Investigations of Flow Over a Hemisphere Using Numerical Simulations (Postprint)

Abstract : The research effort discussed here addresses the use of numerical simulations to predict the flow physics of a transonic flow over a hemisphere representing a laser beam director turret. Different computational fluid dynamics codes, including Loci-Chem, CFD and Vulcan, were used to ascertain their capability to predict these complex flow surrounding this structure. In addition, various types of turbulence models were tested, such as unsteady Reynolds-averaged Navier-Stokes (URANS), detached eddy simulation (DES), and hybridRANS/LES. The numerical results were compared with the experiment conducted at Auburn University. Results showed that the URANS simulations using Loci-Chem and CFD overdamped the shear layer fluctuation associated with the hemispherical turret. Using the DES and hybrid RANS/LES turbulence models, Loci-Chem was able to capture the unsteady flow structures, such as the shear layer fluctuation, and the rolling motion of the vortex shedding. These solutions agreed well with the experimental data, as measured in the wall-pressure measurements, instantaneous density images, and optical path difference (OPD) analysis. Neither CFD nor Vulcan with these high fidelity turbulence models predicted the basic unsteady flow structures, and these solutions were not used to compute the OPD to compare with the experimental data.