副气流中He流量变化对流场混合状态的影响

在保持主气流流量和副气流中I2的流量不变的条件下,改变副气流中He的流量,数值模拟氧碘化学激光器拉伐尔喷管内的流场混合特性。结果表明,随着副气流中He的流量的增加,副气流垂直穿透主气流的深度逐渐变大,主、副气流混合状态也逐渐变好,直至氧碘气流混合均匀。     

Determining the Optimal Contour of a Three-Dimensional Supersonic Jet Engine Outlet System

The problem of determining the optimal contour of a two-dimensional jet engine outlet system was solved in [1] using the direct method of the calculus of variations. In this study the method is developed for designing the optimal contour of a three-dimensional outlet system providing maximum thrust in a given direction.     

Properties and applications of cold supersonic gas jet

By analyzing the formation mechanism of a supersonic gas jet, a set of equations which describe the atomic beam properties were established. The influence of initial temperature, initial pressure, background gas pressure and pumping speed was discussed in detail. A simulation program was developed based on the equations, and the results under different initial conditions were obtained. The results are in good agreement with the experimental data, and suggest that, in order to get much smaller transverse momentum in collision experiments, it is necessary to lower the initial temperature and the initial pressure of the supersonic gas jet, together with increasing the pumping speed. These results are very instructive for construction of a new generation of cold supersonic gas jets.     

Surface ionization detector with a supersonic free jet for gas chromatography some applications

A new design for a gas chromatographic surface ionization detector based upon hyperthermal positive surface ionization has been developed: There were two requirements: supersonic free jet nozzle and the high work function surface of Re-oxide. This detector, which is highly sensitive in response to all organic compounds, can be operated as an universal detector with an additional selectivity towards some species that have low ionization energy, but with selectivity to a much lesser degree than a conventional surface ionization detector. The minimum detectable amount of toluene is ca. 10⁻¹² g/s with a linearity greater than 10⁴. Some applications are demonstrated using three examples for the analysis of different formulations: (1), terpene mixture, (2), polycyclic aromatic hydrocarbon mixture and (3), alkyl alcohol mixture.     

Global entropy solutions to the compressible Euler equations in the isentropic nozzle flow for large data: Application of the generalized invariant regions and the modified Godunov scheme

We study the motion of isentropic gas in nozzles. This is a major subject in fluid dynamics. In fact, the nozzle is utilized to increase the thrust of rocket engines. Moreover, the nozzle flow is closely related to astrophysics. These phenomena are governed by the compressible Euler equations, which are one of crucial equations in inhomogeneous conservation laws.In this paper, we consider its unsteady flow and devote to proving the global existence and stability of solutions to the Cauchy problem for the general nozzle. The theorem has been proved in Tsuge (2013). However, this result is limited to small data. Our aim in the present paper is to remove this restriction, that is, we consider large data. Although the subject is important in Mathematics, Physics and engineering, it remained open for a long time. The problem seems to rely on a bounded estimate of approximate solutions, because we have only method to investigate the behavior with respect to the time variable. To solve this, we first introduce a generalized invariant region. Compared with the existing ones, its upper and lower bounds are extended constants to functions of the space variable. However, we cannot apply the new invariant region to the traditional difference method. Therefore, we invent the modified Godunov scheme. The approximate solutions consist of some functions corresponding to the upper and lower bounds of the invariant regions. These methods enable us to investigate the behavior of approximate solutions with respect to the space variable. The ideas are also applicable to other nonlinear problems involving similar difficulties.     

Assessment of gas thermodynamic characteristics on fluidic thrust vectoring performance: Analytical,experimental and numerical study

The cross injection in a supersonic flow is an issue encountered in several aerodynamic applications such as fuel injection in scramjet combustor, missile control, drag reduction and thrust vector control. In a recent work, an analytical model has been presented to calculate the fluidic thrust vectoring performance for a supersonic axisymmetric nozzle. The model is able to take into account both the injected gas thermodynamic properties and the geometrical nozzle characteristics. The analytical model has been successfully validated following the cold air flow experimental analysis, in the case of fluidic thrust vectoring applied to conical nozzle. The aim of this work is to show how far the injected gas thermodynamic properties, different from that of the nozzle main flow, could influence the fluidic thrust vectorization parameters.In this work, the experimental performance of the fluidic thrust vectoring concept, using numbers of gases as injectant, has been qualitatively and quantitatively analyzed. Schlieren visualization, force balance and wall pressure measurements were used in the case of a truncated ideal contour nozzle. The experimental results are compared to the numerical and analytical findings.Performance analysis are conducted and basic conclusions are drawn in terms of thermodynamic gas properties effect on the fluidic thrust vector system. The primary effect was related to the gas molecular weight and its specific heat ratio product. It is observed that for fixed injection conditions, the vectoring angle is higher when the injected gas molecular weight and specific heat ratio product is less than that of the primary gas. For a given mission of the launcher, it can be concluded that the mass of the embedded gas, used for the fluidic vectorization system, can be significantly reduced, depending on its molecular weight and specific heat ratio.     

Investigations of gas and particle dynamics in first generation needle-free drug delivery devices

Abstract. Transdermal powdered drug delivery involves the propulsion of solid drug particles into the skin by means of high-speed gas-particle flow. The fluid dynamics of this technology have been investigated in devices consisting of a convergent-divergent nozzle located downstream of a bursting membrane, which serves both to initiate gas flow (functioning as the diaphragm of a shock tube) and to retain the drug particles before actuation. Pressure surveys of flow in devices with contoured nozzles of relatively low exit-to-throat area ratio and a conical nozzle of higher area ratio have indicated a starting process of approximately 200 s typical duration, followed by a quasi-steady supersonic flow. The velocity of drug particles exiting the contoured nozzles was measured at up to 1050 m/s, indicating that particle acceleration took place primarily in the quasi-steady flow. In the conical nozzle, which had larger exit area ratio, the quasi-steady nozzle flow was found to be overexpanded, resulting in a shock system within the nozzle. Particles were typically delivered by these nozzles at 400 m/s, suggesting that the starting process and the quasi-steady shock processed flow are both responsible for acceleration of the particle payload. The larger exit area of the conical nozzle tested enables drug delivery over a larger target disc, which may be advantageous. Received 12 March 2000 / Accepted 8 June 2000     

Experimental Investigation Of Spray Cooling Heat Transfer On Straight Fin Surface Under Acceleration Conditions

A spray cooling heat transfer experiment on straight fin surface under acceleration conditions was conducted to investigate the effects of acceleration, flow rate, and nozzle height. The results show that the acceleration can improve the heat transfer performance in a limited way. In addition, whether in the acceleration or stationary condition, the flow rate as well as the nozzle height has the same impact on the spray cooling performance. It is also observed that the surface temperature can influence the effect of flow rate on spray cooling performance, and the cooling performance becomes worse with the increase of nozzle height.     

Flow-induced noise in a suction nozzle with a centrifugal fan of a vacuum cleaner and its reduction

Noise reduction in a vacuum cleaner with a brush nozzle for cleaning a bed blanket is investigated numerically in fluid dynamic aspects. Governing equations describing nonlinear flow fields in a suction nozzle are solved simultaneously. The components of a rotary fan, a brush drum, and a separation block are installed in the nozzle. First, flow patterns in the nozzle are analyzed and based on them, flow resistance is evaluated to find a primary noise source. Flow resistance induces the loss of a suction performance as well as noise generation. In the brush nozzle, the separation block and the rotary fan obstruct smooth air flow and result in high level of noise emission. The rotation of the fan itself affects little noise generation. From the numerical results, a method to reduce noise and maintain the suction performance is suggested. In this method, the suction performance is increased through the optimization of the separation block, which is attained by the modification of its shape. And then, the height of a fan blade is shortened, leading to the performance loss. At the cost of it, the sound power level of noise is reduced by 4-5 dB(A) and at the same time, the tonal noise and the sound quality are improved appreciably. The method has been verified by experimental tests. It is found that in the brush nozzle, flow resistance is critical in noise emission and accordingly, fluid dynamic approach to noise reduction is effective.     

Flow and atomization characteristics of a twin-fluid nozzle with internal swirling and self-priming effects

A twin-fluid nozzle was proposed for low-pressure atomization. The nozzle is featured by swirling air flows in the mixing chamber. Liquid medium is thereby inhaled due to the pressure difference. An experimental work was performed to investigate the atomization performance of the nozzle and the hydrogen peroxide solution served as the liquid medium. Droplet size and droplet velocity were measured. Effects of the diameter of the air-injection orifice and the air-injection pressure were investigated. The results show that small droplet size is achieved with the proposed nozzle. As the spray develops, Sauter mean diameter (SMD) of the droplets decreases first and then increases, irrespective of the variation of the air-injection orifice diameter and the air-injection pressure. Overall SMD varies inversely with the air-injection orifice diameter and air-injection pressure. Near the nozzle, cross-sectional velocity distribution exhibits a peak-valley pattern, which is replaced with uniformized velocity distributions away from the nozzle. Similarity of cross-sectional radial velocity distribution at different air pressures is evidenced. Furthermore, the correlation between droplet size and droplet velocity is established.