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)