Session: 37-12 LES, DES and Scale Resolving Methods

Paper Number: 80476

80476 - A Coupled Computational Aero-Acoustics (CAA)/ Large-Eddy Simulation (LES) Approach for the Pressure Calculation in Internal Low-Mach Number Flows 

Keywords : Large-Eddy-Simulation; Computational Aeroacoustics; Implicit linear acoustic solver; Pressure calculation in internal low-Mach number flows; Complex geometry

 

This paper is devoted to the development of a hybrid Computational Aero-Acoustics (CAA) / Large-Eddy Simulation (LES) approach tailored for the numerical calculation of aeroacoustic noise and pressure in internal low-Mach number flow. The hybrid method presented in this paper is based on the coupling of a fractional-step method used to solve the low-Mach number Navier-Stokes equations and a linear implicit acoustic solver. Each time step of a simulation is divided into two parts. First, the time-dependent incompressible Navier-Stokes equations are solved with a modified projection method, which describes the large turbulent scales of the flow. In this method, an elliptic Poisson equation is solved to obtain the dynamic pressure. Then, a linear acoustic perturbation transport equation of Helmholtz type is solved implicitly with a specific right-hand side to take into account the acoustic sources of the flow. The consistency of the two solvers is obtained by ensuring that the time averaging of the Poisson and Helmholtz equations leads to the same equations. Unlike the dynamic pressure obtained from the Poisson equation, the pressure field resulting from the Helmholtz equation is composed of both dynamic and acoustic contributions. The main difficulty in this coupling comes from the different time scales of the dynamic and acoustic pressures. Advancing the two solvers with the same convective time step requires a non-dissipative and non-dispersive time-integration method for the Helmholtz equation. The Newmark’s time integration method combined with implicit Non Reflecting Boundary Conditions (NRBC) are implemented for solving implicitly the Helmholtz equation. This second-order in time method is unconditionally stable and dissipation-free even at high acoustic CFL. Stabilization if necessary can be added by modifying the Newmark’s method coefficients.

 

The coupled method is validated in different cases. First, the linear acoustic solver is validated by performing a ping-test in a closed 3D box in order to verify that it is able to predict the pure acoustic perturbations and modes in closed domain using a time-dependent solver. A similar unsteady test-case is then carried out in the geometry of the PRECCINSTA industrial burner which consists of a plenum connected to a combustion chamber by a swirler, thus validating the behavior of the solver in a complex geometry. Finally, the coupled CAA/LES method is applied on the PRECCINSTA configuration in the case of cold flow and the results are compared with compressible results coming from the literature. Very good agreement is found with the available data thus demonstrating the soundness of the present method. 

Presenting Author: Pierre Benez CORIA

Presenting Author Biography: I am a PhD student working for Safran Helicopter Engines at CORIA lab (FRANCE). My PhD Topic is the Large Eddy Simulation (LES) of the subsonic flow in low-pressure mixed centrifugal/volumetric fuel pumps. The goal of my PhD is to develop a method to perform the LES of the pump performances and the pressure field in the pump to detect possible cavitation phenomena. Main topics : Large-Eddy-Simulation, Fuel pumps simulation, Compressible flows

Authors:

Pierre Benez CORIA
Vincent Moureau CORIA
Ghislain Lartigue CORIA
Guillaume Ribert CORIA
Marine Robin Safran Helicopter Engines