Influence of the discrete component of acoustic oscillations on the flow in an underexpanded supersonic jet

Abstract

An experimental study of the flow in an axisymmetric underexpanded air jet emerging from a sonic or supersonic nozzle into a submersion chamber is described. It is shown that reflective panels .placed in the external field near the nozzle exit reinforce the discrete component of the acoustic field and shorten both the initial section of the jet and its range, where the latter is characterized by the dependence of the velocity head at the jet axis on the distance from the nozzle exit. The intervals of overpressures for which the discrete component is present in the panel-impeded jet are determined for various Mach numbers M at the nozzle exit. It is shown that the half-wavelength of the discrete component coincides satisfactorily with the average length of two to four "cells" of the initial section. It is confirmed by an experimental investigation with a panel placed axisymmetrically or transversely relative to the jet axis that the discrete component affects the gas-dynamical structure of the jet within the first cell of the jet. It is shown that the "wavelength" of the dependence p~ = f (z ~ for x = const is half the wavelength of the discrete component and can be used to determine the latter. The range of the jet can be significantly affected by varying the discrete component through the proper placement of an axisymmetric panel or relative placement of half-panels. 1. The experiment was conducted on conical nozzles with a half-angle ~ = 0 to 10 ~ Compressed air from a bank of storage cylinders was delivered to a spherical receiver with a volume V r = 0.14 m 3. The specified pressure Po in the receiver was regulated by a throttle and was measured with a standard manometer of class 0.35. The air jet emerged through the nozzle into a test-stand chamber with a volume of ~ 100 m 3. The nozzle dimensions and overpressure range in which it operated were as follows: