Underwater shockwave – Illumination comparison

Correct lighting is crucial when imaging challenging scientific phenomena and critical industrial processes.

The video shows a comparison of three different illuminations that are used to capture an underwater shockwave:
– Left: CAVILUX HF laser illumination, 50 ns pulses, camera exposure 290 ns
– Center: CW laser, camera exposure 290 ns
– Right: Metal halide lamp, camera exposure 680 ns

Video credit: Professor Tokitada Hashimoto at Saga University, Japan and Nobby Tech Ltd.

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Defense Industry

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Defense industry typically involves applications having targets that are extremely fast and small which require very accurate and fast monitoring methods. We have experience in imaging of various defense applications such as different kinds of ballistic objects, collisions, shockwaves and explosion studies. CAVILUX laser illumination enables extremely fast, even ultra-high-speed lighting which is essential for acquiring high-quality images of these phenomena.

Ballistics

Explosions

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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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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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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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Formation of shockwaves in gel

Creation of shockwaves during the creation of cavitation in gel with shadowgraph imaging , camera shutter 250 ns, 500.000 fps. Left video taken with cw metal halide lamp. Right video taken with CAVILUX Smart laser illumination with a 20 ns illumination pulse. Video material by Prof. Umemura and Prof. Yoshizawa, Tohoku University, Japan in co-operation with Nobby Tech Ltd.

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High-Speed Visualization of Unsteady Processes in a Scramjet Combustion Chamber Using CAVILUX Smart Diode Laser

Shockwave

Author: Stuart Laurence, German Aerospace Center (DLR)

1 Introduction

Scramjets (supersonic combustion ramjets) are a technology for high-speed propulsion, potentially allowing large performance advantages over rockets. Despite decades of development, however, significant obstacles remain to the routine deployment of scramjets for access-to-space or high-speed travel. One critical issue associated with scramjets is that of inlet unstart, defined as the upstream displacement or disgorging of the original inlet shock system. The resulting detached shock that forms in front of the inlet leads to large flow spillage, reducing performance, and can also produce violent, unsteady loading on the engine, potentially resulting in its destruction. One possible cause of inlet unstart is abnormal operating conditions inside the combustion chamber of the engine, leading to the upstream propagation of pressure disturbances which can displace the inlet shock system. Such a process was cited as the reason for the failure of the second X-51 flight, for example. In order to predict, detect, and prevent such unstart events, it is thus necessary to study the responsible mechanisms inside the combustion chamber, and to determine how the transient phenomena that accompany incipient unstart may manifest themselves. This is the focus of the present investigation.

2 Experimental configuration

All experiments were performed in the HEG (High Enthalpy shock tunnel Göttingen) facility of the German Aerospace Center (DLR). The HEG is a reflected-shock wind tunnel, capable of reproducing a wide variety of flow conditions at Mach numbers from approximately 6 to 10. The test time of the facility is limited to a few milliseconds; while this still allows the study of a range of high-speed flow problems, it makes visualization, particularly of unsteady phenomena, especially challenging.

The model configuration for the present study is a full-scale reproduction of the fuelled flow path of the HyShot II flight experiment. HyShot II was the first successful test in the HyShot program, run by the University of Queensland, Australia, designed to provide reference supersonic combustion data at hypersonic Mach numbers. The configuration is thus an academic one, rather than a practical thrustproducing engine; however, the simple design and convenient optical access made the Hyshot II an ideal candidate for the present study. The flowpath is shown in the right part of figure 1. The intake consists of a simple 18º wedge; the boundary layer generated on this surface is swallowed by a boundary-layer bleed channel, rather than being allowed to enter the combustion chamber. The combustion chamber is a constant-area duct of 300 mm length, 9.8 mm height and 75 mm width. Hydrogen fuel is injected 58mm downstream of the intake-side leading edge in the wall-normal direction through four port-holes. The exhaust consists of a simple two-dimensional expansion. A schematic drawing of the model inside the HEG test section is shown in the left part of figure 1.

In the present experiments, the wind tunnel was run in a manner to reproduce the flight conditions of the HyShot II flight experiment at 28 km altitude. The free-stream Mach number was approximately 7.4. Hydrogen fuel was injected at various pressures to induce both steady and unsteady combustion conditions.

application_note_dlr_fiure_1

Figure 1: (Left) Schematic drawing of the HyShot II scramjet model in the HEG test section: (a) HEG nozzle; (b) valve for hydrogen injection. (Right) Flow path for the HyShot II scramjet (upside-down relative to the left schematic): (c) intake ramp; (d) boundary-layer bleed channel; (e) injection location; (f) cowl-side combustion chamber wall; (g) injector-side wall; (h) exhaust surfaces.

An important component of the present study was visualization of the flow and combustion features; thus, windows were installed in the model, providing optical access to almost the entire combustion chamber. The first type of imaging implemented was Schlieren, for which a conventional Z-type arrangement was employed. The Schlieren technique visualizes the first spatial derivative of the flow density, and is thus useful for imaging features such as shocks, boundary layers, and shear layers in compressible flows. Highspeed Schlieren imaging is challenging in facilities such as HEG, because of both the short test times and the significant amounts of self-luminosity produced by the hot gases in the test flow. This luminosity can potentially overwhelm the light source. If the flow is combusting, as in the present case, the luminosity problem is further aggravated. The use of CAVILUX Smart illumination laser for visualization in the present experiments overcame this problem, as the monochromatic nature of the light produced allowed the insertion of a narrow band-pass filter in the light path, effectively removing the self-luminosity. The incoherent nature of the light also eliminated the speckle and diffraction edges typically associated with laser light sources. A further advantage of this light source was the short pulse duration (here ~30 ns), which effectively freezes the flow structures. The CAVILUX Smart was employed together with a Shimadzu HPV-1 high speed camera, with frame rates of 16 or 32 kfps.

The second type of imaging was OH* chemiluminescence visualization, again using the Shimadzu HPV-1 (without a light source). OH is one of the intermediate products in the combustion of hydrogen; thus, the concentration of the electronically excited radical, OH*, gives a good indication of the onset of the flame. OH* also has the advantage of emitting strongly over a narrow wavelength band (near 310 nm), so by placing a narrow band-pass filter of this wavelength in front of the camera, line-of-sight intensity distributions of this radical can be easily obtained. By combining Schlieren and OH* chemiluminescence visualizations then, we can draw links between the flow and combustion features seen inside the combustion chamber.

3 Results

First we concentrate on results obtained for low hydrogen injection pressures, which resulted in steady combustion conditions developing inside the combustion chamber. In figure 2 are shown Schlieren and OH* visualizations of the flow region close to the injection location (the visualized region is approximately 80 mm long). The injection port-holes are located at the lower left corner of each image. The barrel shock created by the interaction of the injected hydrogen with the incoming test-flow is clearly seen in the Schlieren image, as are several of its reflections down the duct. The injection jets themselves are also visible; the freezing of the turbulent structures by the short laser-pulse duration is shown to good effect Application notes – R&D Combustion Schlieren imaging Cavitar Ltd › www.cavitar.com here. The penetration depth is approximately one-half of the duct height by the downstream end of the visualization window. In the OH* image, there is no evidence of combustion occurring directly at the point of injection; rather, combustion appears to be initiated close to the injector-side wall by the first reflection of the barrel shock. The temperature and pressure rise across the shock thus seem to be sufficient to bring the hot hydrogen in the boundary layer to the sides of the injection jets to ignition conditions. Combustion remains isolated to the boundary layer until the second reflection of the barrel shock, which “kicks” the flame further out into the duct and increases the intensity of combustion. These images thus show a clear linkage between the flow and combustion features.

application_note_dlr_fiure_2

Figure 2: (Above) Schlieren image of the flow in the HyShot II combustion chamber near the injection location (seen at the bottom left corner) for steady combustion conditions. (Below) OH* chemiluminescence image of the same region.

As the amount of injected hydrogen was increased, it was noted from pressure transducer measurements that a pressure disturbance would develop and begin to propagate upstream, signaling the onset of unstart. As the nature of this disturbance was not clear, high-speed visualizations were captured of the unsteady development, and sequences from these are shown in figure 3. In the left column is shown a sequence of the flow region close to the injection location (the same region as in figure 2). Initially (1.4 ms) we see that the picture is similar to that for the steady combustion case (note that the exposure time for the OH* image is reduced here, which explains the apparent weakness of the observed combustion). At 3.5 ms, however, we first see the arrival of a shock structure on the cowl-side wall in the Schlieren image, with an accompanying bulging feature in the OH* image. These continue to move upstream, until a quasi-steady configuration arises from around 4.4 ms, with the shock lodged on the cowl-side wall just downstream of the injectors, and the main combustion region located immediately downstream of the impingement point of this shock on the injector-side wall. The appearance of the OH* structure as it moves upstream suggests the development of a separated flow region on the injector-side wall, as the increased residence time in such regions greatly enhances the hydrogen ignition. Unsteady flow structures in the Schlieren images also support this interpretation. In the final image (7.0 ms), the shock structure has continued moving upstream past the injector, but this is after the steady test time and may be a result of the unsteady inflow conditions that subsequently develop.

In the right column of figure 3 are shown corresponding images from the central combustion chamber further downstream. From 2.5 ms, the development of a shock train on the cowl-side wall is visible; this shock train quickly strengthens and moves upstream. Such shock trains in scramjet combustors are typically caused by one of two mechanisms: boundary-layer separation due to the adverse pressure gradient, or thermal choking due to excessive heat release driving the flow to sonic conditions (at which point a steady flow situation is no longer possible). In the OH* images, a gradual intensifying of the combustion is observed, but notably absent is an OH* feature that follows the shock train motion (as observed in the upstream sequence). This suggests that the shock-train development is not linked to boundary-layer separation, and is rather due to thermal choking, which contradicts the findings of previous authors who have investigated this configuration. The boundary-layer separation observed in the upstream sequence must thus develop at some later point in the propagation of the shock train.

application_note_dlr_fiure_3

Figure 3: Quasi-synchronous Schlieren and OH* chemiluminescence visualizations of the transient flow (near) near the injector and (right) in the central combustion chamber.

4 Conclusions

Through high-speed Schlieren visualizations employing CAVILUX Smart laser and OH* chemiluminescence imaging, we have investigated the unsteady flow and combustion phenomena leading up to unstart in a model scramjet engine. Incipient unstart was seen to take the form of a shock train that developed in the central combustion chamber and subsequently propagated upstream. By comparing Schlieren and OH* images, we were able to rule out boundary-layer separation as the primary mechanism for this unsteady development (although separated regions were observed further upstream); thermal choking due to excessive heat release was thus isolated as the responsible mechanism.

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 works at the German Aerospace Center (DLR), Göttingen, on supersonic combustion, boundary-layer transition, and experimental methods for high-speed flows.

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Shockwaves During Cavitation Creation with Sonosensitizer

Japanese Journal of Applied Physics, Volume 53, Number 7S

Author: Jun Yasuda, Takuya Miyashita, Shin Yoshizawa and Shin-ichiro Umemura, Graduate School of Engineering and Second Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan

“Acoustic cavitation bubbles are microbubbles generated by the highly negative pressure of ultrasound. They are known to enhance the thermal bioeffect of high-intensity focused ultrasound (HIFU) treatment. Other than the use of the thermal bioeffect, sonodynamic treatment using the sonochemical bioeffect of ultrasound has been proposed. In sonodynamic treatment, a sonosensitizer is activated through the collapse of cavitation bubbles to induce a therapeutic effect sonochemically. Rose Bengal (RB) has the potential to be such a sonosensitizer. Highly efficient as well as controlled generation of cavitation bubbles is crucial for realizing effective as well as safe sonodynamic treatment. The effect of RB on cavitation generation was investigated to achieve such controlled generation. The amount and behavior of the cavitation bubbles generated by a triggered HIFU sequence in the presence of RB were observed using a high-speed camera for estimating the effect of RB. Results showed that RB increased the area of the cavitation cloud and the lifetime of sustained cavitation bubbles.”

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