Self-oscillations in an underexpanded jet flowing into a barrier

The distribution of the phases and amplitudes of the static pressure fluctuations with self-oscillations of an underexpanded jet flowing into a barrier is obtained experimentally in the present paper. The distribution of the Mach number in the compressed layer and in the subsonic flow in front of the barrier is shown. The results of the measurements of the characteristics of the self-oscillation process are discussed.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 38–43, November–December, 1977.     

Measurements of mean and fluctuating wall shear stress beneath spanwise-invariant separation bubbles

 Pulsed-wire measurements of wall shear stress have been made beneath two separation bubbles. In one a cross flow was generated by means of a (25°) swept separation line. Fluctuating stresses in orthogonal “streamwise” and cross-flow directions are very nearly equal and independent of at least moderate cross flow velocity. These fluctuations are largely determined by large-scale motions in the outer flow, whereas the mean shear stresses are not. The pdf of the “streamwise” fluctuations is unchanged by the cross flow. When a cross flow is present the pdf of the cross-flow stresses is similar to the “streamwise” pdf. Dependence on Reynolds number is the same in both flows. Received: 10 April 1998/Accepted: 17 July 1998     

Propagation of an underexpanded turbulent jet in a parallel supersonic flow

The characteristics of supersonic off-design turbulent jets discharging into parallel supersonic flows are investigated numerically using approximate equations for the effective turbulent viscosity which are derived by analysis of the experimental data.     

Measurements of concentration per size class in a dense polydispersed jet using planar laser-induced fluorescence and phase Doppler techniques

In dense two-phase flows, it is well known that phase Doppler anemometry is not well suited for the measurement of concentration and mass flux. Laser diagnostics based on fluorescence can provide the dispersed phase concentration but without discrimination between size classes. We present a new method of coupling the two techniques, in order to extract the local value of concentration and flux per size class. The method is applied to an axisymmetric turbulent jet, laden with polydispersed droplets 1–90 μm. Droplet concentration profiles are obtained in the development zone (x/d ₀ < 20) of the dense jet and are used to study droplet dispersion. The results are then introduced into the momentum transport equations to analyze the influence of droplets on the carrier phase. We show that the local decrease of the rate of variation of mean momentum with mass loading is due both to an increase in interfacial transfer rate and to a decrease in turbulent diffusion effects. Received: 20 November 2000 / Accepted: 3 April 2001     

Calculation of the interaction of an axisymmetric supersonic underexpanded jet with an obstacle

The method of integral relations [1] and the method of characteristics are used to construct a scheme for the numerical solution of the problem of the interaction of a supersonic underexpanded jet with an obstacle. The results of calculations are presented.The author wishes to thank his scientific coworker I. I. Kuhlin for compiling and debugging the program.     

Measurements of temperature,density, pressure,and their fluctuations in supersonic turbulence using laser-induced fluorescence

A laser-induced fluorescence (LIF) method has been developed that provides simultaneous measurements of temperature, density, and their fluctuations owing to turbulence in unheated compressible flows. Pressure and its fluctuations are also deduced using the equation of state. Fluorescence is induced in nitric oxide that has been seeded into a nitrogen flow in concentrations of 100 ppm. Measurements are obtained from each laser pulse, with a spatial resolution of 1 mm and a temporal resolution of 125 ns. The method was applied to a supersonic, turbulent, boundary-layer flow with a free-stream Mach number of 2. For stream conditions in the range from 150–300 K and 0.3–1 atm, temperature is measured with an uncertainty of approximately 1% rms, while density and pressure uncertainties are approximately 2% rms.     

Simultaneous temperature and 2D velocity measurements in a turbulent heated jet using combined laser-induced fluorescence and LDA

 This paper presents an efficient technique for the characterization of thermal transport properties in turbulent flows. The method is based on the temperature dependence of fluorescence, induced by laser radiation, of an organic dye. The laser-induced fluorescence technique is combined with 2D laser Doppler anemometry, in order to measure in the same sample volume simultaneously and instantaneously the temperature and velocity. The technique is demonstrated on a turbulent heated round jet: the mean and fluctuating dynamic and thermal fields are investigated, and the temperature-velocity cross-correlations are determined in order to characterize the turbulent diffusivity and the turbulent Prandtl number. Received: 30 October 1997/Accepted: 14 July 1998     

Three-dimensional structure of flow in a supersonic underexpanded jet

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 42–47, July–August, 1991.     

Experimental research on the laws of propagation of an underexpanded jet in a subsonic counterplan

The fields are obtained of total pressures and velocities along the axis of a jet flowing out into a subsonic counterflow from an isolated conical nozzle with semiaperture angle _a = 10°. The nozzle was located at the vertex of a cone with half-angle = 75° at the vertex and ratio of the radii at the midsection and the nozzle equal to 10. It is established that for an underexpanded jets in sub- and supersonic counterflows the main dimensionless number generalizing the data on the distribution of the gas-dynamic parameters in the jet at various pressure-ratio numbers n, and Mach numbers of the counterflow M and of the jet M_a, is the ratio of the momentum flux density J_a of the jet to the velocity head q: J=J_a/q. Generalizing dependences are obtained for the distribution of the total pressure and the velocity along the axis of the jet, and also for the jet range.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 186–188, May–June, 1986.     

Flow characteristics of an underexpanded jet and its application to the study of droplet breakup

The jet from an axiymmetric convergent nozzle has been investigated at pressure ratios of 1.9 and 3.6 corresponding to exit Mach numbers of unity and 1.49. Velocity characteristics were measured with a laser-Doppler velocimeter and complemented by shadography which showed the structure of the expansion-compression waves. The sinuous longitudinal variations of the axial velocity are shown to be large at the higher pressure ratio with amplitudes which decreased with increasing distance from the jet exit and from the axis. The use of the jet for the quantification of droplet breakup is considered and it is evident that the higher pressure ratio requires careful consideration of the location at which a droplet is allowed to fall into the jet.Financial support from the Ministry of Defence under agreement 2037/001/CBDE is gratefully acknowledged.     

Measurements of aerosol product in an axisymmetric co-flow jet

An experimental investigation explored the effects of varying reactant concentration and Reynolds number on the formation of product in a jet of air/N₂/HCl flowing into a co-issuing stream of air/NH₃. Turbulent mixing resulted in the production of NH₄Cl particles by a chemical reaction with negligible heat release. Laser light was elastically scattered in the transition regime between Rayleigh and Mie scattering from the particles. Scattered light intensity served as an indicator of particle mass concentration. Radial profiles of mean and root mean square concentrations were obtained in the self-similar far field region of the jet. The stoichiometric mixture fraction was varied by varying the concentration of NH₃ in the co-flowing stream. It was found that the “flame” length decreased with increasing stoichiometric mixture fraction, and was independent of Reynolds number. The overall amount of product decreased as the stoichiometric mixture fraction was increased from 0.06 to 0.27, while the amount of limiting reactant was the same in both cases. Received: 28 April 1998/Accepted: 16 November 1999     

Mixing in a confined turbulent impinging jet using planar laser-induced fluorescence

 The non-intrusive Planar Laser-Induced Fluorescence (PLIF) technique was applied to the study of the mixing of a turbulent water jet impinging orthogonally onto a flat surface. A procedure for calibrating the system at each pixel of a CCD camera array was first developed and tested. Post-processing of the PLIF data gave quantitative results of good quality. The mixing at the entrance of the deflection zone was also investigated. Average concentration fields in the centre plane of the jet were calculated and compared with Large Eddy Simulations (LES) and also with data from the literature. Probability density functions, space coefficients of correlation and radial concentration fluctuation profiles were calculated to further quantify the spreading of the jet, both in the free and deflection zones. Inside the deflection region, a slight tendency towards intensified mixing at the outer edge of the jet was found. This was attributed to a deceleration of the fluid which resulted in accelerated diffusion. Received: 11 July 1997 / Accepted: 9 January 1998     

Inverse feedback mechanism in self-oscillations in flow of an underexpanded supersonic jet against a planar obstacle

Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 4, pp. 59–63, July–August, 1991.