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How to find U* for wall roughness in LES model |
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Karthik V
Join Date: Mar 2024
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Hello everyone,
I’m studying the wall roughness effects on a wall using LES turbulence model. In Ansys Fluent 2024 R1, 3 new method is introduced for LES viscous model to change the effect of wall roughness and they are: Kader Blending Wall Functions Harmonic Blending Wall Functions Based on r+ Werner and Wengle Wall Treatment Out of these 3 methods, we can give physical roughness only for Harmonic Blending Wall Functions Based on r+ For wall roughness effects in turbulent wall-bounded flows, we have three distinct roughness regimes based on a nondimensional roughness height K_s^+. Hydrodynamically smooth when (K_s^+≤2.25) Transitional when ( 2.25〖<K〗_s^+≤2.25) Fully rough when (K_s^+>90) Here to find out K_s^+, we have the formula: K_s^+=ρK_s u^*/μ Where, ρ= Density of the fluid K_s= Physical wall roughness height μ= Viscosity of the fluid u^*=C_μ^(1/4) k^(1/2) C_μ value is given a default value in k-ϵ viscous model. Whereas it’s not mentioned in LES turbulence model. My query is how to obtain the u^* value from Ansys Fluent, so that I can identify the distinct roughness regime by substituting the physical wall roughness height and other parameters |
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harmonic wall, les model, u star |
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