Pressure and force distributions on a sharp-nosed circular cylinder at large angles of inclination to a uniform subsonic stream

Abstract

This paper reports an experimental investigation of pressure and force distributions on a sharp-nosed circular cylinder inclined to a uniform low-speed air flow under conditions of laminar separation of the boundary layer. The main concern is with the out-of-plane force (i.e. the side force if the body is at incidence). The experimental model consisted of an extensively pressure-tapped cylinder to which four different noses were fitted. The results show that there is an oscillatory distribution of out-of-plane force along the cylinder for most of the inclination range 0-90°. The amplitude of this distribution is strongly affected by nose shape in conditions where the out-of-plane force extends onto the nose. At very high angles of inclination the oscillatory distribution disappears and is replaced by a vortex pattern like that found on an infinite yawed cylinder. The general nature of the out-of-plane force is found to be consistent with the impulsively started flow analogy. Unsteadiness in the flow was found to cause a serious reduction in many of the time-averaged values. The unsteadiness is ascribed to the switching of the flow pattern due to free-stream turbulence. Measurements of the time histories of certain pressures enabled values of the force in the unswitched state to be calculated. The Reynolds number was found to have an important influence at inclinations above 55°. However, it was also found that the range of Reynolds numbers over which this effect occurs can depend on the scale of the model.

Recent progress on the study of asymmetric vortex flow over slender bodies

“…Lamont and Hunt [32], Dexter and Hunt [33] were among the first to propose some influence factors which may lead to the repeatability problem for wind tunnel test results. The first factor: Lamont and Hunt [32] found that the freestream turbulence of wind tunnels may cause the switching of the asymmetric vortex into their mirror image states if the turbulence level is large enough, resulting in the repeatability problem. Therefore they proposed that this kind of experimental test should be carried out in a low turbulence wind tunnel.…”

“…As mentioned above, the roll angle effect on the asymmetric vortex flow over slender bodies has been studied extensively by many scholars [18,[29][30][31][32][33][34][35]. The research group [18,29,[32][33][34] leaded by Hunt was among the earliest to work on this flow phenomenon.…”

“…A great difficulty has been experienced in repeating the test results during the wind tunnel experiments for a pointed slender body model at high angle of attack [18,[28][29][30][31][32][33][34][35]. Large discrepancies exist between the results obtained by different investigators and even between the tests performed by the same investigator.…”

Three-dimensional boundary layer and vortex wake over a cone at high angle of attack: study of asymmetries

“…Different means are used to reduce asymmetries or to remove them: e.g., roughness on the pointed body surface can be used (Lamont and Hunt 1976;Ericsson and Reding 1981;Modi et al 1984); blunting near the nose, or adding modifying elements (such as strakes, helical trips, nose booms .... ) are worthy solutions (Modi et al 1984;Stahl 1990;Rao 1977;Coe et al 1972;Sarpkaya 1966). Finally, the lateral forces and moments can be suppressed by blowing near the nose (Cornish and Jenkins 1978;Skow and Peake 1982;Mourtos and Roberts 1987).…”

Holographic Investigation of Slender Body Vortex Wakes.

“…Previous experimental investigations of the flow behind a missile at high angle of attack have shown that the asymmetric vortex wake and resulting side force is sensitive to roll angle and tunnel turbulence level (1)(2)(3)(4). In addition, it is known that for some angles of attack, the vortices may be bi-stable; the asymmetric vortex structure may suddenly switch from one stable state to another (3)(4)(5).…”