Large-eddy simulations of temporally accelerating turbulent channel flow

Abstract

The unsteady turbulent channel flow subject to the temporal acceleration is considered in this study. Large-eddy simulations were performed to study the response of the turbulent flow to the temporal acceleration. The simulations were started with the fully developed turbulent channel flow at an initial Reynolds number of Re₀ = 3500 (based on the channel half-height and the bulk-mean velocity), and then a constant temporal acceleration was applied. During the acceleration, the Reynolds number of the channel flow increased linearly from the initial Reynolds number to the final Reynolds number of Re₁ = 22,600. The effect of grid resolution, domain size, time step size on the simulation results was assessed in a preliminary study using simulations of the accelerating turbulent flow as well as simulations of the steady turbulent channel flow at various Reynolds numbers. Simulation parameters were carefully chosen from the preliminary study to ascertain the accuracy of the simulation. From the accelerating turbulent flow simulations, the delays in the response of various flow properties to the temporal acceleration were measured. The distinctive features of the delays responsible for turbulence production, energy redistribution, and radial propagation were identified. Detailed turbulence statistics including the wall shear stress response during the acceleration were examined. The results reveal the changes in the near-wall structures during the acceleration. A self-sustaining mechanism of turbulence is proposed to explain the response of the turbulent flow to the temporal acceleration. Although the overall flow characteristics are similar between the channel and pipe flows, some differences were observed between the two flows.

Keywords:

• temporal acceleration
• unsteady flow
• channel flow
• large-eddy simulation

Acknowledgements

The research leading to these results has received support from the European Union Seventh Framework Programme FP7/2007-2013 AirPROM (Grant Agreement FP7 270194, www.airprom.eu). The support from the UK Turbulence Consortium (Grant EP/G069581/1, EP/L000261/1) is also acknowledged. This work used the HECToR and ARCHER, the UK National Supercomputing Service (http://www.archer.ac.uk).

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

The research leading to these results has received support from the European Union Seventh Framework Programme FP7/2007-2013 AirPROM [grant agreement FP7 270194, www.airprom.eu]. The support from the UK Turbulence Consortium [grant EP/G069581/1, EP/L000261/1] is also acknowledged.