Non-equilibrium Condensation Of Moist Air Research Articles

Transonic moist air flows with release of latent heat by non-equilibrium condensation

This study proposes a numerical method for solving transonic moist air flows with non-equilibrium condensation by taking FLUENT as the secondary development platform. The governing equations consist of moist air motion equations with an additional source term in the energy equation, which considers the effects of heat addition, and a set of four ordinary differential equations that are related to the generation of condensate mass. The moist air motion equations are solved using the standard features of the code in FLUENT, whereas the four ordinary differential equations are modelled using the user-defined-scalar transport modelling provided by FLUENT. This numerical method is validated both under internal and external flow conditions in a turbine cascade and over the NACA 0012 airfoil. Further investigations include testing the moist air flows in a compressor cascade channel and over the asymmetric RAE 2822 airfoil. The results show that the non-equilibrium condensation of moist air under transonic flow condition has a significant influence on the flow field structure and the aerodynamic performance of the turbine and compressor cascade.

Effect of condensing moist air on unsteady shock waves around a symmetric disk in transonic internal flows

Shock waves are often observed around a symmetric disk in transonic or supersonic internal flow fields. In these cases, shock wave-boundary layer interaction becomes complex and induces the unsteady self-excited shock oscillations in the flow field. However, when water vapor is contained in the main flow, rapid expansion of the flow may give rise to non-equilibrium condensation of moist air. In the present study, the effect of condensing moist air flows on unsteady behavior of shock waves around a symmetric disk is studied numerically. The flow fields were investigated at two pressure ratios (total back pressure to total reservoir pressure) of 0.739 and 0.500. Results showed that in the absence of non-equilibrium condensation, the shock wave oscillates alternatively between the upper and lower disk surfaces at the pressure ratio of 0.739 and in the wake region at 0.500. However, in the presence of non-equilibrium condensation, the flow field aerodynamic instabilities such as root mean square of pressure oscillation and shock induced oscillations frequencies were reduced significantly compared with those in the absence of non-equilibrium condensation. In addition, the total pressure loss increased and wake frequency was reduced in case with condensing moist air flows.

Transonic Moist Air Flow around a Symmetric Disc Butterfly Valve with Non-Equilibrium Condensation

Transonic flow around a symmetric disc butterfly valve is associated with the appearance of shock waves on valve surfaces. In this case, the interaction between shock waves and boundary layers becomes complex and thus generates the flow-induced aerodynamic instability. In the transonic or supersonic flow where vapour is contained in the main flow, the rapid expansion of the flow may give rise to non-equilibrium condensation. In the present study, the effect of non-equilibrium condensation of moist air on the shock-induced flow field oscillation around a butterfly valve was investigated numerically. The results showed that in cases with non-equilibrium condensation, the flow field aerodynamic instabilities such as root mean square of pressure oscillation and shock-induced oscillation frequency are reduced significantly compared with those without the non-equilibrium condensation. Moreover, the total pressure loss increases and the vortex shedding frequency is reduced with non-equilibrium condensation.

Supersonic moist air jet impingements on flat surface

Pronounced aeroacoustic resonances are exhibited in the flowfield where a jet emerges from an orifice or a nozzle and impinges on a solid surface. One instance where such resonances are produced is in a high speed jet impingement, such as in the space launch vehicle systems, jet-engine exhaust impingement, and in the short take-off and vertical landing (STOVL) aircraft, etc. A highly unsteady flowfield leading to a drastic increase of noise level with very high dynamic pressure and thermal loads are noticed on nearby surfaces results dramatic lift loss, severe ground erosion and hot gas ingestion to the inlet in the jet engines. This highly unsteady behavior of the impinging jets is due to a feedback loop between the fluid and acoustic fields. In actual jet flow, the working gas may contain condensable gas such as steam or moist air. In these cases, the non-equilibrium condensation may occur at the region between nozzle exit and an object. The jet flow with non-equilibrium condensation may be quite different from that without condensation. Therefore, in this study, the effect of the non-equilibrium condensation of moist air on the axisymmetric under-expanded supersonic impinging jet on a vertical flat plate was investigated numerically.

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.

Effect of non-equilibrium condensation of moist air on unsteady behaviour of shock waves around a circular arc blade

The unsteady phenomena in the transonic flow around airfoils are observed in the flow field of fan, compressor blades and butterfly valves, and this often causes serious problems such as the aeroacoustic noise, the vibration. In the transonic or supersonic flow where vapour is contained in the main flow, the rapid expansion of the flow may give rise to a non-equilibrium condensation. However, the effect of non-equilibrium condensation on the transonic internal flows around the airfoil has not yet been clarified satisfactorily. In the present study, the effect of non-equilibrium condensation of moist air on the self-excited shock wave oscillation on a circular arc blade was investigated numerically. The results showed that in the case with non-equilibrium condensation, frequencies of the flow oscillation became smaller than those without the non-equilibrium condensation.

The effect of non-equilibrium condensation on supersonic air flows over rectangular cavities

Numerical simulations have been carried out for a supersonic two-dimensional flow over open, rectangular cavities (length-to-depth ratios are L/D = 1.0 and 3.0) in order to investigate the effect of non-equilibrium condensation of moist air on supersonic internal flows around the cavity for the flow Mach number 1.83 at the cavity entrance. In the present computational investigation, a condensing flow was produced by an expansion of moist air in a Laval nozzle. The computational results showed that the upstream traveling compression waves become weaker than those without the condensation. Consequently, the weaker compression waves cannot excite the shear layer strongly and amplitudes of oscillation in the cavity became smaller than those without the condensation. The occurrence of the non-equilibrium condensation in case of L/D = 1.0 affected strongly the amplitude and frequency of oscillation in the cavity compared with L/D = 3.0.

2351 遷音速流中の対称円弧翼周りの流れに及ぼす非平衡凝縮の影響(S46-5 圧縮性流れの基礎と応用(混相流),S46 圧縮性流れの基礎と応用)

The unsteady phenomenon in the transonic flow around airfoils is observed in the flow fields of fan, compressor blades and butterfly valves, and this causes often serious such problems as the aeroacoustic noise and the vibration. In the transonic or supersonic flow where vapour is contained in the main flow, the rapid expansion of the flow may induce a non-equilibrium condensation. However, the effect of non-equilibrium condensation on the transonic internal flows around the airfoil has not yet been clarified satisfactorily. In the present study, the effect of non-equilibrium condensation of moist air on the self-excited shock wave oscillation on a circular arc blade was investigated numerically. The results showed that in the case with non-equilibrium condensation, the frequency of the flow oscillation became smaller than that without the non-equilibrium condensation.

Effect of Non-equilibrium Condensation of Moist Air on Flow Fields in a Ludwieg Tube (Case with Condensation Upstream of Nozzle)

Effect of Non-equilibrium Condensation of Moist Air on Flow Fields in a Ludwieg Tube (Case with Condensation Upstream of Nozzle)

부족팽창 습공기제트에 관한 수치해석적 연구

The under-expanded jet discharged from a nozzle or an orifice has been extensively employed in industrial applications and aerospace technologies. A number of studies have been made to investigate the under-expanded jet structures such as Mach disk, barrel shock wave, jet boundary configuration, etc. In the current study, a computational work is performed to investigate the effect of non-equilibrium condensation of moist air on the under-expanded jet, which is discharged from a sonic nozzle. The results obtained are compared with an available experimental data. It is found that non-equilibrium condensation of moist air alleviates the oscillations of the under-expanded jet, and can increase Mach disk diameter, without changing the location.

Time-dependent characteristics of the nonequilibrium condensation in subsonic flows

High-speed moist air or steam flow has long been of important subject in engineering and industrial applications. Of many complicated gas dynamics problems involved in moist air flows, the most challenging task is to understand the nonequilibrium condensation phenomenon when the moist air rapidly expands through a flow device. Many theoretical and experimental studies using supersonic wind tunnels have devoted to the understanding of the nonequilibrium condensation flow physics so far. However, the nonequilibrium condensation can be also generated in the subsonic flows induced by the unsteady expansion waves in shock tube. The major flow physics of the nonequilibrium condensation in this application may be different from those obtained in the supersonic wind tunnels. In the current study, the nonequilibrium condensation phenomenon caused by the unsteady expansion waves in a shock tube is analyzed by using the two-dimensional, unsteady, Navier-Stokes equations, which are fully coupled with a droplet growth equation. The third-order TVD MUSCL scheme is applied to solve the governing equation systems. The computational results are compared with the previous experimental data. The time-dependent behavior of nonequilibrium condensation of moist air in shock tube is investigated in details. The results show that the major characteristics of the nonequilibrium condensation phenomenon in shock tube are very different from those in the supersonic wind tunnels.

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 discussed for cases with and without occurrence of condensation upstream of nozzle.

417 ルトビーク管内流れに及ぼす湿り空気の非平衡凝縮の影響(O.S.4-5 凝縮相を伴う圧縮性流れ)(O.S.4 圧縮性流れ・衝撃波)

417 ルトビーク管内流れに及ぼす湿り空気の非平衡凝縮の影響(O.S.4-5 凝縮相を伴う圧縮性流れ)(O.S.4 圧縮性流れ・衝撃波)

Effect of nonequilibrium condensation of moist air on transonic flow fields

When condensation occurs in a supersonic flow field, the flow is affected by the latent heat released. In the present study, a condensing flow was produced by an expansion of moist air in nozzle with circular bump models and shock waves occurred in the supersonic parts of the flow fields. The experimental investigations were carried out to show the effects of initial conditions in the reservoir and nozzle geometries on the shock wave characteristics and the turbulences in the flow fields. Furthermore, in order to clarify the effect of condensation on the flow fields with shock waves, 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 effect of condensation on the aspect of flow field has been clarified.

湿り空気の非平衡凝縮が遷音速流れ場に及ぼす影響

湿り空気の非平衡凝縮が遷音速流れ場に及ぼす影響

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 affected by the latent heat released. In the present study, 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. 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 flow 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.