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-   -   shear stress scalar definitions? (http://www.cfd-online.com/Forums/cfx/19562-shear-stress-scalar-definitions.html)

 Novak Elliott April 6, 2003 01:45

shear stress scalar definitions?

Hi all,

In the CFX solver manual there is listed several user scalars quanitfying the shear stress:

XY NODAL SHEAR STRESS | YZ NODAL SHEAR STRESS | - defined at all cells ZX NODAL SHEAR STRESS |

and

X SHEAR STRESS | Y SHEAR STRESS | - defined only at boundary cells Z SHEAR STRESS |

However, I was unable to find definitions of these 6 values. Am I right in assuming that the XY, YZ, ZX NODAL SHEAR STRESS values correspond to the 6 pairs of shear stresses on the 6 cell faces, that is: TauXY = TauYX = viscosity * (du/dy + dv/dx), TauYZ = TauZY = viscosity * (dv/dz + dw/dy), and TauZX = TauXZ = viscosity * (du/dz + dw/dx) respectively?

Also, at a wall boundary there are two orthogonal shear stress vectors tangential to the wall. Are the X, Y and Z SHEAR STRESS scalars the x, y and z components of the vector sum of the two shear stress vectors? In which case, for a wall that is located, for example, in a z-plane, the X and Y SHEAR STRESS scalars are simply TauZX (=viscosity*du/dz, dw/dx=0) and TauZY (=viscosity*dv/dz, dw/dy=0) and Z SHEAR STRESS is zero?

I intend to calculate drag force and I'd rather make use of the inbuilt scalars than calculate the partial derivatives myself (although GRADV looks obvious enough).

cheers, Novak.

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