The complicated flow in the tip region of a finite circular cylinder in uniform cross flow has been examined at the Reynolds numbers 0·85 × 105, 1·8 × 105, and 7·7 × 105. Simultaneous measurements of the surface-pressure and wake-velocity fluctuations have revealed the existence of a shedding regime in the tip region that is distinct from the one prevailing on the main body of the cylinder. In particular, this regime can be unstable and intermittent, can have a cellular structure in the wake, or can be subcritical when the main flow is supercritical.

A spectral study of a hot-wire investigation in the near wake of a finite circular cylinder of high-aspect ratio is reported. The measurements included frequency spectra and cross correlations in span wise and stream wise directions. The study identifies four spanwise regions, in terms of frequency, in the immediate wake of the finite cylinder.Nomenclature D = diameter of circular cylinder d f = wake width at end of formation region / = frequency of vortex shedding / = length of circular cylinder l f = formation length R xy (T) = cross-correlation function UQ = freestream speed x = streamwise coordinate (see Fig. 1) y = crosswise coordinate perpendicular to span of cylinder (see Fig. 1) z = spanwise coordinate (see Fig. 1) T = time

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ResultsThe typical case considered is for a freestream Mach number of 2.0, a Reynolds number of 0.296X 10 6 based on the distance X SHK from the leading edge to the shock impingement point, and an incident shock angle of 32.585 deg. 4 For this set of data, the shock is strong enough (pressure ratio =1.4) to trigger separation. The computation was done for five cases: 1) no suction along the wall, 2) normal suction, 0 = 90 deg at the location from X/X SHK = 0.7817 to 1.1569,3) vectored suction, 0 = 45 deg at the locations as in case 2, 4) normal suction from X/X SHK = Q.1\92 to 0.8442, and 5) vectored suction at the same locations as in case 4.The computed surface pressure distribution in the interaction region is presented in Fig. 2. For the vectored upstream suction case 5, the pressure jump is closes to the inviscid flow conditions case and reaches its postshock value quite smoothly. It is interesting to note that the pressure rise is steeper than that corresponding to normal suction. Though the pressure plateau indicating separation has vanished for all the examples in which suction is considered, the upstream vectored suction has a minimum effect in the downstream direction (Fig. 3).This study indicates that the upstream vectored suction not only eliminates separation but that its influence in the neighborhood is limited. If the prior knowledge of separation bubble location is not available or some minor changes in the input data are required, a judicious choice of upstream vectored suction can control the flow effectively. However, a detailed assessment regarding the locations, rates, and angles, for such suction should be carried out to optimize its fruitful usage.