![]() I’m not really sure if I have to “aim for a value” of skin friction close to any of the theoretical formulas, or it is a case of refine (focusing on walls and boundary layer elements) until I reach a stable result of skin friction in my simulations (that changes less than 1% between refinements) and consider that solution mesh independent. So, I am aware this formulas are only approximations. I have read literature reviewing this topic and I’ve read that boundary layers of 3D slender objects don’t behave like those of a flat plate, and skin friction calculated using this formulas could be underestimating this drag component. Depending on which one I use I get slightly different theoretical skin friction drag coefficients and hence the proportion of Cf / total Cd is also variable (from 82% to 89%). Schoenherr) or others that include some modifications that account for experimental data (like the ITCC 57 formula). Hence, my references for this value are the different formulas based on the turbulent boundary layer of a flat plate (e.g. I started with a proportion of skin friction to total drag (Cf / total Cd) of 31% and I have raised it to 71%.įrom the theory, I know that a streamlined 3D object (like a submarine hull) should have a very high skin friction drag component, but I don’t really have a solid value to aim for because there is no way to measure the experimental value of the skin friction drag. Reducing the size of the mesh at the wall boundary and reducing the size of the boundary layer mesh increases the value of the skin friction component and also causes the pressure drag to reduce. I am also trying to stick to the good practises of meshing, like using y+ values close to 1, with the purpose to achieve more accurate calculation of the shear stresses on the walls. ![]() I am performing mesh sensitivity studies, to refine its resolution and distribution. ![]() ![]() I am finding that my simulation results tend to underestimate the viscous component (frictional drag) and overestimate the pressure component of drag. I am trying to validate the turbulence models and mesh with known published data on airship or submarine design (you can see the design of the rotationally symmetrical objects I am using in the. I am performing 3D external flow simulations at high Reynolds numbers (10^6 - 10^8) using RANS turbulence models such as SST. ![]()
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