Transient behaviour of decelerating turbulent pipe flows

This investigation characterises the time response and transient turbulence dynamics undergone by rapidly decelerating turbulent pipe flows. A series of direct numerical simulations flows between two steady Reynolds numbers were conducted for this purpose. The statistical analyses reveal that undergo four coherent, unambiguous transitional stages: inertial (stage I), a dramatic change sign in viscous force associated with decay shear stress at wall together mild sublayer; friction recovery II), progressive inertia near-wall region; III), balanced both overlap regions; core relaxation IV), slow region. FIK identity derived Fukagata, Iwamoto Kasagi ( Phys. Fluids , vol. 14, 2002, L73–L76) was used to understand further how flow influence skin coefficient $C_f$ ). results show although plateaus during fourth stage, contribution keeps decaying, undershoots finally recovers attain its final value. evolution azimuthal vorticity $\omega _\theta$ ) flux reveals as is decelerated, layer negative produced excursion. As progresses, propagates wall-normal direction, attenuating pre-existing producing levels.