Dr Mohammed Afsar

Strathclyde Chancellor's Fellow

Mechanical and Aerospace Engineering

Personal statement

M.Z. Afsar holds a Masters in Aeronautical Engineering (2003) from the University of Bristol for which he received several commendations including the Royal Aeronautical Society Award and Rolls Royce prize. His research career began in the summer of 2002 when, still as an undergraduate, he obtained a Research Assistantship at the Department of Applied Physics of Yale University. Here he worked as an experimentalist, conducting Particle Image Velocimetry measurements in laminar flames using laser diagnostic tools. He holds a PhD from the University of Cambridge (2009) in Engineering. His PhD thesis was in Aeroacoustics and focused on Applied Mathematical aspects of jet noise theory and modelling. Following this, he received a number of research fellowships (culminating with the NASA Post-doctoral program) that allowed him to work at the NASA Glenn Research Center with world-famous Applied Mathematicians, Drs. Marvin Goldstein and S. J. Leib, on a variety of problems in Aeroacoustics, Turbulence modelling and Rapid-distortion theory. Between July 2013--April 2016 he was based at Imperial College London (Dept. of Mathematics) working under the Chapman Fellowship and Laminar Flow Control platform grant mainly with Professor X. Wu. Before joining Strathclyde University he was a visiting academic at Queen Mary University (in June-July 2016) and a remote visitor for the Stanford University Center for Turbulence Research summer program. He is a regular visitor to the Department of Mathematics at Kashmir University in Srinagar (India) and his research interests include Asymptotic analysis, Aeroacoustics, Turbulence theory & modelling, Boundary-Layer Transition and Applied Mathematical methods.

Expertise

Has expertise in:

    Main scientific results

    • We showed how optimally placed surface deformations hamper Gortler vortex growth rate and the temporal growth rates of resulting secondary instabilities (with A. Sescu, Mississippi State University).
    • We showed how non-parallel flow effects re-distribute the “two-peak” asymptotic structure of the Green’s function in the acoustic analogy approach so that a heated supersonic flow is quieter than an isothermal flow (with A. Sescu, Mississippi State University).
    • Showed how negative correlation in upstream turbulence affects the low frequency roll-off of the jet-surface interaction noise spectrum.
    • Working with NASA colleagues, we extending the Rapid-distortion theory of turbulence to compressible transversely sheared mean flows with physically realizable upstream boundary conditions (with M. E. Goldstein & S. J. Leib, NASA Glenn Research Center). This theory was applied to trailing edge noise problem.
    • We showed that non-parallel flow introduces a “two-peak” spatial structure in the Green’s function for predicting the low frequency jet noise in isothermal air jets under an appropriate asymptotic distinguished limit (with M. E. Goldstein, NASA Glenn Research Center & A. Sescu, University of Toledo).
    • Generalized spherical shell turbulence models to cylindrical shells in the axi-symmetric kinematic representation of the Reynolds stress auto-covariance tensor. This was validated against LES of high subsonic isothermal jet & PIV of incompressible water jet.

Prizes and awards

Joint guest editor for a volume of invited papers at Philosophical Transactions of the Royal Society of London Journal.
Recipient
9/1/2019
Global Engagements Fund (GEF) 2018
Recipient
5/7/2018
STEM for Britain 2018
Recipient
12/3/2018

More prizes and awards

Qualifications

Education:

  • (Jan) 2004 – (Sept.) 2008: PhD in Aeronautical Engineering at Cambridge University, Department of Engineering. 

  • (Sept.) 1999 – 2003: First Class honours in Aeronautical Engineering M.Eng. at Bristol University, Department of Aeronautical Engineering.

Reviewer for:

  • Physics of Fluids
  • AIAA Journal
  • Journal of Fluid Mechanics

Member:

  • American Physical Society

Publications

Effect of large-scale mixing on the axisymmetric structure of turbulence correlations in complex dual stream jets
Afsar M Z, Gryazev V, Markesteijn A, Karabasov S
2020 AIAA Aviation and Aeronautics Forum and Exposition, pp. AIAA 2020-2573 (2020)
https://doi.org/10.2514/6.2020-2573
Improved jet noise predictions in subsonic flows using an approximate composite asymptotic expansion of the adjoint Green's function in Goldstein's analogy
Afsar M Z, Sescu A, Leib S J
2020 AIAA Aviation and Aeronautics Forum and Exposition, pp. AIAA 2020-2572 (2020)
https://doi.org/10.2514/6.2020-2572
The relationship between the surface pressure spectrum and transverse velocity spectrum in a Rapid-distortion theory model of trailing edge noise
Afsar M Z
2020 AIAA Aviation and Aeronautics Forum and Exposition (2020)
https://doi.org/10.2514/6.2020-2540
Investigation of fast GPU-based algorithms for jet-surface interaction noise calculations
Afsar M Z, Stirrat S A, Kokkinakis I W
2020 AIAA Aviation and Aeronautics Forum and Exposition (2020)
https://doi.org/10.2514/6.2020-2564
Analysis of the non-parallel flow-based Green's function in the acoustic analogy for complex axisymmetric jets
Afsar M Z, Sescu A, Gryazev V, Markesteijn A, Karabasov S
2020 AIAA Aviation and Aeronautics Forum and Exposition, pp. AIAA 2020-2507 (2020)
https://doi.org/10.2514/6.2020-2507
Passive noise control strategies for jets exhausting over flat surfaces : an LES study
Horner Colby, Sescu Adrian, Afsar Mohammed, Collins Eric, Azarpeyvand Mahdi
2020 AIAA Aviation and Aeronautics Forum and Exposition (2020)
https://doi.org/10.2514/6.2020-2552

More publications

Teaching

ME101 - Heat & Flow 1 (Basic Fluid Mechanics)

ME201 - Aero Design  (Flight Mechanics)

ME405 - Heat & Flow 4  (Heat transfer)

ME530 - Aero-acoustics (Mainly on Applied Mathematics)

 

Research interests

Current research involves mathematical & numerical analysis of jet flow turbulence for Aero-acoustics problems such as jet noise and trailing/leading edge noise. I am also interested in mathematical modeling of boundary layer transition (receptivity and secondary instability theory) and wall turbulence.

Fields of scientific interest

Particular:

  • Secondary instabilities of streamwise vortex flows
  • Trailing/leading edge noise
  • Rapid-distortion theory of turbulence
  • Jet noise modeling in heated/isothermal flows
  • Kinematic and dynamic modeling of jet turbulence

General:

  • Perturbation methods in Applied Mathematics
  • Wiener-Hopf Technique
  • Complex analysis

 

Professional activities

An overview of the Rapid-distortion theory approach to jet surface interaction noise modelling
Speaker
31/1/2020
Sixteenth International Conference on Flow Dynamics, November 6 - 8, 2019, Sendai, Miyagi, Japan
Participant
7/11/2019
Philosophical Transactions A: Mathematical, Physical and Engineering Sciences (Journal)
Peer reviewer
1/11/2019
Validity of a non-parallel flow asymptotic theory for the adjoint vector Green's function within the generalized acoustic analogy
Speaker
1/5/2019
A formal asymptotic approach to modeling low frequency jet noise in heated and unheated air jets
Speaker
1/11/2016

More professional activities

Projects

Doctoral Training Partnership 2018-19 University of Strathclyde | Stirrat, Sarah
Afsar, Mohammed (Principal Investigator) Cartmell, Matthew (Co-investigator) Stirrat, Sarah (Research Co-investigator)
01-Jan-2019 - 01-Jan-2023
Jet noise modeling in heated and isothermal supersonic air jets
Afsar, Mohammed (Principal Investigator) Sescu, Adrian (Principal Investigator) Sassanis, Vasilis (Principal Investigator)
We use asymptotic methods to approximate the adjoint vector Green's function for the linearized Euler equations when the mean flow is non-parallel (and specifically is slowly diverging, with an asymptotically small spread rate). The Green's function solution is used in the generalized acoustic analogy to predict far field sound together with an algebraic-exponential turbulence model.


01-Jan-2018 - 31-Jan-2018
Comparison of trailing edge noise model with Large-Eddy Simulations
Afsar, Mohammed (Principal Investigator) Sescu, Adrian (Co-investigator)
We use rapid-distortion theory on transversely sheared mean flows to analyse the sound radiation produced by the interaction of a two-dimensional jet with the downstream edge of a flat plate. The results are compared with Large Eddy simulations to show the consistency of the upstream boundary condition for the convected quantity in the basic theory.
01-Jan-2017 - 01-Jan-2018
Optimal control of Gortler vortices using surface deformations
Sescu, Adrian (Principal Investigator) Afsar, Mohammed (Co-investigator)

The control of stream-wise vortices in high Reynolds number boundary layer flows often aims at reducing the vortex energy as a means of mitigating the growth of secondary instabilities, which eventually delay the transition from laminar to turbulent flow. In this paper, we aim at utilizing such an energy reduction strategy using optimal control theory to limit the growth of G ̈ortler vortices developing in an incompressible laminar boundary layer flow over a concave wall, and excited by a row of roughness elements with span-wise separation in the same order of magnitude as the boundary layer thickness. Commensurate with control theory formalism, we transform a constrained optimization problem into an unconstrained one by applying the method of Lagrange multipliers. A high Reynolds number asymptotic framework is utilized, wherein the Navier-Stokes equations are reduced to the boundary region equations (BRE), in which wall deformations enter the problem through an appropriate Prandtl transformation. In the optimal control strategy, the wall displacement or the wall transpiration velocity serve as control variables, while the cost functional is defined in terms of the wall shear stress.
01-Jan-2017 - 01-Jan-2018

More projects

Address

Mechanical and Aerospace Engineering
James Weir Building

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