Numerical Investigation of High-Speed Turbulent Boundary Layers of Dense Gases

Abstract

High-speed turbulent boundary layers of a dense gas (PP11) and a perfect gas (air) over flat plates are investigated by means of direct numerical simulations and large eddy simulations. The thermodynamic conditions of the incoming flow are chosen to highlight dense gas effects, and laminar-to-turbulent transition is triggered by suction and blowing. In the paper, the behavior of the fully developed turbulent flow region is investigated. Due to the low characteristic Eckert number of dense gas flows ( Ec = U 2 ∞ ∕c p,∞ T ∞ ), the mean velocity profiles are largely insensitive to the Mach number and very close to the incompressible case even at high speeds. Second-order velocity statistics are also weakly affected by the flow Mach number and the velocity spectra are characterized by a secondary peak in the outer region of the boundary layer because of the higher local friction Reynolds number. Despite the incompressible-like velocity and Reynolds-stress profiles, the strongly nonideal thermodynamic and transport-property behavior of the dense gas results in unconventional distributions of the fluctuating thermo-physical quantities. Specifically, density and viscosity fluctuations reach a peak close to the wall, instead of vanishing as in perfect gas flows. Additionally, dense gas boundary layers exhibit higher values of the fluctuating Mach number and velocity divergence and a larger dilatational-to-solenoidal dissipation ratio in the near-wall region, which represents a major deviation from high-Mach-number perfect gas boundary layers. Other significant deviations are represented by the more symmetric probability distributions of fluctuating quantities such as the density and velocity divergence, due to the more balanced occurrence of strong expansion and compression events.

Finite-rate chemistry effects in turbulent hypersonic boundary layers: a direct numerical simulation study

“…The well developed spectra indicate that a fully turbulent state has been reached at this position. The spectral content is not significantly altered by chemical effects, and the overall trend is similar to perfect-gas simulations [50]. All of the spectra exhibit a peak in the buffer layer, at the same location were the Reynolds stresses and the temperature fluctuations peak (see figure 10).…”

Assessment of a high-order shock-capturing central-difference scheme for hypersonic turbulent flow simulations

“…The amount of numerical dissipation introduced at a point of the computational domain is adjusted by means of properly-devised sensors, allowing to switch on shock-capturing capabilities where needed. Shock-capturing highorder central-difference schemes have been successfully applied, for instance, to overexpanded jet flows with shock cells [30] and highspeed boundary layers of perfect gases up to Mach 6 [31], as well as to the direct and large-eddy simulations of high-speed flows of singlespecies, molecularly complex gases at thermodynamic conditions close to the liquid/vapor critical point up to Mach 6 [32][33][34][35]. However, their suitability for the numerical simulation of severe hypersonic, chemically reacting flows with strong shocks and stiff chemical reactions has not yet been assessed.…”

“…The goal of the present study is twofold: (i) to assess the capability of a high-order shock-capturing central scheme, used in our previous works [32,35], to robustly predict compressible flows with shock waves and chemical nonequilibrium effects while accurately resolving fine-scale turbulent structures; and (ii) to demonstrate the suitability of the non-linear numerical dissipation of the scheme to act as a SGS regularization in under-resolved turbulent flow simulations. The scheme uses tenth-order accurate finite-difference approximations of the non-linear fluxes, supplemented with a higher-order extension of Jameson's adaptive artificial dissipation [25].…”

Assessment of a high-order shock-capturing central-difference scheme for hypersonic turbulent flow simulations

“…The amount of numerical dissipation introduced at a point of the computational domain is adjusted by means of properly-devised sensors, allowing to switch on shock-capturing capabilities where needed. Shock-capturing high-order central-difference schemes have been successfully applied, e.g., to overexpanded jet flows with shock cells [30] and high-speed boundary layers of perfect gases up to Mach 6 [31], as well as to the direct and large eddy simulation of high-speed flows of single-species, molecularly complex, heavy gases at thermodynamic conditions of the order of magnitude of the liquid/vapor critical point up to Mach 6 [32,33,34,35]. However, their suitability for the numerical simulation of severe hypersonic, chemically reacting flows with strong shocks and stiff chemical reactions has not yet been assessed.…”

“…The goal of the present study is twofold: i) to assess the capability of a high-order shock-capturing central scheme, used in our previous works [32,35], to robustly predict compressible flows with shock waves and chemical non-equilibrium effects while accurately resolving fine-scale turbulent structures; and ii) to demonstrate the suitability of the non-linear numerical dissipation of the scheme to act as a SGS regularization in under-resolved turbulent flow simulations. The scheme uses tenth-order accurate finite-difference approximations of the non-linear fluxes, supplemented with a higher-order extension of Jameson's adaptive artificial dissipation [25].…”