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The impact of single and double Gurney flaps of heights within the range of hGF=0.000c-0.075c is determined for a typical symmetrical airfoil (NACA 0015) by numerical simulations using an unsteady Reynolds-averaged Navier-Stokes approach. The optimal scaling of the Gurney flap to maximize the lift-to-drag ratio of the airfoil is revisited and confirmed to depend on the boundary-layer thickness in the region where it is deployed. Appropriate scaling rules for both single and double Gurney flap are proposed. Studying the Gurney flap's pressure distribution at a finely resolved level highlights its effect on the overall foil's pressure distribution. Finally, the unsteady simulations carried out are harnessed to determine the shedding frequencies generated by the flaps and the flow structures associated with them, hinting at the physical mechanisms by which Gurney flaps may increase lift at a low drag cost, thus improving the lift-to-drag ratio of the airfoil. [ABSTRACT FROM AUTHOR]

The existence of a flow-based scaling for the Gurney flap heights resulting in an increase in lift-to-drag performance was established by making an appropriate choice of the boundary thickness. An appropriate scaling for the maximum Gurney flap included parameters, such as flow regime, Reynolds number, angle of attack and airfoil geometry. Beneficial results were obtained for 1% to 2% chord Gurney flaps after testing seven Gurney flaps.

A detailed numerical investigation of the flow behind a square cylinder at a Reynolds number of 21,400 is conducted to assess the ability of the delayed detached-eddy simulation (DDES) modeling approach to accurately predict the velocity recovery in the wake of a bluff body. Three-dimensional unsteady Reynolds-averaged Navier-Stokes (URANS) and DDES simulations making use of the Spalart-Allmaras turbulence model are carried out using the open-source computational fluid dynamics (CFD) toolbox OpenFOAM-2.1.x, and are compared with available experimental velocity measurements. It is found that the DDES simulation tends to overestimate the averaged streamwise velocity component, especially in the near wake, but a better agreement with the experimental data is observed further downstream of the body. The velocity fluctuations also match reasonably well with the experimental data. Moreover, it is found that the spanwise domain length has a significant impact on the flow, especially regarding the fluctuations of the drag coefficient. Nonetheless, for both the averaged and fluctuating velocity components, the DDES approach is shown to be superior to the URANS approach. Therefore, for engineering purposes, it is found that the DDES approach is a suitable choice to simulate and characterize the velocity recovery in a wake. [ABSTRACT FROM AUTHOR]