Rotation of the thrust vector of a two-dimensional nozzle by means of displacing the critical surface

The method of thrust vector deflection by means of displacing the critical surface of a nozzle is numerically and experimentally investigated. The displacement is realized at the expense of extending rotatable walls, or deflectors, into the flow; in this case, one of the edges of the critical surface is displaced from the throat onto the deflector surface. Two nozzle configurations, with short and long deflectors, are studied. The thrust vector deflection angles and the nozzle thrust coefficients are determined in the thrust vector deflection regime. For the configuration with long deflectors the angle of rotation of the thrust vector amounts to 30° and is determined by the effect of jet ejection toward the opposite wall, similar with the Coanda effect.     

Prediction of flow and heat transfer in narrow rotating rectangular channels using Reynolds stress model

A computational study is performed on three-dimensional turbulent flow and heat transfer in a rotating rectangular channel with aspect ratio (AR) of 10:1, oriented 120° from the direction of rotation. The Focus is on high rotation and high-density ratios effects on the heat transfer characteristics of the 120° orientation. The Reynolds stress model (RSM), which accounts for rotational effects are used to compute the turbulent flow and heat transfer in the rotating channel. The effects of rotation and coolant-to-wall density ratio on the fluid flow and heat transfer characteristics is reported on a range of rotation numbers and density ratios (0 < Ro < 0.25 and 0.07 < Δρ/ρ < 0.4). The computational results are in good agreement with experimental data within ±15%. The results show that the density ratio, rotation number and channel orientation significantly affect the flow field and heat transfer characteristics in the rotating rectangular channel. Flow reversal occurs at high rotation number and density ratio.     

Velocity and Reynolds stresses in a precessing jet flow

 A novel fluid mixing device, described elsewhere, has been shown to have a dramatic effect on the combustion characteristics of a fuel jet. The main features of the flow are the deflection of the jet between 30° and 60° from the nozzle axis and its precession about that axis. Many of the factors governing the nozzle instabilities which drive the mixing in the external field are imprecisely defined. It is the aim of the present paper to examine, in isolation from the nozzle instabilities, the influence of precession on a deflected jet as it proceeds downstream from the nozzle exit. The fluid dynamically driven phenomena within the nozzle which cause the precession are in the present investigation replaced by a mechanical rotation of a nozzle from which is emerging a jet which is orientated at an angle from the nozzle axis. By this means the effect of precession on the deflected jet can be investigated independently of the phenomena which cause the precession. The experimental data reported here has been obtained from measurements made using a miniature, rapid response four-hole “Cobra” pitot probe in the field of the precessing jet. Phase-averaged three dimensional velocity components identify the large scale motions and overall flow patterns. The measured Reynolds stresses complement the velocity data and are found to be compatible with the higher entrainment rates of the jet found in earlier investigations. Received: 8 November 1995 / Accepted: 27 September 1996     

Nozzle thrust increase by flow rotation

Until recently, in constructing optimum supersonic axisymmetric nozzles, gas motions without rotation about the axis have been considered. This question has been studied rather completely for equilibrium gas flows in [1–6]. Avoidance of flow rotation is a limitation which may reduce the nozzle thrust, other conditions being equal. It is easy to show that for zero nozzle length or for a length that permits obtaining uniform flow at the exist that maximum thrust is provided by uniform flow parallel to the nozzle axis. If the length limitation does not make it possible to do this, then the use of freedom in the gas rotation may increase the nozzle thrust. Using a very simple example it is shown that this possibility is realized.     

Phase-resolved flow characteristics between two shrouded co-rotating disks

Flow characteristics in the interdisk midplane between two shrouded co-rotating disks were experimentally studied. A laser-assisted particle-laden flow-visualization method was used to identify the qualitative flow behaviors. Particle image velocimetry was employed to measure the instantaneous flow velocities. The flow visualization revealed rotating polygonal flow structures (hexagon, pentagon, quadrangle, triangle, and oval) existing in the core region of the interdisk spacing. There existed a difference between the rotating frequencies of the polygon and the disks. The rotating frequency ratio between the polygonal flow structure and the disks depended on the mode shapes of the polygonal core flow structures—0.8 for pentagon, 0.75 for quadrangle, 0.69 for triangle, and 0.6 for oval. The phase-resolved flow velocities relative to the bulk rotation speed of the polygonal core flow structure were calculated, and the streamline patterns were delineated. It was found that outside the polygonal core flow structure, there existed a cluster of vortex rings—each side of the polygon was associated with a vortex ring. The radial distributions of the time-averaged and phase-resolved ensemble-averaged circumferential and radial velocities were presented. Five characteristic regions (solid-body rotation region, hub-influenced region, buffer region, vortex region, and shroud-influenced region) were identified according to the prominent physical features of the flow velocity distributions in the interdisk midplane. In the solid-body rotation region, the fluid rotated at the angular velocity of the disks and hub. In the hub-influenced region, the circumferential flow velocity departed slightly from the disks’ angular velocity. The circumferential velocities in the hub-influenced and vortex regions varied linearly with variation of radial coordinates. The phase-resolved ensemble-averaged relative radial velocity profiles in the interdisk midplane at various phase angles exhibited grouping behaviors in three ranges of polygon phase angles (θ = 0 and α/2, 0 < θ < α/2, and α/2 < θ < α) because three-dimensional flow induced similar flow patterns to appear in the same range of polygon phase angles.     

Effect of external flow on the flow rate of a gas discharged through an orifice

The dependence of the flow coefficient of a gas jet ejected from an orifice/nozzle into a subsonic/transonic cross-flow on the flow and the jet Mach numbers, the off-design ratio, the nozzle inclination angle, β, and other determining parameters is considered. The physical nozzle flow pattern is constructed on the basis of experimental data obtained for 0.3< M_∞<1.75 and β=60°, 90°, and 120°. The results of measuring the pressure upstream and downstream of the orifice and on the windward and leeward orifice generators are presented. It is shown that the flow rate coefficient of a jet ejected into a cross-flow may exceed that of a similar jet outflowing into a flooded space. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 3, pp. 65–70, May–June, 1998.     

Flow structures of gaseous jets injected into water for underwater propulsion

Gaseous jets injected into water are typically found in underwater propulsion,and the flow is essentially unsteady and turbulent.Additionally,the high water-to-gas density ratio can result in complicated flow structures;hence measuring the flow structures numerically and experimentally remains a challenge.To investigate the performance of the underwater propulsion,this paper uses detailed Navier-Stokes flow computations to elucidate the gas-water interactions under the framework of the volume of fluid(VOF) model.Furthermore,these computations take the fluid compressibility,viscosity,and energy transfer into consideration.This paper compares the numerical results and experimental data,showing that phenomena including expansion,bulge,necking/breaking,and back-attack are highlighted in the jet process.The resulting analysis indicates that the pressure difference on the rear and front surfaces of the propulsion system can generate an additional thrust.The strong and oscillatory thrust of the underwater propulsion system is caused by the intermittent pulses of the back pressure and the nozzle exit pressure.As a result,the total thrust in underwater propulsion is not only determined by the nozzle geometry but also by the flow structures and associated pressure distributions.     

Thrust shock vector control of an axisymmetric conical supersonic nozzle via secondary transverse gas injection

Transverse secondary gas injection into the supersonic flow of an axisymmetric convergent–divergent nozzle is investigated to describe the effects of the fluidic thrust vectoring within the framework of a small satellite launcher. Cold-flow dry-air experiments are performed in a supersonic wind tunnel using two identical supersonic conical nozzles with the different transverse injection port positions. The complex three-dimensional flow field generated by the supersonic cross-flows in these test nozzles was examined. Valuable experimental data were confronted and compared with the results obtained from the numerical simulations. Different nozzle models are numerically simulated under experimental conditions and then further investigated to determine which parameters significantly affect thrust vectoring. Effects which characterize the nozzle and thrust vectoring performances are established. The results indicate that with moderate secondary to primary mass flow rate ratios, ranging around 5 %, it is possible to achieve pertinent vector side forces. It is also revealed that injector positioning and geometry have a strong effect on the shock vector control system and nozzle performances.     

The morphology of ice-structure in a planar nozzle subjected to forced internal convection flow

The present paper deals with the ice-formation in a planar nozzle with various convergence angles. Experiments have been carried out for different wall cooling parameters B in the range between 4 and 25 and for different flow rate Reynolds numbers in the range of 5,000 < Re _4h  < 50,000 for two different convergence angles of the nozzle. For all experiments with the larger convergence angle of the nozzle (2.5°), only smooth ice-layers could be observed. However, for the nozzle with the smaller convergence angle (1.25°), also wavy ice-layers could be detected. This interesting result is a justification for the hypothesis that the formation of wavy ice-layers is caused by flow laminarisation (due to the rapid growth in ice-layer thickness with increasing axial position from the inlet) and retransition to the fully turbulent state (after the acceleration falls below a certain critical value). Thus, this paper proves for the first time, that wavy ice-layers are suppressed by superimposed strong flow acceleration.     

Optimal Profiling of the Supersonic Part of a Plug Nozzle Contour

The problem of the optimal profiling of the supersonic part of a plug nozzle contour is solved within the framework of the ideal (inviscid and non-heat-conducting) gas model. The contours obtained provide a thrust maximum for given uniform sonic flow in the radial critical section of the nozzle, given constraints on the nozzle dimensions, and a given outer pressure (counterpressure). The initial sonic regions of the optimal contours are profiled on the basis of the condition that there the flow Mach number is unity. Varying the initial sonic region length makes it possible to construct nozzles of different sizes. The possibilities of the computational programs developed are demonstrated with reference to the example of plug nozzles, optimal when operated in a vacuum. It is shown that low thrust losses are obtained even for moderate nozzle dimensions. In the examples calculated, the optimal plug nozzles provide a greater thrust than the optimal axisymmetric and two-dimensional nozzles with an axial sonic flow for the same lengths and gas flow rates.     

Technique for experimental determination of the total thrust-aerodynamic characteristics of aircraft models

A method of experimental determination of the force characteristics of nozzles (thrust, lift, and pitching moment) simultaneously with the aerodynamic characteristics of an aircraft model in a supersonic flow in proposed. The tests were conducted for a special methodical model, with equilibrium of the thrust and drag jorces being reached. It is shown that the internal force characteristics of the nozzle and the drag of the model, as well as the effective lift and pitching moment (with account of propulsion), can be determined from the measured thrust of the propulsion simulator. Institute of Theoretical and Applied Mechanics, Siberian Division, Russian Academy of Sciences, Novosibirsk 630090. Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 40, No. 6, pp. 73–82, November–December, 1999.     

Study on micronozzle flow and propulsion performance using DSMC and continuum methods

In this paper, both DSMC and Navier–Stokes computational approaches were applied to study micronozzle flow. The effects of inlet condition, wall boundary condition, Reynolds number, micronozzle geometry and Knudsen number on the micronozzle flow field and propulsion performance were studied in detail. It is found that within the Knudsen number range under consideration, both the methods work to predict flow characteristics inside micronozzles. The continuum method with slip boundary conditions has shown good performance in simulating the formation of a boundary layer inside the nozzle. However, in the nozzle exit lip region, the DSMC method is better due to gas rapid expansion. It is found that with decreasing the inlet pressure, the difference between the continuum model and DSMC results increases due to the enhanced rarefaction effect. The coefficient of discharge and the thrust efficiency increase with increasing the Reynolds number. Thrust is almost proportional to the nozzle width. With dimension enlarged, the nozzle performance becomes better while the rarefaction effects would be somewhat weakened.The project supported by the National Natural Science Foundation of China (10372099). The English text was polished by Boyi Wang     

导弹水下点火推力峰值问题的数值研究

通过对燃烧室内燃气采用常微分控制方程,对喷管-燃气泡流场采用准一维模型,数值研究了导弹水下点火初期推力峰值与燃气泡初始体积、喷管尾盖打开压强、发射深度等参数的关系。对水流场采用势流理论并通过边界元方法求解,水流场和燃气泡流场由交界面上的压力连续和速度连续条件相互耦合;利用准一维气流场模型计算得到的结果表明导弹在水下点火后瞬间所受推力将急剧增大,与利用球形气泡模型得到的结果一致。计算结果还表明推力峰值随着燃气泡初始体积的增加迅速降低,随着喷管尾盖打开压强的增加而增大,随尾盖质量的增加而增大;在一定范围内发射深度的变化对推力峰值影响较小,计算结果可为工程设计部门提供参考。     

Reconsideration of inviscid shock interactions and transition phenomena on double-wedge geometries in a M ∞ = 9 hypersonic flow

Shock polar analysis as well as 2-D numerical computation technique are used to illustrate a diverse flow topology induced by shock/shock interaction in a M _∞ = 9 hypersonic flow. New flow features associated with inviscid shock wave interaction on double-wedge-like geometries are reported in this study. Transition of shock interaction, unsteady oscillation, and hysteresis phenomena in the RR ↔ MR transition, and the physical mechanisms behind these phenomena are numerically studied and analyzed.     

Combined Numerical and Experimental Investigation of a 15-cm Valveless Pulsejet

The pulsejet, due to its simplicity, may be an ideal micro propulsion system. In this paper, modern computational and experimental tools are used to investigate the operation of a 15-cm overall length valveless pulsejet. Gas dynamics, acoustics and chemical kinetics are studied to gain understanding of various physical phenomena affecting pulsejet operation, scalability, and efficiency. Pressure, temperature, thrust, and frequency are measured as a function of valveless inlet and exit lengths and different geometries. At this length scale, it is necessary to run the pulsejets on hydrogen fuel. Numerical simulations are performed utilizing CFX to model the 3-D compressible vicious flow in the pulsejet using the integrated Westbrook–Dryer single step combustion model. The turbulent flow and reaction rate are modeled with the k–ɛ model and the Eddy Dissipation Model (EDM), respectively. Simulation results provide physical insight into the pulsejet cycle; comparisons with experimental data are discussed.     

Experimental evaluation of side-loads in LE-7A prototype engine nozzle

During development tests of the LE-7A prototype engine, severe side-loads were observed. The side-load peaks appeared only in certain limited conditions during start-up and shut-down transients. To investigate phenomena causing those severe side-loads observed in the LE-7A prototype engine nozzle, series of cold-flow tests and hot-firing tests as well as CFD analyses were conducted. As a result of the hot-firing tests, two different phenomena were found to cause severe side-loads in the LE-7A prototype engine nozzle. One was a restricted shock separation (RSS) flow structure and the other was a phenomenon termed “separation jump,” the rapid movement of the separation location in the vicinity of the step. A step was installed in the LE-7A prototype to supply film-cooling gas. Hot-firing test results showed that RSS can occur for a limited mixture ratio. Detailed flow structure of RSS on the nozzle surface was revealed by the cold-flow tests. Measured pressures and visualized images of cold-flow tests clarified the mechanism causing the separation jump. The key phenomenon ruling the separation jump was found to be the base flow behind the step. Based on the results of the present study, the latest LE-7A engine nozzle design has been changed to eliminate the severe side-load.

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Imaging of an underexpanded nozzle flow by UV laser Rayleigh scattering

 Rayleigh scattering of ultra-violet laser light is applied as a diagnostic tool to record gas density distributions in a supersonic nozzle flow. The output beam of a pulsed ArF excimer laser (λ=193.4 nm) is focussed into a thin light sheet radially intersecting a dry air flow emanating from a circular nozzle. An intensified CCD camera is used to record the Rayleigh scattered light in a direction perpendicular to the light sheet. Since the Rayleigh scattering intensity is directly proportional to the local gas density, this results in two-dimensional gas density distribution maps of radial slices through the flow. Images of the flow density are presented for stagnation pressures between 0.2 and 0.7 MPa (0.1 MPa ≡1 bar), showing the transition from subsonic to supersonic flow and, at higher pressures, the formation of a Mach disk. Density maps can be recorded with single laser pulses, effectively freezing the flow structure on a 20 ns time scale. The diamond pattern, characteristic for underexpanded supersonic nozzle flows, is quantitatively monitored, with the experimental results being in reasonable agreement with predictions from a simplified theoretical model. Received: 25 September 1996/Accepted: 19 May 1997     

Study of the Aerodynamic Characteristics of Chevron Nozzles on the Basis of a Numerical Calculation of the Flowfield

The flow in a convergent nozzle equipped with chevrons and the flow around the chevrons are numerically simulated and studied on the basis of the numerical integration of the system of Reynolds equations closed by a differential model for the turbulent viscosity. From the calculated results, the flow pattern, the action of the chevrons on the flow, the circulation generated, and the values of the parameters characterizing the streamwise vorticity are determined. The results of calculations of the thrust and flow-rate characteristics of nozzles equipped with chevrons are presented. The data for chevron and conical nozzles are compared.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 76–88.Original Russian Text Copyright © 2005 by Brailko and Krasheninnikov.     

Control of a submerged jet in a thin rectangular cavity

An innovative method is presented for control of an oscillatory turbulent jet in a thin rectangular cavity with a thickness to width ratio of 0.16. Jet flow control is achieved by mass injection of a secondary jet into the region above the submerged primary jet nozzle exit and perpendicular to the primary nozzle axis. An experimental model, a 2-D and a 3-D computational fluid dynamics (CFD) model are used to investigate the flow characteristics under various secondary injection mass flow rates and injection positions. Two-dimensional laser Doppler anemometry (LDA) measurements are compared with results from the CFD models, which incorporate a standard k–ε turbulence model or a 2-D and 3-D realisable k–ε model. Experimental results show deflection angles up to 23.3° for 24.6% of relative secondary mass flow are possible. The key to high jet control sensitivity is found to be lateral jet momentum with the optimum injection position at 12% of cavity width (31.6% of the primary nozzle length) above the primary nozzle exit. CFD results also show that a standard k–ε turbulence closure with nonequilibrium wall functions provides the best predictions of the flow.     

Drag force on quasi-axisymmetric scramjets at various flight Mach numbers: theory and experiment

The net axial force on a non-fuelled quasi-axisymmetric scramjet model designed for operation at Mach 6 was measured in the T4 Stalker tube at The University of Queensland using a single-component stress wave force balance. The design used was a variant of a model that was tested previously at Mach 6. The new model was equipped with a modified thrust nozzle that was designed to improve the performance of the nozzle. Tests were performed to measure the drag force on the model for Mach 6, Mach 8 and Mach 10 shock tunnel nozzles for a range of flow conditions. The nozzle-supply enthalpy was varied from 3 to 10 MJ/kg and the nozzle-supply pressure from 35 to 45 MPa. For the test model, the drag coefficient increased with increasing nozzle-supply enthalpy. The test results are compared with a force prediction method based on simple hypersonic theories and three-dimensional CFD. The test results are in good agreement with the predictions over the wide range of conditions tested. The re-designed model has a more efficient nozzle but this comes at the expense of increased drag associated with the modifications required for the cowl. The results indicate that this type of vehicle design is not likely to be suitable for flight above Mach 8.

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