The instantaneous and average structure of a supersonic underexpanded jet is studied numerically and experimentally. The photos obtained in experiments with different exposure times and the Pitot pressure measurements are compared with the results of the numerical simulation performed using an implicit large-eddy method. We note that the jet flow instability, disturbance growth, and transition to turbulence lead to the situation, in which the instantaneous flow structure can be considerably different from the average structure. The flow pattern observable in the calculations is in good agreement with that presented in the experimental photos obtained with short exposure times. Both calculated and experimental data indicate that an important role in the jet flow dynamics is played by large-scale vortex structures that exist against the background of small-scale turbulence. The calculated and experimental Pitot pressure distributions are similar with each other, up to a certain distance from the nozzle exit section. Further downstream, the experimental and calculated Pitot pressures start to increase rapidly but the calculations predict the onset of this growth at a greater distance from the nozzle than it is observable in the experiments.

A high-velocity flow in an axisymmetric nozzle containing a central body and pylons is studied. The influence of the geometry of the main and additional pylons on the gas-dynamic and thrust characteristics at the nozzle exit in the flow regime with n_pr= 2.25 ( n_pr is the ratio of the pressure in the settling chamber to the ambient pressure) is determined. Azimuthal nonuniformity of the flow at the nozzle exit is detected. The maximum azimuthal nonuniformity is observed in the wake behind the pylons. It is shown that a three-dimensional transonic flow is formed in the nozzle duct with the pylons mounted in the minimum free cross section; local supersonic regions closed by weak shock waves are formed in this flow. It is found that the formation of such a shock wave structure is responsible for nozzle thrust reduction by 12

Using the example of studying the supersonic underexpanded jet initial section, the issue of interpreting the experimental visualization data and Pitot pressure measurement data using the results of numerical calculations (2d RANS k-ω SST) is discussed. It is shown that the gradient S-shaped feature of the gas-dynamic structure near the nozzle exit, observed in the form of a barrel shock, is a characteristic that separates the expansion and compression regions, and downstream is transformed into a barrel shock. It has been established that the reason for the observed S-shaped curvature of this feature is the axisymmetric nature of the jet flow.

Detailed data on the measurement of the gas-dynamic parameters of the flow in the jet field at a large value of the relative total pressure (Npr = 70) are presented. A significant increase in the measured total pressure in the first cell of a supersonic weakly underexpanded jet has been experimentally revealed. An explanation is given of this effect associated with the mixing process in the region behind the Mach disk of the peripheral high-pressure flow and the axial flow behind the Mach disk. This explanation based on the data of the numerical calculation of the flow. Experimental data can be used to verify the results of numerical calculations.

The present work is devoted to the experimental study of a high-speed jet exhausting from a model dual-stream jet nozzle which was performed using non-contact (shadow visualization) and probing (Pitot pressure tube) methods for measuring gas-dynamic parameters. Azimuthal non-uniformity of the pressure distribution, whose magnitude in the external duct is much higher than that in the internal one, is revealed. The cause for the formation of the 3D flow structure is related to the supporting pylons installed inside the nozzle contours and with the formation of a transonic flow mode in the external duct.

The paper presents the results of an experimental and numerical study of the gas-dynamic structure of a supersonic jet exhausting in ambient space. The results of numerical calculation and experimental data are compared, a feature of the shock-wave structure of the flow near the nozzle exit due to the formation of a high-speed circular flow is revealed. The origin of such a circular flow is accompanied by significant density gradients, which is registered by visualization the flow, as well as according to numerical modeling data.

Abstract The work is devoted to the experimental study of a high-speed jet exhausting from a model dual stream jet nozzle, performed using non-contact (shadow visualization) and probe (total-pressure pneumatic receiver) methods for measuring gasdynamic quantities. Azimuthal non-uniformity of the pressure distribution, whose value in the external duct is much higher than that in the internal duct, is revealed. The cause for the formation of the spatial flow structure is related to the supporting pylons inside the nozzle contour and to the occurrence of a transonic flow regime in the external duct.

В статье описано автоматизированное координатное устройство, применяемое для позиционирования модели и перемещения зонда по заданной программе при экспериментальных исследованиях на вертикальной струйной установке. Подсистема сбора данных и управления позволяет задавать алгоритм перемещения датчика по двум координатам для конкретных экспериментов, в том числе по сложной траектории, как в ручном режиме от пульта управления, так и в автоматическом по заданной программе. Система управления координатным устройством является составной частью системы автоматизированного сбора экспериментальных данных на вертикальной струйной установке ИТПМ СО РАН.

The paper presents the investigation results of the flow structure of cold supersonic jets flowing out of model nozzles with a Mach number on the exit Ma = 3.5: an axisymmetric nozzle, a nozzle with a rectangular critical section, a beveled nozzle with a rectangular critical section. Flow schlieren images and transverse measured total pressure profiles in the flow are presented. The influence of the critical section shape and the beveled exit section on the shock-wave structure of the flow is described.

Currently, various countries are working to create a prospective manned reentry space vehicle of a new generation. The development of a new manned reentry space vehicle is conditioned by the necessity to increase the number of crew members, increase the carrying capacity, and improve the accuracy of landing at a given point on the earth's surface. The listed requirements for the appearance of the prospective reentry space ship and the increase in its dimensions lead to an increase in its cost, which entails the expediency of its reusability. This imposes additional conditions on the design of the spacecraft. The braking of the reentry vehicle is carried out by aerodynamic braking in the atmosphere upper layers, the parachutes usage and the use of a multi-jet braking system near the landing surface. With this braking method, the task is to effectively control the braking jet propulsion system at landing regimes [1].

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.

This paper presents an experimental study of spatial stationary structure of the high-speed jet flowing from the dual-stream jet nozzle which interior structure is taken into account. The research was made for transonic gas dynamic regime of the flow. The influence of internal nozzle design elements such as supporting pylons and pressure pipes on the pressure distribution along the azimuth in the outer and inner flows of the dual-stream jet nozzle is determined. The formation of significant azimuth disturbances in the outer contour of the nozzle is revealed.

The work is devoted to the investigation of the influence of the thin obstacle presence in the high-speed jet flow on its characteristics. Interest in this phenomenon is caused by the fact that during the transonic jet flow parameters probe measurements it was noted, that a growth of low-frequency pulsations, tonal and discrete tones appear in the acoustic noise when a pylon is immersed. It is established that discrete and tonal components change their frequency as the distance from a thin obstacle to the nozzle exit is changed. The existence of a mechanism for transferring perturbations from the pylon is shown, which consists in the fact that pulsations from the pylon close the self-oscillating loop through acoustic radiation propagating from the jet through the surrounding medium to jet root.

The turbulent properties of a supersonic jet were studied related to a high level of pressure pulsation found in model jets of a reentry flight vehicle approaching the landing ground. This study comprised measurements of total pressure at a small-size target using a dynamic pressure probe placed in a free jet. The most comprehensive data about jet turbulence can be obtained by direct transformation of the pressure reading at the stagnation point near the target into the normalized velocity. The oscillogram of normalized velocity produces the velocity average value, root-mean-square value as well as turbulence intensity and turbulence spectrum. It was demonstrated that a high level of turbulence for a high-head jet retains along the supersonic core length and at the beginning of subsonic interval.

The paper presents a description of the procedure used for determining the aerodynamic characteristics (forces and moments acting on a model of a flying vehicle) obtained from the results of pressure measurements on the surface of a model of a re-entry vehicle with operating retrofire brake rockets in the regime of hovering over a landing surface is given. The algorithm for constructing the interpolation polynomial over interpolation nodes in the radial and azimuthal directions using the assumption on the symmetry of pressure distribution over the surface is presented. The aerodynamic forces and moments at different tilts of the vehicle are obtained. It is shown that the aerodynamic force components acting on the vehicle in the regime of landing and caused by the action of the vertical velocity deceleration nozzle jets are negligibly small in comparison with the engine thrust.