Effect of Nonequilibrium Condensation of Moist Air on the Boundary Layer in a Supersonic Nozzle

When condensation occurs in supersonic flow fields, the flow is thected by the latent heat released. In the present study, Navier-Stokes equations were solved numerically using a 3rd-order MUSCL type TVD finitedifference scheme with a second-order fractionabetep for time integration. Baldwin-Lomax model, that is the algebraic model, called the zero equation model was used in the computations. The effects of initial conditions (initial degree of supersaturation and total temperature in the reservoir) on condensing fiow of moist air in a supersonic circular half nozzle were investigated. In this case, the effect of condensation on the boundary layer was also discussed in detail. As a result, the simulated flow fields were compared with experimental data in good agreement, and the velocity and temperature profiles were largely changed by condensation.

A Study of the Gas Flow through a LNG Safety Valve

A safety valve functions to control an upper limit of pressure inside the LNG line of transportation. If the pressure inside the safety valve nozzle exceeds a predetermined value on the valve sheet which plugs the nozzle, an excess of LNG discharges through the gap between the nozzle exit and valve sheet. In this situation, the forces acting on the valve sheet are gasdynamic forces generated by the discharge of LNG and mechanical forces supported by the spring behind the valve sheet. The flow through the gap is very complicated, involving vortices, flow separation, and shock waves. These affect adversely on the system accompanying with noise and vibration. The present study aims at understanding the flow physics of safety valve. A computational work using the twodimensional, axisymmetric, compressible Navier-Stokes equations is carried out to simulate the gas flow between the nozzle exit and valve sheet, and compared with the theoretical results. It has been found that there exists a distance between nozzle exit and valve sheet in which the thrust coefficient at the valve sheet increases abruptly.

Study on the Characteristics of Supersonic Coanda Jet

Techniques using Coanda effect have been applied to the fiuid control devices. In this field, experimental studies were so far performed for the spiral jet obtained by the Coanda jet issuing from a conical cylinder with an annular slit, thrust vectoring of supersonic Coanda jets and so on. It is important from the viewpoints of effective applications to investigate the characteristics of the supersonic Coanda jet in detail. In the present study the effects of pressure ratios and nozzle configurations on the characteristics of the supersonic Coanda jet have been investigated experhoentally by a schlieren optical method and pressure measurements. Furthermore, Navier-Stokes equations were solved numerically using a 2nd-order TVD finite-volume scheme with a 3rd-rorder three stage Runge-Kutta method for time integration. k - ε model was used in the computations. The effects of initial conditions on Coandaflow were investigated numerically As a result, the simulated flow helds were compared with experimental data in good agreement qualitatively.

Numerical Study for Hysteresis Phenomena of Shock Wave Reflection in Overexpanded Axisymmetric Supersonic Jet

When the high-pressure gas is exhausted to the vacuum chamber from the supersonic nozzle, the overexpanded supersonic jet is formed at specific condition. In two-dimensional supersonic jet, furthermore, it is known that the hysteresis phenomena for the reflection type of shock wave in the flow field is occurred under the quasi-steady flow and for instance, the transitional pressure ratio between the regular reflection （RR） and Mach reflection （MR） is affected by this phenomenon. Many papers have described the hysteresis phenomena for underexpanded supersonic jet, but this phenomenon under the overexpanded axisymmetric jet has not been detailed in the past papers. The purpose of this study is to clear the hysteresis phenomena for the reflection type of shock wave at the overexpanded axisymmetric jet using the TVD method and to discuss the characteristic of hysteresis phenomena.

Passive Control of Transonic Flow Fields with Shock Wave Using Non-equilibrium Condensation and Porous Wall

When non-equilibrium condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, in order to control the transonic flow field with shock wave, a condensing flow was produced by an expansion of moist air on a circular bump model and shock waves were occurred in the supersonic parts of the fields. Furthermore, the additional passive technique of shock / boundary layer interaction using the porous wall with a cavity underneath was adopted in this flow field. The effects of these methods on the shock wave characteristics were investigated numerically and experimentally. The result obtained showed that the total pressure loss in the flow fields might be effectively reduced by the suitable combination between non-equilibrium condensation and the position of porous wall.

Passive Control of Steady Condensation Shock Wave

When condensation occurs in supersonic flow fields, the flow is affected by the latent heat released, and if the heat released exceeds a certain quantity, a condensation shock wave will occur There are many papers for the passive control of shock-boundary layer interaction using the porous wall with a plenum underneath on the application of the technique to transonic airfoil flows. In the present study, this passive technique is applied to the control of a steady condensation shock wave generated in a supersonic nozzle. In order to clarify the effect of the passive shockboundary layer control on condensation shock, Navier-Stokes equations were solved numerically using a 3rd-order MUSCL type TVD finite-difference scheme with a second-order fractional-step for time integration. As a result, the simulated flow fields were compared with experimental data in good agreement and the aspect of the flow field has been clarified.

Effect of Non-Equilibrium Condensation of Moist Air on Flow Field in Ludwieg Tube

The time-dependent behavior of non-equilibrium condensation of moist air through a Ludwieg tube with a diaphragm downstream is investigated by using a computational fluid dynamics work. The two-dimensional, compressible, Navier-Stokes equations, fully coupled with the condensate droplet growth equations, are numerically solved by a third-order MUSCL type TVD finite-difference scheme with a second-order fractional time step. Baldwin-Lomax turbulence model is employed to close the governing equations. The present computations represent the experimental flows well. The results obtained show that for an initial relative humidity over 40 %, the periodic excursions of the condensation shock occurs in the Ludwieg tube, and the frequency increases with the initial relative humidity. It is also found that total pressure loss due to non-equilibrium condensation in the Ludwieg tube should not be ignored even for a very low initial relative humidity. Furthermore, the variations of condensation properties are also

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.

A Computational Investigation on the Control of Cavity-Induced Pressure Oscillations Using Sub-Cavity

A computational investigation has been conducted to determine the effectiveness of a passive control technique of attenuating cavity-induced pressure oscillations in a confined two-dimensional supersonic flow. The passive control technique is achieved by fitting two flat plates near the front wall of a square cavity at Mach number 1.83 at the cavity entrance. The results showed that the flat plates attached near the front wall of the cavity, discouraged the formation of feedback loop which is widely believed to be the reason of cavity resonance. The resultant amount of attenuation of pressure oscillations was also dependent on the length of the flat plate used as an oscillation suppressor.

Experimental Study of Twin Pulse Jet Engines for Power Plant Application

The total efficiency of power plants depends on the energy conversion in a combustor and a turbine .Considerably higher energy transfer rates can be obtained from a pulsed combustion.but unsteady flow of a single jet combustor reduces the turbine efficiency.Therefore.two pulse combustors were set in parallel and connected to a settling chamber that supplies a flow with constant pressure to the turbine.The aim of investigations presented here is a demonstration of technical feasibility for industrial applications and to show the benefits obtained from the pulse combustors.