An experimental investigation of underexpanded jets from oval sonic nozzles

 Underexpanded jets from oval sonic nozzles were experimentally studied for various pressure ratios up to 20.3. The results revealed that the barrel type of shock structure was present only in the major axis plane except at low aspect ratios. The results also revealed that the jet spreading rate in the minor axis plane of the nozzle was much higher compared to that in the major axis plane, resulting in axis switching of jets. The cross sectional area of these jets were considerably higher compared to the axisymmetric jets indicating higher interface area for viscous mixing in the near field region and increased mixing in the far field region clear of shock structure. Received: 7 January 1997 / Accepted: 7 August 1997     

On the flow in underexpanded supersonic water jets

The problem of a supersonic water jet exhausting from a cylindrical nozzle in the underexpansion regime is solved. The calculations are made with allowance lor splitting. The distributions of the parameters over the jet are given. It is shown that the splitting region depends on the degree of underexpansion of the regime. The solution is found by the method of stabilization based on the difference scheme of Godunov, Zabrodin, and Prokopov [3] generalized to the case of flow with splitting.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 155–157, March–April, 1982.I thank G. A. Atanov for discussing the work.     

Nonstationary processes in starting strongly underexpanded jets

Results of the investigation of nonstationary efflux of argon by the electron-beam-sounding method are presented in [1]. Comparing the regularities obtained in that paper for the front motion of material during efflux from a nozzle with computations [2] for nonstationary expansion from a spherical source and the experimental results in [3] permitted clarification of the singularities of the influence of counter pressure and the temperature factor in jet expansion. The density distribution in nonstationary nitrogen and argon jets is obtained in this paper and study of the regularities of the front motion of the escaping gas is continued.Translated from Zhurnal Prikladnoi Mekhiniki i Tekhnicheskoi Fiziki, No. 1, pp. 34–40, January–February, 1978.     

Solution of the problem of flow of a non-axisymmetric swirling submerged jets

This paper considers the problem of a non-axisymmetric swirling jet of an incompressible viscous fluid flowing in a space flooded with the same fluid. The far field of the jet is studied under the assumption that the angular momentum vector corresponding to the swirling of the jet is not collinear to the momentum vector of the jet. It is shown that the main terms of the asymptotic expansion of the full solution for the velocity field are determined by the exact integrals of conservation of momentum, mass, and angular momentum. An analytical solution of the problem describing the axisymmetric swirling jet is obtained.     

Asymmetric flow of subsonic and sonic jets over an infinite wedge

A study is made of the flow of subsonic or sonic jets over an infinite wedge when the stagnation streamline bifurcates at the tip of the wedge. This regime can be realized only for a definite (previously unknown) relationship between the geometrical parameters. The problem is solved in the hodograph plane by the numerical method of [1] developed for the problem of a profiled Laval nozzle. A solution to the asymmetric problem obtained in the hodograph plane can be realized physically only for a definite relationship between the boundary values for the flow function. This relationship (which generalizes Prandtl's well-known formula [2] derived for asymmetric flow of incompressible jets over a plate on the basis of the momentum theorem) is obtained by analyzing the asymptotic behavior of the solution near the stagnation point. Examples of calculations are given.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 2, pp. 137–141, March–April, 1980.     

Shock wave calibration of under-expanded natural gas fuel jets

Natural gas, a fuel abundant in nature, cannot be used by itself in conventional diesel engines because of its low cetane number. However, it can be used as the primary fuel with ignition by a pilot diesel spray. This is called dual-fuelling. The gas may be introduced either into the inlet manifold or, preferably, directly into the cylinder where it is injected as a short duration, intermittent, sonic jet. For accurate delivery in the latter case, a constant flow-rate from the injector is required into the constantly varying pressure in the cylinder. Thus, a sonic (choked) jet is required which is generally highly under-expanded. Immediately at the nozzle exit, a shock structure develops which can provide essential information about the downstream flow. This shock structure, generally referred to as a “barrel” shock, provides a key to understanding the full injection process. It is examined both experimentally and numerically in this paper.

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Development of shock wave and vortex structures in unsteady jets

The paper deals with the formation of a gaseous jet behind a sonic nozzle. The nozzle was located at the end wall of a shock tube. A specially made two-direction shadow system, which ensured a simultaneous recording of side-on and head-on images of the jet, as well as a diffraction interferometer were used. On the basis of the data obtained, an analysis of the vortex structure of the jet was carried out, the amplitude of the azimuthal instability was measured and the spatial distribution of the density in the gaseous flow was obtained. Comparison between the experimental density distribution, numerical results and a nonself-similar point source blast wave model was conducted.This article was processed using Springer-Verlag T_EX Shock Waves macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Similarity of flows in strongly underexpanded jets of viscous gas

The fulfillment of the conditions formulated in [1] for the similarity of flows in strongly under-expanded jets of a viscous, thermodynamically ideal gas is studied. The limits of applicability of these conditions are established on the basis of exact solutions of the one-dimensional Navier —Stokes equations and experimental investigations.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika zhidkosti i Gaza, No. 6, pp. 117–125, November–December, 1978.     

Numerical calculations of supersonic underexpanded jets in a cocurrent flow with the use of parabolized Navier-Stokes equations

Results of a numerical study of three-dimensional supersonic jets propagating in a cocurrent flow are described. Averaged parabolized Navier-Stokes equations are solved numerically on the basis of a developed scheme, which allows calculations in supersonic and subsonic flow regions to be performed in a single manner. A jet flow with a cocurrent flow Mach number 0.05 ⩽ M_∞ ⩽ 7.00 is studied, and its effect on the structure of the mixing layer is demonstrated. The calculated results are compared with available experimental and numerical data. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 3, pp. 54–63, May–June, 2008.     

Flow and heat transfer in underexpanded nonequilibrium jets of an induction plasmatron

The results of experimental and numerical investigations of heat transfer to a cylindrical flatended model in underexpanded high-enthalpy air jets, including those flowing out through cylindrical heads of an elongated channel, are presented for the case of the operating parameters of the 100-kW VGU-4 plasma gun.     

HF-plasmatron experiment and numerical simulation of heat transfer in underexpanded dissociated-nitrogen jets

Experiments on heat transfer in underexpanded supersonic jets of high-enthalpy nitrogen are performed on the VGU-4 induction high-frequency plasmatron at a pressure of 10.4 GPa in a compression chamber. At gas flow rates of 2.4 and 3.6 g/s and HF generator powers of 45 and 64 kW the heat fluxes to the copper, stainless steel, MPG-7 graphite, and quartz surfaces are measured at the stagnation point of a water-cooled cylindrical, flat-ended model, 20 mm in diameter. In the same regimes the stagnation pressures are measured. The effect of the surface catalyticity with respect to nitrogen atom recombination on the heat flux is demonstrated and the qualitative catalyticity scale of the studied materials is established. In the supersonic regimes nonequilibrium nitrogen plasma flow in the discharge channel of the plasmatron and the underexpanded jet flow past the model are numerically simulated for the experimental conditions. The experimental and calculated data on the stagnation pressures and the heat fluxes to cooled surfaces of the metals, graphite, and quartz are compared.     

Shock wave structures ahead of nonuniform fan cascades

We study shock wave structures (SWS), consisting of shock waves and expansion waves between them, that occur in supersonic flow past nonuniform fan cascades when the velocity component normal to their front (“axial” component) is subsonic. The cascade nonuniformity is due to the scatter in the setting angles of identical blades, either sharp or blunt. A result of the uniformity is the generation of combined noise, whose frequencies are much smaller than the fundamental frequency of the uniform cascade, and slower nonlinear SWS attenuation. The accurate and fast “simple wave method” and “nonlinear acoustics approximation”, together with numerical algorithms for integrating Euler equations on overlapping grids (in calculating flow past blunt edges) and on SWS-adapted grids, are applied to determine the “guiding” action of nonuniform cascades and to describe the SWS evolution. The application of the Fourier analysis gives the sound field spectrum. The use of blades with rectilinear initial regions of the “backs” for reducing supersonic fan blade noise is efficient only at small (less than 0.25°) scatter in the setting angles. The shock wave structures attenuate more rapidly ahead of nonuniform cascades composed of blunt blades than ahead of those with sharp blades. For uniform cascades the blade bluntness effect is not large.     

Flow of a mixture of gas and solid particles in supersonic underexpanded jets

The presence of a second phase in a gas jet flowing out of a nozzle leads to considerable changes in the flow pattern [1–3]. Thus, as the particle concentration increases, the central jump in compression [shock wave] moves in the direction of the nozzle cutoff, while the Mach number on the axis of the jet in front of the forward jump diminishes. In this paper we shall consider the numerical solution of the problem of an axisymmetrical, two-phase, underexpanded jet flowing out of a straight nozzle into a submerged space. It is assumed that the distribution of the flow parameters is uniform over the jet cross section and that no thermal or dynamic retardation of the particles occurs.