An Examination of MHz Rate PIV in a Heated Supersonic Jet

Abstract

An experimental investigation of a high temperature, supersonic jet conducted at the University of Mississippi's National Center for Physical Acoustics is described. Time-resolved particle image velocimetry (PIV) was used in the acquisition of flow field velocity measurements eight inches downstream of a two inch axissymmetric supersonic nozzle operating at a Mach number of 1.56 and total temperature of $1350^{\circ}F$. A MHz rate gate-intensified CCD framing camera was used in conjunction with a pulse-burst laser system in the acquisition 308 image sequences. Each sequence consisted of 16 images with a temporal spacing of $1\mu s$ between each frame. A background on high-speed measurement techniques and jet aeroacoustics as well as the experimental setup, operational conditions, and experimental results involving the velocity field are described in detail. A number of experimental hurdles had to be overcome in order to increase the data quality. These include the construction of a sound insulating box to prevent image blurring caused by the high acoustic levels within the test environment, the alignment of the Cordin's eight internal cameras to ensure one optical path, and the reduction of noise inherent to the Cordin's images through various filtering methods. The velocity fields were obtained through the use of standard PIV analysis as well as High Dynamic Range (HDR) PIV using dynamic evaluation via ordinary least squares (DEVOLS) algorithm. Proper orthogonal decomposition (POD) was used to reconstruct the velocity fields in order to improve their quality. This method was successful in eliminating much of the noise remaining in the velocity fields. Time resolved velocity sequences are displayed to show the characteristics of the turbulent shear layer in the supersonic jet. The average acceleration fields are shown are poor in quality due to various experimental obstacles.