Location Of Shock Wave Research Articles

Local acoustic shock velocity and shock structure recovery measurements in glow discharges

Simultaneous local acoustic shock wave velocity measurements show that the upstream velocity exceeds the downstream velocity inside a low pressure positive column nitrogen plasma in contrast to the opposite behavior in neutral gas. The shock velocity increase is also dependent on the direction of the applied electric field.

Errata Simple Method of Supersonic Flow Visualization Using Watertable

Fig. 4 Flow over a 5.8-deg half-angle wedge with Mach 1.5 nozzle. Figure 4 shows the 5.8-deg wedge placed 2 mm (0.08 in.) from the exit of the Mach 1.5 nozzle. The shock induced boundary-layer separation occurs at the same location downstream of the nozzle exit as in Fig. 3. This is to be expected since the incident shock wave is produced by the overexpanded jet and is not a function of model position. Here the separation bubble is about 3 mm thick. This strong interaction suggest that the boundary layer on the wedge is laminar. IV. Conclusion A flow visualization method suitable for high-speed flows has been demonstrated. The laser light sheet combined with digital imaging provides a capability to resolve flow structure with lowlight levels. The images obtained in this study clearly show the extent and location of shock waves as well as boundary-layer interactions. Natural condensation of water vapor was found to provide more than adequate light scattering particles for flow visualization. A flow tracer may need to be injected into flows where stagnation conditions are not conducive to natural condensation. The thermodynamic effect of condensation on the flow must be considered in determining the amount of injection so that local stagnation temperatures are not significantly altered. With appropriate seeding and illumination, the adaptation of the present scheme to an operating compressor rotor using a pulsed laser light source appears promising. Technical details are currently under study.

How the bow shock does it

Between the world of living organisms and inanimate objects exists a zone inhabited by animate, but nonliving, physical entities. These fascinating, and often nonlinear systems exhibit characteristics which in many ways mimic that of simple biological organisms. They seem to have an instinctive desire to accomplish certain tasks, and devise many creative strategies to achieve their goal. The bow shock, the topic of this paper, is one of the inhabitants of this zone and it forms due to solar wind interaction with the Earth's magnetic field. As one would expect, its goal is to decelerate and divert the supersonic solar wind flow around the magnetosphere. But unlike the usual shock waves, it has to accomplish the task without the use of collisions; quite a challenge indeed. A bigger challenge, however, has been for us to use space age technology and supercomputers to find out how the bow shock does it! We have made much progress; many of the pixels are in place but the picture is not complete. What we have found is a truly fascinating and complex story which is a testament to the creativeness of the bow shock. Depending on the upstream Mach number (ratio of the solar wind speed to the sound speed) and location on the paraboloid surface of the shock, a different strategy for dissipation of the flow energy into heat is utilized. In some regimes, the transition from upstream to downstream takes place on short ( ∼100 km) length scales, while in others, the shock transition is masked with an extended region of electromagnetic waves and turbulence. As part of the dissipation process, electrons and ions are reflected off the shock. The interaction between the solar wind and the reflected particles forms the foreshock, a region extending many Earth radii upstream of the shock. The foreshock is populated by a variety of electrostatic and electromagnetic waves, making it a great natural laboratory for studies of nonlinear wave‐particle interactions. Among these are the fast magnetosonic waves which steepen to form spatially localized shock waves, named shocklets! Creation of shocklets by the bow shock is not quite reproduction, but is close enough to stir the imagination and make one marvel at its parallelism to live organisms. There are many motivations for the study of the bow shock. One set deals with the inherent interest in collisionless shocks,and how it can be used to enhance our knowledge of nonlinear plasma physics, collisionless dissipation, particle acceleration, and their extension to astrophysical settings. The other concerns the influence of the bow shock on magnetospheric phenomena. Before reaching the magnetopause, the solar wind is greatly modified by the bow shock through heating, deceleration, and considerable enhancement of its field fluctuations.

Pressure-Sensitive Paint Measurements on a Supersonic High-Sweep Oblique Wing Model

The pressure-sensitive paint method was used in the test of a high-sweep oblique wing model, conducted in the NASA Ames 9- by 7-ft Supersonic Wind Tunnel. Surface pressure data was acquired from both the luminescent paint and conventional pressure taps at Mach numbers between M = 1.6 and 2.0. In addition, schlieren photographs of the outer flow were used to determine the location of shock waves impinging on the model. The results show that the luminescent pressure-sensitive paint can capture both global and fine features of the static surface pressure field. Comparison with conventional pressure tap data shows good agreement between the two techniques, and that the luminescent paint data can be used to make quantitative measurements of the pressure changes over the model surface. The experiment also demonstrates the practical considerations and limitations that arise in the application of this technique under supersonic flow conditions in large-scale facilities, as well as the directions in which future research is necessary in order to make this technique a more practical wind-tunnel testing tool.

Improved manufacturing processes with high power lasers

The first part of this paper gives a general idea of overall trends and points of importance for the different laser applications. Some new interesting laser processes have been proposed but have not reached a significant industrial exploitation up to now. Reasons for industrial acceptance of laser processes are explained. Process improvements are discussed on the example of laser cutting and machining of cacities. Both applications are characterized by a high speed gas jet. For the material removal processes the influence of the nozzle design for the assisting gas flow is investigated. Numerical simulations of the gas flow are carried out and compared with Schlieren photos. Normal jet impingement of newly designed nozzles and conventionally used nozzles is compared at various nozzle stand off distances. In order to calculate shock wave locations and strengths correctly the Navier Stokes equations in finite volume form have been modified. Furthermore supersonic effects in the cut kerf are investigated. The importance of quality and process control is shown and discussed for the removal processes. For machining of cavities an appropriate depth controller is of main importance for an industrial exploitation. This process is discussed in detail and the problems for designing a closed loop controller are explained. Furthermore an industrial in-process sensor for laser cutting is presented, which allows to supervise the cut quality.

Convergence of Second-Order Schemes for Isentropic Gas Dynamics

Convergence of a second-order shock-capturing scheme for the system of isentropic gas dynamics with ${L^\infty }$ initial data is established by analyzing the entropy dissipation measures. This scheme is modified from the classical MUSCL scheme to treat the vacuum problem in gas fluids and to capture local entropy near shock waves. Convergence of this scheme for the piston problem is also discussed.

Engineering approach to the prediction of shock patterns in bounded high-speed flows

A two-dimensional symmetric wedge configuration representative of a single high-speed intake in steady flow was investigated. The analysis presented here is intended as an engineering approach for estimating certain features of the internal shock system. The primary interest here is the prediction of the size and location of the almost-normal shock wave that develops when the leading-edge shocks intersect at angles above a certain critical value that is less than the wedge detachment angle. The almost-normal shock wave is frequently referred to as the 'Mach stem', Parametric studies enabled the sensitivity of the Mach stem height to various flowfield parameters to be examined, thus indicating how accurately these parameters must be measured in a given experiment. Results of these predictions were compared with those of a steady-flow experiment performed at nominal freestream Mach numbers from 2.8 to 5. The predicted stem heights were consistently lower than the mean experimental values, attributable both to experimental uncertainties and to certain simplifying assumptions used in the analysis. Modification of these assumptions to better represent the test environment improved the analytical results.

Convergence of second-order schemes for isentropic gas dynamics

Convergence of a second-order shock-capturing scheme for the system of isentropic gas dynamics with L ∞ {L^\infty } initial data is established by analyzing the entropy dissipation measures. This scheme is modified from the classical MUSCL scheme to treat the vacuum problem in gas fluids and to capture local entropy near shock waves. Convergence of this scheme for the piston problem is also discussed.

Separation control using moving surface effects - A numerical simulation

A numerical study is conducted to investigate the effects of forebody boundary-induced vorticity (FBIV) on the development of the laminar/turbulent boundary layers over modified NACA 0012, NACA 63-218 airfoils having leading-edge rotation. Here, we utilize an implicit finite-difference procedure to solve the two-dimensional compressible full Reynolds-averaged Navier-Stokes equations on a body-fitted curvilinear coordinate system. For the subcritical and supercritical flows considered, convergence to steady state is expedited through the use of locally varying time steps. Of special interest to the present study is the effect of varying the leading-edge circumferential speed, and, hence, the strength of the FBIV, on the following: 1) location of the point(s) of laminar and/or turbulent separation, 2) the size of the separated flow region above the airfoil, 3) the strength and location of shock waves, and 4) the computed sectional lift coefficients. Similar to circulation control airfoils, for subcritical onset flows, numerical results have indicated that with such a leading-edge device, aerodynamic lift forces can be augmented without the need to change the airfoil's angle of attack and/or chord Reynolds number. Qualitative comparisons with smoke wire flow visualization results and available experimental data are presented.

Lithotripsy of gallstones by means of a quality-switched giant-pulse neodymium:Yttrium-aluminum-garnet laser: Basic in vitro studies using a highly flexible fiber system

The quality-switched neodymium:yttrium-aluminum-garnet laser represents a new instrument for athermal fragmentation of gallstones by transformation of optical energy into mechanical energy in the form of shock waves via local plasma formation. A highly flexible 300-μm fiber transmission system was used in basic investigations to determine the influence of varying pulse repetition rates (5–30 Hz) and pulse energies (15 and 20 mJ) on shock wave intensity and stone fragmentation in vitro for 105 biliary calculi of known size and chemical composition. After performance of 1200 shock wave pressure measurements using polyvinylidenefluoride hydrophones, stone fragmentation was analyzed by determination of fragment removal rates (volume of fragments removed per fragmentation time), ablation rates (mean volume removed per laser pulse), and median fragment sizes for each laser setting. With the quality-switched neodymium:yttrium-aluminumgarnet laser system, all concrements could be reliably disintegrated into small fragments (median diameter, 0.7–1.7 mm). Compared with pure cholesterol stones, a significantly higher fragment removal rate was achieved in cholesterol stones containing 30% calcium phosphate (P = 0.039), in cholesterol stones containing 20% pigment (P = 0.015), and in pure pigment stones (P = 0.007). Fragment removal rates, local shock wave pressures, and median grain sizes were significantly higher at a pulse energy of 20 mJ than with 15 mJ. Shock wave pressures showed a distinct dependence on pulse repetition rates at 20 mJ, yet not at 15 mJ. Because there is no evident hazard of thermal damage to tissue using the quality-switched neodymium:yttrium-aluminum-garnet laser, it appears to be a promising device for nonsurgical biliary stone therapy.

A spatial marching technique for the inviscid blunt body problem

A technique has been developed for obtaining approximate solutions of the inviscid, hypersonic flow on a blunt body with a spatial marching scheme. The scheme introduces the Vigneron pressure gradient approximation into the momentum equation in the direction along the body surface. The resulting governing equations are hyperbolic. With a specified shock wave these equations are solved at the stagnation streamline with an iteration procedure and are solved in the downstream direction with a marching scheme. The complete Euler equations are solved with the numerical scheme when the flow is supersonic. A global iteration procedure is required to obtain the shock wave location. The approximate results from the spatial marching technique are compared with the complete solution of the Euler equations for flow over a sphere. The two results are shown to be in approximate agreement and the spatial marching technique provides useful engineering predictions while requiring considerably less computational time.

Gastrointestinal Laser Endoscopy—Future Horizons

The laser, especially the neodymium:yttrium-aluminum-garnet device, has been a dominant influence on the development of gastrointestinal therapeutic endoscopy. More than 2,000 such procedures were performed in the first 5 years of experience with laser endoscopy at the Mayo Clinic. The major areas for future development are (1) the control of acute and chronic gastrointestinal bleeding, (2) the palliation of malignant gastrointestinal neoplasms, and (3) the management of benign and malignant obstructive lesions of the biliary tract. Refinements in laser devices, delivery systems, and techniques such as photodynamic therapy will be needed to achieve more selective tissue destruction. Improvements in the new adjunctive endoscopic methods of electronic (video) endoscopy and ultrasonography may enhance evolving laser applications by more accurately identifying diseased tissues and guiding their destruction.

Flow mechanism of .LAMBDA.-type pseudoshock waves in a straight-square duct.

This paper is concerned with the internal structure of λ-type pseudoshock waves in a straight-square duct. The experiments were carried out for M1=1.77, where M1 Was the flow Mach number just ahead of the pseudoshock wave, using a two-component, dual-beam laser Doppler velocimeter (LDV) and double exposure laser holographic interferograms. The velocity distributions in the pseudoshock wave were measured in detail. The variations of velocity and boundary layers displacement thickness were clarified. Especially, the displacement thickness increased at the shock wave locations and decreased in the regions between the shock waves. The velocity distributions calculated by the density distributions, which were measured by using the holographic technique, were compared with the results from LDV. It was found that the central flow in the pseudoshock wave was closely related to the isentropic flow, while the flow near the wall was closely related to the adiabatic flow.

Laser Lithotripsy — The New Wave

Currently more than 90% of all common bile duct concrements can he removed via the endoscopic retrograde route by means of endoscopic papillotomy, stone extraction by baskets and balloon catheters, or mechanical lithotripsy. Oversized, very hard or impacted stones however often st ill resist conventional endoscopic therapy. Laser lithotripsy represents a promising new endoscopic approach to the nonsurgical treatment of those common bile duct stones. Currently only short-pulsed laser systems with high power peaks but low potential for thermal tissue damage are used for stone fragmentation. Systems in clinical applications are the pulsed free-running-mode neodymium YAG (Nd:YAG) laser (1064 nm, 2 ms) and the dye laser (504 nm, 1 to 1.5 μs). Energy transmission via highly flexible 200 ìm quartz fibres allows an endoscopic retrograde approach to the stone via conventional duodenoscope or mother-baby-scope systems. New systems currently in preclinical and first clinical testing are the Q-switched Nd:YAG laser (1064 nm, 20 ns) and the Alexandrite laser (700 to 815 nm, 30 to 500 ns). By means of extremely short nanosecond pulses (10-9s) for the induction of local shock waves at the stone surface, possible tissue damage is even more reduced. No complications have been reported so far after applying laser lithotripsy clinically in about 120 patients worldwide. Compared to extracorporeal shock wave treatment, laser lithotripsy can be executed in any endoscopy unit in the scope of the endoscopic pretreatment and does not require general anesthesia, which is often necessary for extracorporeal shock wave lithotripsy.

Shock wave location on a slender transonic body of revolution

Shock wave location on a slender transonic body of revolution

Sublimating chemical technique for boundary-layer flow visualizationin flight testing

With the introduction of modern aircraft utilizing laminar flow, flow visualization has become an important diagnostic tool in determining aerodynamic characteristics such as surface flow direction and boundary-layer state. Oil flow and sublimating chemical techniques are discussed, and the use of sublimating chemicals is examined in detail. Oil is used to visualize boundary-layer transition location, shock-wave location, regions of separated flow, and surface flow direction. Sublimating chemicals are used to visualize both the location and mode of boundary-laye r transition. The different modes of transition are characterized by different patterns in the developed sublimating chemical coating. The discussion includes interpretation of these chemical patterns and the temperature and velocity operating limitations of the chemical substances. Information for selection and application of appropriate chemicals for a desired set of flight conditions is provided.

Evidence of Reynolds number sensitivity in supersonic turbulent shocklets

A local shock wave can destroy the evolution of supersonic combustion in a scramjet. The Reynolds number correlation of the systems of internal shock waves produced in such turbulent free shear layers are presently noted to imply that a direct connection with turbulence intensity exists. By way of this connection, as well as the adjustability of the Reynolds number, opportunities emerge for the control of turbulent shocklets; this will in turn allow control of their influence on supersonic mixing.

163 - Second Generation Local Shockwave Lithotripsy – Clinical Evaluation

163 - Second Generation Local Shockwave Lithotripsy – Clinical Evaluation

Shocked Molecular Hydrogen from Star Forming Regions

Near infrared (2 micron) emission lines from molecular hydrogen provide a powerful probe of the morphology and energetics of outflows associated with stellar birth. The H2 emission regions trace the location of shock waves formed when the high velocity outflow from young stars encounters dense quiescent gas. Since H2 is the dominant coolant of the hot post-shock molecular gas, the H2 lines provide a measure of the fraction of the total mechanical luminosity radiated away from the cloud.

Recent research on the flow through turbine blade rows.

Recent research on the flow through turbine blade rows covers the following regions : (i) theoretical analyses of inviscid and viscous compressible flow through cascades or turbine stage, (ii) experimental investigations of the cascades and turbine stages, (iii) secondary flow, (iv) unsteady flow, (v) design methods, (vi) wet steam flow, and (vii) special turbines. In this review, research carried out over the past five years was dealt with. As regards the development in computing methods of internal flow, a time-marching method of viscous compressible transonic flow through a stage and an inviscid unsteady flow calculation was explained. As for secondary flow, theoretical analysis has been improved significantly as of late. However, more information on the turbulence structure of blade boundary layers and on the mixing process in the downstream of blade rows and the effect of leading edge vortices are necessary. Unsteady flow in a blade row due to the wake of the upstream blade row can be well described, but the more important unsteady flows in the low pressure stages, caused by non-uniform flow at low flow rate conditions or due to the fluctuation of the shock wave location, remain unsolved.