Results are presented of a series of experiments which were carried out with great care to produce accurate, comparable results in which the relatively small changes in the flow past a circular cylinder associated with varying blockage ratios can be clearly distinguished. The experiments cover a range of blockage from 2 to 16% and of aspect ratios from 4 to 10. End plates were fitted to the cylinders in all experiments.For blockage ratios less than 6%, it is shown that the effects of blockage on pressure distribution and the drag coefficient are small and that the Strouhal number is unaffected by blockage. For blockage ratios in the range 6–16%, there is considerable distortion of the flow due to blockage and the effects are complex. The pressure distribution is of a different form and the Strouhal number changes. Hoevever, conflicting influences result in a blocked drag coefficient which is not very different from that at no blockage. Reduction in aspect ratio has effects on drag coefficient and on base pressure coefficient which are similar to those associated with increase in blockage ratio.It is concluded that blockage correction procedures based on the momentum method and on the image method are unsatisfactory in their prediction of the unblocked drag coefficient but the momentum method predicts the unblocked base pressure coefficient quite well.

Experiments were carried out using models having L/D [les ] 2 and the resulting pressure distributions and vortex shedding characteristics are presented. A simple visualization technique which provides explanations of some of the measured results is described. It is concluded that splitter planes reduce the drag markedly by stabilizing the separation points and produce a wake narrower than that for a plain cylinder, raise the base pressure by as much as 50% and affect the Strouhal number to a lesser degree. Careful measurement techniques have enabled these effects to be presented accurately.

The work reported in part 1 has been extended to cover flows past circular cylinders with wake splitter plates having 2 [les ] L/D [les ] 7 and to include flows past normal flat plates with splitter plates having L/D [les ] 3·7. Pressure distributions and wake Strouhal numbers were measured and visualization studies carried out. The results obtained indicate that no further changes would be produced by lengthening the splitter plates beyond the limits tested.The combined results of parts 1 and 2 provide coherent descriptions of the effects of wake splitter plates for all values of L/D of significance for the two profiles, which are representative of two distinct classes of bluff bodies, viz., those with cross-sections of curvilinear shape for which the flow separation points are not determined uniquely by the geometry and those for which the separation points are fixed.

No abstract

237order of magnitude as that of model A. Since buildings in model A have set-backs from the street, the open space between the second and third rows is wider than the corresponding space in model B. It would be presumed that ventilation in lightwells connected to the street space would have higher values in model A than in model B. Velocity measurements prove otherwise, however, as demonstrated in Fig. 3. It is further noticed in Fig. 3 that the velocity in the third row lightwell of model A decays with increasing free stream velocity until it vanishes. This interesting behaviour is attributed to vortices taking place in street spaces (Ghazi 1975).Model C was considered in order to study the effect of side passages. The only difference between models B and C is that the latter has no side passages. Measurements indicate that ventilation in the back space of the first side passage of model B is 12 times that of C. This is explained by the observation that the first side passage faces the wind directly, while the other passages are exposed to vortex flow, whereby they lose their effectiveness. Velocities at other locations in model B, however, are slightly lower than those in C. The indications are that, introduction of side passages significantly improves ventilation conditions in the first back space, whereas it adversely affects ventilation in the remaining rows. ConclusionsComparison between airflow measurements on models A and B, which represent detached and attached buildings, respectively, shows that ventilation in back spaces between rows of buildings in model B is superior to that in the narrow back spaces of model A. On the other hand, high airflow is attained in the side spaces of model A. The side passages of model B considerably improve ventilation conditions in the first back space, while marginally affecting the conditions of rear rows of a group of buildings. Furthermore, the airflow in lightwells of model B is not significantly influenced by the presence of side passages.In conclusion, experimental results suggest that a combination of one frontal attached row with side passages, followed by rows of attached buildings with no side passages would be an arrangement superior to the layouts considered. AcknowledgementsThis work was partly sponsored by Grant AT-5-79 of King Abdulaziz City for Science and Technology (KACST). ReferencesAynsley, R. M.; Melbourne, W.; Vickery, B. J. 1977: Architectural aerodynamics. London: Applied Science Ghazi, M. A. 1975: Experimental investigation of the effect of surface discontinuity on step-backward flow. M.Sc. Thesis, Faculty of Engineering, Cairo University Givoni, B. 1976: Man, climate and architecture. 2nd edn. London: Applied Science Mohsen, M. A.; Olwi, I. A.; Ghazi, M. A. 1987: Aerodynamics and ventilation in buildings: Experimental investigation. Solar Wind Technol. 4, 501-507 Olgyay, V. 1963: Design with climate-bioclimatic approach to architectural regionalism. New Jersey: Prinston Univ. Press Olwi, I. A.; Ghazi, M. A.; Mohsen, M. A. 1988: Wind tunnel sim...