Investigation of Gas Seeding for Planar Laser-Induced Fluorescence in Hypersonic Boundary Layers

Abstract

Numerical simulations of the gas-seeding strategies required for planar laser-induced fluorescence in a Mach 10 (approximately Mach 8.2 postshock) airflow were performed. The work was performed to understand and quantify the adverse effects associated with gas seeding and to assess various types of seed gas that could potentially be used in future experiments. In prior experiments, NO and NO2 were injected through a slot near the leading edge of a flatplate wedge model used in NASA Langley Research Center's 31 in. Mach 10 air tunnel facility. In this paper, nitric oxide, krypton, and iodine gases were simulated at various injection rates. Simulations showing the deflection of the velocity boundary layer for each of the cases are presented. Streamwise distributions of velocity and concentration boundary-layer thicknesses, as well as vertical distributions of velocity, temperature, and mass distributions, are presented for each of the cases. A comparison between simulated streamwise velocity profiles and experimentally obtained molecular tagging velocimetry profiles using a nitric oxide seeding strategy is performed to verify the influence of such a strategy on the boundary layer. The relative merits of the different seeding strategies are discussed. The results from a custom solver based on OpenFOAM version 2.2.1 are compared against results obtained from ANSYS® Fluent version 6.3. Nomenclature c p = specific heat at constant pressure, kJ∕kg∕K D i;j = binary diffusion coefficient, m 2 ∕s D i;m = diffusion coefficient of species i into the mixture, m 2 ∕s h i = sensible enthalpy of species i, kJ∕kg h s = sensible enthalpy, kJ∕kg I = identity matrix J i = diffusion flux of species i, kg∕m 2 ∕s Kn = Knudsen number k = thermal conductivity, W∕m∕K Ma = Mach number M i = molar mass of species i, kg∕kmol P = pressure, Pa P inf = freestream pressure, Pa P stag = stagnation pressure, Pa P w = wall pressure, Pa R = ideal gas constant, J∕K∕mol Re = Reynolds number R i = mass source of species i S h = enthalpy source, kJ∕s∕m 3 T = temperature, K T stag = stagnation temperature, K t = time, s U = velocity, m∕s U e = boundary-layer edge velocity, m∕s W z = wedge width, mm w c = species mass fraction of interest x = distance from leading edge, m x slot = length of seed slot, mm Y i = mass fraction of species i α = thermal conductivity divided by specific heat at constant pressure, kg∕m∕s β = oblique shock angle δ = boundary-layer thickness, m δ c = concentration boundary-layer thickness, m θ plate = plate angle of attack μ = viscosity, kg∕m∕s ρ = density, kg∕m 3 σ i;j = average species collision diameter, m τ = viscous stress tensor, Pa Ω d = diffusion collision integral Ω v = viscous collision integral

Krypton Tagging Velocimetry (KTV) Investigation of Shock-Wave/Turbulent Boundary-Layer Interaction

“…Local seeding of different types of gas (including Kr) was investigated by Arisman et al 87 In that work, the researchers investigated how different seed gases diffused in high-speed boundary layers. They found that the diffusion was acceptable at typical wind-tunnel time/length scales in high-speed laminar boundary layers.…”

Influence of AR injection on shielding layer properties and surface protection from transient high heat loads under the QSPA plasma exposures

“…The obtained experimental results on the Ar shield formation and its influence on the plasma energy absorption by the target surface could be used for benchmarking the developed numerical simulation codes (for example, TOKES code [7]). It is worth mentioning that material protection from the impacts of plasma and the resulting high heat and particle loads on the surfaces is of undoubted interest not only for fusion reactor design [1,2], but also for solving a wide range of fundamental and applied problems (space engineering [24,25], plasma technologies [26], etc). For example, with the help of gas seeding, it is possible to vary the thermal load on materials when they are processed with powerful pulsed plasma flows in technologies for modifying surface layers in order to improve the performance characteristics of materials.…”

Stability of Supersonic Flow with Injection

“…The experiments performed in this work were complemented by unsteady simulations of the Navier-Stokes equations using the opensource finite-volume CFD package OpenFOAM [21]. The specific flow solver used is a modification by Arisman et al [22] of the wellknown rhoCentralFoam solver (rhoCentralBinaryFoam) and includes diffusion of species assuming Fickian diffusion and realistic mass diffusivities for each species. rhoCentralBinaryFoam uses a finite volume discretization to solve the continuity, momentum, energy, and species diffusion equations with the second-order, semi-discrete, nonstaggered central-upwind scheme of Kurganov and Tadmor.…”