Advanced Laser Diagnostics Development for Stereoscopic Imaging of Gaseous High Speed Flows

The coupled interactions between turbulent flow and thermal non-equilibrium (TNE) are physical and chemical processes with significant implications in turbulent heat transfer, fluid mixing, and fluid transport associated with high-speed vehicles and propulsion systems. Understanding the coupling mechanism allows one to utilize energy exchange for intelligent control of basic fluid dynamics processes. However, the elucidation of this mechanism necessitates quantifying the correlation of velocity fluctuations and scalar distributions. Thus, the development of reliable diagnostic techniques capable of simultaneous measurement of such quantities is necessary. Since turbulence is intrinsically three-dimensional, the measurement of the three-component velocity is imperative. The goal of this research is to develop a laser-based diagnostic technique as a non-intrusive approach to simultaneously measure three-component velocity and scalar fields to understand the coupling between turbulence and thermal non-equilibrium. It extends our recently developed Vibrationally Excited Nitric Oxide Monitoring (VENOM) method, which enables (1) the simultaneous measurement of 3D-velocity and planar temperature in cold, high-speed flows and (2) investigation of mean and instantaneous fluctuations in velocity and temperature. Experimental measurements of velocity and temperature across an oblique shock using the VENOM technique result in mean values within 21 m/s for the three components of velocity and 20 K for planar temperature when compared to oblique shock calculations. This extended stereoscopic VENOM system is expected to push forward the development of next-generation VENOM, i.e., dual-plane stereoscopic VENOM, for unprecedented characterization of fluid elements in three dimensions

Characterization of Collisional Energy Transfer in Flow Diagnostic Methods

The characterization of hypersonic flow fields requires an understanding of both chemical reactions and nonequilibrium effects. While current computation models can predict behaviors for laminar and turbulent transitions in these types of flows, experimental data is still needed to further validate these models. Specifically, the simultaneous measurement of velocimetry and thermometry can provide comparisons to the values of turbulent kinetic energy and turbulent heat flux of these models. In this work, measurements of collisional energy transfer are reported for the temperature dependent collisional quenching of NO (A, ²Σ⁺) by benzene and hexafluorobenzene. Transitions between laminar and turbulent flow behaviors could potentially be instigated with thermal nonequilibrium in these flows. This work briefly reports on laser-induced nonequilibrium measurements which have displayed this type of transition between flow behaviors. Two species in particular for implementing this nonequilibrium are benzene and hexafluorobenzene. A quantitative determination of the local number density of these molecular species for a gaseous flow can be performed in a temperature dependent manner via collisional quenching. In this work, measurements of collisional energy transfer are reported for the temperature dependent collisional quenching of NO (A, ²Σ⁺) by benzene and hexafluorobenzene in NO/N₂ flow fields. There are a number of techniques exist for the characterization of gaseous flow fields with simultaneous thermometry and velocimetry. In this work, a detailed error analysis of the invisible ink nitric oxide monitoring technique is presented. This method involves the initial creation of vibrationally excited NO seeded into a flow with two subsequent “read” measurements; one mapping displacement of the original position of the vibrationally excited NO and a second “read” step to map a second distinct rotational state of NO laser induced fluorescence, providing a temperature measurement. This analysis was performed with a comprehensive kinetics program which both tracks the vibrational excitation of all species present in a flow field as well as the thermal perturbation caused by the invisible ink method. This analysis was performed for three distinct flow facilities located at the National Aerothermochemistry Lab; a pulsed hypersonic test cell, a supersonic high Reynold’s number facility, and a high enthalpy expansion tunnel

Characterization of Collisional Energy Transfer in Flow Diagnostic Methods

The characterization of hypersonic flow fields requires an understanding of both chemical reactions and nonequilibrium effects. While current computation models can predict behaviors for laminar and turbulent transitions in these types of flows, experimental data is still needed to further validate these models. Specifically, the simultaneous measurement of velocimetry and thermometry can provide comparisons to the values of turbulent kinetic energy and turbulent heat flux of these models. In this work, measurements of collisional energy transfer are reported for the temperature dependent collisional quenching of NO (A, ²Σ⁺) by benzene and hexafluorobenzene. Transitions between laminar and turbulent flow behaviors could potentially be instigated with thermal nonequilibrium in these flows. This work briefly reports on laser-induced nonequilibrium measurements which have displayed this type of transition between flow behaviors. Two species in particular for implementing this nonequilibrium are benzene and hexafluorobenzene. A quantitative determination of the local number density of these molecular species for a gaseous flow can be performed in a temperature dependent manner via collisional quenching. In this work, measurements of collisional energy transfer are reported for the temperature dependent collisional quenching of NO (A, ²Σ⁺) by benzene and hexafluorobenzene in NO/N₂ flow fields. There are a number of techniques exist for the characterization of gaseous flow fields with simultaneous thermometry and velocimetry. In this work, a detailed error analysis of the invisible ink nitric oxide monitoring technique is presented. This method involves the initial creation of vibrationally excited NO seeded into a flow with two subsequent “read” measurements; one mapping displacement of the original position of the vibrationally excited NO and a second “read” step to map a second distinct rotational state of NO laser induced fluorescence, providing a temperature measurement. This analysis was performed with a comprehensive kinetics program which both tracks the vibrational excitation of all species present in a flow field as well as the thermal perturbation caused by the invisible ink method. This analysis was performed for three distinct flow facilities located at the National Aerothermochemistry Lab; a pulsed hypersonic test cell, a supersonic high Reynold’s number facility, and a high enthalpy expansion tunnel