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, Uo, was 4m/s so that the Reynolds number based on hill height was about 3 x 104. 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=CUoH2/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.

NAME

GNDPs

PDPs (problem definition parameters)

MPs (measured parameters)

Re

Hill aspect ratio

Scalar location

detailed data

DOAPs

EXP1 Hill flow & dispersion

3 x 104

3,5,8

xs/L=±1 or 0, and zs=0.25H, 0.5H, H and 1.5H

C, U, stresses

U/Uo C/Co, uw/Uo2, etc.

Table A Summary description of all test cases

MP 1

Normalised C

MP2

U (ms-1)

MP3

stresses

DOAPs, or other

miscellaneous data

EXP 1

File names given in Table C

As filenames

Listed in table D

As filenames 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

Table B Summary description of all measured parameters and available data files. Tabulated data available are provided in the files listed in Tables C and D. Note that the flat surface reference case is in the file: Flatrefcase.dat.

Data filename

Data filename

Data filename

NO HILL

Flatrefcase.dat

HILL 3

h301s.dat

h302s.dat

h303s.dat

h304s.dat

h305s.dat

h306s.dat

h307s.dat

h308s.dat

h309s.dat

h310s.dat

h311s.dat

h312s.dat

h313s.dat

h314s.dat

h315s.dat

h316s.dat

HILL 5

h501s.dat

h502s.dat

h503s.dat

h504s.dat

h505s.dat

h506s.dat

h507s.dat

h508s.dat

h509s.dat

h510s.dat

h511s.dat

h512s.dat

h513s.dat

h514s.dat

h515s.dat

h516s.dat

HILL 8

h801s.dat

h802s.dat

h803s.dat

h804s.dat

h805s.dat

h806s.dat

h807s.dat

h808s.dat

h810s.dat

h811s.dat

h812s.dat

h813s.dat

h814s.dat

h815s.dat

h816s.dat

h817s.dat

TABLE C List of available data files for velocities and turbulent stresses.

NO HILL

Surface concentrations for source heights 29, 59, etc., mm.

Flatref029G.dat

Flatref059G.dat

Flatref117G.dat

Flatref176G.dat

Flatref234G.dat

Flatref351G.dat

Vertical profiles, for 29 and 117mm source heights and given x mm.

FlatrefC029S585V.dat

FlatrefC117S330V.dat

FlatrefC117S585V.dat

FlatrefC117S1170V.dat

FlatrefC117S1600V.dat

FlatrefC117S1872V.dat

HILL 3

Surface concentrations for source heights at 29 or 59mm, located at Upwind base (Uw), Summit (Su) or Downwind base (Dw) of hill.

h3CUwS29G.dat

h3CSuS29G.dat

h3CDwS29G.dat

h3CDwS59G.dat

HILL 5

Surface concentrations for source heights at 29mm and located at Upwind base (Uw), Summit (Su) or Downwind base (Dw) of hill.

h5CUwS29G.dat

h5CSuS29G.dat

h5CDwS29G.dat

HILL 8

Surface concentrations for source heights at 29 or 59mm and located at Upwind base (Uw), Summit (Su) or Downwind base (Dw) of hill.

h8CUwS29G.dat

h8CSuS29G.dat

h8CDwS29G.dat

h8CDwS59G.dat

TABLE D List of available data files for normalised concentrations. © ERCOFTAC 2004 Test Cases - Further Details © ERCOFTAC 2004 Description of Experiment

This is given above. © ERCOFTAC 2004 Boundary Data

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. © ERCOFTAC 2004 Measurement Errors

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. © ERCOFTAC 2004 Measured Data

The original data is contained in text files as Case 69 on the ERCOFTAC database, at the web address: http://cfd.me.umist.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. © ERCOFTAC 2004 References

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

Site Design and Implementation: Atkins and UniS

       Top        	      Next