The Aerodynamic Characteristics of a Circular Cylinder with Tangential Blowing in Uniform Shear Flows.

Uniform-shear flow over a circular cylinder at low Reynolds numbers

“…In the case of shear rate, the mean drag remains nearly constant for low shear rates, and then slightly decreases with increasing shear rate for K\0:1. The variation behavior agrees well with those of previous studies (Kwon et al, 1992;Hayashi et al, 1993;Lei et al, 2000;Sumner and 2003). In addition, with increasing blockage ratio, the mean drag greatly increases regardless of the Reynolds number and shear rate, which implies that the blockage effect plays an important role in the characteristics of uniform-shear flow over a circular cylinder.…”

“…In the case of a positive shear rate ðK40Þ, the mean lift coefficient is negative ðC L o0Þ all over the ranges of the Reynolds number and blockage ratio considered in the present study, indicating that the mean lift is exerted from the side of the higher free-stream velocity to that of the lower one. Despite the difference in the Reynolds number, the present results agree well with those of Jordan and Fromm (1972), Hayashi et al (1993), Lei et al (2000), and Sumner and Akosile (2003), but substantially differ from those of Tamura et al (1980), Yoshino and Hayashi (1984), and Wu and Chen (2000). Such discrepancies were also pointed out by Lei et al (2000) and Sumner and Akosile (2003), but a plausible reason has not yet been forthcoming.…”

“…Therefore, more systematic study on the shear flow is required for further improved understanding of engineering bluff-body flows. For such a study, the Jordan and Fromm (1972) 400 See caption % 0 CFD Tamura et al (1980) 40; 80 020:4 % 0 CFD Kiya et al (1980) 3521500 020:25 2:7217 EM Yoshino and Hayashi (1984) 80 020:4 % 0 CFD Kwon et al (1992) 60021600 020:25 6:7216 EM Hayashi et al (1993) 6 Â 10 4 020:045; 0:15 6:7 E M Wu and Chen (2000) À 022:67 % 0 CFD Lei et al (2000) 8021000 020:25 12:5 CFD Sumner and Akosile (2003) 429 Â 10 4 0:0220:07 1:822:7 E M CFD ¼ computational fluid dynamics, EM ¼ experimental measurement. Jordan and Fromm (1972) used the time-averaged flow of a turbulent jet for the uniform-shear flow case.…”

“…The direction of the mean lift force has also to be addressed with regard to the conflicting issues among previous studies. Jordan and Fromm (1972), Hayashi et al (1993), Lei et al (2000) and Sumner and Akosile (2003) claimed that the mean lift was exerted from the side of the higher free-steam velocity to that of the lower one, whereas Tamura et al (1980) and Yoshino and Hayashi (1984) asserted that it was in the opposite direction. In addition, Wu and Chen (2000) argued that the mean-lift direction should vary depending on the magnitude of shear rate.…”

Staggered circular cylinders immersed in a uniform planar shear flow

“…The velocity gradient of the uniform shear flow is characterized by a dimensionless shear parameter, K ¼ AD=U C : The shear parameter identifies a flow as having no shear (K ¼ 0), low to moderate shear (K being small), or strong shear (K being large), although there is no commonly accepted definition of what constitutes low, moderate or strong shear. Previous experimental studies have shown that a uniform planar shear flow causes the circular cylinder to experience a lower mean drag force than in a uniform flow (Adachi and Kato, 1975;Hayashi et al, 1991Hayashi et al, , 1993Kwon et al, 1992;Sumner and Akosile, 2002); the mean drag force is represented by the dimensionless drag coefficient, C D ð¼ 2F D =rU 2 C DL; where F D is the mean drag force, r is the fluid density, and L is the span of the cylinder). The shear flow also causes an asymmetric mean static pressure distribution on the surface of the cylinder, which results in a small steady mean lift force directed towards the low-velocity side (Adachi and Kato, 1975;Hayashi et al, 1991Hayashi et al, , 1993Sumner and Akosile, 2002); the mean lift force is represented by the dimensionless lift coefficient, C L ð¼ 2F L =rU 2 C DL; where F L is the mean lift force).…”