[mazhar16823]

Hi,

I want to evaluate the thickness of first layer close to the wall and total boundary layer thickness (to be used as total prism layer thickness).

I want to compute Chord Reynold's number first, for that I have chord length values for each location on the blade. Does it mean that I have to calculate Chord Reynold's number at each location of the blade to get Y (BL thickness)?

If this is the case, it will only give me the thickness for first layer close to the wall because I will use y+ value in the wall distance equation as given on https://www.cfd-online.com/Wiki/Y_pl...nce_estimation. This estimation tool uses Reynold's number based on length of boundary layer.

And then how will I get total prism layer thickness? Any suggestions.

[Hamidzoka]

Hi;
The chord-based Re seems reasonable to estimate the first cell width all over the blade.
But note that the first cell width strongly depends on the selected turbulence model. So the very first step is to select proper turbulence model since different turbulence models apply completely different strategies to model near wall flow behavior.
Regarding the boundary layer thickness you have two controlling parameters, namely, expansion ratio and number of prism layers.
It should be mentioned that setting proper parameters to resolve the boundary layer needs a try and error process and some parameters like turbulence viscosity ratio can be used to assess it. Further explanations can be found in the literature.

Regards

[mazhar16823]

Originally Posted by Hamidzoka

Hi;
The chord-based Re seems reasonable to estimate the first cell width all over the blade.
But note that the first cell width strongly depends on the selected turbulence model. So the very first step is to select proper turbulence model since different turbulence models apply completely different strategies to model near wall flow behavior.
Regarding the boundary layer thickness you have two controlling parameters, namely, expansion ratio and number of prism layers.
It should be mentioned that setting proper parameters to resolve the boundary layer needs a try and error process and some parameters like turbulence viscosity ratio can be used to assess it. Further explanations can be found in the literature.

Regards

Thanks for your comments. I will us Re_Theta model. However, my query was how to compute Chord based Re as I have chord length for each section of the blade. Even, if I just take chord length of a section close to the root of blade I will have to use one value for y+ to determine the thickness of first prism layer from the Y equation given here https://www.cfd-online.com/Wiki/Y_pl...nce_estimation, but how about the rest (total prism layer thickness)?

[Flowkersma]

Hi Mazhar,

From the results of your simulation, you can calculate the wall shear stress which is needed to calculate the first cell wall distance. Beforehand you can estimate it from the flat plate theory for instance.

Best, Mikko