Three-Dimensional Structure of Non-Equilibrium Homogeneous Condensation Flow in a Supersonic Rectangular Nozzle

Numerical simulations have been carried out for a supersonic three-dimensional rectangular arc nozzle, where a secondary flow toward the center of the curvature occurs due to the shape of the nozzle. It is known that secondary flow causes longitudinal vortices to form near the wall of the nozzle corner, making the nozzle outlet flow unstable and induces loss of transport energy. When the working fluid is a condensable gas with relatively large latent heat such as moist air or steam, rapid accelerated expansion in the nozzle causes non-equilibrium condensation due to supersaturation. After the release of latent heat during phase transition, nozzle flow continues expanding at an equilibrium saturation condition. In the absence of foreign particles, e.g. ions or dust particles, condensation nuclei are formed in the gas itself causing non-equilibrium homogeneous condensation. Supersonic nozzle flow properties vary considerably due to the occurrence of condensation phenomenon. The objective of this study is to investigate the effect of non-equilibrium homogeneous condensation on the longitudinal vortices which form in the range close to the corner of rectangular arc nozzle numerically.

Effects of Supersonic Nozzle Geometry on Characteristics of Shock Wave Structure

Interaction between the normal shock wave and the turbulent boundary layer in a supersonic nozzle becomes complex with an increase of a Mach number just before the shock wave. When the shock wave is strong enough to separate the boundary layer, the shock wave is bifurcated, and the 2nd and 3rd shock waves are formed downstream of the shock wave. The effect of a series of shock waves thus formed, called shock train, is considered to be similar to the effect of one normal shock wave, and the shock train is called pseudo-shock wave. There are many researches on the configuration of the shock wave. However, so far, very few researches have been done on the asymmetric characteristics of the leading shock wave in supersonic nozzles. In the present study, the effect of nozzle geometry on asymmetric shock wave in supersonic nozzles has been investigated experimentally.

Numerical Study on Transonic Flow with Local Occurrence of Non-Equilibrium Condensation

Characteristics of transonic flow over an airfoil are determined by a shock wave standing on the suction surface. In this case, the shock wave/boundary layer interaction becomes complex because an adverse pressure gradient is imposed by the shock wave on the boundary layer. Several types of passive control techniques have been applied to shock wave/boundary layer interaction in the transonic flow. Furthermore, possibilities for the control of flow fields due to non-equilibrium condensation have been shown so far and in this flow field, non-equilibrium condensation occurs across the passage of the nozzle and it causes the total pressure loss in the flow field. However, local occurrence of non-equilibrium condensation in the flow field may change the characteristics of total pressure loss compared with that by non-equilibrium condensation across the passage of flow field and there are few for researches of locally occurred non-equilibrium condensation in a transonic flow field. The purpose of this study is to clarify the effect of locally occurred non-equilibrium condensation on the shock strength and total pressure loss on a transonic internal flow field with circular bump. As a result, it was found that shock strength in case with local occurrence of non-equilibrium condensation is reduced compared with that of no condensation. Further, the amount of increase in the total pressure loss in case with local occurrence of non-equilibrium condensation was also reduced compared with that by non-equilibrium condensation across the passage of flow field.

Numerical Study on the Effect of Unsteady Downstream Conditions on Hydrogen Gas Flow through a Critical Nozzle

A critical nozzle (sonic nozzle) is used to measure the mass flow rate of gas. It is well known that the coefficient of discharge of the flow in the nozzle is a single function of Reynolds number. The purpose of the present study is to investigate the effect of unsteady downstream condition on hydrogen gas flow through a sonic nozzle, numerically. Navier-Stokes equations were solved numerically using 3rd-order MUSCL type TVD finite-difference scheme with a second-order fractional-step for time integration. A standard k-ε model was used as a turbulence model. The computational results showed that the discharge coefficients in case without pressure fluctuations were in good agreement with experimental results. Further, it was found that the pressure fluctuations tended to propagate upstream of nozzle throat with the decrease of Reynolds number and an increase of amplitude of pressure fluctuations.

A Computational Study of Thrust Vectoring Control Using Dual Throat Nozzle

Dual throat nozzle (DTN) is fast becoming a popular technique for thrust vectoring. The DTN is designed with two throats, an upstream minimum and a downstream minimum at the nozzle exit, with a cavity in between the upstream throat and exit. In the present study, a computational work has been carried out to analyze the performance of a dual throat nozzle at various mass flow rates of secondary flow and nozzle pressure ratios (NPR). Two-dimensional, steady, compressible Navier-Stokes equations were solved using a fully implicit finite volume scheme. The present computational results were validated with available experimental data. Based on the present results, the control effectiveness of thrust-vectoring is discussed in terms of the thrust coefficient and the coefficient of discharge.

Effects of Heterogeneous Condensation on the Transonic Flow Fields on a Bump Model

In the present study, effect of the heterogeneous condensation on the characteristics of shock wave generated on the bump model in the transonic flow field was investigated numerically. As a result, it was found that, for the flow field with steady adiabatic shock wave on the bump model, the condensation with heterogeneous nucleation has a strong effect on the whole flow field, and it reduced the strength of the shock. Furthermore, the total pressure loss was dependent on the concentration of the solid particles per unit volume.

Effect of Nozzle Inlet Shape on Annular Swirling Flow with Non-Equilibrium Condensation

Recently,by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow,a separating and extracting techniques of condensate gas have been developed.This technique can reduce the size of the device and don't use chemicals.In the present study,by using a non-equilibrium condensation phenomenon of moist air occurred in the supersonic flow in the annular nozzle composed of an inher body and an outer nozzle with a swirl,the possibility of separation of the condensable gas and the effect of shape of nozzle inlet on the flow field were examined numerically.

Unsteady Shock-Flow Characteristics in an Over-Expanded Rocket Nozzle

A numerical investigation of transient side-loads in an axisymmetric over-expanded thrust optimized contour nozzle is presented.These nozzles experience side-loads during start-up and shut-down operations,because of the flow separation at nozzle walls.Two types of flow separations such as FSS and RSS shock structure occur.A two-dimension numerical simulation has been carried out over an axisymmetric TOC nozzle to validate present results and investigate oscillatory flow characteristics for start-up processes.Reynolds Averaged Navier-Stokes equations are numerically solved using a fully implicit finite volume scheme.Governing equations are solved by coupled implicit scheme.Reynolds Stress turbulence model is selected.Present computed pressure at the nozzle wall closely matched with experiment data.A hysteresis phenomenon has been observed between these two shock structures.The transition from FSS to RSS pattern during start-up process has shown maximum nozzle wall pressure.Nozzle wall pressure and shear stress values have shown fluctuations during the FSS to RSS transition. The oscillatory pressure has been observed on the nozzle wall for high pressure ratio.Present results have shown that magnitude of the nozzle wall pressure variation is high for the oscillatory phenomenon.

Transonic Moist Air Flow around a Circular Arc Blade with Bump

The unsteady phenomena in the transonic flow around airfoils are observed in the flow field of fan, compressorblades and butterfly valves, and this causes often serious problems such as aeroacoustic noise and the vibration.In recent years, the effect of bump wall on the flow field around an airfoil has been investigated experimentallyand as a result, it was observed that the bump wall is effective for the control of shock wave on the airfoil. In thetransonic or supersonic flow field, a rapid expansion of moist air or steam gives rise to non-equilibrium condensation.In the present study, the effect of non-equilibrium condensation of moist air on the self-excited shock waveoscillation around a circular arc blade with or without a bump on the blade was investigated numerically. The resuitsshowed that the non-equilibrium condensation significantly reduced the flow field unsteadiness such as rootmean of pressure oscillation and frequency compared to the case without the non-equilibrium condensation.

Control of the Asymmetric Flow in Rocket Nozzles

In some rocket nozzle flows, the existence of the transition from FSS to RSS and the occurrence of asymmetric flow are known in previous researches. As a result, the transition causes excessive side-loads that may damage the nozzle. Thus, it is important to investigate the method in order to control the asymmetric flow separation. In the present study, the relationship between the asymmetric separation and the rate of change of the pressure ratio with time was investigated from the point of view of the transition from FSS to RSS in the supersonic nozzle experimentally. Further, change of the flow separation by using step and cavity, and the possibility of the control was demonstrated. As a result, it was shown that the method using a cavity was effective for the control of the separation pattern.

Hysteretic Phenomenon of Shock Wave in a Supersonic Nozzle

In recent years, hysteretic phenomena in fluid flow systems drew attention for their great variety of industrial and engineering applications. When the high-pressure gas is exhausted to atmosphere from the nozzle exit, the expanded supersonic jet with the Mach disk is formed at a specific condition. In two-dimensional expanded supersonic jet, the hysteresis phenomenon for the reflection type of shock wave is occurred under the quasi-steady flow and the transitional pressure ratio between the regular reflection and Mach reflection is affected by this phenomenon. However, so far, there are very few researches for the hysteretic phenomenon of shock wave in a supersonic internal flow and the phenomenon has not been investigated satisfactorily. The present study was concerned with the experimental and numerical investigations of hysteretic phenomena of shock wave in a supersonic nozzle, and discussed the relationship between hysteresis phenomenon and rate of the change of pressure ratio with time.

Effect of Axisymmetric Sonic Nozzle Geometry on Characteristics of Supersonic Air Jet

The effect of nozzle geometry on sonic line and characteristics of supersonic air jet was studied. Computational fluid dynamics was applied in this study. The axisymmetric nozzle geometries investigated were two different contour converging nozzles, two different conically converging sharp-edged nozzles and a sharp-edged orifice. The results show that the supersonic jet structure, sonic line and streamlines in supersonic jet are strongly influenced by the nozzle geometry, and the total pressure loss increases with the increase of Mach disk diameter. The present numerical simulation is an effective tool to evaluate compressible flows in supersonic air jet.

Annular Supersonic Swirling Flows with Heterogeneous Condensation

In recent years,separating and extracting technologies of condensate gas have been developed by combining a swirl flow with non-equilibrium condensation phenomena of condensate gas generated in a supersonic flow.The technology can reduce the size of the device and does not use chemicals.However,there are many unresolved problems for performance of the separation,extraction and operating principle.Therefore it is necessary to research further in order to improve the performance of the equipment.In the present study,the numerical study was carried out to clarify the effect of the heterogeneous condensation on the characteristics of the swirling flow field in a supersonic annular nozzle,and the differences between homogeneous condensation and heterogeneous condensation in the flow field.As the results,it is found that the condensation flow with a swirl affects the position of sonic line,the generating position of condensate and the radial distribution ratio of liquid phase.

Effect of Non-Equilibrium Condensation of Moist Air on Unsteady Behaviour of Shock Waves around a Circular Arc Blade

在在机翼附近的接近音速的流动的不稳定的现象在扇子，压缩机片和蝴蝶阀门的流动地里被观察，并且这经常引起象 aeroacoustic 噪音那样的严重问题，颤动。在蒸汽在主要流动被包含的接近音速或超声的流动，流动的快速的扩大可以产生一个非平衡冷凝作用。然而，在机翼附近的接近音速的内部流动上的非平衡冷凝作用的效果还没令人满意地被澄清了。在现在的学习，圆形的弧片上的自我刺激的冲击波摆动上的潮湿的空气的非平衡冷凝作用的效果数字地被调查。结果证明在有非平衡冷凝作用的情况中，没有非平衡冷凝作用，流动摆动的频率变得比那些小。

Study of Spiral Flow Generated through an Annular Slit

The effect of pressurized air inlets in the reservoir upstream of the annular slit on characteristics of the axial and tangential velocity components is investigated numerically, and the mechanism of occurrence of spiral nozzle flow is clarified. In simulations, Unified Platform for Aerospace Computational Simulation (UPACS) is used. The governing equations under consideration are the unsteady compressible Navier - Stokes. A second-order finite volume scheme with MUSCL (Roe scheme) is used to discretize the spatial derivatives, and a second order-central difference scheme for the viscous terms, and a MFGS (Matrix Free Gauss Seidel) is employed for time integration. Spalart-Allmaras model was used as a turbulence model. The results obtained are compared with velocity distributions in the experiment measured by the two-component fiber optic laser Doppler velocimeter system. The existence of discrete pressurized air inlets that leads to the occurrence of asymmetrical characteristics is a very important factor for the formation of spiral flow.

Effect of Annular Slit Geometry on Characteristics of Spiral Jet

A spiral flow using an annular slit connected to a conical cylinder does not need special device to generate a tangential velocity component of the flow and differs from swirling flows. Pressurized fluid is supplied to an annular chamber and injected into the convergent nozzle through the annular slit. The annular jet develops into the spiral flow. In the present study, a spiral jet discharged out of nozzle exit was obtained by using a convergent nozzle and an annular slit set in nozzle inlet, and the effect of annular slit geometry on characteristics of the spiral jet was investigated by using a Laser Doppler Velocimeter (LDV) experimentally. Furthermore, velocity distributions of the spiral jet were compared with those of a normal jet.

Passive Control of Condensation Shock Wave in Prandtl-Meyer Expansion Flow

In this paper,the effects of the passive technique by using the slotted wall on the characteristics of a condensation shock wave generated in a Prandtl-Meyer flow were investigated experimentally.Furthermore,in order to clarify the variation of condensation properties in the flow field.navier-Stoker equations were solved numerically using a 3rd-order MUSCL type TVD finite-difference scheme with a second-order fractional-step for time integration.Baldwin-Lomax odel was used as a turbulence model in the computations.From experimental results,it was found that the shock strength on the slotted wall became weak in compariosn with no passive case(solid wall),and the present passive technique was the most effective when a foot of the condensation shock wave was located at the middle of slotted wall.Furthermore.it was confirmed numerically that the passive technique was also effective for the unsteady condensation shock wave.

Generating and Focusing of Underwater Expansion Wave using a Silicon Resin Reflector

In the present study, an ellipsoid reflector was designed and produced using silicon resin in order to generate and focus expansion wave in water for the purpose of a medical application. Across an expansion wave the static pressure, temperature and density decrease, as a result, negative pressure is given behind the expansion wave generated in the water, and then a tensile stress is induced. As an acoustic impedance of the silicon resin is almost similar to that of water, the interface of air-silicon resin would be regarded as the same with that of the air-water. A high voltage discharge was used as an energy source of underwater shock wave. When the underwater shock wave reflects on this interface, it is already clear that the shock wave converts to the expansion wave. The generation and focusing of the expansion wave were carried out and the phenomena were observed by flow visualization using a high-speed camera.

Investigation on Temperature Separation and Flow Behaviour in Vortex Chamber

In the previous researches, it is known that the swirl flow in circular pipe causes the temperature separation. Recently, it is shown that the temperature separation occurs in a vortex chamber when compressed air are pumped into this device from the periphery. Especially, in a cavity installed in the periphery of the chamber, the highest temperature was observed. Therefore, it is expected that this device can be used as a heat source in the engineering field. In recent researches, the mechanism of temperature separation in vortex chamber has been investigated by some researchers. However, there are few researches for the effect of diameter and volume of vortex chamber, height of central rod and position of cavity on the temperature separation. Further, no detailed physical explanation has been made for the temperature separation phenomena in the vortex chamber. In the present study, the effects of chamber configuration and position of the cavity on temperature separation in the vortex chamber were investigated experimentally.

Control of Transonic Flow Fields Using Local Occurrence of Non-Equilibrium Condensation

Control of supersonic flow fields with shock wave is important for some industrial fields. There are many studies for control of the supersonic flow fields using active or passive control. When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by latent heat released. Many studies for the condensation have been conducted and the characteristics have been almost clarified. Further, it was found that non-equilibrium condensation can control the flow field. In these studies, the condensation occurs across the passage of the flow field and it causes the total pressure loss in the flow field. However, local occurrence of non-equilibrium condensation in the flow field may change the characteristics of total pressure loss compared with that by the condensation across the passage of the nozzle and there are few for researches of locally occurred non-equilibrium condensation in supersonic flow field. The purpose in the present study is to clarify the effect of local occurrence of non-equilibrium condensation on the transonic flow field in a nozzle with a circular bump. As a result, local occurrence of non-equilibrium condensation reduced the shock strength and total pressure loss in the transonic flow field by flowing the moist air from trailing edge of the circular bump to the mainstream.