paulharrison Posted March 9, 2020 Share Posted March 9, 2020 Hi, I am new to CFD, and trying to understand. I am reading the nice review of the mathematics behind LINCOM at: RIS_R_900.pdf. I take Eqs. (8) and (9) with the substitution (10), and we clearly have 4 equations in 4 unknowns. Very good. We expand according to (11) and (12). Here I understand that we have doubled the number of unknowns to 8. But some magic (presumably Reynolds averaging) gives the extra equations (13)-(15), which seem to be 5 equations, probably with some redundancy. So let us say 4, and we still have enough constrains. Still good.At this point, however, I notice that Eq. (14) looks like a typing error. Since the right hand side is a vector zero, I have to assume that on the LHS here, we mean Curl(\bold v), (the curl symbol has been omitted). But I am anyway mystified at this point, since if I look to Eq. (2), I find that\bold V = (cos th, sin th, 0) (U*0/kappa)ln(z/z_0)Now, it seems to me that the curl of this "background flow" is not zero at all. In fact, it is a rotational flow.So, is the notation \bold V intended to mean different things in eqs. (2) and (14), or is Eq.(14) meant to mean something other than curl (\bold V)=\bold 0?Thanks in advance for any clarification.Best Wishes,Paul Harrison. Link to post

Morten Posted March 10, 2020 Share Posted March 10, 2020 Hi Paul,You are right, the background flow is not irrotational, but I just think Eqn. 14 states that the flow field has no gradient. This is true for the two horizontal dimensions, since the background flow is the same everywhere. It is also true for the vertical direction, since its vertical component is zero. Report RisÃ¸-R-900 focussed on roughness-change perturbations. The model for effects of variable terrain elevation was revised in RisÃ¸-R-1356. Cheers,MortenReferences:https://backend.orbit.dtu.dk/ws/portalfiles/portal/7766601/RIS_R_900.pdfhttps://backend.orbit.dtu.dk/ws/portalfiles/portal/7726842/ris_r_1356.pdf Link to post

paulharrison Posted March 10, 2020 Share Posted March 10, 2020 Dear Morten,Thanks for your kind answer. I will think a little more about it. Thanks also for the later reference, which I had not seen. I have just downloaded it and will read it with interest.Cheers, Paul. Link to post

## Recommended Posts

## Create an account or sign in to comment

You need to be a member in order to leave a comment

## Create an account

Sign up for a new account in our community. It's easy!

Register a new account## Sign in

Already have an account? Sign in here.

Sign In Now