Supersonic Diffuser Research Articles

Performance Analysis of a Two-Dimensional Supersonic Diffuser

The aim of this work is to study the attainable velocities for a supersonic diffuser. Numerical analysis is carried out to identify the supersonic characteristics. The deceleration of air from free stream supersonic velocities in the 2D channel has been studied and analysed at a specific altitude. Ramp instalment maximizes the total pressure recovery. The geometry is generated in CATIA software and 2-D flow numerical simulation is done using ANSYS-CFD V15.0. Flow analysis is done by keeping the altitude constant and varying the inlet Mach number. A comprehensive study from the analysis provides the range in which Mach number at the inlet can be varied for a supersonic aircraft. The obtained flow phenomena in the supersonic diffuser domain are reported with the help of Mach number, static pressure, and velocity plots.

Flowing-gas diode pumped alkali lasers: theoretical analysis of transonic vs supersonic and subsonic devices.

We examine transonic diode pumped alkali laser (DPAL) devices as a simpler alternative to supersonic devices, suggested by B.D. Barmashenko and S. Rosenwaks [Appl. Phys. Lett. 102, 141108 (2013)], where complex hardware, including supersonic nozzle, diffuser and high power mechanical pump, is required for continuous closed cycle operation. Three-dimensional computational fluid dynamics modeling of transonic (Mach number M ~0.9) Cs and K DPALs, taking into account the kinetic processes in the lasing medium is reported. The performance of these lasers is compared with that of supersonic (M ~2.5) and subsonic (M ~0.2) DPALs. For Cs DPAL the maximum achievable power of transonic device is lower than that of supersonic, with the same resonator and Cs density at the laser section inlet, by only ~3% implying that supersonic operation mode has only small advantage over transonic. On the other hand, for subsonic laser the maximum power is by 7% lower than in transonic, showing larger advantage of transonic over subsonic operation mode. The power achieved in supersonic and transonic K DPALs is higher than in subsonic by ~80% and ~20%, respectively, showing a considerable advantage of supersonic device over transonic and of transonic over subsonic.

Optimization of a supersonic wind tunnel diffuser using genetic algorithm

Purpose– The purpose of this paper is to find the optimum design of diffuser of supersonic wind tunnel in order to access the minimum overall pressure drop in wind tunnel, using evolutionary algorithm.Design/methodology/approach– The authors developed a genetic algorithm (GA) code to calculate the shape of a diffuser with flexible walls in order to have the maximum pressure recovery. The two-dimensional turbulent and compressible flow was analyzed numerically using shear-stress transport and Advection Upstream Splitting Method (AUSM)+ turbulence models and its optimization with GA.Findings– The results of this study indicate that elitist GA promises a powerful method for optimization of the wind tunnel diffuser. Separation zone is reduced by 22.2 percent at the convergent part of diffuser and 56 percent at the divergent part of diffuser. The efficiency of new optimized wind tunnel diffuser increased by 83 percent in comparison to the sample of supersonic wind tunnel.Originality/value– It has been observed that AUSM+ method and shape design optimization using GA are robust and efficient technique to optimize wind tunnel diffuser.

Conceptual redesign of the B-1B bomber inlets for improved supersonic performance

This paper presents a conceptual study of two alternative inlet concepts for the United States Air Force B-1B bomber to provide for improved supersonic performance with expansion of capabilities to high-altitude, high-speed flight at Mach 2.0. The two inlet concepts are two-dimensional, variable-ramp inlet systems designed to replace the current fixed-geometry, pitot inlets of the B-1B. One inlet incorporates a two-ramp system, while a second inlet incorporates a two-ramp system containing an isentropic contour. The entire inlet system including the supersonic diffuser, throat, cowl lip, and subsonic diffuser sections was designed to maximize the total pressure recovery at the engine fan face to achieve maximum thrust by the engine at Mach 2.0 conditions. Analytic methods implemented into the MATLAB and the NASA SUPIN codes are used to design and analyze the two-dimensional inlet concepts. In addition, WIND-US computational fluid dynamics simulations were used to check and improve the results of the analytic design methods. The results suggest that at Mach 2.0, the total pressure recovery of the inlets could increase from 0.70 to 0.94. The inlet capture area and cowl drag increased; however, the overall improvements resulted in a 98% thrust increase over the existing inlet at the design point.

Discontinuity of Gas-dynamic Variables in the Center of the Compression Wave

The purpose of research-the study of the flow in the center of the centered isentropic compression waves. Gas-dynamic discontinuities cover shocks, shockwaves, interfaces and sliding surfaces and also the center of the centered compression wave one-dimensional and two-dimensional. For a long time there has been no analysis of the shockwave structures arising in the center of compression waves. At the same time, the problem of development of supersonic and hypersonic air inlets demands to consider the process of the stream isentropic compression. This problem is connected (three-dimensional case) to the problem of arising inside the streams of hinged shocks as opposite to the usual discontinuities not resulted by interaction of supersonic streams, waves and discontinuities, but like from nowhere. This study sets the problem for study in the terms of the developed theory of the interference of gas-dynamic discontinuities of the area of existing solutions for the structures of possible types. We have obtained the relations describing the parameters in the center of the compression wave. We have considered the neutral polar of neither compression meeting the case when in the center of the compression wave there neither shocks nor depression waves. The analysis of properties of the centered compression wave adds to the theory of stationary gas- dynamic discontinuities. We have specified the borders of the shock structure existence area optimal for development of supersonic diffusers.

Numerical simulations of convergent-divergent nozzle and straight cylindrical supersonic diffuser

The flowfields inside a contour and a conical nozzle exhausting into a straight cylindrical supersonic diffuser are computed by solving numerically axisymmetric turbulent compressible Navier-Stokes equations for stagnation to ambient pressure ratios in the range 20 to 34. The diffuser inlet-to-nozzle throat area ratio and exit-to-throat area ratio are 21.77, and length-to-diameter ratio of the diffuser is 5. The flow characteristics of the conical and contour nozzle are compared with the help of velocity vector and Mach contour plots. The variations of Mach number along the centre line and wall of the conical nozzle, contour nozzle and the straight supersonic diffuser indicate the location of the shock and flow characteristics. The main aim of the present analysis is to delineate the flowfields of conical and contour nozzles operating under identical conditions and exhausting into a straight cylindrical supersonic diffuser.

Continuous detonation in a supersonic flow of a hydrogen-oxygen mixture

The problem of continuous spin detonation in a supersonic flow in a flow-type annular combustor is considered in a two-dimensional unsteady formulation. The dynamics of the detonation wave in a hydrogen-oxygen mixture with isentropic and shock-wave compression of the flow in the input diffuser is studied. It is shown that the mass flow rate of the mixture through the combustor decreases as continuous spin detonation is formed, and a steady regime with a “detached” shock wave is observed at the entrance of the supersonic diffuser. For a contoured combustor, the limit from above is obtained for the Mach number of the incoming supersonic flow at which a continuous detonation regime is obtained.

Geometry optimization of the diffuser for the supersonic wind tunnel using genetic algorithm and adaptive mesh refinement technique

Design of two-dimensional supersonic diffusers as a part of the wind tunnel is investigated in this paper. A methodology based on the mixture of try-and-error method and optimization algorithm is developed to handle the design problem. In the first design step, using try-and-error approach, the main parameters related to the geometry of diffuser such as length, angle and area ratio between the throat and the outlet are determined assuming a diffuser with linear walls. The design criterion in this step is the fact that the shock wave should be created near the diffuser throat in order to benefit from the maximum efficiency of diffuser. In the second design step, considering the optimization methodology, it is tried to improve the optimum design obtained in the first step by modifying the wall point locations and keeping the rest of the geometry fixed. Hence, an optimization problem is defined to find the best curve for the diffuser wall instead of the a linear one used the in the first step. The objective function of this problem is to minimize the output Mach number using Genetic Algorithm (GA). The fluid flow is evaluated using the Euler equations in the conservative form where the Streamline-Upwind/Petrov–Galerkin (SUPG) finite element scheme is used to discretize the flow equations. In order to capture the flow solution around the shock waves accurately, the adaptive mesh refinement technique is coupled to the flow solution. The demonstrated results show the efficiency of the proposed method for designing supersonic diffusers.

2차목 초음속 디퓨저의 형상 변화에 따른 성능에 관한 실험적 연구

본 연구에서는 고공 환경 모사를 위하여 2차목 초음속 디퓨저를 Normal Shock Model를 이용하여 설계/제작하였다. 2차목 디퓨저의 주요 설계 변수인 2차목 디퓨저의 길이와 직경 변화에 따른 성능 특성을 고찰하기 위하여, 상온 고압 질소 가스를 이용하여 디퓨저 성능 실험을 수행하였다. 다양한 디퓨저 길이에 따른 실험 결과 2차목 디퓨저의 시동 특성은 디퓨저 입구 길이(L<SUB>d</SUB>)가 증가함에 따라 아주 미세하게 향상되었으나, 2차목 디퓨저 길이비(L<SUB>st</SUB>/D<SUB>st</SUB>)와 확대부 길이(L<SUB>s</SUB>)의 증가에 따라서는 크게 향상되었다. 또한 다양한 디퓨저 직경 변화에 따른 실험 결과, 시동 압력과 진공 챔버 압력은 모두 이론 설계 면적비(A<SUB>d</SUB>/A<SUB>st</SUB>) 근처에서 가장 우수한 성능을 보였다.

Effects of distributed pressure gradients on the pressure–strain correlations in a supersonic nozzle and diffuser

AbstractDirect numerical simulation (DNS), based on high-order numerical schemes, is used to study the effects of distributed pressure gradients on the redistribution of fluctuating kinetic energy in supersonic nozzle and diffuser flow with incoming fully developed turbulent pipe flow. Axisymmetric geometries and flow parameters have been selected such that shock waves are avoided and streamline curvature remains unimportant. Although mean extra rates of strain are quite small, strong changes in Reynolds stresses and their production/redistribution mechanisms are observed, in agreement with findings of Bradshaw (J. Fluid Mech., vol. 63, 1974, pp. 449–464). The central role of pressure–strain correlations in changing the Reynolds stress anisotropy is highlighted. A Green’s function-based analysis of pressure–strain correlations is presented, showing remarkable agreement with DNS data.

光腔与扩压器的一体化优化数值模拟

The performance of supersonic diffuser downstream the cavity in chemical oxygen-iodine laser pressure recovery system can obviously influence the flow field quality in cavity, and its static pressure recover and total pressure loose performance can determine the pressure recovery system size downstream the diffuser. This paper uses the numerical simulation method to research the influence of supersonic diffuser design parameter such as diffuser angle and diffuser outline and back pressure and so on. The study shows that, the static pressure ratio was increased about 33% and the total pressure recover coefficient was increased to 0.484 by means of adding a constant section with wedges between the cavity and the supersonic diffuser. At the same time, the flow filed quality such as static pressure and Mach number distribution in cavity was obviously improved.

Theoretical and Experimental Activity on Ejector Refrigeration

Ejector refrigeration has been studied at DIEF (Dipartimento di Ingegneria Industriale Firenze) since the ‘90s. Use of environmentally safe fluids (steam) was addressed. A two-stage prototype with cooling capacity 5kW was optimized and built. Later, the CRMC prescription for the design of the supersonic diffuser was focused. By a gradual reduction of the fluid velocity and a continuous profile, the CRMC design promises a reduction of the normal shock that usually develops in the mixing chamber. A second 40 kWf prototype was designed in 2010 for an industrial partner (Frigel Firenze s.p.a.). The design procedure used a thermodynamic code accounting for real gas behavior. This code gives a first design of the mixing chamber and diffuser according to the CRMC criterion. It also gives an estimation of the friction loss along the diffuser. A comparison between different operating fluids was performed and resulted in the selection of R245fa. A first design of the ejector was manufactured in carbon fiber. The primary nozzle is mounted on a movable support, in order to change its axial position with respect to the mixing chamber. In terms of COP, first results were below the values predicted by the simulation code. Meanwhile a numerical simulation was in progress with FLUENT. From the first CFD results it was decided that the diffuser throat had to be moved forward from the primary nozzle exit, in order to allow a complete mixing between the primary and secondary flows, and enlarged, the losses encountered in the mixing process being higher than expected and hence the fluid density lower. This produced a second ejector design, which was manufactured and tested in 2012, showing improved performance. These results suggested a third design, with a further lengthened diffuser, which has undergone a complete testing campaign, allowing validation of the CFD results. The activity performed till now suggests that ejector refrigeration plants have a robust operation and can be easily manufactured at relatively low cost with off-the-shelf components, a part from the ejector itself, which however represents a small fraction of the system cost. However, the COP is lower with respect to absorption refrigeration and hence needs substantial improvement through detailed thermodynamic and CFD design optimization.

On the Assessment of Compressibility Effects of Two-Equation Turbulence Models for Supersonic Transition Flow with Flow Separation

An assessment of two-equation turbulence models, the low Reynolds k-<TEX>${\varepsilon}$</TEX> and k-<TEX>${\omega}$</TEX> SST models, with the compressibility corrections proposed by Sarkar and Wilcox, has been performed. The compressibility models are evaluated by investigating transonic or supersonic flows, including the arc-bump, transonic diffuser, supersonic jet impingement, and unsteady supersonic diffuser. A unified implicit finite volume scheme, consisting of mass, momentum, and energy conservation equations, is used, and the results are compared with experimental data. The model accuracy is found to depend strongly on the flow separation behavior. An MPI (Message Passing Interface) parallel computing scheme is implemented.

초음속 디퓨져 내부 역압력 구배에 대한 수치적 연구

초음속 디퓨져에서 천이구간에 대해서 수치적 기법에 의한 분석을 수행하였다. 수치기법으로는 초음속 디퓨져의 내부유동해석을 위하여 2차원 축대칭 Navier-Stokes equation와 <TEX>$k-{\epsilon}$</TEX> 난류모델을 사용하였으며, 로켓엔진 연소실의 천이 구간의 압력변화에 따라서 디퓨져 내부의 마하수 및 진공챔버의 온도 분포를 비교 검토하였다. 초음속 디퓨져의 작동과정에서 진공챔버 내부에 연소가스가 유입되어지고 이러한 현상에 따라서 진공챔버 내부의 압력 및 온도가 상승하는 결과를 확인하였다. 이러한 유동현상에 따라서 천이과정에서 압력 및 온도 상승을 방지하는 시스템이 필요하다. A study is analyzed on the adverse pressure gradient and the transient regime of supersonic diffuser with Computational Fluid Dynamic. The flow field of supersonic diffuser is calculated using Axisymmetric two-dimensional Navier-Stokes equation with <TEX>$k-{\epsilon}$</TEX> turbulence model. The transient simulation is compared in terms of mach number and static temperature of vacuum chamber according to pressure variation of rocket engine combustion chamber. Combustion gas flow into the vacuum chamber during operation of the supersonic diffuser. According to this phenomenon, the pressure and the temperature rise in the vacuum chamber were observed. Thus, the protection system will be necessary to prevent the pressure and temperature rise in the transition process during operation of the subsonic diffuser.

Design of an ejector cycle refrigeration system

A design procedure, based on a one-dimensional simulation, is presented for an ejection refrigeration system. Heat exchangers are included in the calculation, accounting for temperature differences between the fluids and for pressure losses. The ideal gas assumption, which is quite common in the literature concerning ejector systems, is avoided. Furthermore, the supersonic diffuser is designed with a continuous profile, without cylindrical piece, controlling the variation of momentum along the flow path and accounting for friction. At design conditions, this should reduce the irreversibility due to the normal shock. A comparison between different operating fluids is presented and R245fa is selected. The results of the design procedure and the expected performance, in terms of first and second law efficiency, are presented.

A study of the supersonic ejector–diffuser system with an inlet orifice

Supersonic ejectors are simple mechanical components, which generally perform mixing and recompression of two fluid streams. Ejectors have found many applications in engineering. In aerospace engineering, they are used for high altitude testing (HAT) of a propulsion system by reducing the pressure of a test chamber. It is composed of three major sections: a vacuum test chamber, a propulsive nozzle, and a supersonic exhaust diffuser. This paper aims at the improvement in HAT facility by focusing attention on reducing exhaust back flow into the test chamber, since alteration of the backflow appears as one of the potential means of significantly improving its performance. The simplest backflow-reduction device was an orifice plate at the duct inlet, which would pass the jet and entrained fluid but impede the movement of fluid upstream along the wall. Results clearly showed that the performance of the ejector–diffuser system was improved for a certain range of system pressure ratios, whereas the orifice plate was detrimental to the ejector performance for higher-pressure ratios. It is also found that, there is no change in the performance of diffuser with an orifice at its inlet, with respect to its pressure recovery. Hence, an appropriately sized orifice system should produce considerable improvement in the ejector–diffuser performance in the intended range of pressure ratios.

Design and Performance Analysis of a Supersonic Diffuser for Plasma Wing Tunnel

Design and Performance Analysis of a Supersonic Diffuser for Plasma Wing Tunnel

氧碘化学激光器直线分段扩开型扩压器实验研究

氧碘化学激光器直线分段扩开型扩压器实验研究

액체로켓엔진 연소기를 이용한 고고도 환경 모사용 디퓨저 시동특성 연구

본 연구에서는 액체 로켓 엔진의 고온 연소 가스를 이용하여 축소형 고고도 환경 모사용 초음속 디퓨저 성능 실험을 수행하였다. 실험 장치는 연소실, 진공 챔버, 디퓨저로 구성되어 있다. 고고도 환경 모사 시험은 연소실 압력이 약 26, 29, 32barg 세 조건으로 수행하였고, 세가지 조건에서 모두 디퓨저는 성공적으로 시동되었으며 진공 챔버 압력이 약 140torr로 형성하였다. 이전의 상온 고압 가스를 이용한 디퓨저의 시동 특성과 비교하였을 때 시동 압력과 압력 분포 등의 시동 특성의 경향성은 유사하였으나, 고온 환경으로 인하여 진공 챔버에 형성되는 압력은 2배 정도 높은 것을 확인하였다. 본 연구 결과는 향후 실물형 고고도 환경 모사 시험 설비를 구축하는데 기초 자료로 활용될 수 있을 것으로 판단된다. Performance tests of a supersonic exhaust diffuser were conducted by using a liquid rocket engine for simulating high-altitude environment. The experimental setup consisted of a combustion chamber, a vacuum chamber and a diffuser. The combustion tests for simulating high-altitude environment were carried out at three cases by chamber pressure variation(26, 29, 32barg). The test results showed that the diffuser was started at all case and vacuum chamber pressures were approximately 140torr. The starting pressure using combustion gas was similar with that of cold gas, but the vacuum chamber pressure was relatively high because of high temperature in the vacuum chamber. The results of this test can be used as an essential database for the design of real-scale high-altitude simulation test facility in the future.

Direct numerical simulation of turbulent flow in an axisymmetric supersonic diffuser

Effects of deceleration and mean dilatation on the turbulence structure of supersonic flow in a diffuser with an incoming supersonic fully developed turbulent pipe flow are studied by means of direct numerical simulation. Strong enhancement of the turbulence intensities is observed when the flow undergoes deceleration. Turbulence production and pressure–strain terms in the Reynolds stress budgets are found to increase dramatically leading to increased Reynolds stresses. The central role of pressure–strain correlations in modifying the turbulence structure under these flow conditions is demonstrated and a priori tests of two turbulence models are presented.