Test Data AC5-05
Boundary layer flow and dispersion over isolated hills and valleys
Application Challenge 5-05 © copyright ERCOFTAC 2004
Overview of Tests
Full details of the experimental procedures are provided in Kurshudyan et al (1981). Here we summarise the summary given in CA. The upstream (simulated, neutrally stable atmospheric) boundary layer was developed using a combination of an inlet fence and distributed (10mm, sanspray) roughness. At the hill location (but in its absence), 8.7m downstream of the fence, the boundary layer was only slowly developing and had a depth of about 1m. Profiles of the mean velocity and turbulence stresses are included in the data set, along with all the data obtained for the three hill cases. This data set can be found in the ERCOFTAC database (case 69) and is the final smoothed data generated by Trombetti et al (1991), see Measured data. The free-stream velocity, U0, was 4m/s so that the Reynolds number based on hill height was about 3x104. The scalar source was a 15mm diameter porous sphere, which provided a neutrally buoyant, isokinetic release, with a continuously monitored (constant) flow rate, Q. Averaging times for velocities, stresses and concentrations were at least two minutes, with sampling rates high enough to ensure that statistical errors arising from a finite sample size were insignificant.
Velocity and turbulence profiles were obtained at numerous axial locations. For example, for the lowest slope hill (which had a total length at z=0, a=2L, of 16H or about 1872mm) profiles were taken at x/H=±16, ±8, ±4 and 0, i.e. at one hill length upstream and downstream from the summit, at the upwind and downwind base and half-way up and down the hill slopes. (Note that the x-coordinate origin is the z=0 position beneath the hill summit). Similar relative positions were used for the other hills. The source stack positions were xs/L=±1 or 0, and zs=0.25H, 0.5H, H and 1.5H for each axial location. For each stack position (xs, zs) and each hill (and also the no-hill case), surface concentration profiles were obtained to downwind fetches where the concentration had fallen by at least two orders of magnitude from its maximum. In addition, vertical profiles were obtained at the same x-locations as those used for the flow profiles and corresponding cross-stream profiles were also obtained (generally only at z=zs). The raw concentration values were normalised as: Cn=CU0H2/Q and it is these normalised data which are contained in the aforementioned database. There are no ‘global’ parameters (e.g. hill amplification factors) contained in the database. Most of the computational comparisons contained in CA consist of profile comparisons, although some of these are normalised – e.g. surface concentration normalised by its maximum value or by the corresponding maximum ground level concentration in the absence of the hill.
|Re||Hill aspect ratio||Scalar location||Detailed data||DOAPs|
|EXP1 Hill flow and dispersion||3x104||3, 5, 8||Xs/L = ±1 or 0, and Zs = 0.25H, 0.5H, H and 1.5H||C, U, stresses||U/U0 C/C0 uw/U02, etc|
|MP1 Normalised C||MP2||MP3 stresses||DOAPs or other miscellaneous data|
|EXP 1 File names given in Table C||As file names listed in Table D||As file names in the form: hnms.dat where n is hill case (3, 5 or 8) and m is a two- digit file number Listed in Table C||Specified in files listed in Table C||Specified in files listed in Table C|
|Data filename||Data filename||Data filename|
|HILL 3||HILL 5||HILL 8|
|NO HILL||HILL 3||HILL 5||HILL 8|
|Surface concentration for source heights 29, 59 etc., mm||-|
|Flatref029G.dat||Surface concentration for source heights at 29 or 59 mm, located at Upwind base (Uw), summit (Su), or Downwind base (Dw), of hill.||Surface concentrations for source heights at 29mm and located at Upwind base (Uw), Summit (Su), or Downwind base (Dw), of hill.||Surface concentrations for source heights at 29mm or 59mm and located at Upwind base (Uw), Summit (Su), or Downwind base (Dw) of hill.|
|Vertical profiles, for 29 and 117mm source heights and given x mm.||h3CDwS29G.dat||h5CDwS29G.dat||h8CDwS59G.dat|
Test Cases - Further Details
Description of Experiment
This is given above.
The upstream boundary layer data is included in the database. The surface roughness length, zo and normalised friction velocity, u*/Uo, in the usual notation, were 0.16mm and 0.047, respectively. Total turbulence kinetic energy was not measured (although individual profiles of axial and vertical stress and shear stress are available), so in the computations it was estimated – see below.
Errors in the hot wire data were reckoned to be within the usual limits obtainable with careful calibration (including proper yaw calibration) – i.e. ±2% on mean velocity and 10-15% in the stresses (normalised by the Uo2). The experimental programme included considerable effort to ensure as high an accuracy as possible. Concentration data was obtained using standard Flame Ionisation Detector techniques and the errors were estimated to be between 4 and 20%; consequent errors in the normalised data are similar, since the accuracy of monitoring both Q and Uo was high.
The original data is contained in text files as Case 69 on the ERCOFTAC database, at the web address: http://cfd.mace.manchester.ac.uk/ercoftac/. Access to these files is limited and will not be of much help, but they were used to construct the files listed in Tables C & D above. These include data on mean and turbulent velocities and scalar concentrations for three hills and with the various source locations specified earlier.
Busuoli, M., Trombetti, F. & Tampieri, F. (1993). Data sets for studies of flow and dispersion in complex terrain: I) the RUSVAL wind tunnel experiment (flow data). CNR Technical Report No.3, FISBAT-RT-93/1
Castro, I.P. & Apsley, D.D. (1997). Flow and dispersion over topography: a comparison between numerical and laboratory data for two-dimensional flows. Atmos. Env., 31, 839-850.
Khurshudyan, L.H and Snyder, W.H & Nekrasov, I.V (1981). Flow and dispersion of pollutants over two-dimensional hills. U.S. Env. Prot. Agcy. Rpt. No. EPA-600/4-81-067. Res. Tri. Pk., NC.
Khurshudyan, L.H and Snyder, W.H & Nekrasov, I.V, I.V and Lawson R.E., Thompson R.S. & Schiermeier F.A. (1990). Flow and dispersion of pollutants within two-dimensional valleys. U.S. Env. Prot. Agcy. Rpt. No. EPA-600/4-79-051. Res. Tri. Pk., NC.
Maurizi, A. (2000) Numerical simulation of turbulent flows over 2D valleys using three versions of the k-ε closure model. J. Wind Eng. Ind. Aero., 85, 59-73.
Trombetti, F., Martano, P. & Tampieri, F. (1991). Data sets for studies of flow and dispersion in complex terrain: I) the RUSHIL wind tunnel experiment (flow data). CNR Technical Report No.1, FISBAT-RT-91/1
© copyright ERCOFTAC 2004
Contributors: Ian Castro - University of Southampton