Experiments on the flow past a circular cylinder at very high Reynolds number

Measurements on a large circular cylinder in a pressurized wind tunnel at Reynolds numbers from 10^6 to 10^7 reveal a high Reynolds number transition in which the drag coefficient increases from its low supercritical value to a value 0.7 at R = 3.5 × 10^6 and then becomes constant. Also, for R > 3.5 × 10^6, definite vortex shedding occurs, with Strouhal number 0.27

On the problem of turbulence

A central theme in the history of the turbulence problem is about the method of ‘closure’ in the models and ‘theories’ which have been proposed. Closure has invariably been by empirical calibration with experimental data. In this note we draw attention to a paper by Morris, Giridharan and Lilley, in which for the first time empiricism is obviated. For the turbulent mixing layer, this is accomplished by including in its description the mechanism for production of turbulent shear stress (i.e. turbulent momentum transfer), by large-scale instability waves. Some implications for the theory of turbulent shear flows are discussed

The compressible turbulent shear layer: an experimental study

The growth rate and turbulent structure of the compressible, plane shear layer are investigated experimentally in a novel facility. In this facility, it is possible to flow similar or dissimilar gases of different densities and to select different Mach numbers for each stream. Ten combinations of gases and Mach numbers are studied in which the free-stream Mach numbers range from 0.2 to 4. Schlieren photography of 20-ns exposure time reveals very low spreading rates and large-scale structures. The growth of the turbulent region is defined by means of Pitot-pressure profiles measured at several streamwise locations. A compressibility-effect parameter is defined that correlates and unifies the experimental results. It is the Mach number in a coordinate system convecting with the velocity of the dominant waves and structures of the shear layer, called here the convective Mach number. It happens to have nearly the same value for each stream. In the current experiments, it ranges from 0 to 1.9. The correlations of the growth rate with convective Mach number fall approximately onto one curve when the growth rate is normalized by its incompressible value at the same velocity and density ratios. The normalized growth rate, which is unity for incompressible flow, decreases rapidly with increasing convective Mach number, reaching an asymptotic value of about 0.2 for supersonic convective Mach numbers

An experimental study of geometrical effects on the drag and flow field of two bluff bodies separated by a gap

This paper describes an experimental investigation of the shielding effects of various disks placed coaxially upstream of an axisymmetric, flat-faced cylinder. Remarkable decrease of the drag of such a system was observed for certain combinations of the basic geometric parameters, namely the diameter and gap ratios. For such optimum shielding the stream surface which separates from the disk reattaches smoothly onto the front edge of the cylinder, in what is close to a ‘free-streamline’ flow; alternatively, the flow may be viewed as a cavity flow. For the optimum as well as other geometries, flow pictures, pressure distributions and some LDV measurements were also obtained. From these, several flow regimes depending on the gap/diameter parameters were identified. Variations on the axisymmetric disk–cylinder configuration included a hemispherical frontbody, rounding of the front edge of the cylinder and a change from circular to square cross-section

On the Effect of Air Pressure on Strouhal Number

The experimental measurements of reference 1 show an effect of free-stream pressure on Reynolds Number relation for a vortex-shedding cylinder

Some Measurements of Flow in a Rectangular Cutout

The flow in a rectangular cavity, or slot, in the floor or a wind tunnel is described by the results or pressure and velocity measurements. Pressure distributions on the cavity walls as well as measurements of friction are presented. The effects of varying depth-breadth ratio are shown

The effect of a density difference on shear-layer instability

Measurements of mass flow rate and mean density have been made in separated laminar boundary layers with large transverse density gradients. Two-dimensional shear layers were formed by exhausting a half-jet of one gas into a reservoir of another gas with a different molecular weight. Two freons with a density ratio of 1-98 and unusual properties which permitted the measurement of the mass flow rate with a single hot wire were used. A n analysis of the mass flow rate fluctuations showed that a negative density gradient (i.e. light gas flowing into heavy) increases the amplification rate of the instability oscillations and reduces the frequency and wave number. Opposite trends were observed when the density gradient was positive. These findings are in agreement with recent theoretical predictions

On density effects and large structure in turbulent mixing layers

Plane turbulent mixing between two streams of different gases (especially nitrogen and helium) was studied in a novel apparatus. Spark shadow pictures showed that, for all ratios of densities in the two streams, the mixing layer is dominated by large coherent structures. High-speed movies showed that these convect at nearly constant speed, and increase their size and spacing discontinuously by amalgamation with neighbouring ones. The pictures and measurements of density fluctuations suggest that turbulent mixing and entrainment is a process of entanglement on the scale of the large structures; some statistical properties of the latter are used to obtain an estimate of entrainment rates. Large changes of the density ratio across the mixing layer were found to have a relatively small effect on the spreading angle; it is concluded that the strong effects, which are observed when one stream is supersonic, are due to compressibility effects, not density effects, as has been generally supposed

Small is good

Dave Belden's letter announcing the award was really a surprise, almost a shock. At first l wondered whether it was another example of a story which you may have heard and which, I believe, originated in the FSU. Two friends are at a grand reception sipping cocktails when one notices a man with his chest almost completely covered with medals. Says one to the other, "Do you have any idea what those medals are for?" and the other replies ... Well, you see that one at the top left? That one was a mistake: and the others followed automatically ... I humored myself out of that thought but not out of a feeling of guilt. You see, I suddenly felt terrible that I was not a member of the ASME. There had been opportunities but somehow l had let them go by. One reason is that I was concerned about another onslaught of communications, information and other paper that always results and require attention. Fortunately, ASME lost no time in relieving my guilt. In a few weeks I received a nice invitation and forms to fill out, and am I am Member No. 6143358. And sure enough, information has begun to roll in: a beautiful, glossy magazine, notice of various meetings, etc