Burst Mode Filtered Rayleigh Scattering and Particulate Impacts in Hypersonic Facilities

Abstract

The study of hypersonic environments is of particular interest to both military and civilian stakeholders. These environments can be difficult to study via conventional probe-based methods which can induec changes in the flow field or incur damage. Laser-based diagnostic methods provide a non-intrusive alternative, requiring only optical access. By pairing certain laser diagnostic techniques with ultra-high repetition rate burst-mode laser systems hypersonic environments can be more fully time resolved.

Part of this work applies a laser diagnostic technique known as burst-mode filtered Rayleigh scattering to a tripped hypersonic boundary layer wake flow. This technique employs CO2 flow seeding to provide temperature dependent flow visualization data collected at 250 kHz. This data was taken at various flow cross sections and flow Reynolds numbers. Spectral analysis of the data provided frequencies associated with specific flow structures.

This work also developed a multi-property filtered Rayleigh scattering technique for use in high enthalpy hypersonic facilities. A large part of this work was the development of a filtered Rayleigh scattering modelling for high temperature air focused on accounting for the chemical changes of high temperature air mixtures. The experimental apparatus required by this technique uses a combinatino of a double imaged optical collection setup with knowledge of the facility stagnation enthalpy to collect temperature, pressure, and two component velocity maps. The technique was applied to an under expanded jet at 250 kHz as a subscale low enthalpy experimental proof of concept.