Modeling an active grid generated turbulence decay using a coupled transient RANS model with a stochastic turbulence simulator.

Kinetic energy decay in grid turbulence has been studied over the past few decades. The computational fluid dynamics approach used includes tuning closure coefficients of turbulence RANS models to match the decay exponent. We take a completely different approach to model turbulence decay in which the closure coefficients in a transient k-w SST model are not tuned. Rather, a 3D time-resolved velocity field is specified for the domain inlet using a stochastic turbulent inflow simulator (TurbSim). Power spectral density (PSD) data to be used in TurbSim is obtained from laboratory water tunnel experiments fitted with a Makita-type active grid. Statistical properties like mean velocity, Reynold’s stress, and turbulence decay for different grid operating conditions are compared to test the modularity of this approach. The methodology developed in this study is robust and can be used to model grid-generated turbulence decay.