An experiment on the flow past a finite circular cylinder at high subcritical and supercritical Reynolds numbers

Abstract

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.

Experimental investigation on the aerodynamic loads and wake flow features of a low aspect-ratio circular cylinder

“…The lowest Strouhal number, about 0.08, was found in correspondence to the cell located in proximity to the model free-end, whereas for the remaining cells the associated Strouhal number increases by moving towards the model base. A lower frequency, about half of the one corresponding to vortex shedding, was also found by Ayoub and Karamcheti (1982) for a model with h=d % 12 and tested at Re % 0:85 Â 10 5 . A cellular vortex shedding with a lower frequency of St % 0:07 was observed in Khalak and Williamson (1996) for cylinders with aspect-ratio 8.5 and 10.…”

“…The wakes of finite circular cylinders in cross-wind are dominated by the velocity fluctuations induced by the alternate vortex shedding from the body sides, as documented by Farivar (1981), Ayoub and Karamcheti (1982), Fox et al (1993), Bearman (2011), Griffith et al (2011), Suthon and Dalton (2011) and Visscher et al (2011), in which the presence of clear vortex shedding from most of the cylinder span, with frequencies of the same order as those typical of twodimensional flow, was found for models with aspect-ratio h=d 4 10 (where h is the cylinder height and d its diameter). However, a decrease of the frequency was found in a zone approaching the upper end of the cylinders, probably due to an increase in the formation length of the shed vortices.…”

“…Besides the vortex shedding frequency, in the wake flow several authors (see e.g. Ayoub and Karamcheti, 1982;Farivar, 1981;Khalak and Williamson, 1996;Luo et al, 1996) detected another spectral component in the wake flow, which is characterized by a lower frequency and is connected with the dynamics of vorticity structures originated over the model free-end. Conversely, for the present velocity measurements a low spectral component is not found, which is most probably due to the low aspect-ratio, h/d ¼3, of the analyzed model.…”

Aerodynamic correlation of linked buildings

“…This is because the flow around the top is complicated, which can be attributed to downwash from the tip flow which disrupts the organized structure of wake fluctuations, resulting in the positive, albeit slight, correlation. Similar trends were noted by Ayoub and Karamcheti (1982) and Kareem et al (1989). Consequently, the negative correlation around the top of the building is weak, even becoming positive.…”

Time–frequency analysis of the dynamics of different vorticity structures generated from a finite-length triangular prism

“…Considering circular cylinders, pressure and velocity measurements have shown the presence of clear vortex shedding from most of the cylinder span with Strouhal numbers of the same order as those typical of 2D flows (see e.g. Farivar, 1981;Ayoub and Karamcheti, 1982;Fox et al, 1993). However, a lower frequency was found in a zone approaching the free-end of the cylinders and in Park and Lee (2000) these fluctuations were shown to be associated with a couple of counter-rotating streamwise vortices originating from the model free-end.…”