# Wall Shear stress in 3D

• nikosb

#### nikosb

I have computed the flow past a golfball and I am trying to calculate the shear stress on the surface of the golfball but I am having trouble figuring out how the wall shear stress is defined on 3D complex surfaces.
When I am on the main part of the golfball that it is similar to that of the sphere the calculation of the wall shear stress is straightforward. From the surface I move a distance "h" along the normal and compute the tangential velocity. In this case I choose the tangential velocity to be aligned with the azimuthal plane.
However when I am in the dimples, it is hard to choose a single tangential velocity as there are infinite number of tangents and not anyone of them is necessarily aligned with an azimuthal plane. How do I choose the tangential velocity in such a case?

Thanks

Not sure how you do that as the flow across the dimples slip (or break off). You probably don't have any shear stress at the deepest point in the some of the dimples

## What is wall shear stress in 3D?

Wall shear stress in 3D refers to the tangential force per unit area acting on a surface in a three-dimensional flow field. It is a measure of the frictional force exerted by a fluid on a solid surface.

## How is wall shear stress calculated?

Wall shear stress can be calculated using the Navier-Stokes equations, which describe the motion of viscous fluids. It is also commonly approximated using the law of the wall, which relates the wall shear stress to the velocity gradient near the wall.

## What factors affect wall shear stress in 3D?

The wall shear stress in 3D is affected by various factors such as fluid viscosity, velocity, density, and surface roughness. It is also influenced by the geometry and orientation of the surface in relation to the flow direction.

## Why is wall shear stress important in 3D flow?

Wall shear stress is important in 3D flow because it can significantly impact the behavior and performance of a fluid system. It can affect the heat and mass transfer, drag and lift forces, and the stability and turbulence of the flow.

## How is wall shear stress measured in 3D flow?

Wall shear stress can be measured using various techniques such as hot-wire anemometry, laser Doppler anemometry, and pressure-sensitive paint. These methods involve directly or indirectly measuring the velocity gradient near the wall to calculate the wall shear stress.