NDLI: Direct Numerical Simulation of an Accelerating Channel Flow

Content Provider	Springer Nature Link
Author	Seddighi, M. He, S. Vardy, A. E. Orlandi, P.
Copyright Year	2013
Abstract	Direct Numerical Simulation of a linearly accelerating channel flow starting from an initially statistically steady turbulent flow has been performed. It is shown that the response of the accelerating flow is fundamentally the same as that of the step-change transient flow described in He and Seddighi (J Fluid Mech 715:60–102, 2013). The flow structure again behaves like a boundary layer bypass transition undergoing three distinct phases, namely, (i) initially (pre-transition), the flow is laminar-like and the pre-existing turbulent structures are modulated resulting in elongated streaks leading to a strong and continuous increase in the streamwise fluctuating velocity but little changes in the other two components; (ii) it then undergoes transition when isolated turbulent spots are generated which spread and merge with each other, and (iii) they eventually cover the entire surface of the wall when the flow is fully turbulent. The similarity between the turbulence responses in the two flows is significant noting the contrasting features of the two types of mean flow unsteadiness: in the step-change flow, a sharp boundary layer is resulted in nearly instantly on the wall which closely resembles the spatially developing boundary layer, whereas the linear flow acceleration causes a continuing change of velocity gradient adjacent to the wall which propagates into the flow field with time, resulting in a gradually-developing boundary layer. There are, however, quantitative differences in the detailed behavior of the two flows and especially the transition is much delayed in the accelerating flow. It is also shown that the late pre-transition and early transition stages in both flows are characterised by significantly increased inwards sweep events in the wall region and ejection events in the outer layer. The flatness of the wall-normal velocity increases markedly near the wall around the time of onset of transition as a consequence of the huge intermittency of the velocity fluctuations. That is, there are long periods of quiescent flow coupled with occasional turbulent bursts.
Starting Page	473
Ending Page	502
Page Count	30
File Format	PDF
ISSN	13866184
Journal	Flow, Turbulence and Combustion
Volume Number	92
Issue Number	1-2
e-ISSN	15731987
Language	English
Publisher	Springer Netherlands
Publisher Date	2013-10-25
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Unsteady Turbulence Transition Channel flow Engineering Fluid Dynamics Fluid- and Aerodynamics Engineering Thermodynamics, Heat and Mass Transfer Automotive Engineering
Content Type	Text
Resource Type	Article
Subject	Physics and Astronomy Physical and Theoretical Chemistry Chemical Engineering

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