Flow investigation in separation zones ahead of supersonic jets in a subsonic stream

The flow in the three-dimensional separation zone of a turbulent boundary layer on a plate in front of a supersonic jet injected perpendicularly to the subsonic drifing flow is considered. The purpose of the investigation is to establish the physical singularities of subsonic flow around a supersonic jet obstacle and to obtain dependences of the geometric flow characteristics on the free-stream and injected-jet parameters. Results of an experimental investigation permitted proposing approximate dependences of the geometric three-dimensional separation-zone characteristics which appear in the subsonic stream ahead of a jet obstacle.     

Flow in the zones of separation of a turbulent boundary layer in front of a subsonic jet injected through a circular nozzle

Flow taking place in the three-dimensional region of separation formed by the interaction of a subsonic stream with a single subsonic jet emerging from a circular hole in a plate perpendicular to the stream is considered. The aim of the investigation is to discover the physical characteristics of the flow in the three-dimensional separation zone in front of a subsonic jet obstacle and to determine the principal laws governing the geometrical and hydrodynamic characteristics of the flow as functions of the parameters of the driving stream and jet.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 34–41, May–June, 1973.     

Pressure pulsations on an obstacle in a jet

At the present time, much attention is devoted to auto-oscillations that arise from the interaction between a supersonic underexpanded jet and an obstacle that it encounters at right angles [1, 2]. There are far fewer data on the pressure pulsations on an obstacle in the absence of auto-oscillations [3–6]. However, in many cases the highest total levels of the pressure pulsations are observed when the barrier is situated at fairly large distances from the nozzle opening and the pressure pulsations have a random nature. We have investigated the pressure pulsations on a plate normal to a supersonic strongly underexpanded jet. The pulsation characteristics were measured for an arrangement of the obstacle when auto-oscillations are absent. We have established dependences that generalize the results of measurement of the pulsation characteristics at both subsonic and supersonic velocities on the jet axis directly in front of the obstacle. We have also investigated the correlation between the pressure pulsations on the plate and external acoustic noise. We have obtained the dependence of the level of the acoustic noise on the value of the maximal pressure pulsations on the plate.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 1, pp. 163–167, January–February, 1980.     

Mechanism of self-oscillations in a supersonic jet impact onto an obstacle 1. Obstacle with a spike

Results of numerical simulations and experimental investigations of self-oscillations arising in the case of impingement of an overexpanded or underexpanded jet onto an obstacle with a spike are reported. The mechanisms of the emergence and maintaining of self-oscillations for overexpanded and underexpanded jets are elucidated. It is demonstrated that self-oscillations are caused by disturbances in a supersonic jet, which induce mass transfer between the supersonic flow and the region between the shock wave and the obstacle. The feedback is ensured by acoustic waves generated by the radial jet on the obstacle. These waves propagate in the gas surrounding the jet, impinge onto the nozzle exit, and initiate disturbances of the supersonic jet parameters. In the overexpanded jet, these disturbances penetrate into the jet core, where they are amplified in oblique shock waves.     

Experimental and numerical analysis of the jet dispersion from a bent chimney around an obstacle

An experimental study and a numerical modelling analysis were carried out simultaneously to study the flow field structure issuing from a chimney around an obstacle. The main purpose of this study is to evaluate the impact of the jet emitted from a chimney (bent or straight) on the dynamics and the turbulent features of the surrounding flow. The consideration of these features is particularly pertinent to the understanding of mixing between the interacting flows which may be very important in controlling pollutant dispersion in the atmosphere. The experimental data are depicted by means of a PIV technique; whereas the numerical three-dimensional model is simulated through the resolution of the different governing Navier–Stokes equations. The volume finite method, together with the second order turbulent closure model (RSM), was adopted. Variations in obstacle form (cylindrical or parallelepiped) and chimney configuration (bent or straight) were tested and features studied were: the global jet plume, the windward and leeward jet spread; the size, location and magnitude of the reverse flow region; the penetration and the deflection of the jet trajectory around the obstacle. All these considerations allowed us to characterize well the impact of the injection of the jet emitted from the chimney within the crossflow, and its spreading around the obstacle and within the whole domain. Such characterization is very important with regard to pollutant dispersion and consequently to the environmental impact. Indeed, the different species contained within the emitted fumes are mainly directed by the velocity components and their mixing and progression within the domain and around the obstacle are closely related.     

Numerical investigation of the steady-state conditions of interaction of a supersonic underexpanded jet with a plane obstacle located perpendicular to its axis

The results are presented of the numerical investigation of the interaction of a supersonic axisymmetrical jet of a nonviscous and nonthermally conductive gas, flowing from a conical nozzle into a space with reduced pressure, with a plane obstacle. The presence of a triple point of intersection of the shock wave issuing from the obstacle with the trailing and reflected oblique compression shock is characteristic for the conditions considered in the paper. The solution of the problem is obtained by numerical integration of the gasdynamic equations by means of monotonic difference schemes of a straight-through calculation with first-order accuracy. The interaction of supersonic gas jets with surfaces is a vast problem and is one of the trends being developed intensively in the theory of jet streams. Of the whole multiplicity of problems of practical interest, the two-dimensional case of the normal collision between a supersonic axisymmetrical jet and a plane obstacle has been studied in most detail. As a result of the investigations carried out, many characteristic mechanisms of these flows have been revealed. Together with the numerous experimental papers, several reports have been published (for example, [1–4]) in which various numerical methods are employed to solve this problem. In addition to the method of integral relations used in [1], an implicit difference scheme [2] and explicit schemes of straight-through calculation [3, 4] have been used to calculate the subsonic zone of increased pressure in front of the obstacle. However, an extensive investigation of the special features of the action of a supersonic underexpanded jet on a plane obstacle, at a very small distance from the nozzle exit, still has not been carried out up to the present. In this paper, a solution of this problem is undertaken by the numerical method described in [4] using difference schemes [5, 8].Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 49–56, September–October, 1976.The authors express sincere thanks to A. N. Kraiko, é. A. Ashratov, and U. G. Pirumov for constant interest and support in carrying out this project.     

Calculation of the Pulsed Jet of a Powder Water Cannon under Water

The results of a numerical investigation of a pulsed submerged water jet flowing out from the nozzle of a powder water cannon are given. A mathematical model of the process is constructed and the results of the numerical calculations for a water cannon of specific design are given. The water flow in the water cannon is considered in the quasi-one-dimensional formulation and the submerged jet propagation and its interaction with an obstacle are considered in the axisymmetric formulation. It is shown that the external conditions only slightly affect the water cannon parameters and that for various distances from the obstacle the maximum pressure of the pulsed jet on the obstacle is close to the initial jet dynamic pressure.     

Interaction of a supersonic pulse jet with an obstacle

The nonstationary interaction between a supersonic pulse jet and a flat plate perpendicular to the jet axis is studied experimentally and numerically. The time dependences of the pressure and heat flux at various points on the obstacle and the spatial distribution of the density are obtained experimentally. The nonstationary flow is calculated numerically by the Godunov method. The experiments and calculations reveal the effect of the reflected starting shock wave and the front part of the swirled gas outflow on the distribution of the dynamic and thermal loads acting on the plate, in both time and space. Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 45–51, March–April, 1998. This research was carried out with partial financial support from the Russian Foundation for Fundamental Research (project No. 96-02-16170).     

Impact of a hydroabrasive jet on material: Hydroabrasive wear

The wear of steel plates under the impact of a hydroabrasive jet was studied experimentally by varying the distance between the sample surface and the nozzle, the angle of impingement of the jet on the plate, and the abrasive concentrations in water and in the ambient medium (jet in air, submerged jet). The results are compared with available data on the structure of the jet and jet flow around an obstacle. It is shown that the addition of abrasive particles to the liquid can be used to study the liquid jet flow around an obstacle because the form of surface wear allows one to determine the region of impact of the jet core, the deceleration region, and the near-wall flow region before flow separation.     

Interaction of a supersonic flow with a transverse jet injected through a circular aperture in a plate

A flow pattern created by the interaction of a supersonic flow with a transverse sonic or supersonic jet injected normally to the direction of the main flow through a circular aperture in a plate is considered. The pressure rises in front of the jet owing to the retarding action of the incident flow. The boundary layer building up on the wall in front of the injection nozzle is accordingly detached. The flow pattern in the region of interaction between the jet and the external flow is illustrated in Fig. 1. The three-dimensional zone of detachment thus formed deflects the incident flow from the wall, and in front of the jet a complicated system of sharp jumps in contraction develops. A three-dimensional system of jumps also develops in the jet itself.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No, 5, pp. 193–197, September–October, 1970.     

Dynamics of single and twin circular jets in cross flow

2D-PIV is used to investigate the near field jet dynamics of a single and a tandem twin jet in cross flow at a blowing ratio of 3. The flow characteristics that were studied included jet trajectory and penetration, windward and leeward jet spread, and the size, location and magnitude of the reverse flow region. The tandem jet setup resulted in configuration where the rear jet was shielded by the front jet that allowed the rear jet to penetrate deeper into the cross stream. The penetration of front jet was found to be comparable to that of the single jet in the near field. Asymmetric jet spread was observed both in the windward and leeward side with higher jet spread in the leeward side for both the single and tandem jet configuration. Furthermore, for the tandem jet condition, the presence of rear jet was found to affect the windward spread of the front jet minimally. The windward and leeward spreads of the rear jet were observed to be decreased by the presence of the front jet. Reverse flow zones confined between the front and rear jets in tandem setup was also observed to be stronger than that of a single jet. A turbulent kinetic energy (TKE) analysis indicates that the behavior of a jet in tandem setup follows the same trend as that of an axisymmetric turbulent jet with low turbulence in the jet core and higher turbulence in the jet shear layer that subsequently transitions to high turbulence production in the jet core as the jet shear layers on windward and leeward side of the jet coalesce.     

Optimal penetration of a liquid jet into an obstacle

The velocity distribution and cross-sectional area along a jet which will assure maximum depth of penetration are found for a given jet energy within the framework of the hydrodynamic theory of liquid jet penetration into an obstacle. Also found is the velocity distribution along the jet which will assure ultimate tension of its elements upon approaching the obstacle. The possibility is exhibited of applying the theory elucidated to construct cumulative charges with elevated punch-through capacity.     

Modulations of a weak shock wave through a turbulent slit jet

The pressure modulation of a weak shock wave induced by a Nd:YAG laser pulse when passing across a turbulent slit jet was experimentally investigated. With the slit jet the peak overpressure became smaller by an average of 12%, with a standard deviation of 27%. Clear relationships were obtained between the overpressure history and the experimentally observed shock front deformation, which was visualized as differential schlieren images. The peak overpressure was increased when the originally spherical blast wave front was locally flattened, whereas it was decreased when a hump in the shock wave front was formed.     

On the possibility of blowing a gas jet into a supersonic flow without formation of a three-dimensional boundary-layer separation zone

We consider the flow formed by the interaction of a supersonic flow and a transverse sonic or supersonic jet blown at right angles to the direction of the main flow through a nozzle whose exit section is in a flat wall. When a gas jet is blown through a circular opening [1] the pressure rises in front of the jet because of the stagnation of the oncoming flow. This leads to separation of the boundary layer formed on the wall in front of the blowing nozzle. The resulting three-dimensional separation zone leads to a sharp increase in the pressure and the heat fluxes to the wall in front of the blowing nozzle, which is undesirable in many modern applications. The aim of the present investigation was to find a shape of the exit section of the blowing nozzle for which there is no three-dimensional separation zone of the boundary layer in front of the blowing nozzle.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 162–165, May–June, 1979.     

Pressure pulsations during interaction between a subsonic jet and the subsonic section of a supersonic jeton a flat obstacle

Pressure pulsations were measured during in-leakage of a subsonic jet and the subsonic section of a heated supersonic jet on a flat obstacle. Data have been obtained on the total and spectrum levels of the pressure pulsations at different spacings X of the obstacle from the nozzle exit. It is shown that when the obstacle is disposed at the section of the jet where the local velocity is subsonic, the pulsation levels outside the dependence on the conditions at the nozzle exit (Mach number Maxa 0 a 3.0; stagnation temperature T₀=280–1200K) vary in direct proportion to the local velocity head q. The ratio between the total level and q is (/g)=0.2–0.3. It is established that for a subsonic velocity ahead of the obstacle, all the spectra obtained for different values of M _a , T₀, d _a and X in the coordinates Sh=f(d/V) and (₁*/q)(V/d) will lie on a single generalized spectrum. Here ₁* is the pulsation level in a 1-Hz band, and d and V are, respectively, the jet diameter and velocity directly in front of the obstacle.Translated from Izvestiya Akademiya Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 172–174, September–October, 1975.     

Formation of a pulsed jet behind a supersonic nozzle when the gas can relax at the entrance to the nozzle

The formation of a pulsed jet behind supersonic nozzles is considered when relaxation processes take place in the gas entering the nozzle. In a general formulation, the problem of the motion of the front of the exhausting matter and the disturbances accompanying it in the process of formation of a pulsed jet is determined by a large number of parameters, which characterize the exhausting gas and the residual gas of the pressure chamber and also the geometry of the flow conditions. A reliable computational model of a pulsed jet does not exist. To construct such a model, experiments are required in a wide range of boundary and initial conditions. An investigation was made into flow of shockheated argon, nitrogen, and carbon dioxide out of nozzles set up at the end of a shock tube. Generalized dependences were obtained for describing the motion of the front of the nonstationary jet and the wave in front of it in a wide range of the initial pressure-difference parameters and variation of the stagnation temperatures. The choice of the generalized parameters when relaxation of the excited internal degrees of freedom of the molecules of the gas can occur at the entrance to the nozzle is discussed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 129–135, November–December, 1980.     

Numerical solution of the problem of the impact of a jet on an obstacle

We shall investigate the initial stage of the impact of an axisymmetric fluid jet having a plane face on a rigid obstacle. An example of a numerical calculation by a finite-difference method [1] is cited.     

Start shock waves and the vortex structures arising in the formation of jets

Experimental studies were made of the state behind a shock wave arising in front of a pulse jet in formation, and the development of the vortex structure of the jet itself. A comparison was made of the experimental axial density distribution in the jet in the region between the front of the gas and the primary shock wave with the solutions to the problem of an expanding spherical piston and the nonself-similar problem of a point explosion. Moscow Translated from Izvestiya, Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 146–150, September–October, 1988.     

Numerical investigation of “lateral” interaction with an obstacle of an axisymmetric jet exhausting into vacuum

The problem of the interaction of a strongly underexpanded axisymmetric jet with an obstacle for which the normal to the surface makes an angle near /2 with the jet axis is rather laborious for numerical solution due to the high disequilibrium of the gas-dynamic parameters in the peripheral part of the jet and the three-dimensional nature of the flow in the interaction region. Therefore, the results at present available have mainly been obtained experimentally [1, 2]. Among the theoretical studies made in this direction, it is necessary to mention Ivanov and Nazarov's [3], which gives the results of numerical investigation of lateral interaction of a jet with obstacles of various shapes in the case of weakly underexpanded jets when the flow in the interaction region is everywhere supersonic. In the present paper, a study is made of the case when a jet exhausts into vacuum and in front of the obstacle there is a detached shock wave, behind which there is mixed subsonic and supersonic three-dimensional flow.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 49–54, November–December, 1982.We thank V. I. Uskov for assistance in the present work.