[FluidKo]

Hello everyone

I have a question of Spalart Allmaras Model.

What does 'blocking wall effect' mean physically?

In Spalart Allmaras model, destruction of turbulence is proportion to turbulence and is inversely proportion to distance.
I want to know why Spalart and Allmaras think like that.
How they get that inspiration in terms of physics?

Here is my guess why Spalart and Allmaras claim like that.
If it is not right, please tell me the accurate reason why they claim like that.

"Destruction of turbulence viscosity is inversely proportion to distance."
I've seen below sentence.
"there is a “blocking effect” from a wall that is felt at a distance by the pressure and acts as a destruction entity for the Reynolds shear stress"
I don't understand accurate meaning of this sentence because I'm not good at English.
But I've guessed the meaning of this sentence like below.
Let's assume there is a flow that is forwarding to the wall.
It can be both mean flow and fluctuating flow.
As wall is approached, pressure nearby wall is risen.
Because there is a stagnation point nearby wall and we can see pressure rise from Bernoulli's equation.
Therefore I think eddy can't rotate and fluctuate to the wall because high pressure of stagnation point is blocking the motion of eddy.
This is why I think destruction of turbulence viscosity is inversely proportion to the distance from the wall.
If eddy want to rotate and fluctuate actively, eddy should be placed far from the wall.

"Destruction of turbulence viscosity is proportion to turbulence viscosity itself."
High turbulence viscosity means there is a active rotation of eddy.
Eddy mixes up and down actively for high turbulence viscosity.
But if eddy is too big, eddy used to dive into viscous sublayer where molecule viscosity is dominant by No slip condition.
It means big eddy used to be destructed by molecule viscosity(No slip condition)
Big eddy can't rotate perfectly and be attached to the wall by No slip condition.
I think this is why turbulence viscosity is proportion to turbulence viscosit itself.

These are just my guess.
Is it right?
If there is something wrong please tell me the accurate reason of why Spallart and Allmaras claim like that.
Thanks

[FluidKo]

I've asked this question to professor Spalart by e-mail.
And Thankfully he has answered to me.

Destruction of turbulence viscosity is inversely proportion to distance.
The reason of this is same with my opinion

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"Destruction of turbulence viscosity is inversely proportion to distance."
I've seen below sentence.
"there is a “blocking effect” from a wall that is felt at a distance by the pressure and acts as a destruction entity for the Reynolds shear stress"
I don't understand accurate meaning of this sentence because I'm not good at English.
But I've guessed the meaning of this sentence like below.
Let's assume there is a flow that is forwarding to the wall.
It can be both mean flow and fluctuating flow.
As wall is approached, pressure nearby wall is risen.
Because there is a stagnation point nearby wall and we can see pressure rise from Bernoulli's equation.
Therefore I think eddy can't rotate and fluctuate to the wall because high pressure of stagnation point is blocking the motion of eddy.
This is why I think destruction of turbulence viscosity is inversely proportion to the distance from the wall.
If eddy want to rotate and fluctuate actively, eddy should be placed far from the wall.

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The reason why destruction of turbulence is proportion to turbulence itself is different with my opinion.
I've considered molecule viscosity(No slip condition) but assumption of this model is inviscid flow.
So adapting molecule viscosity is not adequate to this model.
Then why destruction of turbulence is proportion to turbulence itself?
It is just same reason with reason why destruction of turbulence is inversely proportion to distance.
As distance becomes longer, mixing length becomes longer and it means turbulence and turbulence viscosity also become higher.
So relation between turbulence intensity and destruction of turbulence viscosity is just in the same context with relation between destruction of turbulence viscosity and distance.

Thanks
I dedicated this letter to professor Spalart.