Fundamental studies on free stream acceleration effect on drag force in bluff bodies

Abstract

This paper describes fundamental studies on free stream acceleration effect on drag force in bluff bodies. The flow with gradual velocity increase assumed an accelerated flow. The wind tunnel tests were conducted in order to investigate the difference of aerodynamic characteristics between non-accelerated flow and accelerated flow. The experimental models were a circular cylinder and a square cylinder. In an accelerated flow, the condition of free stream was an acceleration of about 3.6m/s 2 . Experimental Reynolds number varied between form 4.0×10 4 to 1.64×10 5 . The pressure distributions and the aerodynamic force were measured in both case of nonaccelerated flow and accelerated flow. In case of a circular cylinder, the drag of accelerated flow is lower than that of non-accelerated flow in the low Reynolds number regime. Then, it becomes higher than that of non-accelerated flow in the high Reynolds number regime. On the other hand, in case of a square cylinder, the drag of accelerated flow is higher than that of non-accelerated flow in the whole Reynolds number regime. If a separation point can be movable such as the circular cylinder, the additional momentum due to flow acceleration leads to delay separation and to decrease the drag in the low Reynolds number regime. If a separation point is nearly fixed such as a square cylinder, the additional momentum due to acceleration always affects to increase the drag than that of non-accelerated flow. Based on this research, it is expected that the roof shape of high speed train where the separation point is movable has the advantages to reduce the effect of accelerated flow such as strong crosswind/gust.

Effects of highly pulsatile inflow frequency on surface-mounted bluff body wakes

“…Geophysical flows as a whole are often unsteady or impulsive. While often of a higher Re, coastal flows and studies of gusts share some physics with this investigations and could be informed by it (Mei & Liu 1993;Lee et al 2011;Hench & Rosman 2013). In addition to steady flows around bluff bodies, oscillatory flows and impulsively started flows there are other fluid dynamics phenomena which provide some background to the present study.…”

“…While often of a higher , coastal flows and studies of gusts share some physics with this investigations and could be informed by it (Mei & Liu 1993; Lee et al. 2011; Hench & Rosman 2013).…”

Optimal Shape of Blunt Device for High Speed Vehicle

“…On the other hand, in the cases of the rectangular contact strip and a streamlined contact strip, although the Reynolds number increases from 50,000 to 4×10 5 , the drag coefficient of the rectangular shape changes little because the separation point does not move and a vortex is still generated in high Reynolds number regions. Also, the drag coefficient of the streamlined contact strip is almost constant even in high Reynolds number regions, unlike to that of the rectangular shape [21]. Therefore, it is reasonable that the results of the general rectangular contact strip and the optimized contact strip at the Reynolds number of 50,000 would still remain valid in the real condition.…”

New Numerical and Measurements Flow Analyses Near Radars

“…Blunt body flow analyses are very important in Engineering. Most bodies and structures do not present a streamlined shape; for this reason, an accurate analysis of wake regions would lead to a major understanding of turbulence flows and turbulence reduction mechanisms [1]. Blunt bodies in turbulent flow conditions can lead to material fatigue and damage, and therefore, to increased drag and energy consumption.…”