turbulence

Describes both the macro and micro meteorological structure of strong winds in the earths boundary layer. Discusses the wind speed spectrum, characteristics of mean flow and gustiness and the structure of turbulence. Concludes that almost all theproperties of the wind that might be needed in structural design can be estimated from the mean-wind field and the groundroughness. Suggests areas for further research.

Gives short state-of-the-art review of knowledge of wind turbulence. Mentions results from field investigations. Summarizes available knowledge. An appendix discusses hot-wire anemometry. Gives bibliography of subject.

States that porosity is the most important single parameter describing shelterbelts but is very difficult to measure or define. Describes a method for categorizing wind breaks in terms of porosity using only measured minimum leeward-wind velocity. Gives theoretical expressions for the flow through a porous shelterbelt. Describes experiment to measure wind velocities around shelterbelts of low, medium and high porosity. Shows that wind measurements could be made any height without affecting relative reduction in velocity.

Shows by comparison with simplified methods for dimensioning structural beams that the degree of tightness of a shell is not the arithmetic sum of the leakage of components. States that leakage occurs where there is a pressure difference caused by wind, temperature difference and fans. The amount of leakage depends on whether the air flow is laminar or turbulent. Gives equations for the calculation of leakage in buildings without ventilation, with natural ventilation, with mechanical evacuation and with both mechanical inlet and evacuation.

Reviews wind research prior to 1958, which was based on the simple concept of a smooth air flow resulting in static design loads for most structures. States that research for the past ten years has benefited from three innovations. These are theimplementation of a statistical theory of turbulence, experimentation with turbulent boundary layers and the collection of full-scale measurements to identify and evaluate the real wind structure.

After a general introduction on the cause of wind, the dependence of wind speed increase with height on surface roughness and atmospheric stability is discussed. For the purpose of wind load calculation on structures this speed increase is often approximated by the pth power of height where the exponent p varies both with roughness, stability and the height of the layer in question. The last mentioned variation implies that extrapolations of p above its determination height cannot be depended upon.

Describes method for simulating natural wind boundary layer in a conventional, short working section, aeronautical wind tunnel. Boundary layers, which may be as thick as one-half of the working section height are generated by spires at the working section inlet. This approach is used to measure mean wind pressures and pressure spectra on a model of a tall building in downtown Montreal. Measurements are repeated using the long roughness fetch technique for boundary layer generation and results from the two methods compared.

Describes the ventilation of buildings by analogy with electric circuits and derives expressions for ventilation with and without flow through ducts in the roof. Finds that in general ventilation rate will vary linearly with wind velocity. Considers the effect of shelter belts on wind velocity and derives expression for sheltered ventilation rate. Suggests that eddy motion caused by shelters may be important. Gives measurements made on models in wind tunnels to show the affect on wind pressure of sheltering buildings at various distances.

Treats measurements of ventilation rates in a model building and wind tunnel. 2 types of opening, circular holes and model windows were tested under 2 wind cOnditions. one wind condition was selected to give maximum flow through the model; with theother, ventilation was mainly due to turbulent pressure fluctuations. Illustrates different characteristics of theopenings. Draws comparisons between measurements and theoretical predictions. Discusses use of wind tunnels for ventilation studies. NOTES: A further comment on this paper was published in Building and Environment vol.15 no.141.

Analyses wind pressure records, taken during 5 different windstorms on 2 levels in a 400ft (122m) high office building in downtown Montreal March 1964 pressure fluctuations on an actual building. Preliminary work done to compare full-scale measurements with wind tunnel measurements indicates that simulation of basic statistical properties of wind pressure fluctuations can be successful when carried out in a boundary layer type of wind tunnel.