Pseudo-shock Wave Research Articles

プラズマジェットで支援された超音速燃焼場に対する 擬似衝撃波形成の影響に関する数値解析

Hydrogen combustion assisted by the oxygen plasma jet (PJ) in a Mach 1.9 supersonic internal flow was numerically investigated. Mixing and combustion behavior were compared between upstream and downstream fuel injections. For hydrogen injection downstream of the PJ, only weak combustion occurred even with a relatively high electric power input because of the rapid decrease in the ignitability of the PJ plume in the downstream. In contrast, intensive combustion easily occurred for hydrogen injection upstream of the PJ, with a relatively low electric power input, and a pseudo shock wave (PSW) was formed upstream of the fuel injector. The position of the PSW strongly affected the fuel mixing with the main airflow. The mixing and combustion of the fuel were rapidly enhanced by the formation of the leading shock wave of the PSW upstream of the fuel injector. Counter-rotating vortex pairs behind the fuel jet and PJ were enlarged by the PSW formation. The enlarged vortex structure behind the PJ was the main cause of the combustion enhancement.

On the behaviour characterization of metallic cellular materials under impact loading

This paper reviews the common mechanical features of the metallic cellular material under impact loading as well as the characterization methods of such behaviours. The main focus is on the innovations of various testing methods at impact loading rates. Following aspects were discussed in details. (1) The use of soft nylon Hopkinson/Kolsky bar for an enhanced measuring accuracy in order to assess if there is a strength enhancement or not for this class of cellular materials under moderate impact loading; (2) The use of digital image correlations to determine the strain fields during the tests to confirm the existence of a pseudo-shock wave propagation inside the cellular material under high speed impact; (3) The use of new combined shear compression device to determine the loading envelop of cellular materials under impact multiaxial loadings.

Investigation of the pseudo-shock wave in a two-dimensional supersonic inlet

AbstractThis paper describes experimental and numerical investigations into the multiple shock waves/turbulent boundary layer interaction in a supersonic inlet. The test model has a rectangular shape with an asymmetric subsonic diffuser of 5°. Experiments were conducted to obtain the visualization images and static pressure data by using supersonic wind tunnel. Numerical simulation was performed by solving the RANS equations with the Menter’s SST turbulent model. The inflow condition was a free-stream Mach number of 2.5 and a unit Reynolds number of 7.6 × 10 7 /m. Numerical results showed good agreement with the experimental results. Based on this agreement, the flow characteristics which are often very difficult to obtain experimentally alone were analyzed with the aid of numerical simulation. The structures, pressure and velocity distributions, and total pressure loss of the pseudo-shock wave in the supersonic inlet were presented in detail from flow visualization images and static pressures.Graphical Abstract[IMAGE]

Shock Waves in Supersonic Two-Phase Flow of CO2 in Converging-Diverging Nozzles

CO2 is a promising alternative to hazardous, ozone-depleting and global-warming refrigerants. It is more suitable to the ejector refrigeration cycle than to the vapor compression cycle. However, shock waves significantly reduce the efficiency of the ejector nozzle and, therefore, they must be investigated to improve the efficiencies of the nozzle and the ejector and the coefficient of performance of the ejector refrigeration cycle. This paper elucidates the types of shock waves in two-phase flow of CO2 in converging-diverging nozzles and their relationship to inlet conditions and two-phase thermodynamic states. Shock waves in supersonic liquid-vapor flows with low and medium quality through the diverging sections of the nozzles were investigated. Strong-and thin-equilibrium shock waves were calculated and considered as the ideal limiting case of actual shock waves. Pseudo-shock waves and dispersed shock waves were obtained from the experiment. Both were weaker than the equilibrium shock waves and indicated relaxation phenomena. Based on a theoretical model, the pseudo-shock waves had long relaxation times. The large liquid droplets formed could not be easily decelerated by the vapor. Conversely, the dispersed shock waves had short relaxation times. The small liquid droplets formed could be easily decelerated by the vapor, but the deceleration was less rapid than that in the equilibrium shock waves.

NUMERICAL INVESTIGATIONS OF PSEUDO-SHOCK WAVES IN VARIABLE CROSS-SECTION DUCTS

The Pseudo-Shock Wave (PSW), which appears when supersonic flow in duct decelerates to subsonic, is a complicated process due to the interaction between boundary layer and shock wave. It significantly affects the performance and efficiency of flow devices. In this paper, PSW in two kinds of variable cross-section ducts, edge-varied and corner-varied, was investigated through CFD numerical simulation. Compared to the rectangular duct, a shorter and wider separation region is appeared in the corner of the edge-varied duct while the strongest separation is laterally propagated across the entire plane of the corner-varied duct's side wall. This makes the performances of varied ducts different from traditional constant cross-section ducts.

Numerical analysis of pseudo-shock flow diffusion phenomenon in variable cross-section ducts

The pseudo-shock wave (PSW) region of flow diffusion, which appears when a supersonic flow in a duct decelerates to a subsonic flow, is a complicated process involving a multi-faceted interaction between the duct's peripheral boundary layer and the central shock-wave field. It is made up of an upstream shock train region, comprised of lambda and oblique shock waves, and a downstream mixing region, both of which significantly influence the effective performance of the desired flow diffusion process. In this article, the PSW in two variable-cross-sectional ducts, edge- and corner-varied in transforming from a rectangular to a circular duct moving downstream, was researched through computational fluid dynamics (CFD) numerical simulation. The PSW flowfields in circular and rectangular ducts were also computed to be counterparts. The identical inflow parameters ( Ma = 2.0, T0 = 298 K and P0 = 100 kPa) in combination with different pressure ratios ( Pb/ Pi = 2.8—3.8) were considered. The characteristics of the PSW phenomenon, such as the leading edge of the PSW, length of the shock train, mass-weighted average parameters at the exit, and so on, were analysed. For these cases, with the same pressure ratio Pb/ Pi = 3.8, the shock train length in the corner-varied duct is the shortest, and its capability of supporting backpressure is the weakest of the four ducts. For these cases, with the same leading edge of the PSW at X = 0.167 L, a shorter and wider corner flow separation region appears in the variable-cross-sectional edge-varied duct in comparison with the rectangular duct. With regard to the length of shock train, level of internal drag, and capability to support backpressure, the edge-varied duct is the superior design choice. An advantage of the edge-varied duct is the improved internal drag: an additive thrust is produced to partly offset the drag due to the duct's axial divergence-angle setting. Based on an analysis of the PSW flow pattern in these ducts, it has been established that the wall-pressure distributions of the shock train can be well predicted by the modified Waltrup formula after the introduction of an equivalent diameter and an exponent α for Reθ.

Experimental study on shock wave structures in constant-area passage of cold spray nozzle

Cold spray is a technique to make a coating on a wide variety of mechanical or electric parts by spraying solid particles accelerated through a high-speed gas flow in a converging-diverging nozzle. In this study, pseudo-shock waves in a modeled cold spray nozzle as well as high-speed gas jets are visualized by schlieren technique. The schlieren photographs reveals the supersonic flow with shock train in the nozzle. Static pressure along the barrel wall is also measured. The location of the head of pseudo-shock wave and its pressure distribution along the nozzle wall are analytically explained by using a formula of pseudo-shock wave. The analytical results show that the supersonic flow accompanying shock wave in the nozzle should be treated as pseudo-shock wave instead of normal shock wave.

高温ガス噴射と燃焼による擬似衝撃波の形成とその混合への影響

In the ram/scramjet engines, transition of the combustion mode from subsonic one to supersonic one is very important in their performance and operation. The subsonic mode combustion occurs behind a pseudo-shock wave (PSW) in a isolator, while the PSW disappears in the supersonic mode. The mode transition sometimes shows hysteresis feature caused by strong interaction among shock waves, mixing and combustion. It is necessary to understand the mechanism of this interaction for prediction of the scramjet engine performance. In our previous study, the PSW was produced by mechanically controlling back pressure of a duct, and its effect on the mixing was investigated. In the present study, the PSW was produced by hot gas injection from a N2 or H2/N2 plasma torch in a Mach 2.3 airstream. The distributions of gas composition, pitot pressure, and stagnation temperature at the exit of the test section as well as the wall pressure distribution were measured to investigate the mechanism of PSW formation by heat addition and its influence to the mixing.

413 擬似衝撃波を伴う超音速内部流動に関する研究 : 矩形ダクト内の擬似衝撃波の形成過程と特性(1)(OS4-3 高速流れと衝撃波現象の解明と制御,OS4 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

413 擬似衝撃波を伴う超音速内部流動に関する研究 : 矩形ダクト内の擬似衝撃波の形成過程と特性(1)(OS4-3 高速流れと衝撃波現象の解明と制御,OS4 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

413 擬似衝撃波を伴う超音速内部流動に関する研究 : 矩形ダクト内の擬似衝撃波の形成過程と特性(2)(OS4-3 高速流れと衝撃波現象の解明と制御,OS4 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

This paper describes an experimental study on the supersonic internal flows with Pseudo-Shock Waves (PSW) in a straight square duct with cross section of 80×80mm^2, using the pressure-vacuum type Mach 2 and Mach 4 supersonic wind tunnel of Muroran Institute of Technology. The formation process and characteristics of the Mach 2 and Mach 4 PSW were investigated by high speed digital camera observation and duct wall pressure fluctuation measurements. The free stream Mach number and unit Reynolds number just upstream of the PSW were M_∞=1.96, Re_∞=2.43×10^7m^<-1> and M_∞=3.98, Re_∞=2.22×10^7m^<-1>.

501 衝撃波を伴う超音速内部流動の研究 : マッハ2と4擬似衝撃波内のせん断応力分布(宇宙工学)

501 衝撃波を伴う超音速内部流動の研究 : マッハ2と4擬似衝撃波内のせん断応力分布(宇宙工学)

An Experiment on Choking Phenomena in Supersonic Fanno Flows

An experimental study was performed on the choking due to the friction in supersonic Fanno flows in long constant-area ducts. The results show that the choking condition of the flow is much different from the calculated value by the previous one-dimensional theory. For a given inlet Mach number and a friction coefficient of a duct, for example, the maximum possible length of the duct is shorter than that predicted by the theory. The reason has been well explained by replacing a normal shock wave assumed in the theory by a pseudo-shock wave in real flow.

Three-dimensional computation of magnetohydrodynamics in a weakly ionized plasma with strong MHD interaction

A large-scale pulsed MHD generator with an MHD channel of 4.5 m, having demonstrated the maximum electric power output of 510 MW, is studied numerically with a time-dependent three-dimensional analysis. It is shown that strong oblique shock waves are generated at a connection between the nozzle and insulating walls, traveling to the channel exit. The strong oblique shock waves cause fluctuations of gasdynamic quantities along the x-direction, resulting in a slight decrease of the Faraday current density. As a result, the strong oblique shock waves deteriorate slightly the generator performance. It is also shown that a strong pseudo-shock wave with a large boundary-layer separation is induced by the strong MHD interaction under the condition of a low channel voltage. The boundary-layer separation becomes large near the anode because of the strong Lorentz force in the y-direction attributed to the large Hall current. It is also shown that the cross-sectional secondary flow attributed to the Hall current on the y– z plane is not induced under the present conditions.

Study on shock wave and turbulent boundary layer interactions in a square duct at Mach 2 and 4

In this paper, the outline of the Mach 4 supersonic wind tunnel for the investigation of the supersonic internal flows in ducts was firstly described. Secondly, the location, structure and characteristics of the Mach 2 and Mach 4 pseudo-shock waves in a square duct were investigated by color schlieren photographs and duct wall pressure fluctuation measurements. Finally, the wall shear stress distributions on the side, top and bottom walls of the square duct with the Mach 4 pseudo-shock wave were investigated qualitatively by the shear stress-sensitive liquid crystal visualization method. The side wall boundary layer separation region under the first shock is narrow near the top wall, while the side wall boundary layer separation region under the first shock is very wide near the bottom wall.

902 擬似衝撃波を伴う超音速内部流動に関する研究 : マッハ4およびマッハ2擬似衝撃波の振動現象(2)(OS9-1 高速流れと衝撃波現象の解明と制御,OS9 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

This paper describes an experimental study on the supersonic internal flows with Pseudo-Shock Waves (PSW) in a straight square duct with cross section of 80×80mm^2, using the pressure-vacuum type Mach 4 and Mach 2 supersonic wind tunnel of Muroran Institute of Technology. The free stream Mach number and unit Reynolds number just upstream of the PSW were M_∞=3.98, R_∞=2.22×10^7m^<-1> and M_∞=1.96, R_∞=2.43×10^7m^<-1>. The oscillation phenomena of Mach 4 and Mach 2 PSW were clarified by high speed digital camera observation and duct wall pressure fluctuation measurements.

901 擬似衝撃波に対する面積拡大効果と加熱効果(2)(OS9-1 高速流れと衝撃波現象の解明と制御,OS9 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

Pseudo-shock wave, which plays an important role in the transition of combustion-mode of the dual-mode ramjet engine, was investigated in diverging ducts with experiment and numerical simulation. Heat was added to Mach 1.8 airstream by a plasma torch and combustion of hydrogen. In order to estimate effect of divergence, a quasi-one dimensional model was proposed. The model agreed the results of the numerical simulation as well as those of experiments using only the plasma torch. The model suggested that the combustion efficiency of hydrogen discretely injected was low.

901 擬似衝撃波に対する面積拡大効果と加熱効果(1)(OS9-1 高速流れと衝撃波現象の解明と制御,OS9 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

901 擬似衝撃波に対する面積拡大効果と加熱効果(1)(OS9-1 高速流れと衝撃波現象の解明と制御,OS9 高速流れと衝撃波現象の解明と制御,オーガナイズドセッション)

Study on Internal Supersonic Flows with Pseudo shock Wave Using Liquid Crystal Flow Visualization Method

The flow visualization technique using shear-sensitive liquid crystal is applied to the investigation of a Mach 2 internal supersonic flow with pseudo-shock wave (PSW) in a pressure vacuum supersonic wind tunnel. It provides qualitative information mainly concerning the overall flow structure, such as the turbulent boundary layer separation, reattachment locations and the dimensionalities of the flow. Besides, it can also give understanding of the surface streamlines, vortices in separation region and the corner effect of duct flow. Two kinds of crystals with different viscosities are used in experiments to analyze the viscosity effect. Results are compared with schlieren picture, confirming the effectiveness of liquid crystal in flow-visualization.

215 擬似衝撃波を伴う超音速内部流動に関する研究 : マッハ4擬似衝撃波の構造と振動現象(流体工学(3))

215 擬似衝撃波を伴う超音速内部流動に関する研究 : マッハ4擬似衝撃波の構造と振動現象(流体工学(3))

401 超音速矩形ダクト内のマッハ4擬似衝撃波の構造と壁面せん断応力分布(OS4-1 高速流れと衝撃波現象の基礎と応用(内部流れ),OS4 高速流れと衝撃波現象の基礎と応用,オーガナイズドセッション)

401 超音速矩形ダクト内のマッハ4擬似衝撃波の構造と壁面せん断応力分布(OS4-1 高速流れと衝撃波現象の基礎と応用(内部流れ),OS4 高速流れと衝撃波現象の基礎と応用,オーガナイズドセッション)