# Turbulent flow

Abubakar
Member
Posts:

**46**Hi,

Name of the video-Closure of RANS Equations - Lesson 5, Basic of Turbulent flow course. ** "The instructor is saying that quite often we ignored the kinetic energy term due to the negligible contribution of normal stress compared to turbulent stress"** I think it should opposite, right? because the contribution of turbulent stress is more there will be more kinetic energy since they are directly proportional to each other.

I hope you understand my question.

Thank you,

Abubakar khan

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## Comments

251MemberHello,

Turbulent kinetic energy is defined as 𝑘=0.5((𝑢′ 𝑢′ ) +(𝑣′ 𝑣' ) + (𝑤′ 𝑤′ ) ). The terms inside the brackets are referred to as the normal stresses. Based on the Boussinesq approximation, Reynolds stress can be written as a combination of the Strain rate tensor (made up of the mean flow velocity gradients) and the turbulent kinetic energy. Because the velocity fluctuations (u’,v’,w’) and the normal stresses are generally very small compared to the mean flow velocity gradients, the turbulent kinetic energy part of the Reynolds stress formulation can be ignored.

Hope this helps.

Thanks,

Kalyan

140MemberThank you @Kalyan Goparaju sir for your quick support. I have two follow-up questions:

251MemberHello,

Kalyan

140MemberGot it @Kalyan Goparaju sir thank you for your help.