Total Pressure and Temperature Imaging in Non-Reacting Flows Using Filtered Rayleigh Scattering

Simultaneous measurement of pressure, temperature, and particle-free velocity in highspeed turbulent flows is of critical interest in contemporary research. In addition, instantaneous measurement of these thermodynamic properties is ideal to study dynamic flow fields. The present work proposes a method for simultaneous measurement of pressure, temperature, and velocity (required for total pressure and temperature measurements) in non-reacting laminar and turbulent air jets. A combination of laser Rayleigh scattering (LRS) and filtered Rayleigh scattering (FRS) is employed to measure the thermodynamic properties. A two-camera arrangement (FRS/LRS) for instantaneous pressure and temperature measurement and a three-camera arrangement for pressure, temperature, and velocity measurement are demonstrated. The gas density dependence of the LRS signal and the density and spectral dependence of the FRS signal at a fixed laser wavelength (convolution of Rayleigh-Brillouin scattering with the iodine notch filter transmission spectrum) were leveraged (no frequency scanning) to obtain instantaneous 2D pressure, temperature, and velocity fields. A series of independent calibration mappings for pressure and temperature was performed to comprehend the scaling relations of the FRS signal with various thermodynamic properties. Velocity scaling relations were obtained from the theoretical calculations with a scope of simultaneous velocity measurement with the use of Particle Image Velocimetry for detailed velocity calibration in the future. This will lead to accurate measurements of local flow fields. In this work, temperatures for laminar air jets heated by a hot and vitiated coflow (products of methane/air premixed flame) were obtained using the obtained calibration map. Temperature results from multiple FRS views are compared with the LRS results and thermocouple measurements.