Flow peculiarities in the bottom region of experimental aircraft models
Authors: Sidnyaev N.I., Battulga Enkhjargal
Published in issue: #5(161)/2025
Category: Aviation and Rocket-Space Engineering | Chapter: Aerodynamics and Heat Transfer Processes in Aircrafts
The paper presents results of studies in the experimental aerodynamics related to the problem of sudden expansion of the external compressible flow behind the bottom section of the aircraft experimental models and the bottom pressure. It postulates that significant part of the total resistance is the resistance caused by the bottom rarefaction. The paper shows that the bottom pressure is lower than that atmospheric at the high flight velocities. The proposed methods are connected with the aerodynamic and ballistic testing, and make it possible to study the bottom pressure dependence on the flight Mach number and the supporting devices. A series of experiments shows that the boundary layer provides a certain effect on the bottom pressure. The paper presents a detailed study of the flow behind the spheres fixed on a magnetic suspension in a helium flow at M = 16. To study the area behind the spheres at the distance of 1 to 50 body diameters, the pressure was measured using a full-pressure tube. Two spheres were tested with the 19 and 9.5 mm diameters computed from the body size at the different Reynolds numbers in the range from 45,400 to 109,000. Study results show that transition to the turbulent flow should occur inside the region under consideration. However, the voltage drop measurements on the hot-wire anemometer are leading to a conclusion that the trace is most likely laminar. The paper presents detailed pressure distributions in the total head tubes along the axis and the radius. They are compared with the experimental data for a flat cylinder at the same Mach number, data obtained on a ballistic track, and data obtained according to two theories. The measured root-mean-square values of the voltage drop on the hot-wire anemometer are constant and have a very small value at the trace axis, but they increase sharply at the trace edges.
EDN LSVYIJ
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