[sharada77]

Pardon me if this questions sounds silly....i am a novice to Fluid dynamics..
I want to know how the free stream velocity of a fluid varies along a curved surface(It decreases or increases)...How the boundary layer development affects this free stream velocity.
I also want to know how the drag force affects the heat transfer co-efficient.

[vetnav]

Hello Sharada,

The question is too general to answer, usually if x is the stream wise direction in laminar boundary layer theory we assume external flow varies as ~ x^m where the variable 'm' take different values.

Lets assume the flow is laminar as you move downstream from the nose of the object as the thickness of the boundary layer grows the free stream velocity should increase in order to satisfy the mass conservation.

A perfect reference to answer your question is the book "Laminar boundary layers" by L. Rosenhead, for basics you can refer the famous book "Boundary layer theory" by H. Schlichting.

Hope this information is helpful

Best
Naveen

[sharada77]

Thank you Naveen

[sharada77]

Can anyone please explain me why in laminar fluid flow surface roughness is neglected but taken into account only in turbulent flows...

[vetnav]

Surface roughness results in small disturbances in the flow, when the flow is laminar (Reynolds number is small) these disturbances are killed immediately by the viscous effects, but when the flow is turbulent (Reynolds number large) any small disturbance will grow and will effect the flow behavior.

You can think this in terms of relative importance of inertial and viscous forces also.

As you said you are not familiar with fluid mechanics I will put it simply

Laminar flow ---> small disturbances gets killed.

Turbulent flow ---> infinitesimally small disturbances also grow and affect the flow.

Hope I did not confuse you more.

[sharada77]

thankyou so much .........

[sharada77]

I am learning meshing(both structured and unstructred) on Ansys icem cfd tool...i want to know what are different variables we have to check for performing quality check in unstruvtred meshes and structured meshes.

I also want to know if aspect ratio, and skewness is important to check in unstructred meshes..if yes why it is important and what is the optimum value.
Please suggest what changes should be made in meshing to get the optimum values.