Transient Flow Lab
Learn more about the Transient Flow Lab
The Transient Flow Lab (TFL) undertake research in the area of general Fluid Mechanics and in particular on unsteady turbulent flow. Numerical and experimental approaches are being used to investigate wide range of applied as well as fundamental flow problems. The main research interests are as below:
• Unsteady turbulent flow (Numerical: DNS/LES; Experiment: PIV/LDV) (Smooth-wall, Rough wall)
• Blood flow
• Marine Renewable Energy
• Turbulent flow over rough surfaces
Study of transient-transient turbulent flow over rough surfaces
Direct numerical simulation is performed of a transient flow in a channel consisting of a rough bottom wall made of close-packed 3-D pyramid roughness and a smooth top wall. The unsteady flow started from an initially statistically steady turbulent flow with and increased linearly, within a very short time, to a final Reynolds number ranging from. The corresponding equivalent sand roughness Reynolds for the initial and final flows are respectively and . The research is looking into study unsteady flow behaviour in the transitionally-rough regime.
Figure 2. Turbulent-turbulent transient flow over rough surface.
Turbulent drag reduction over backswimmer textured surfaces
Using Direct Numerical Simulations DNS, this study examines the turbulent drag reduction for the novel implementation of the Backswimmer insect inspired texture geometry. Simulations are performed for a channel flow at low friction Reynolds number (Re = 180). Turbulence statistics and the detailed flow structures are compared against those used for the smooth channel flow. Preliminary results shows drag reduction (DR) of 20%.
High Performance Computing (HPC)
We use national, regional and Faculty-level high-performance computing (HPC) facilities. Our Faculty’s and departmental Linux-base HPC computer clusters comprise ~400 computational cores which are continuously being under development to be upgraded to higher computational cores.
STOKES is our local High Performance Computing (HPC) resource. It provides computing capabilities for our students and researchers within the centre.
CHAPSim is an in-house CFD package which simulate channel and pipe flow using state-of-the-art DNS/LES approaches. It has mainly been developed by Dr Mehdi Seddighi, (Seddighi, 2011, He and Seddighi, 2013) based on the methods/subroutines proposed by Orlandi (2001); some further developments of the code have been carried out through contributions made by few PhD students and Post-docs under supervision of Dr Mehdi Seddighi and Prof. Shuisheng He (University of Sheffield).A second order central finite difference method is used to discretize the spatial derivatives of the governing equations on a rectangular grid, where a three-dimensional staggered mesh is employed with a non-uniform spacing in the direction normal to the wall. For the time advancement, a low storage third-order Runge-Kutta scheme is used for the non-linear terms and a second order Crank-Nicholson scheme is used for the viscous terms, which are combined with a fractional-step method described by (Orlandi, 2001, Kim and Moin, 1985). The Poisson equation for the pressure is solved by an efficient 2-D FFT (Orlandi, 2001). The roughness is treated using an immersed boundary method (IBM). A hybrid method of Message-Passing Interface (MPI) and Open Multi-Processing (OpenMP) is used to parallelize the code. Alongside with the solver, CHAPSim includes post-processing subroutines which calculates various order of turbulence statistics and also quantities for flow visualizations; the subroutines in particular, are tailored to study transient flows. The code has successfully been using on several computer clusters including STOKES, ICEBERG, ShARC, POLARIS, HECToR and ARCHER.
Experiments are carried out in a closed return wind tunnel at the Byrom Street Campus at Liverpool John Moores University. The working test section of the wind tunnel is 0.4m wide by 0.4m high. The normal range of air velocity is 0 to 35 m/s. The wind tunnel is equipped with a Plint and Partners Ltd. three component balance to measure various components of aerodynamic forces.
Seddighi M, He S. 2017. Turbulent-turbulent transient flow in a transitionally rough regime International Symposium on Turbulence and Shear Flow Phenomena, TSFP10
Khosh Aghdam S, Ricco P, Seddighi M. 2015. Turbulent drag reduction by hydrophobic surfaces with shear-dependent slip length 15th European Turbulence Conference
Seddighi M, He S, Vardy AE, O’Donoghue T, Dubravka P. 2015. Near-wall behaviour of transient flow in a channel with distributed 3-D roughnessInternational Symposium on Turbulence and Shear Flow Phenomena, TSFP9
Seddighi M, He S. 2012. Turbulence structure in a rapidly accelerating channel flow
Mathur A, Seddighi M, He S. 2018. Transition of Transient Channel Flow with High Reynolds Number Ratios Entropy, 20(5) >DOI
Mathur A, Gorji S, He S, Seddighi M, Vardy AE, ODonoghue T, Pokrajac D. 2018. Temporal acceleration of a turbulent channel flow Journal of Fluid Mechanics, 835 :471-490 >DOI
He S, He K, Seddighi M. 2016. Laminarisation of flow at low Reynolds number due to streamwise body force Journal of Fluid Mechanics, 809 :31-71 >DOI
He K, Seddighi M, He S. 2016. DNS study of a pipe flow following a step increase in flow rate International Journal of Heat and Fluid Flow, 57 :130-141
Seddighi M, He S, Pokrajac D, O'Donoghue T, Vardy AE. 2015. Turbulence in a transient channel flow with a wall of pyramid roughness Journal of Fluid Mechanics, 781 :226-260 >DOI
He S, Seddighi M. 2015. Transition of transient channel flow after a change in Reynolds number Journal of Fluid Mechanics, 764 :395-427 >DOI
Seddighi M, He S, Vardy AE, Orlandi P. 2014. Direct numerical simulation of an accelerating channel flow Flow, Turbulence and Combustion, 92 :473-502 >DOI
Gorji S, Seddighi M, Ariyaratne C, Vardy AE, O'Donoghue T, Pokrajac D, He S. 2014. A comparative study of turbulence models in a transient channel flow Computers and Fluids, 89 :111-123 >DOI
He S, Seddighi M. 2013. Turbulence in transient channel flow Journal of Fluid Mechanics, 715 :60-102 >DOI
Seddighi M, He S, Orlandi P, Vardy AE. 2011. A comparative study of turbulence in ramp-up and ramp-down unsteady flows Flow, Turbulence and Combustion, 86 :439-454 >DOI
Teaching and Learning
Fluid Mechanics I (4104MECH)
- Module Level: undergraduate – level 4
- Module Syllabus: Spring 2018
- Number of enrolled Students: 192 (Spring 2018)
Fluid Mechanics III (6108MECH)
- Module Level: undergraduate – level 6
- Module Syllabus: Fall 2018
- Viscous flow, boundary layer theory, Blasius solution, von Karman's momentum integral equation
- Number of enrolled Students: 65 (Fall 2018)
Computational Fluid Dynamics (CFD)
- Module Level: post graduate – MSC and level 7
- Module Syllabus: Spring 2018
- Introduction to CFD/Ipython Notebook, Steady diffusion problems (Ipython Notebook; html), Introduction to numerical solution for linear algebraic equations, Steady convection-diffusion problems, Steady N.S. equation - SIMPLE algorithm, Unsteady N.S. equation – Chorin (projection) algorithm, Verification & Validation in CFD, Introduction to Turbulence - RANS
- Number of enrolled Students: 58 (Spring 2018)