The effects of tunnel blockage and aspect ratio on the mean flow past a circular cylinder with Reynolds numbers between 104 and 105

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 6y0, it is shown that the effects of blockage on pressure distribution and the drag coefficient arc small and that the Strouhal number is unaffected by blockage. For blockage ratios in the range 6-lSyo, 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.However, conflicting influences result in a blocked drag coefficient which is not verydifferent from that at no blockage. Reduction in aspect ratio has effects on dragcoefficient 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

Simulation of wind flow around three-dimensional buildings

In this paper results from a computer simulation of wind flows around prismatic bodies using a k-ε{lunate} model of turbulence are compared with full scale and wind tunnel tests done by others. The agreement is good, both in the wake region and elsewhere, and is particularly good for flow around a cube in which the overall error level in both pressures and velocities is about 5-10%. This is comparable with the error achievable with well controlled wind tunnel tests

On the estimation of the optimum accelerator for sor applied to finite element methods

A simple procedure is described which provides a numerical estimate of the optimum accelerator for the successive overrelaxation (SOR) process when applied to finite element methods. The procedure has been applied successfully in a number of controlled experiments, and the results of three of these are presented in detail. Comparison with finite difference methods shows that it may be possible to predict a sharp estimate of the optimum accelerator before computation begins

Fluctuating lift and drag forces on finite lengths of a circular cylinder in the subcritical Reynolds number range

Spanwise cross-correlations of fluctuating pressures and of elemental fluctuating forces have been measured on long smooth circular cylinders with end plates in the central part of the span where "long" cylinder conditions exist. The data have been obtained at subcritical Reynolds numbers over the range 104 to 2·1 × 105 for blockage ratios 0·0425, 0·06 and 0·095 and at turbulence levels of 0·002, 0·0125, 0·03, 0·055 and 0·075. By use of the cross-correlation curves, factors have been calculated which allow the r.m.s. force coefficients for finite lengths of "long" cylinders to be derived from elemental force coefficients. These conversion factors have been applied to previously measured elemental force coefficients to produce coefficients of r.m.s. forces for finite lengths of cylinder up to 50 diameters for the ranges of conditions detailed above

Shap eeffects on resistance to uniform flow in open channels

The effects of the shape of the cross-section on flow resistance in open channels has received considerable attention from hydraulic engineers for many years. Many investigators have tried to introduce parameters to represent the cross-section shape effect but their results have been inconclusive. Some of the techniques previously used to deal with this problem are reviewed and their shortcomings are discussed. A new method for dealing with shape effect is developed in this paper from considerations of dimensional analysis and using the experimental data of TRACY and LESTER and of SHIH and GRIGG. This method, which is referred to as KAZEMIPOUR’S method, employs new parameters more representative of the effect of cross-sectional shape on flow resistance in open channels than those previously used and offers solutions more rational than those previously proposed. The shape factor developed is Y = Y1/Y2, where Y1, equal to (Equation presented), reflects the effects of non-uniform distribution of shear stress on the boundary as the shape of cross-section departs from an infinitely wide rectangle and Y2., is a function of the width/average depth, or aspect ratio of the cross-section. It is demonstrated that application of this shape factor shifts the experimental data for open channel resistance on to the universal diagrams for flow resistance in circular pipes for a variety of cases. The shape factor establishes a simple correlation between open channel and pipe flow and permits the universal resistance diagrams and formulae available for pipe flow to be used to calculate the friction factor and average velocity in open channel flow. The effectiveness of the method has been demonstrated for smooth turbulent flow in rectangular, triangular and trapezoidal cross-sections and for rough and transitional turbulent flow in rectangular cross-sections and this suggests that its applicability may be much wider

Measurements of Fluctuating Pressures and Forces on a Circular Cylinder in the Reynolds Number Range 104 to 2·5 × 105

Experiments have been carried out on long, smooth, circular cylinders to establish accurate data on the fluctuating pressure distributions and r.m.s. lift and drag forces in sub-critical flow (10