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A surface roughness model extending the Langtry-Menter transition model has been implemented in a RANS framework. The model, originally proposed by Dassler, Kozulovic, and Fiala, introduces an additional scalar field roughness amplification quantity. This value is explicitly set at rough wall boundaries using surface roughness parameters and local flow quantities. This additional transport equation allows non-local effects of surface roughness to be accounted for downstream of rough sections. This roughness amplification variable is coupled with the Langtry-Menter model and used to modify the criteria for transition. Results from flat plate test cases show good agreement with experimental transition behavior on the flow over varying sand grain roughness heights. Additional validation studies were performed on a NACA 0012 airfoil with leading edge roughness. The computationally predicted boundary layer development demonstrates good agreement with the experimental results. New experimental tests using multiple roughness configurations were conducted to further validate and calibrate the model. Finally modifications are discussed to potentially improve the behavior of the Langtry-Menter transition model at high Reynolds numbers and angles of attack.

A two-dimensional experimental and computational examination of the effect of splitter plate length on a flatback airfoil on both aerodynamic performance and vortex shedding behavior is presented. The FB-3500-1750 airfoil is a thick airfoil with a blunt trailing edge designed for the inboard region of wind turbine blades. Its maximum thickness is 35% of the airfoil chord, with a trailing edge thickness of 17.5%. In the present study, the FB-3500-1750 was tested in the University of California, Davis aeronautical wind tunnel at Reynolds numbers of 666,000 with fixed transition. The wind tunnel results are compared with computational predictions obtained using OVERFLOW, a Reynolds-Averaged NavierStokes solver. Drag reductions of at least 27% from the baseline were observed both experimentally and computationally with the inclusion of a splitter plate with length 50% tTE. Additionally, increasing splitter plate length was shown to continue to decrease the base drag. Maximum lift reductions and earlier stall angles were also observed with increasing splitter plate length though in the wind tunnel tests with the 50% tTE case, the loss in was limited to 5%. Examining vortex shedding behavior, increases in the nondimensional shedding frequency, Strouhal number, were seen with increasing splitter plate length.