In the present paper, we give a brief overview of the studies of supersonic jet flows which were performed recently with the aim of gaining experimental data on the formation of the shock-wave structure and jet mixing layer in such flows. Considerable attention is paid to a detailed description of discharge conditions for supersonic jets, to enable the use of measured data for making a comparison with numerical calculations. Data on the 3D flow structure in the mixing layer of the initial length of a supersonic jet are reported. Scientific interest in this phenomenon is due to its practical significance in studying the possibility of intensifying the mixing process as well as in studying the sound-generation process.

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Shock-Wave Structure of Supersonic Jet Flows

The steady-state structure of supersonic underexpanded jet flow at Ma = 1 is experimentally investigated. The measured total pressure distributions are presented in different cross sections and along the jet axis. Certain distinctive features of the supersonic jet flow are revealed. Among these are considerable fluctuations of the density distribution in the mixing layer formed behind the triple point on the normal shock in the jet. They are due to the presence of vortex structures in the internal mixing layer. The data obtained are used in testing the results of numerical calculations.

Gasdynamic structure of an axisymmetric supersonic underexpanded jet

Shock waves appear in numerous high-speed propulsion applications, including intakes, nozzles, and transonic and supersonic turbomachinery. The aerodynamic performance in bladeless turbines, which is designed for work extraction under such conditions, is dominated by flow separation induced by shock-wave pressure gradients. The large velocity gradients pose limitations on flowfield characterization using particle-based optical diagnostics, such as particle image velocimetry and laser Doppler anemometry. These limitations, along with challenges in seeding the flow, can be overcome by tracking the molecules already present in the flow. This paper presents kHz-rate femtosecond laser electronic excitation tagging (FLEET) to excite long-lived fluorescence of nitrogen molecules, acting as in-situ flow tracers. A multi-point variation of this approach was demonstrated in an optically accessible linear turbine test section, developed to investigate bladeless turbines. The femtosecond laser is coupled with an intensified CMOS camera with a frame rate of 200 kHz. High-speed measurements were made of the steady and unsteady performance in the bladeless turbine, with particular attention to capturing flow structures, spatial velocity gradients, and transient events such as unstarting of the supersonic passages.

https://iopscience.iop.org/article/10.1088/1361-6501/ab7062/pdf

Application of femtosecond laser electronic excitation tagging (FLEET) velocimetry in a bladeless turbine

A method of correction of particle image velocimetry (PIV) data for reconstruction of the gas velocity based on the particle velocity in supersonic underexpanded jets is considered. The method is based on estimating the velocity lag of tracer particles on the basis of their velocity relaxation parameter as a correction to PIV data in the Newton approximation of interphase interaction. It is shown that the velocity relaxation parameter of tracer particles in flows with velocity jumps can be determined from the initial PIV data. Correction with the found parameter of velocity relaxation of the phases provides good accuracy.

Correction of PIV data for reconstruction of the gas velocity in a supersonic underexpanded jet

The paper studies the process of liquid atomization in high-speed gas jets with application to a subject of high-rate fuel nozzles. Experiments were carried out for gas-liquid jet with the central-axis feeding of liquid to the outlet of a confuser-type nozzle with pumping of air in subsonic and supersonic flow regimes. The energy balance approach was developed for describing a gas-liquid jet. This provided us the needed data for comprehensive description of the gasliquid jet: gas velocity field without liquid, shadow visualization of geometry and wavy structure of a jet with liquid and with pure gas, velocity profiles for liquid phase, spray droplet size, spray concentration and spatial distribution. The gas-liquid flow was characterized by Weber number from the time of liquid jet breakup till the final spray.

Liquid atomization in a high-speed coaxial gas jet

Methods of reconstruction of the gas flow velocity from the measured velocity of disperse phase particles are considered. It is demonstrated that available approaches are limited by the low velocity nonequilibrium of the phases. A method of correction of particle image velocimetry (PIV) data on the basis of measuring the parameters of velocity relaxation of particles is proposed for measuring the gas velocity in high-gradient flows. The method is experimentally tested in the flow behind a shock wave with submicron tracers. A possibility of using this method in flows with gas-dynamic discontinuities is demonstrated.

Measurement of gas velocity in a high-gradient flow, based on velocity of tracer particles

Investigation of supersonic nonisobaric jet structure

Communicative competence of a teacher: professional deficiency or norms of pedagogical ethics

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A. A. Pivovarov

Papers

Measurement of gas velocity in a high-gradient flow, based on velocity of tracer particles

Investigation of supersonic nonisobaric jet structure

Correction of PIV data for reconstruction of the gas velocity in a supersonic underexpanded jet

Communicative competence of a teacher: professional deficiency or norms of pedagogical ethics

Induction time of liquid drop breakup in an accelerating flow