My Engineering Research And Publications

My area of research during PhD studies was Turbulent Boundary Layer Flows of Newtonian Fluids, which itself is a sub-branch of the Fluid Dynamics or Aerodynamics. Fluid dynamics deals with the flow of any fluid (air, water or another liquid, a gas, molten metals etc) around or inside an object of interest. Aerodynamics deals only with the flow of air around or inside an object of interest.

A fluid flow can be laminar, turbulent or transitional (in between).  In a laminar flow, a physical quantity like velocity or pressure will be the same at a point in space (x,y,z) if measured at multiple instants of time. In a turbulent flow, these physical quantities fluctuate randomly even if measured at the same point at different instants of time.

Almost all of the fluid flows of engineering interest are turbulent (while those of medical interest are mostly laminar like blood flow in a vessel). Furthermore, these flows can be classified as wall-bounded (boundary layers, wall jets, channel and pipe flows etc) and free shear flows (like jets, wakes). Boundary layer is the part of flow very near a solid boundary like the body of a car or frame of an aircraft etc.

Turbulent flows are everywhere around us. The most evident example is the atmospheric flow.  The simulation for weather prediction deals with the turbulent flow equations. Its industrial applications include air flow around airplanes, automobiles, ships, wind turbines, gas turbines, compressors, gas, oil and water pipelines etc.  Flows of gas turbines (jet engines) are further complicated by the combustion of gases and heat transfer problems. It is the same for automobile engines or other internal combustion engines that feature "Turbulent Combustion Flows".

Turbulent flows have the quality of sticking longer to the walls (i.e., delayed separation) as compared to laminar flows and thats why we see dimples on golf balls. Dimples provide a rough surface that makes the boundary layer turbulent and hence air flow remains attached longer to the ball and ball itself goes a longer distance.  Vortex generators (small fins) installed on aircrafts and automobiles transitions and energises the boundary layer and the flow remains attached for longer.

Turbulence is also of interest in the applications where enhanced mixing or diffusion is required. Turbulent diffusion or mixing is much faster than the molecular diffusion. It is this reason that automobile engine manufacturers try to increase turbulence in the cylinders through swirls for better mixing of air and fuel vapours.

Turbulent flows afford a much higher convection heat transfer rates than the laminar flows and therefore are employed in situations where heat transfer demands are high (cooling or heating).  and Automobile and some aircraft (piston-engined) engine cooling systems use turbulent flow of coolant inside the radiator for enhanced cooling rates. Also cooling is improved by the flow of a turbulent air across the radiator. Jet engines also benefit from the turbulent flow for enhanced cooling rates of the turbine blades.

Turbulent flow is also of importance to aeroacoustics (aerodynamic noise). Lighthill's wave equation shows that Reynolds stress (product of velocity fluctuations and density) generates noise. This means that to control the acoustic signature of objects traveling through fluids, turbulence has to be taken into consideration.

Turbulent flows constitute a branch of science that has still not been mastered in theory. Analytical solutions are not possible in general and hence experimental and computational approaches are used for the prediction of desired parameters like skin friction, skin temperature, heat transfer, pressure distribution or flow separation.

There are also situations where we would like to avoid turbulent flow to reduce skin friction drag (like in gas or oil pipelines or some aircraft designs). This technique of maintaining laminar flow over part of the wings was used on the famous P-51 Mustang fighter in the Second World War. Today there is a renewed interest in the laminar flow wings for airliners.

It is amazing that no Pakistani Engineering Univeristy is offering a course on the Turbulent Flows. It is partly due to the fact that very few engineers are qualified in this area.

Fluid dynamics is also studied by mathematicians but the approach of mathematicians to Fluid dynamics is not the same as that of engineers. Engineering approach is an applied one, related more to technology rather than to pure physics. The fact that no general theory exists for turbulent flows means that either experimental or computational approach through CFD softwares has to be adopted, something with mathematicians rarely do.

My own study was related to the detection and characterisation of the vortical structures in the boundary layer flow and also finding length and velocity scales for self-similar solutions of the boundary layer equations.
 

Vortex detection was carried out on the instantaneous data obtained from Direct Numerical Simulation (DNS) of a wall-bounded flow. The algorithms were programmed in the Interactive Data Language (IDL). IDL can be thought of as comparable to MatLab in its capabilities.

The second theme of research was finding the Self-Similar Solutions for the boundary layer equations. Self-Similar solutions transform the partial differential equations (PDEs) of a given flow into the ordinary differential equations (ODEs), which are much easier to handle.

Here are some of my publications (Conference papers) with links;

A Specific Behaviour of Adverse Pressure Gradient Near Wall Flows, Progress in Wall Turbulence: Understanding and Modeling: Proccedings of the WallTurb International Workshop held in Lille, France, April 21-23 2009.

Link: https://books.google.fr/books?id=cr1nAfZ0dTQC&pg=PA257&lpg=PA257&dq=Progress+in+Wall+Turbulence+syed+imran+shah+adverse+pressure+gradient&source=bl&ots=lYjQ19PxWP&sig=EnPuxvhPgNoM5otjycJRH7YAgJM&hl=en&sa=X&ei=TJOWVenPMcivswHckpnQDQ&ved=0CCEQ6AEwAA#v=onepage&q=Progress%20in%20Wall%20Turbulence%20syed%20imran%20shah%20adverse%20pressure%20gradient&f=false




A New Velocity Scale for Turbulent Boundary Layers with Adverse Pressure Gradients, 17th Australasian Fluid Mechanics Conference, Auckland, New Zealand, 5-9 December 2010.


Link: people.eng.unimelb.edu.au/imarusic/proceedings/17/376_Paper.pdf



Vortical Structures in A Wall-Bounded Flow With Recirculation,  20ème Congrès Français De Mécanique (CFM 2011), Besançon, France, 28 Août - 2 Septembre 2011.


Link: http://documents.irevues.inist.fr/bitstream/handle/2042/46337/cfm2011_134.pdf?sequence=1&isAllowed=y


Vortical Structures in Wall-Bounded Turbulent Flows With Recirculation, 13th European Turbulence Conference, Warsaw, Poland, 12-15 September, 2011.

Link: http://iopscience.iop.org/1742-6596/318/2/022022/