Direct numerical simulations of supersonic turbulent channel flows of dense gases
Article dans une revue avec comité de lecture
The influence of dense-gas effects on compressible wall-bounded turbulence is investigated by means of direct numerical simulations of supersonic turbulent channel flows. Results are obtained for PP11, a heavy fluorocarbon representative of dense gases, the thermophysics properties of which are described by using a fifth-order virial equation of state and advanced models for the transport properties. In the dense-gas regime, the speed of sound varies non-monotonically in small perturbations and the dependency of the transport properties on the fluid density (in addition to the temperature) is no longer negligible. A parametric study is carried out by varying the bulk Mach and Reynolds numbers, and results are compared to those obtained for a perfect gas, namely air. Dense-gas flow exhibits almost negligible friction heating effects, since the high specific heat of the fluids leads to a loose coupling between thermal and kinetic fields, even at high Mach numbers. Despite negligible temperature variations across the channel, the mean viscosity tends to decrease from the channel walls to the centreline (liquid-like behaviour), due to its complex dependency on fluid density. On the other hand, strong density fluctuations are present, but due to the non-standard sound speed variation (opposite to the mean density evolution across the channel), the amplitude is maximal close to the channel wall, i.e. in the viscous sublayer instead of the buffer layer like in perfect gases. As a consequence, these fluctuations do not alter the turbulence structure significantly, and Morkovin’s hypothesis is well respected at any Mach number considered in the study. The preceding features make high Mach wall-bounded flows of dense gases similar to incompressible flows with variable properties, despite the significant fluctuations of density and speed of sound. Indeed, the semi-local scaling of Patel et al. (Phys. Fluids, vol. 27 (9), 2015, 095101) or Trettel & Larsson (Phys. Fluids, vol. 28 (2), 2016, 026102) is shown to be well adapted to compare results from existing surveys and with the well-documented incompressible limit. Additionally, for a dense gas the isothermal channel flow is also almost adiabatic, and the Van Driest transformation also performs reasonably well. The present observations open the way to the development of suitable models for dense-gas turbulent flows.
Showing items related by title, author, creator and subject.
Article dans une revue avec comité de lectureGLOERFELT, Xavier; ROBINET, Jean-Christophe; SCIACOVELLI, Luca; CINNELLA, Paola; GRASSO, Francesco (Cambridge University Press (CUP), 2020)A study of dense-gas effects on the stability of compressible boundary-layer flows is conducted. From the laminar similarity solution, the temperature variations are small due to the high specific heat of dense gases, ...
Article dans une revue avec comité de lectureSCIACOVELLI, Luca; GLOERFELT, Xavier; PASSIATORE, Donatella; CINNELLA, Paola; GRASSO, Francesco (Springer, 2020-03)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 ...
Article dans une revue avec comité de lectureSCIACOVELLI, Luca; CINNELLA, Paola; GLOERFELT, Xavier (Springer Verlag (Germany), 2018)Dense gas effects, encountered in many engineering applications, lead to unconventional variations of the thermodynamic and transport properties in the supersonic flow regime, which in turn are responsible for considerable ...
Article dans une revue avec comité de lectureSCIACOVELLI, Luca; CINNELLA, Paola (American Society of Mechanical Engineers, 2014)Transonic flows through axial, multi-stage, transcritical ORC turbines, are investigated by using a numerical solver including advanced multiparameter equations of state and a high-order discretization scheme. The working ...
Numerical investigation of dense gas flows through transcritical multistage axial Organic Rankine Cycle turbines Communication avec acteSCIACOVELLI, Luca; CINNELLA, Paola (2013)Many recent studies suggest that supercritical Organic Rankine Cycles have a great potential for lowtemperature heat recovery applications, since they allow better recovery efficiency for a simplified cycle architecture. ...