Influence of nozzle vibrations on the aerodynamic characteristics of a jet

The results of investigations of the aerodynamic characteristics of turbulent jets issuing from nozzles and subjected to the action of various kinds of low-frequency vibrations — transverse, longitudinal, and torsional (during axisymmetric vibrations of the nozzle around the longitudinal axis) — are presented. Data on the laws governing changes in the average and pulsation velocities along the jet axis, as well as on the spectra of velocity pulsations in the zone of jet mixing, have been obtained. It has been established that at low-frequency vibrations of the nozzle a noticeable intensification of jet mixing is attained. The same effects as on acoustic excitation of a jet are observed. The experiments were carried out at Reynolds numbers Re = 2∙10⁴–8∙10⁴.     

Acoustic Excitation of Noncircular Turbulent Jets

Results of experimental investigation of turbulent mixing in jets flowing out of nozzles with different cross sections in the case of low and highfrequency acoustic excitation of the jets are presented. The influence of the shape of the cross section of a nozzle on the acousticexcitation sensitivity of a jet flowing out of it is analyzed.     

Hydrodynamic structures — elements of the self-sustained oscillation system in the flow

The character of hydrodynamic disturbances in the near-wall shear flow inducing self-oscillations in the channel has been investigated. Experiments have been performed in a small and a large wind tunnel at a flow velocity of 10–40 m / sec. It has been found that excitation of self-oscillations becomes possible as a result of narrow-band acoustic radiation generation by not only vortex formations but also large-scale coherent structures in the region of the laminar-turbulent transition and in the turbulent boundary layer.     

Calculation of compressible flow in a short vortex chamber

A method for calculating a compressible turbulent flow in a short vortex chamber that incorporates calculations of the boundary layer at the end walls by the integral method and of the discharge by the theory of an ideal atomizer has been proposed. The magnitudes of pressure and circulation on the radius of the outlet orifice of the chamber, obtained in determining the boundary layer, have been used as input parameters in calculating the discharge, and the gas process has been regarded as isothermal. Favorable agreement between the calculated results and the experimental data has been found. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 5, pp. 152–158, September–October, 2006.     

Change of the Sign of the Effect with Increase in the Intensity of High‐Frequency Acoustic Excitation of a Turbulent Jet

Results of an experimental investigation of highfrequency acoustic excitation of turbulent jets for different intensities of the acoustic field are presented. It is shown that upon reaching a certain limiting level of excitation at high frequencies, the sign of the effect changes, i.e., at this level, highfrequency excitation leads to generation of turbulence in the jet rather than its suppression. Hence it follows that the highfrequency acoustic effect that suppresses turbulence is most efficient within an optimum range of frequencies and at an optimum level of excitation.     

Excitation of self-oscillations in flow past a surface with a recess and the possibility of preventing them

The results of experimental investigations of acoustic radiation initiated by hydrodynamic perturbations at the inlet to a cavity on a surface with a stream flowing past it are analyzed. A comparison is made between the processes of formation of large-scale hydrodynamic vibrations in a shear flow shed from the leading edge of the junction of the recess with the surface past which a stream flows and the processes in the region of transition from a laminar boundary layer on the surface of a wing to a turbulent one. The advisability of division of the flow inhomogeneity in the zone of the junction in order to prevent or weaken self-oscillations in the flow is estimated. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 80, No. 3, pp. 148–154, May–June, 2007.     

Relaminarization in supersonic microjets at low Reynolds numbers

Results of measuring the length of the supersonic portion of the air jets that flow out of axisymmetric sonic nozzles 10.4 μm-1 mm in diameter are presented. The measurements are carried out in a range of degree of jet noncalculation of 1–30 and in a wide Reynolds number range, including the laminar and turbulent flow modes. It is shown that the Reynolds number calculated from the nozzle diameter and the outlet parameters of gas is the parameter that governs jet flow. It is found that, for a laminar jet mixing layer, the length of the supersonic portion sharply increases. When the jet mixing layer becomes turbulent, the length of the supersonic portion decreases. The effect of increasing the length of the supersonic portion after its decrease due to the turbulization of flow in a jet and a growth in the Reynolds number is first discovered.     

Strength analysis and optimization of the barrel nozzle of a powder water cannon

We perform the optimization of the barrel nozzle of a powder water cannon. The nozzle profile is specified, which makes it possible to obtain impulsive water jets with the required velocities for the minimum pressure inside the installation. The stress-strain state is analyzed both for the actual experimental device and in the case of its optimal geometry. The numerical calculations are carried out according to the maximum distribution of the pressure of water upon the barrel obtained by using the Godunov method, which enables us to construct a lighter mobile and more powerful device. __________ Translated from Problemy Prochnosti, No. 2, pp. 137–146, March–April, 2006.     

Calculations of turbulent jets with finely dispersed solid admixtures

We suggest a computational-experimental method for determining the hydrodynamic characteristics of a dust-laden gas jet. The method is based on Prandtl-Mieses generalized variables. For this case we obtain an algebraic model of turbulence which allows us to take into account the mutual effect of phases and the initial conditions at the nozzle outlet. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 6, pp. 919–923, November–December, 1997. Original article submitted     

Study of non-reactive isothermal turbulent asymmetric jet with variable density

In the present study, the effects of inlet isothermal jet geometry on the mixing process with variable density have been investigated numerically. Four density ratios were considered, namely R_ρ =7.2, 1.8,1 and 0.66 for He-air, CH4-air, Air-air and CO2-air mixtures respectively. The jets are produced through rectangular and elliptic nozzles with aspect ratio Ar = 2:1. The elliptic and rectangular nozzles have approximately the same exit area as the circular nozzle. A second-order Reynolds stress model (RSM) is used to investigate variable density effects in asymmetric turbulent jets. Comparative studies are presented for the calculations of the variables such as the longitudinal velocity, the longitudinal fluctuating velocity and the turbulent kinetic energy. The results indicate that the asymmetric geometry noticeably enhances mixing in comparison with the axisymmetric case. Typical phenomenon of 3D jets is observed.     

Heat transfer to a laminar flow of toluene of supercritical pressure in the region of development of high-frequency thermoacoustic instability

Results and the procedure of an experimental investigation of heat transfer in combination with high-frequency thermoacoustic self-oscillations of the pressure of toluene, t_liq < t_m, t_w/t_m = 1.15–1.90 are presented. A criterial heat transfer equation in a vast region of excitation of thermoacoustic pressure self-oscillations is proposed, and the boundary for the onset of the development of the oscillatory process is found.     

Initiation of detonation by burning jets

We carried out an experimental investigation of the initiation of a detonation wave by burning jets at the orifice plate outlet. Academic Scientific Complex “A. V. Luikov Heat and Mass Transfer Institute of the Academy of Sciences of Belarus,” Minsk, Belarus. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 69, No. 1, pp 26–32, January–February, 1996.     

Influence of the geometry of the nozzle on the characteristics of an exhaust jet

Two solutions for the parameters of a turbulent exhaust jet of a dual-duct engine — the traditional solution within the framework of Prandtl equations of the type of boundary-layer equations and calculation of the near-range field within the framework of the Navier-Stokes equations with subsequent calculation within the framework of the Prandtl equations for large distances — have been compared. It has been shown that the influence of the real geometry of the nozzle exit section, including the shift of the center body and the main duct forward from the exit section of the cold secondary duct, can be allowed for by correcting the constant of the source term in the differential equation for turbulent kinematic viscosity. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 3, pp. 37–46, May–June, 2006.     

Decrease in the noise of a subsonic turbulent jet ejected from a ring nozzle with longitudinal slots

The results of investigations of the aerodynamic and acoustic characteristics of a jet ejected from a ring nozzle with longitudinal slots are presented. It is shown that these slots markedly influence the jet mixing and substantially decrease the jet noise generated in a wide frequency range. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 79, No. 3, pp. 82–84, May–June, 2006.     

Influence of the plasma of a high-frequency barrier discharge on the structure of the dynamic boundary layer on a flat surface

Methods of obtaining a surface high-frequency barrier discharge have been analyzed. The results of investigation of the influence of this discharge on the characteristics of the dynamic boundary layer on a flat surface have been given. __________ Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 81, No. 1, pp. 55–61, January–February, 2008.     

Experimental and theoretical investigation of Taylor-Görtler instability in the boundary layer on a concave surface

Results of experimental and theoretical investigations of centrifugal instability in the turbulent boundary layer on a concave surface are presented. Linear and nonlinear regularities in the development of this type of instability are revealed. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 70, No. 2, pp. 279–283, March–April, 1997.     

Occurrence and Development of Vortices in Turbulent Jets under the Effect of Sawtooth Sound Waves of Finite Amplitude

Consideration is given to the formation of vortices in turbulent jets under the effect of sawtooth sound waves of finite amplitude in the case of internal longitudinal acoustic action. The convection velocity and the rate of rise of the disturbances are determined. It is shown that the transverse dimensions of the disturbances increase linearly on the initial portion of the flow.     

An experimental study of subsonic microjets escaping from a flat nozzle

We have experimentally studied subsonic laminar gas jets escaping from a flat nozzle with dimensions of 83.3 × 3600 μm. Reynolds numbers calculated for the given nozzle height and average flow velocity at the nozzle output edge ranged within 58–154. The working gas was air at room temperature. Distributions of the gas velocity and its pulsation along the jet axis were determined. It is established that the obtained characteristics of laminar subsonic microjets are fundamentally different from those of macroscopic turbulent jets. Based on the results of velocity pulsation measurements, it is shown that a laminar–turbulent flow transition is present and its position is determined.     

Impact damage detection in composite laminates using nonlinear acoustics

The paper demonstrates the application of nonlinear acoustics for impact damage detection in composite laminates. A composite plate is monitored for damage resulting from a low-velocity impact. The plate is instrumented with bonded low-profile piezoceramic transducers. A high-frequency acoustic wave is introduced to one transducer and picked up by a different transducer. A low-frequency flexural modal excitation is introduced to the plate at the same time using an electromagnetic shaker. The damage induced by impact is exhibited in a power spectrum of the acoustic response by a pattern of sidebands around the main acoustic harmonic. The results show that the amplitude of sidebands is related to the severity of damage. The study investigates also the effect of boundary conditions on the results.