Characteristics of Compression Wave Caused by Reflection of Expansion Wave at Open End of Tube

When an expansion wave propagated along a constant area straight tube reaches at the open end, the negative impulsive wave and the compression wave are formed by the emission and reflection of expansion wave. The negative impulsive wave is emitted toward the surrounding area and causes an impulsive noise like the sonic boom. The compression wave propagates in the tube toward the upstream and may cause the impulsive noise at the surrounding area of tube portal. With the advance of industrial engineering, it seems that the discharging of the expansion wave will become important problems. In this study, the experimental and numerical investigations are carried out using the shock tube and the TVD numerical method. The formation process of compression wave near the open end, the relationship with the compression wave and the expansion wave and the characteristics of compression wave are discussed.     

Characteristics of Spherical Shock Wave and Circular Pulse Jet Generated by Discharge of Propagating Shock Wave at Open End of Tube

When the shock wave propagating in the straight circular tube reaches at the open end, the impulsive wave is generated by the emission of a shock wave from an open end, and unsteady pulse jet is formed near the open end behind the impulsive wave under the specific condition. The pulse jet transits to spherical shock wave with the increase in the strength of shock wave. The strength is dependent on the Mach number of shock wave, which attenuates by propagation distance from the open end. In this study, the mechanism of generating the unsteady pulse jet, the characteristics of the pressure distribution in the flow field and the emission of shock wave from straight circular tube which has the infinite flange at open end are analyzed numerically by the TVD method. Strength of spherical shock wave, relation of shock wave Mach number, distance decay of spherical shock wave and directional characteristics are clarified.     

Discharge of a shock wave from an open end of a tube

IntroductionWhen a Pressure wave such as the shock waveprOPagates along a constant area straight tube andreaches at the open end, an impulsive wave is emittedOutward from the tube exit toward the surrounding areaand causes an impulsive noise laal a sonic boomproduced by a supersonic aircraft. Therefore, someauthors have investigated the discharge of a weakcompression wave from an open end in order to reducethe impulsive noise in relation to'the high speed railWaytUImel in the previous paped'…     

Passive Control of an Impulsive Wave Using a Cavity／Helical Vane System

INTRODUCTIONUnsteadycompressiblegasflowthroughaductisoftenencoullteredinmanyengineeringapplicationsandhasbeeninvestigatedbymanyresearchers.Whenapressurewavegeneratedinsideaductisdischargedfromanopenendoftheduct.animpulsivewave,whichcanbefrequentlycha...     

Effect of exit geometry of tail pipe on the performance of pulse jet engines

In this paper,the effect of geometries of tube open end on the shock,compression and expansion wavespropagating in the tube was investigated numerically and experimentally.One of them is a conventional straightshock tube with an open end.The other has a divergent tail tube at the exit.Applying a divergent tail tube(flaretube)to an open end shock tube,the period of one-cycle process could be shortened and the pressure behind theexpansion wave produced at the exit of the shock tube could be lowered much more below the atmosphericpressure than that produced in the straight tube.The results suggested that the intake air into the engine wassignificantly increased by applying a flare tube instead of a straight tube.     

Unsteady transonic flow control around an airfoil in a channel

Transonic internal flow around an airfoil is associated with self-excited unsteady shock wave oscillation. This unsteady phenomenon generates buffet, high speed impulsive noise, non-synchronous vibration, high cycle fatigue failure and so on. Present study investigates the effectiveness of perforated cavity to control this unsteady flow field. The cavity has been incorporated on the airfoil surface. The degree of perforation of the cavity is kept constant as 30%. However, the number of openings (perforation) at the cavity upper wall has been varied. Results showed that this passive control reduces the strength of shock wave compared to that of baseline airfoil. As a result, the intensity of shock wave/boundary layer interaction and the root mean square (RMS) of pressure oscillation around the airfoil have been reduced with the control method.     

Numerical study of shock tube flows with homogeneous and heterogeneous condensations in rarefaction wave

<正>Shock tubes are devices in which the state of a gas is changed suddenly from one uniform state to another by the passage of shock and expansion waves.In the theory of ideal shock tube flow,it is customarily assumed that the unsteady expansion and shock waves generated by diaphragm rupture are a perfectly centered plane wave.However, such waves are generally not centered,or may not even by plane in practice.In the present research,the time-dependent behavior of homogeneous and heterogeneous condensation of moist air in the shock tube is investigated by using a computational fluid dynamics work.Further,the numerical and experimental studies were carried out in order to investigate the effect of the diaphragm rupture process on the flow characteristics of expansion and shock waves generated near the diaphragm.     

Shock wave smearing by passive control

Normal shock wave, terminating a local supersonic area on an airfoil, limits its performance and becomes a source of high speed impulsive noise. It is proposed to use passive control to disintegrate the shock wave. Details of the flow structure obtained by this method are studied numerically. A new boundary condition has been developed and the results of its application are verified against experiments in a nozzle flow. The method of shock wave disintegration has been confirmed and detailed analysis of the flow details is presented. The substitution of a shock wave by a gradual compression changes completely the source of the high speed impulsive noise and bears potential of its reduction.     

Study on gas and wave in a receiving tube

The gas and wave＇s motion in a receiving tube are investigated numerically and experimentally in the present paper. The results show that, velocity of the contact face rises rapidly as gas is injected into the receiving tube, and then drops sharply after a steady propagation. However, velocity of the wave in the tube is almost linear and the wave can be reflected at the close end of the receiving tube. With increasing of inlet pressure, velocity of the wave and steady velocity of contact face also increase. There is obvious thermal effect as the wave sweeps the gas. The reflected wave can heat the exhausting gas in the open end. As an absorber, an expander and a shrink in the robe can almost completely absorb the reflected wave.     

A Study of the Impulse Wave Discharged from the Exits of Two Parallel Tubes

The twin impulse wave leads to very complicated flow fields, such as Mach stem, spherical waves, and vortex ring. The twin impulse wave discharged from the exits of the two tubes placed in parallel is investigated to understand the detailed flow physics associated with the twin impulse wave, compared with those in a single impulse wave. In the current study, the merging phenomena and propagation characteristics of the impulse waves are investigated using a shock tube experiment and by numerical computations. The Harten-Yee's total variation diminishing (TVD) scheme is used to solve the unsteady two-dimensional compressible Euler equations. The Mach number Ms of incident shock wave is changed below 1.5 and the distance between two-parallel tubes, L/d, is changed from 1.2 to 4.0. In the shock tube experiment, the twin impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. The results obtained show that on the symmetric axis between two-parallel tube     

Study of the Unsteady Condensation of Moist Air in Shock Tube

The major flow physics of the unsteady condensation in the subsonic flows induced by the unsteady expansion waves in shock tube was studied in this paper. The unsteady condensation phenomenon was analyzed by using the two-dimensional, unsteady, Navier-Stokes equations, which were fully coupled with a droplet growth equation. The third-order TVD MUSCL scheme was applied to solve the governing equation systems. The computational results were compared with the previous experimental data. The time-dependent behavior of unsteady condensation of moist air in shock tube was investigated in details. The results show that the major characteristics of the unsteady condensation phenomenon in shock tube are very different from those in the supersonic wind tunnels.     

Prandtl number dependence of unsteady natural convection along a vertical plate in a stably stratified fluid

The Prandtl number dependence of unsteady laminar natural convection along an infinite vertical plate in a thermally stratified fluid is investigated. Flows are induced by an impulsive (step) change in plate temperature and by a suddenly imposed plate heat flux. Analytical solutions of the viscous equations of motion and thermodynamic energy are obtained for Prandtl numbers near unity by the method of Laplace transforms and a regular perturbation expansion. The zeroth-, first- and second-order terms in the expansion are obtained for an impulsive change in plate temperature, while the zeroth- and first-order terms are obtained for a sudden application of a plate heat flux. The developing boundary layers are thicker, more vigorous, and more sensitive to the Prandtl number at smaller Prandtl numbers (<1) than at larger Prandtl numbers (>1). The analytical results are confirmed and extended with results from numerical simulations for Prandtl numbers strongly deviating from unity.     

Thermoacoustic streaming in a tube with isothermal outer surface

Thermoacoustic oscillations at a cycle-steady state in a tube with an isothermal outer wall, and with one end closed and the other end connected to a wave generator, is analyzed based on a linearized theory. From the global mass conservation, an analytical solution has been obtained for the cross-sectional and cycle averaged axial velocity. It is shown that this averaged velocity is non-vanishing due to the mass streaming effect. By analyzing the global momentum balance, it is found that the cycle-averaged pressure depends on the momentum streaming and friction force, and a conservation relationship exists between the momentum streaming and the cycle-averaged pressure for the flow oscillating at a high frequency in a wide tube. An investigation of the global energy balance leads to an expression for thermoacoustic energy streaming. Furthermore, it is shown that the refrigeration effect is mainly caused by the non-vanishing mean velocity, and therefore the mass streaming and the energy streaming are intimately connected.     

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, compressor blades 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 experimentally and as a result, it was observed that the bump wall is effective for the control of shock wave on the airfoil. In the transonic 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 wave oscillation around a circular arc blade with or without a bump on the blade was investigated numerically. The results showed that the non-equilibrium condensation significantly reduced the flow field unsteadiness such as root mean of pressure oscillation and frequency compared to the case without the non-equilibrium condensation.     

Transport from a volatile meniscus inside an open microtube

A generalized model is developed which couples the evaporation at a liquid–air interface with the vapor diffusion processes in air to enable an investigation of the mass transport inside an open microtube. Tube inner diameters ranging from 100 to 1200 μm are considered. Evaporation is strongest at the meniscus junction with the tube wall due to the highest local vapor diffusion flux at this location. A temperature gradient is set up from the axis of the tube to the wall and results in Marangoni convection. The three-dimensional flow structure in the microtube is simulated with the effects of Marangoni convection, buoyancy, and the influx of fluid to the interface being included. For horizontal tubes of diameter 100 μm or larger immersed in a water bath, flow asymmetry due to buoyancy is observed. A large vortex is formed in the lower part of the tube cross-section, while a small vortex forms above. However, the primary cause of asymmetry is found to be the external thermal profile imposed on the microtube, especially when the meniscus is far from the outlet of the tube. The simulated flow patterns are found to be consistent with experimental measurements.     

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.     

Passive control of unsteady condensation shock wave

IntroductionIn the case of moist air or steam rapidly expanding ina supersonic nozzle, nollequilibrium condensation occursin the flow field and the flow will be affected by thelatent heat leleased by condensationll-4]. Thereby, if theheat exceeds a certain quantity, the flow will becomeunstable and oscillations of a periodic flow occurs[5-91. Forthe unsteady condensation shock wave, it is blown thatthere are three types of oscillationslg]. These types aredescribed below:1. Mode l: A condensat…     

Attenuation and distortion of compression waves propagating in very long tube

A lot of phenomena related to propagating various waves are seen when the high-speed train goes through the tunnel, the gas pipeline is broken due to an accident or the air brake of the wagon operates. For instance, a compression wave generated ahead of a high-speed train entering a tunnel propagates to the tunnel exit and spouts as a micro pressure wave, which causes an exploding sound. In order to estimate the magnitude correctly, the mechanism of the attenuation and distortion of a compression wave propagating along a very long tunnel must be understood and the experimental information on these phenomena is required. An experimental investigation is carried out to clarify the attenuation and distortion of the propagating compression wave in a very long tube. Experimental results show that the strength of a compression wave decreases with distance. The attenuation and distortion of compression waves are affected by the initial waveform of the compression wave and by the unsteady boundary layer induced by the propagating wave. The shape of a compression wave becomes different with the propagating distance; that is, a shock wave appears just head of a wavefront and an overshoot on pressure distribution is observed behind a shock wave due to the transition of the unsteady boundary layer.     

Short-time solution for unsteady forced convection heat transfer from an impulsively started circular cylinder

Short-time solution for unsteady heat transfer from an impulsively started circular cylinder is presented. Consideration is given to the case where unsteady temperature field is produced by the sudden imposition of a constant temperature difference between the body and the fluid as the impulsive motion is started. The present theory should be valid for any Prandtl number and for any Reynolds number larger than about 100. The Nusselt number results obtained are compared with the available numerical and theoretical ones.     

Coexisting state of surge and rotating stall in a two-stage axial flow compressor using a double-phase-locked averaging technique

The interaction between surge and rotating stall in an axial flow compressor was investigated from the viewpoint of an unsteady inner flow structure. The aim of this study was to identify the key factor that determines the switching phenomenon of a surge cycle. The main feature of the tested compressor is a shock tube connected in series to the compressor outlet through a diaphragm, slits, and a concentric duplex pipe: this system allows surge and rotating stall to be generated by connecting the shock tube with the compressor, or enables the compression plane wave injection. The unsteady characteristics and the internal flow velocity fluctuations were measured in detail, and the stall cell structure was averaged and visualized along the movement of the operation point under a coexisting state of surge. A coefficient of the cell scale fluctuation was calculated using the result of the averaging, and it confirmed that the processes of inner flow structure change differed from each other according to the next cycle of the surge. The result suggests that the key factor that determines the next cycle is the transformation of the internal flow structure, particularly between the stall cell and the entire circumferential stall, in both the recovering and stalling processes.