All entries for Monday 19 February 2007

February 19, 2007

PhD Work– 19/01/07

10:22


SIMULATIONS

Have sorted files into the correct places so that I have more room again now. Have deleted most of the development runs as I only really need the key runs and the final code to work.

Am currently sorting through the simulations and dividing them into development runs (Stages 1 & 2) and useful runs (Stages 3 & 4).

  • MT01-01: S-A Model testing

Will take one of the wall functions sims which has a fine near wall grid and use this as mt01-01-A01. I will then try a number of different variables and record these simulations for interest. Will set this up now. (Prob use mt01-03-25 aka mt01-03-A01 first)


  • MT01-02: DES testing

I will simplify these by concentrating on the Re=7500 case for now. Then once this is sorted, I can try the lower Re for completeness. Will do this at home later.


  • MT01-03: Wall Functions testing

Have a good 12 runs for this (6 grids with & without) and just need to produce some results. Will do this at home later.


14:32

  • MT01-03: Wall Functions Validation


Here are the latest results for the wall functions validation:

<img style="padding-right:5px;padding-left:5px;" src="/images/apreece/2007/02/19/mt01-01-a01to06uprof.jpg?maxWidth=500" alt='Wall Functions Validation- Velocity Profile without wall functions' title='Wall Functions Validation- Velocity Profile without wall functions' />

<img style="padding-right:5px;padding-left:5px;" src="/images/apreece/2007/02/19/mt01-01-a01to06unearwall.jpg?maxWidth=500" alt='Wall Functions Validation- Near Wall' title='Wall Functions Validation- Near Wall' />

<img style="padding-right:5px;padding-left:5px;" src="/images/apreece/2007/02/19/mt01-01-a01to06vissa.jpg?maxWidth=500" alt='Wall Functions Validation- Vissa profile without wall functions' title='Wall Functions Validation- Vissa profile without wall functions' />

<img style="padding-right:5px;padding-left:5px;" src="/images/apreece/2007/02/19/mt01-01-a07to12uprof.jpg?maxWidth=500" alt='Wall Functions Validation- Velocity Profile with wall functions' title='Wall Functions Validation- Velocity Profile with wall functions' />

<img style="padding-right:5px;padding-left:5px;" src="/images/apreece/2007/02/19/mt01-01-a07to12unearwall.jpg?maxWidth=500" alt='Wall Functions Validation- Near-wall Velocity Profile with wall functions' title='Wall Functions Validation- Near-wall Velocity Profile with wall functions' />

<img style="padding-right:5px;padding-left:5px;" src="/images/apreece/2007/02/19/mt01-01-a07to12vissa.jpg?maxWidth=500" alt='Wall Functions Validation- Vissa Profile with wall functions' title='Wall Functions Validation- Vissa Profile with wall functions' />

Note that the wall functions simulation for A09 (triangles) has some simple error causing the erroneous results.


16:23

  • MT01-03: Turbulent inflow rescaling

Have set running mt01-03-04 which uses an LES formulation (ymin=dx*0.65). Have also set running mt01-03-05 which is a simulation without turbulence treatment.

19:34

  • RS01: Lille bump without F.C.

Have set running rs01-02-A02 which is the same as rs01-02-A01 but with RANS. I may need to limit fv2 to make stable if necessary.

19:42

  • The Lille Bump Set-up

Here are the final values of the boundary layer for the Lille bump.

Full Re

u=10 m/s
d (at 15m) using fully turb bl approx= 0.227 m
d (at 15m) using transitional bl approx = 0.224 m

We shall use the transitional bl approx (although there isn't much in it) This gives the other boundary layer properties as:

d* (at 15m) = 0.02796 m
theta (at 15m) = 0.021764 m
Re(theta) = 1.496 x 10**4
wss (at 15m) = 0.144246 Pa

We cannot model the full Re with the resources available so will model Re/10 (u= 1m/s)

Reduced Re

We want to preserve the boundary layer thicknesses at the inlet so, in essence, we will need to reduce the run-up length. This is done by finding the value of x which corresponds to d=0.224m. This is given as:

x (development length) =11.3 m

This gives the same boundary layer thicknesses (by definition) but gives a reduced Re based on mom. thickness and wall shear stress:

Re(theta) = 1.496 x 10^3 (1496)
wss (at 15m) = 0.002419 Pa (2.419 mPa)

This makes one wall unit equal to:

y+ = 1 > y = 0.328 mm

We plan to use grid spacings of:

dx < 120 mm (nx=300)
dy = 10 mm (ny=100)
dz < 42 mm (nz=50)

Which equates to:

dx+ < 366
dy+ = 31
dz+ < 128

Although the dz+ is greater than 100, this is only for the very edge nodes so I don't think it will be a problem.

From a recent boundary layer simulation to produce the boundary layer with the desired thickness, we get the wall shear stress:

wss =  0.00237 Pa

This compares well with the above estimates (around 2% error)


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