A weak coupling between a near-wall Eulerian solver and a Vortex Particle-Mesh method for the efficient simulation of 2D external flows

We introduce and validate a weak coupling approach between a body-fitted velocity-pressure solver and a Vortex Particle-Mesh (VPM) method in 2D for the simulation of incompressible external aerodynamics. The approach does not involve inner iterations, conserves circulation up to interpolation accuracy without resorting to a panel method, and accommodates different time steps across the solvers. It also utilizes a mixed boundary condition for the body-fitted solver that ensures the continuity of the vorticity field across the solvers. The second order convergence of the methodology is first demonstrated. We then assess it on the flow past a cylinder at various Reynolds numbers (from Re=550 to 9500), and we finally apply it to the flow past an airfoil at Re=5000

Numerical prediction of turbulent heat transfer at low prandlt number

This paper is concerned with comparing different approaches for the numericalprediction of heat transfer in a turbulent channel flow at very low Prandtl number and highReynolds number. Results obtained with a Reynolds Averaged Navier Stokes (RANS) approachat relevant Reynolds numbers for the liquid metal reactor problematic (Reτ = 590, Reτ = 1020),are presented and discussed. Original results obtained with a wall resolved Large EddySimulations (LES) at Reτ = 2000 are provided. The velocity profile agrees very well withthat of a reference Direct Numerical simulation (DNS). The obtained temperature profile canserve as a reference as the energy equation is computed without any Subgrid Scale (SGS) modelat this low Pr

Assessment of RANS and improved near-wall modeling for forced convection at low Prandtl numbers based on LES up to Re_tau=2000

Most promising Generation IV nuclear reactor concepts are based on a liquid metal coolant. However, at low Prandtl (Pr ) numbers such as those of liquid metal, classical approaches derived for unity, or close to unity, Pr fail to accurately predict the heat transfer. This paper assesses the RANS modeling of forced turbulent convection at low Pr and in channel flow. Reference results at high Reynolds (Re ) number are required to ensure that the Peclet number is sufficiently high. Therefore, new reference results were obtained by performing a wall-resolved Large-Eddy Simulation of turbulent channel flows at a friction Reynolds number Re_tau=2000Reτ=2000 and at Pr=0.01Pr=0.01 and 0.0250.025 (this also corresponds to the highest Re Direct Numerical Simulation (DNS) available in the literature for the flow, but without heat transfer). The LES velocity statistics are in very good agreement with those of the DNS and, as validated by the authors in previous publications, the LES approach used here accurately predicts the temperature statistics at low Pr . The LES results are used to assess RANS heat transfer modeling based on the effective turbulent Prandtl number (PrtPrt) concept. Among existing PrtPrt correlations, the correlation by Kays (1994) [10] is shown to yield the best results. Since it is also shown that the near-wall temperature profile does not follow a log-law, a new “law of the wall for temperature” is here proposed, which does not use any blending function. Its use as a wall-function is also validated in actual RANS simulations