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Wind tunnel simulation of the Texas tech building
1617 If I have got your point, a change of model-scale from 1:100 to 1:25 will not significantly influence the pressure parameters mean, r.m.s, and extreme value. At least, this will not be true for the correlation of the pressures. A mismatch of the scale in the order of 4 will significantly change the pressure's correlation and so the load effects design decisive reactions e.g. bending moments.
Author's reply Yes, the integral length scale (L,~) ~ of the parameters used to choose the 1:100 length scale. (See the companion paper by J.E.C. & LSC). At the 10 m level, the full-scale L= is approximately 140 m and in the wind-tunnel, it is 1.4 m (i.e. 1:100). Other values at different elevations in the paper presented on Monday. It seems that I was not clear on your second issue. The mean data was ~ by scale 1:25, 1:50, 1:100 and, indeed, the full-scale. ~ the peak + rms data are generally reduced in magnitude for larger models for all taps investigated to date. (See the Figure 10 in the first paper.) Correlation data have only been collected on the 1:25 model and so I cannot comment on correlation trends.
Wind Tunnel Simulation of the Texas Tech Building. D. Surry
Comment by R. Hoxey 1. 2.
You suggest that peak pressures are related to turbulent flow length scales (short length scale -- higher peaks). Can this be tested by surface pressure admittance functions? A 1 mm tap on a model is equivalent at 1:100 scale to 100 mm full-scale. Is this acting as an averaging area in model studies?
Author's reply 1.
2.
The relationship that I inferred was with the small scales or wavelengths of turbulent fluctuations that appear to affect the separating shear layers and hence affect the fluctuating pressures. Since these are likely to be non-linear relationships, I doubt whether admittance functions would be an appropriate approach. It certainly is, although I doubt whether it's sufficient to explain the significant discrepancies that are being observed. In full-scale, at typical roof height speeds of 10 m/s, the high peaks seem to have characteristic periods of a few tenths of a second, implying wavelengths of a few meters. Thus, one would not expect a 0.1 m diameter tap to reduce the peaks by enough to bring them into agreement with model results.
Comment by It.J. Kind 1.
2.
I was intrigued to see the relatively high negative Cp values in some of your data slides -values of-3 to -4 for mean Cp's and also very high negative peaks. This appears to confirm a point I have been trying to make in recent years. With respect to peak pressures, you mentioned the importance of RMS turbulence level. I would expect the probability density distribution of the wind speed fluctuations to also be important. From the earlier papers, I suspect that the full.scale wind at the Texas Tech site is more 'peaky' than the wind-tunnel flows that we saw this morning.
AuthoFs reply I.
You are correct. 5 to I0 years ago, we were concerned that the high mean suctions were associated as much with scaling problems as they were with proximity to edges. Howeve,, the evidence appears overwhelming that very close to edges, we do indeed see very local high suctions. It is interesting to note that these regions do seem to provide scaling problems as evidenced by the variety of Texas Tech model full-scale comparisons.
1618
The probability distributions between model and full-scale wind have not been compared directly so far as I know. There has certainly been evidence of local non-stationarities which cause significant deviations when they occur. I think that this would be an interesting avenue to pursue.
Author's reply Yes, the integral length scale (L,~) ~ of the parameters used to choose the 1:100 length scale. (See the companion paper by J.E.C. & LSC). At the 10 m level, the full-scale L= is approximately 140 m and in the wind-tunnel, it is 1.4 m (i.e. 1:100). Other values at different elevations in the paper presented on Monday. It seems that I was not clear on your second issue. The mean data was ~ by scale 1:25, 1:50, 1:100 and, indeed, the full-scale. ~ the peak + rms data are generally reduced in magnitude for larger models for all taps investigated to date. (See the Figure 10 in the first paper.) Correlation data have only been collected on the 1:25 model and so I cannot comment on correlation trends.
Wind Tunnel Simulation of the Texas Tech Building. D. Surry
Comment by R. Hoxey 1. 2.
You suggest that peak pressures are related to turbulent flow length scales (short length scale -- higher peaks). Can this be tested by surface pressure admittance functions? A 1 mm tap on a model is equivalent at 1:100 scale to 100 mm full-scale. Is this acting as an averaging area in model studies?
Author's reply 1.
2.
The relationship that I inferred was with the small scales or wavelengths of turbulent fluctuations that appear to affect the separating shear layers and hence affect the fluctuating pressures. Since these are likely to be non-linear relationships, I doubt whether admittance functions would be an appropriate approach. It certainly is, although I doubt whether it's sufficient to explain the significant discrepancies that are being observed. In full-scale, at typical roof height speeds of 10 m/s, the high peaks seem to have characteristic periods of a few tenths of a second, implying wavelengths of a few meters. Thus, one would not expect a 0.1 m diameter tap to reduce the peaks by enough to bring them into agreement with model results.
Comment by It.J. Kind 1.
2.
I was intrigued to see the relatively high negative Cp values in some of your data slides -values of-3 to -4 for mean Cp's and also very high negative peaks. This appears to confirm a point I have been trying to make in recent years. With respect to peak pressures, you mentioned the importance of RMS turbulence level. I would expect the probability density distribution of the wind speed fluctuations to also be important. From the earlier papers, I suspect that the full.scale wind at the Texas Tech site is more 'peaky' than the wind-tunnel flows that we saw this morning.
AuthoFs reply I.
You are correct. 5 to I0 years ago, we were concerned that the high mean suctions were associated as much with scaling problems as they were with proximity to edges. Howeve,, the evidence appears overwhelming that very close to edges, we do indeed see very local high suctions. It is interesting to note that these regions do seem to provide scaling problems as evidenced by the variety of Texas Tech model full-scale comparisons.
1618
The probability distributions between model and full-scale wind have not been compared directly so far as I know. There has certainly been evidence of local non-stationarities which cause significant deviations when they occur. I think that this would be an interesting avenue to pursue.