Moist Air Jet Research Articles

SPONTANEOUS NONEQUILIBRIUM CONDENSATION IN SUPERSONIC JETS IMPINGING ON CAVITY

Spontaneous condensation of moist air in supersonic jets is of considerable interest in a variety of natural and industrial processes. During impingement of supersonic moist air jets, the nonequilibrium homogeneous condensation can be experienced at the region between downstream of nozzle exit and an obstacle. The subsequent release of latent heat thus results in a deceleration of the flow and a rise in pressure, known traditionally as the condensation shock; likely have strong effect on the flow features. The present paper reported of the effect of spontaneous nonequilibrium homogeneous condensation of moist air on the aerodynamic and oscillatory flow features of supersonic jets impinging on cavity. A total variation diminishing (TVD) scheme was used to solve the time dependent Favre averaged Navier–Stokes equations, and the droplet growth equation of liquid phase production for simulating the condensing jets. Both qualitative and quantitative validations of the numerical model were accomplished, and the results showed a good agreement between the computed results and experimental data. Predicted flow and oscillatory features of jets were presented.

Effect of Homogeneous Condensation on the Interaction of Supersonic Moist Air Jets with Resonance Tube

The Hartmann tube, can use for flow-control, is a device which generates high intensity sound through the shock wave oscillations, are created by the interaction of the supersonic jet. In this study, two-phase flow simulations are carried out to characterize the effect of non-equilibrium condensation on the unsteady flowfield of the Hartmann resonance tube. This present numerical work provides a new insight on the flow dynamics and acoustics of the resonance tube – including the shock nature, the tube gas heating, and the effect of non-equilibrium condensation on the flow structure. A TVD numerical method is applied to the Reynolds and Favre-averaged Navier-Stokes equations, and droplet growth equation of liquid phase production. The simulations are performed over a range of nozzle pressure ratios. The numerically simulated flow structure of under-expanded supersonic jets is compared with experimental data. Moreover, the predicted frequency of end wall pressure fluctuations is compared with the experimental results.

Characteristics of Condensing Flows in Shear Layer of Axisymmetric Supersonic Jets

Abstract When the high pressure gas is exhausted to atmosphere, the expanded supersonic jet is formed at a specific condition. In reality, the steam or moist air is usually used as working gas of supersonic moist air jet technologies. In these cases, non-equilibrium condensation may occur within the supersonic jet flow, and there are some researches on this phenomenon. On the other hand, in reality, there is a variety of engineering applications for discharge of the dry air into the atmosphere containing moist air or steam. In this case, non-equilibrium condensation may occur locally within the shear layer and affect the jet structure or energy loss in the flow field. However, the characteristics of non-equilibrium condensing flow in the jet shear layer are not investigated so far satisfactorily. The purpose of this study is to clarify the effect of local occurrence of non-equilibrium condensation in the shear layer on the characteristics of an under- expanded supersonic jet numerically. As a result, it was found that non-equilibrium condensation in shear layer affected the jet entrainment effect.

Shock wave in supersonic moist air jet for a low pressure ratio

In the present study, a computational fluid dynamics work was performed to investigate the occurrence of the shock wave by condensation in supersonic moist air jet. The unsteady, compressible axisymmetric Navier-Stokes equation is solved by TVD(Total Variation Diminishing) scheme in this study. The numerical simulations have been performed for low pressure ratio and various humidities. The results show the occurrence of the shock wave in supersonic moist air jet for a low pressure ratio when Mach disk does not occur, depending on humidity of the air.

1417 軸対称不足膨張噴流における凝縮衝撃波の発生(圧力比と湿り度の影響)(熱工学III)

1417 軸対称不足膨張噴流における凝縮衝撃波の発生(圧力比と湿り度の影響)(熱工学III)

Hysteretic Phenomenon of Underexpanded Moist Air Jet

Moist air jets, corresponding to the range of moderately underexpanded to strongly underexpanded conditions, have been investigated with the help of computational fluid dynamics methods. The equations for nucleation rate and droplet growth are incorporated into the unsteady, compressible Navier-Stokes equations. A third-order total variation diminishing finite difference scheme with monotonic upstream schemes for conservation lows is employed to discretize the spatial derivatives of the governing equations. The experiment is performed to validate the computational predictions. The initial degree of supersaturation is changed to obtain different values of the relative humidity of moist air. The pressure ratio is changed to investigate the characteristic behavior of the jets generated during the transient processes of startup and shutdown. The results obtained show that underexpanded air jet produced during the startup transient of jet behaves different from the shutdown transient process, leading to a hysteretic phenomenon of underexpanded jet. It is also known that the moist air jet reduces the hysteretic phenomenon compared with the dry air jet, and that nonequilibrium condensation that occurs in the underexpanded moist air jet is responsible for these findings.

The effect of nonequilibrium condensation on hysteresis phenomenon of under-expanded jets

Under-expanded jets which are discharged from an orifice or a nozzle have long been subject of researches for aeronautical and mechanical applications. Provided that the jet pressure ratio and nozzle configuration are known, the major features of the steady jet are now well known. However, the jet pressure ratio is often varied even during the process in many practical applications. Many questions remain unanswered with regard to how the supersonic jet responds to the transient process of the pressure ratio and whether the steady jet data for a specific pressure ratio can still bear the same during the transient process of pressure ratio. In the present study, the hysteric phenomenon of under-expanded jets has been investigated with the help of computational fluid dynamics methods. The under-expanded jets of both dry and moist air have been employed to investigate the transient processes of the pressure ratio. The effects of nonequilibrium condensation occurring in the under-expanded moist air jets are explored on the hysteresis phenomenon. It is known that under-expanded air jet produced during the startup transient of jet behaves differently from the shutdown transient process, leading to the hysteric phenomenon of under-expanded jet. It is also known that the moist air jet reduces the hysteric phenomenon, compared with the dry air jet, and that non-equilibrium condensation which occurs in the underexpanded moist air jet is responsible for these findings.

522 湿り空気の湿度が軸対称過膨張噴流の構造に及ぼす影響(流体工学IV)

522 湿り空気の湿度が軸対称過膨張噴流の構造に及ぼす影響(流体工学IV)

Characteristics of Supersonic Impinging Moist Air Jets

Supersonic impinging Jets, such as those occurring in the space launch vehicle systems, multi-stage rocket separation, jet-engine exhaust impingement, terrestrial rocket launch, and in the next generation short take off and vertical landing (STOL) aircraft, generate a highly oscillatory flow with very high unsteady loads on the near by structures and the landing surfaces. These high-pressure and acoustic loads are also accompanied by a dramatic loss in lift during aircraft hover. Previous studies of supersonic impinging jets suggest that the highly unsteady behavior of the impinging jets is due to a feedback loop between the fluid And acoustic fields, which leads to these adverse effects, In actual supersonic jet flow, usually the working gas nu be condensable gas such as steam or moist air. In these cases, the non-equilibrium condensation may occur in the region between nozzle exit and an object. The jet flow with non-equilibrium condensation may be quite different from that without condensation, In the present study, characteristics of under-expanded axisymmetric supersonic impinging moist air jets on a vertical flat plate were investigated numerically.

Generation of overpressure due to condensation in moist air jet

In the present study, a computational fluid dynamics method has been applied to investigate the effects of initial degree of supersaturation at reservoir condition on under-expanded sonic jet structures, such as Mach disk location and diameter, barrel shock wave and jet boundary. The axisymmetric nozzle geometry investigated was a converging nozzle with straight part. As a result, it was found that the overpressures due to condensation generate and the characteristics of flow with generation of overpressure due to condensation in the jet were different from those without condensation.

Study of Moderately Underexpanded Supersonic Moist Air Jets

Supersonic moist air jet technologies are often applied to powerplants and industrial manufacturing processes, but the major features of supersonic moist air jets are not well known to date, including their qualitative characteristics. An experiment is performed to investigate relative humidity effects on underexpanded supersonic jet structures, such as Mach disk location and diameter, barrel shock wave, and jet boundary locations, etc. It is found that the Mach disk diameter and location are significantly influenced by the relative humidity of moist air. The Mach disk in underexpanded moist air jets is located farther upstream than in dry air jets, and the Mach disk diameter for moist air jets is smaller than that of dry air jets. The Mach disk diameter increases slightly as the relative humidity of moist air increases. Empirical equations are obtained for Mach disk diameter and location, as well as locations of the jet boundary and barrel shock, in underexpanded moist air jets.

A Study on Characteristics of Under-Expanded Condensing Jet

The single supersonic free jet discharging from a nozzle or an orifice has been often employed in various industrial processes. A number of studies have been done to detail the major features (Mach disk, barrel shock wave and the jet boundary configuration) of the supersonic jets. In the present study, the numerical computations were performed to investigate the effect of initial degree of supersaturation of moist air at reservoir condition on under-expanded jet structures and the total pressure loss behind the Mach disk. As a result, it was found that the position of Mach disk in the under-expanded moist air jets was almost the same as that in dry air jets. However, the Mach disk diameter increased slightly as the initial degree of supersaturation of moist air increased. Furthermore, the total pressure loss behind the Mach disk for moist air jet changed largely in comparison to that for dry air jet.

A Study on Characteristics of Under-Expanded Condensing Jet

The single supersonic free jet discharging from a nozzle or an orifice has been often employed in various industrial processes. A number of studies have been done on the major features (Mach disk, barrel shock wave and the jet boundary configuration) of the supersonic jets. In the present study, numerical computations were performed to investigate the effect of initial degree of supersaturation of moist air at reservoir condition on under-expanded jet structures and the total pressure loss behind the Mach disk. From these studies, it was found that the position of Mach disk in the under-expanded moist air jets was almost the same as that in dry air jets. However, the diameter of Mach disk increased slightly with an increase in the initial degree of supersaturation of moist air. Furthermore, the total pressure loss behind the Mach disk of moist air jet changed largely in comparison to that of dry air jet.

A study of under-expanded moist air jet impinging on a flat plate

When a gas expands through a convergent nozzle in which the ratio of the ambient to the stagnation pressures is higher than that of the critical one, the issuing jet from the nozzle is under-expanded. If a flat plate is placed normal to the jet at a certain distance from the nozzle, a detached shock wave is formed at a region between the nozzle exit and the plate. In general, supersonic moist air jet technologies with non-equilibrium condensation are very often applied to industrial manufacturing processes. In spite of the importance in major characteristics of the supersonic moist air jets impinging to a solid body, its qualitative characteristics are not known satisfactorily. In the present study, the effect of the non-equilibrium condensation on the under-expanded air jet impinging on a vertical flat plate is investigated numerically in the case with non-equilibrium condensation, frequency of oscillation for the flow field becomes larger than that without the non-equilibrium condensation, and amplitudes of static pressure become small compared with those of dry air. Furthermore, the numerical results are compared with experimental ones.

407 不足膨張噴流構造に及ぼす非平衡凝縮の影響

407 不足膨張噴流構造に及ぼす非平衡凝縮の影響