Measurements are presented of the mean and fluctuating pressure field acting on a two-dimensional square cylinder in uniform and turbulent flows. The addition of turbulence to the flow is shown to raise the base pressure and reduce the drag of the body. It is suggested that this is attributable to the manner in which the increased turbulence intensity thickens the shear layers, which causes them to be deflected by the downstream corners of the body and results in the downstream movement of the vortex formation region. The strength of the vortex shedding is shown to be reduced as the intensity of the incident turbulence is increased.

A study has been made of the influence of grouping parameters on the mean pressure distributions experienced by three dimensional bluff bodies immersed in a turbulent boundary layer. The range of variable parameters has included group density, group pattern and incident flow type and direction for a simple cuboid element form. The three flow regimes associated with increasing group density are reflected in both the mean drag forces acting on the body and their associated pressure distributions. A comparison of both pressure distributions and velocity profile parameters with established work on two dimensional bodies shows close agreement in identifying these flow regime changes. It is considered that the application of these results may enhance our understanding of some common flow phenomena, including turbulent flow over rough surfaces, building ventilation studies and environmental wind around buildings.

ConclusionThe purpose of the present investigation was to systematically define the effect of turbulence on the drag. The results offer a semi-consistent behavior. Cylinders with HID > 0.5 follow a regular influence with turbulence, that is, an increased in the level of turbulence seems to move the smooth flow C DC of a given HID section to the C DC of an equivalent increased HID section. Cylinders with HID < 0.5 do not reach the maximum C DC of 2.9 as the level of turbulence is increased. It also suggests that the vortices strength as well as their formation and the afterbody length HID remain predominant variables in turbulent flow with the additional turbulence intensity. The complex equilibrium in the near wake is a concept that has to be more investigated and how perturbations, as turbulence contained in main stream, play a role in this equilibrium remains to be investigated more fully.

for the balances of a unit mass element. The relevant processes are heating and cooling, vertical motion, friction, motion up or down a pressure gradient, and the total pressure work.What does the heating Q correspond to in the atmosphere? As noted by Panofsky (1978 (c)), the major agencies of heating are radiative flux convergence, and latent heat release in condensation of water vapour; the reverse processes are agencies of cooling. Frictional dissipation (see Fig. 4), whereby bulk flow KE is 'degraded' into IE by molecular viscosity, contributes only to the heating. Molecular conduction can contribute heating or cooling, but is generally unimportant except very close to material surfaces. All these processes occur on the molecular scale and thus tally with the usual thermodynamic picture of heating. Frequently, however, Q is extended to include the convergences or divergences of fluxes carried by eddy motion occurring on a smaller space scale than that of the 'element' of air which is under consideration.Our survey of the energy balances for a single fluid element is now complete. In Part I1 we shall consider the energy balances for the entire volume of a fluid systemthe balances formed by adding together the contributions of every fluid element in the system. REFERENCES ATKINSON, B. W. PANOYSKY, H. A.

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