Implementation of NO LIF Diagnostics to Characterize the Role of Thermal Non-Equilibrium within a Hypersonic Turbulent Boundary Layer

Abstract

A flat plate wedge with a DC glow-discharge plasma along the leading edge was designed to introduce thermal non-equlibrium (TNE) directly into a turbulent boundary layer. Various NO laser induced fluorescence (LIF) techniques were introduced into the hypersonic Actively Controlled Expansion (ACE) wind tunnel facility to quantify the potential role of TNE. The NO was continuously seeded into the settling region upstream of the flow conditioners to mitigate the downstream perturbations within the test section. The NO spatial distribution was relatively localized within the test section core to provide an upper limit concentration of 1%. Following the excitation of the A²Σ⁺ (v′ = 0) ← X²Π₁/₂ (vʺ = 0) transition, the resulting ground state NOᵥ ₌ ₁ population was 16% of the total excited state population with the O₂ accounting for a majority of the collisional quenching. Freestream rotational thermometry measurements suggested the observed fluctuations were on the order of 4% within the test section core. The flat plate rotational thermometry campaign successfully characterized the temperature profile for a range of laminar and turbulent boundary layers. The rotational thermometry measurements concluded the TNE introduced by the plasma did not have an effect on the downstream turbulent behavior. A vibrational thermometry study concluded the nascent NOᵥ ₌ ₁ population introduced by the plasma slowly diffused for the laminar case; however, the mechanically tripped turbulent boundary layer experienced a significant degree of mixing. The freestream velocity fluctuations were 1% and agreed well with previous ACE measurements. The flat plate velocimetry results did not find any evidence of TNE effecting the downstream turbulence. Spanwise velocimetry on the flat plate determined the laminar flow was relatively uniform across the plate and illustrated break down in response to the mechanical trips.