Effects of turbulence boundary conditions on Spalart-Allmaras RANS simulations for active flow control applications

TL;DR

This study evaluates how turbulence boundary conditions affect RANS simulations with the Spalart-Allmaras model for active flow control, demonstrating that proper boundary settings enable cost-effective and reasonably accurate predictions of flow behavior.

Contribution

It identifies optimal turbulence boundary conditions for RANS-SA simulations in active flow control, validating their use for preliminary SJA parameter optimization.

Findings

RANS-SA can predict lift and drag with reasonable accuracy

Proper turbulence jet levels are crucial for flow reattachment

RANS-SA offers a cost-effective alternative to LES for initial design

Abstract

We assess the suitability of Reynolds-Averaged Navier-Stokes (RANS) simulation using the Spallart-Almaras (SA) turbulence model as a closure in analysing the performance of fluidic Active Flow Control (AFC) applications. In particular, we focus on the optimal set of actuation parameters found by Tousi et al. [1, 2] for a SD7003 airfoil at a Reynolds number Re = 6 e4 and post-stall angle of attack alpha = 14 degrees fitted with a Synthetic Jet Actuator (SJA). The Large Eddy Simulation (LES) presented in that work is taken as the reference to identify the best choice of boundary conditions for the turbulence field nu' at both domain inlet and jet orifice in two-dimensional RANS-SA computations. Although SA-RANS is far less accurate than LES, our findings show that it can still predict macroscopic aggregates such as lift and drag coefficients quite statisfactorily and at a much lower computational cost, provided that turbulence levels of the actuator jet are set to a realistic value. An adequate value of nu'is instrumental in capturing the correct flow behaviour of the reattached boundary layers for close-to-optimal actuated cases. This validates the use of RANS-SA as a reliable and cost-effective simulation method for the preliminary optimisation of SJA parameters in AFC applications.