high speed shadowgraphic imaging at 10 million frames per second, Kristoffer Johansen, Jae Hee Song, Paul Prentice (CavLab, Cluster of Ultrasound Science, Technology and Engineering Research, University of Glasgow, UK); Ultrasonics Symposium (IUS), 2016 IEEE International, Date of Conference: 18-21 Sept. 2016.

 

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Jae Hee Song, Kristoffer Johansen, and Paul Prentice

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High-Speed Visualization of Electromagnetic Pulse Welding

Impact welding

Author: Christian Pabst, Darmstadt University of Technology – Institute for Production Engineering and Forming Machines (PtU)

1 Introduction

Impact welding is a process which enables metallurgical bonds even between dissimilar metals. Electromagnetic pulse welding has been developed as one method for impact welding. It draws its energy from charged high-voltage capacitors. The accelerating force on the workpiece is generated by a coil, through which the current is driven by discharging the capacitors.

The main applications of electromagnetic pulse welding are the construction of hybrid space frames, the gas-tight sealing of high-pressure containers or low-ohmic joints between aluminum to copper for the electromobility. The joints produced with impact welding are very tough, because the joint area is not weakened by thermal influences but exhibits fine grains.

The basic mechanisms are understood and illustrated in Figure 1: One workpiece has to impact another at velocities in the range of roughly about 250 m/s and above. The impact has to occur under a certain impact angle. This leads to a collision point (or line) travelling across the surface. Figure 1: Schematic illustration of impact welding. The impact is accompanied by a bright flash which is characteristic for this process. The metallically pure surfaces are then pressed together by the immense pressure of the impact, which finally evokes the metallurgical joint.

Figure 1: Schematic illustration of impact welding.

2 Experimental Configuration

For the basic investigations, a special test rig has been developed at the PtU. It avoids the drawbacks of explosion welding and electromagnetic pulse welding by colliding and welding flat sheets mechanically. The buildup consists of two rotors which are driven by one motor each. Each rotor holds an aluminum tube with a welding specimen mounted at one side. Figure 2 shows the test rig without housing.

Figure 2: Left: Test rig without housing. Right: Rotors with specimens in collision position.


Both rotors have the same sense of rotation, so the specimens’ velocity adds when they meet in the center. When the specimens are welded successfully, they rip off their clamped rest with the help of a predetermined breaking point. The welded specimens and the clamped parts are shown in Figure 3.

Figure 3: Welded specimens (center) with the clamped parts.

3 Imaging Setup

As the actual impact and the joint formation take place in only few microseconds, the process is hard to capture with a conventional high-speed camera. Hence for these research works, an image intensifier camera is used. It allows exposure times and frame delays in the range of nanoseconds at still remarkable spatial resolutions of up to more than 1000 pixels. Filming the impact is accompanied by two more obstacles in addition to the high speeds: During the impact, a bright flash covers the actual joint area. Its formation will be discussed in the following chapter. Exact triggering is the second challenge, because the camera technique does not allow pre-triggering. Due to the fast turning rotors, the exact measurement of the momentary angle is hardly possible. The bright process glare can be suppressed by a trick which is also used when conventional welding processes are investigated. As the glare is usually white, it can be concluded that its intensity is spread almost constantly across all (visible) wavelengths. The light source that is mandatory for high-quality high-speed images only emits light in a small wavelength range. Thus, its intensity is much greater than the process glare, even if the latter appears to be brighter to the human eye. Figure 4 illustrates this issue.

Figure 4: Emitted wavelength range of the light source and the wavelength distribution of the process light.


To suppress all other wavelengths, an optical bandpass filter is fitted to the camera in addition to the special light source. In the experiments, CAVILUX Smart laser illumination system with a nominal wavelength of 640 nm ± 10 nm is used together with a filter for 640 nm ± 5 nm. The laser light is comparably easy to handle, because the light is visible and the emitted beam itself is neither coherent nor collimated which prevents speckling. The laser pulses are synchronized with the camera because their length is limited to a few microseconds only due to the limited duty cycle which prevents a constant illumination. Triggering is realized by using the two rotors as a kind of switch for the trigger circuit.

The following Figure 5 shows the process in two independent experiments immediately after the finished impact with and without bandpass filter. It can be clearly seen that it is almost impossible to investigate the impact in detail without the filter.

Figure 5: Propagation of the jet 20 µs after the impact with (left) and without (right) optical bandpass filter.

Figure 6: Image series taken from the side the process with 2 mm aluminum plates at 3 Mio fps.

Figure 7: Image series taken from the side of the process with 0.74 mm steel plates at 2 Mio fps. The process creates also shockwaves which can be seen in the images.

 

4 Jet Formation and Process Glare

A common explanation for the process glare is that it is caused by the jet. The jet does not only consist of oxides, but also of parent material. The theory states that this parent material burns whilst being emitted and thus causes the intense light. However, it is generally accepted at the same time that high temperatures or even melting do not occur during the impact and welding process. Thus, a sufficient energy source which is capable of initiating the oxidation should actually not exist. In order to examine jetting and glare in more detail, the electromagnetic pulse welding process is investigated under different atmospheres. The complete housing of the test rig has a volume of approximately 1 m³ and is not gas-tight. For the experiments, the coil is covered by an acrylic glass box, which is filled with an inert welding gas. When the enclosure is completely filled with the inert gas, the pulse generator is charged and the weld is established after only few seconds. The following images show the welding of two aluminum sheets with a thickness of 2 mm by a peak current of 300 kA at 20 kHz. Figure 8 shows the welding process with the inert gas atmosphere (left) and with the surrounding air (right). The inert gas does not only significantly decrease the emitted light, but also strongly weakens the emitted pressure wave during the impact.

Figure 8: Electromagnetic pulse welding of two aluminum sheets with (left) and without (right) inert gas atmosphere.


Welds between two copper sheets (Cu-ETP, thickness 1 mm) show a different behavior: Neither the light emission nor the pressure wave is significantly influenced by the surrounding atmosphere. In both cases, it is comparable to aluminum welds with inert gas. These experimental results suggest that an oxidation proceeds during the impact. Aluminum burns with a bright white flame and the oxidation is a highly exothermal reaction. As it can be seen in Figure 5, the emitted jet looks like a cloud of dust. If this dust does not only consist of superficial oxides but also of pure aluminum from the base material, a huge surface is created. Thus, if an appropriate energy source is available, a strong exothermal reaction can occur. This theory is supported by the experiments with the test rig: The extent of the glare and the extent of the jet are almost identical as highlighted in Figure 8. This indicates that jetting and glare are the same phenomenon or at least correlate closely.

Figure 9: Electromagnetic pulse welding of two aluminum sheets with (left) and without (right) inert gas atmosphere.

 

The auto ignition temperature of aluminum strongly depends on the particle size. The past research work in this field shows that the auto ignition of aluminum powder with a particle size of under 10 µm can already happen at about 600 °C. As burning aluminum is even capable of splitting water molecules, a hydrogen explosion due to the atmospheric humidity might occur as well. Copper on the other hand does not burn, which explains why the surrounding atmosphere does not change the light emission.

 

5 Conclusions

Through ultra-high-speed imaging employing a CAVILUX Smart laser illumination and image intensifier camera, it was possible to investigate the jet formation and the process glare in electromagnetic pulse welding. The laser illumination enabled the efficient removal of the thermal light emitted by the process. This provided a detailed view behind the bright process light. With back illumination and short pulse duration it is also possible to observe shockwaves.

The high image quality enabled the verification of the theoretical models and to validate research in that area. More information about the theoretical models and considerations for the source of the temperature that is created for the ignition that creates the process glare can be found from: https://eldorado.tu-ortmund.de/bitstream/2003/33500/1/C.Pabst_Electromagnetic%20pulse%20welding.pdf

 

 

About the author

 

Mr. Christian Pabst (M.Sc.)
Darmstadt University of Technology
Institute for Production Engineering and Forming Machines
Otto-Berndt-Straße 2
64287 Darmstadt
Germany 

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Bubble Collapse Shockwave

University of Glasgow (Scotland) is using CAVILUX Smart to study shockwaves from bubble collapse. Shockwaves are very fast phenomena that can be studied with ultra-high-speed imaging. However, the small size and high speed of the object can create motion blur in the images. Cavitar’s laser illumination provides very short pulses that minimize the effect of motion blur while providing sufficient lighting for images taken at ultra-high-speed.

Read the application note: http://www.cavitar.com/deconvolution-acoustically-detected-bubble-collapse-shockwaves/

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Deconvolution of Acoustically Detected Bubble Collapse Shockwave

This application note is a shortened version of the article “Deconvolution of acoustically detected bubble-collapse shock waves” by Kristoffer Johansen, Jae Hee Song, Keith Johnston and Paul Prentice, used under CC BY.

1 Introduction

When detecting a broadband acoustic signal with a hydrophone, artifacts arising from the convolution the will manifest. This is of particular importance for bubble collapse shock waves as both an apparent negative phase and the peak positive pressure amplitude or incorrectly measured if the signal is not deconvolved. Using high-speed imaging, the collapse of a laser induced bubble is observed, with the subsequent emission of a shock wave. The shock wave is detected by a needle hydrophone at three distances, in which experimental results are compared to theoretical predictions of the shock wave properties. To achieve this the capability of performing unprecedented shadowgraphic imaging of the bubble collapse was paramount, both for controlling the bubble size and a spherical rebound after the collapse. The high speed observation was also used to guide the simulation of the theoretical prediction.

2 Experimental configuration

When a laser pulse of energy sufficient to cause optical break down, is focused into a liquid, a single laser-induced bubble (LIB) forms. A LIB initially undergoes an expansion phase in response to the energy deposition, which the inertia of the host medium decelerates eventually causing the bubble to contract and collapse, often followed by several rebound oscillations. Acoustic detection of the LIB process is characterised by the emission of a series of shock waves. The first is generated by the plasma formed on absorption of the laser pulse, with a second emitted during the collapse of the primary bubble after a duration equal to the oscillation period of the LIB. Successive rebounds may also emit shocks of diminishing pressure amplitudes.

Figure 1: Schematic of experimental setup.

To study the BCSWs reliably, LIBs are generated within a custom built chamber, represented schematically by Fig. 1 measuring 420 x 438 x 220 mm3 and filled with degassed, deionised water. Two of the walls are recessed, allowing imaging optics to be placed in proximity to the intended location of the LIB, facilitating spatial resolution at 7.6 ± 0.1 μm per pixel. A single 4.0 ± 0.2 mJ (instrument error according to manufacturer), 6–8 ns laser pulse (Nano S 130-10 frequency doubled Q-switched Nd:YAG, Litron Lasers, UK), is brought to a focus through a long working distance microscope objective lens (50 x 0.42 NA Mitutoyo, Japan), submerged in a sealed unit, and mounted on an xyz manipulator (Velmex Motor, Bloomfield, NY, USA). High-speed shadowgraphic imaging of the resulting cavitation activity is undertaken at 5 x 106 frames per second (HPV-X2, Shimadzu, Japan), with synchronous 10 ns laser pulses (CAVILUX Smart, Cavitar, Finland) providing the illumination and effective temporal resolution. A delay generator (DG535, Stanford Research Systems, USA) provides electronic triggering to synchronise each of the instruments. The HPV-X2 camera offers 256 frames per image sequence, such that the dynamics of the collapse of a single bubble is sampled sufficiently for modelling purposes. Much of the literature on this type of experiment relies on the selection of frames from a number of different high-speed sequences of a number of different bubbles, under the assumption that each bubble reaches an equivalent maximum radius and undergoes an equivalent collapse.

Figure 2: Video of shockwave created by bubble collapse


Figure 3: High-speed images of a collapsing laser induced bubble with the emission of a shock wave, and a spherical rebound. Imaging is undertaken at 5 million frames-per-second with synchronous 10 ns laser pulses CAVILUX Smart providing the illumination and effective temporal resolution.

3 Results after deconvolution of needle hydrophone

When removing the impulse response from the needle hydrophone via deconvolution, the theoretical competition is in reasonable agreement with the experimental measurement. This is particularly noticeable as the apparent negative phase in the convoluted experimental measurement is gone. Thus, for broadband signals it is important that the measurement is deconvolved with information of both the magnitude and phase, such that the temporal shape the measurement remains a physical.

 


Figure 4: Theoretical computation (stapled black) and deconvolved experimental measurement (solid black) of bubble collapse shock wave at distances 30,40 and 50mm from the nucleation site.

4 Further studies by Glasgow University using CAVILUX

Characterising focused ultrasound via high speed shadowgraphic imaging at 10 million frames per second, Kristoffer Johansen, Jae Hee Song and Paul Prentice, Ultrasonics Symposium (IUS), 2016 IEEE International, Date of Conference: 18-21 Sept. 2016

An analysis of the acoustic cavitation noise spectrum: The role of periodic shock waves, Jae Hee Song, Kristoffer Johansen, Paul Prentice (CavLab, Cluster of Ultrasound Science, Technology and Engineering Research, University of Glasgow, UK); JASA, Volume 140, Pages 2494 – 2505, 2016

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Kristoffer Johansen, Jae Hee Song and Paul Prentice

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Schlieren imaging of TIG welding

TIG Schlieren

Visualization of TIG welding with Schlieren imaging method using Cavitar’s CAVILUX illumination laser. Video taken at 2.000 frames per second. The method enables the observation of protective gas flow with a high level of detail.

Read more about different Schlieren setups.

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TIG welding of aluminium

TIG Welding

Visualization of 5.5 kW TIG welding of aluminum with Cavitar’s CAVILUX illumination laser reveals a clear view to the behavior of melt pool and additive material. Video taken at 20 frames per second – front illumination.

In cooperation with Lappeenranta University of Technology (LUT).

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