6 papers
Analysis of inviscid shear instability of axisymmetric flows
Kengo Deguchi, Haider Munawar, Runjie Song
Simple analytical criteria are derived to determine whether axisymmetric base flows in annuli and pipes are stable or unstable. Both axisymmetric and non-axisymmetric inviscid dist…
Multiscale quasi time-periodic coherent structures in shear flows
Runjie Song, Kengo Deguchi, Genta Kawahara +1
Attempts to disentangle shear-flow turbulence often focus on identifying relatively simple solutions, such as travelling waves or periodic orbits. We show, however, that capturing…
Beyond secondary instability: on the emergence of finite-amplitude waves in Görtler vortices
Runjie Song, Kengo Deguchi
Görtler vortices developing over a concave wall support rapidly oscillating wavelike disturbances through secondary instabilities. Although experiments indicate that the finite-am…
Linear and nonlinear instabilities in highly shear thinning fluid flow through a pipe
Xuerao He, Kengo Deguchi, Runjie Song +1
Shear-thinning fluids flowing through pipes are crucial in many practical applications, yet many unresolved problems remain regarding their turbulent transition. Using highly robus…
Spatial marching with subgrid-scale local exact coherent structures in non-uniformly curved channel flow
Runjie Song, Kengo Deguchi
We propose a novel multiple-scale spatial marching method for flows with slow streamwise variation. The key idea is to couple the boundary region equations, which govern large-scal…
Three-dimensional coherent structures in a curved pipe flow
Runjie Song, Kengo Deguchi
Dean's approximation for curved pipe flow, valid under loose coiling and high Reynolds numbers, is extended to study three-dimensional travelling waves. Two distinct types of solut…