A wind tunnel study of turbulent flow over model hills

Abstract

Abetrsct. Detailed wind tunnel measurements have been made of mean flow and turbulence over a two-dimensional ridge and a circular hill, both having cosine-squared cross-section and maximum slope about 15". The measurements were made in an artificially thickened neutrally stratified boundary layer, and have been compared with results from linear models and rapid distortion theory as appropriate.Our study shows that linear theory gives generally good predictions of the mean flow on the upwind side of the hills, and especially of the flow speedup at the hill top, but that the turbulence is less well predicted. In particular, the measurements show a major increase in the vertical component of turbulence and in the shear stress on the upwind slope of both the two-and threedimensional hills which is not predicted by either equilibrium or isotropic rapid-distortion theories, although this may be partly due to the effect of streamline curvature. Rapid-distortion theory is successful only in describing the streamwise component of turbulence in the outer region of the flow, while in the upper part of the inner region of the flow, the turbulence measurements show disagreement with both the equilibrium and the rapid-distortion theories. Our experiments also confirm that the equilibrium region is a very thin layer close to the surface, while above this region and below the outer region, there is a transitional region where all terms in the stress equation are important.The measurements over the three-dimensional hill suggest that the mean flow and turbulence are broadly similar to those over the two-dimensional ridge, but with reduced perturbation amplitudes. The major differences between the two cases are found on the upwind slope and in the wake where, respectively, horizontal divergence and convergence of the three-dimensional flow are most pronounced.

Measurements of the near‐surface flow over a hill

“…Belcher et al 1993). Notable wind-tunnel studies include those of Britter et al (1981), Gong and Ibbetson (1989) and Finnigan et al (1990). The latter of these studies included surface pressure measurements and analysis of the mean and turbulent ow in a streamline coordinate system, enabling evaluation of the full momentum budget across a hill.…”

A wind tunnel study of turbulent dispersion over two- and three-dimensional gentle hills from upwind point sources in neutral flow

“…The present study is a follow-up to the previous study of turbulent flow over 2-D and 3-D hills (Gong and Ibbetson, 1989) to investigate plume dispersion under the same flow situations. Point sources were introduced at locations upstream of cosine-square shaped hills in the wind tunnel.…”

Turbulent flows over mountainous terrain modelled by the Reynolds equations

“…In addition, flow over a mountainous island (the island Varray in the northern part of Norway) is used as an example of realistic topography. Except for steeper slopes, the idealized setups are comparable to those used by Gong and Ibbetson (1989).…”

“…Some analytical analysis is still possible, and simulations have been comprehended. Experimental knowledge from laboratory measurements and field measurements from atmospheric and ocean environments are essential to increase our understanding of such flows (Jenkins et al, 1981;Mickle et al, 1988;Snyder et al, 1985;394 T. UTNESANDK.J.EIDSVIK Gong and Ibbetson, 1989;Fimrigan et al, 1990;Coppin et al, 1994;Almeida et al, 1993). A state of the art review on the knowledge of flows over hills is given by Taylor et al (1987); Hunt et al (199 1) and Baines (1995).…”