LDA Measurements of Underexpanded Jet Flows from Axisymmetric Nozzle with Solid Tabs

Abstract

An experimental study has been conducted of the jet plume flowfield in the near nozzle exit region of an underexpanded jet issuing from an axisymmetric nozzle. A Nozzle Pressure Ratio (NPR) of 2.32 was used, leading to a moderately strong supersonic jet, but avoiding screech instability phenomena. Some measurements are reported of the ‘clean’ nozzle case, but primarily the data taken have concentrated on a nozzle with two solid tab mixing devices. Particular attention has been paid to the region immediately after nozzle exit (0<x/Dn<3.0) which is the region where the tab-induced streamwise vortices are formed, and also where the jet cross-section distortion is largest. A two-component LDA system was used, enabling measurements of all 3 mean velocity components and turbulent Reynolds stresses, including both normal and shear stress components. Although data exist in the literature on tab-induced flow fields at low speed, the present data set is of significant interest in that it not only extends available knowledge into the high speed compressible region, but also captures the consequences on the shock containing core jet region of the presence in the jet shear layers of the strong 3D streamwise vortices emanating from the tabs. The data set is well suited to act as a validation data set for CFD simulations of this type of flowfield.