Influence of channel bend angle on the turbulent statistics in sharply bent channel flows

Turbulence in wall-bounded flows shows a wide range of regimes, where the interaction between scales significantly occur. Reynolds number is used to characterize the dynamics of fluid corresponding to single phase channel flows. Meanwhile, different flow behavior exists in curved channels even at fixed Reynolds number, where the curvature varies as shown by Brethouwer [Turbulent flow in curved channels, J. Fluid Mech. 931, A21 (2022)]. In the present study, we show how wall-bounded turbulent flow behaves on sharply bending the channel by investigating the time averaged velocity profiles at the straight section, at the bend, and in the inclined section. The well-known logarithmic behavior of the time averaged normalized velocity profile is retained, where the von Karman and the additive constants assume altered values depending on the sharp bend inclination. The near-wall fluctuations at the bend are enhanced, which is due to diffusion of counter-rotating vortices leading to increased turbulent activity. In terms of spatial structure of the random fluctuating field, the two-point correlation statistics suggest that multiple high speed and low speed streak pairs are generated, and there are multiple streamwise vortices of different sizes when bend inclination is increased. Budgets of turbulent kinetic energy are presented for various inclinations of the bend at different sections of the bend channel, which depicts that turbulent kinetic energy is modulated at the bend.

Automated summary

This study investigates the behavior of wall-bounded turbulent flow on sharply bending channels. The time averaged velocity profiles at different sections of the channel show that the well-known logarithmic behavior is retained, but the values of the von Karman and additive constants change with increasing bend inclination. The near-wall fluctuations are enhanced at the bend due to diffusion of counter-rotating vortices. The spatial structure of the random fluctuating field exhibits the generation of multiple high speed and low speed streak pairs, as well as multiple streamwise vortices of different sizes when the bend inclination is increased. Turbulent kinetic energy is modulated at the bend as depicted by the budgets presented for various inclinations of the bend at different sections of the channel.