Browsing by Author "Mahbub Alam, Md."

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    Application of maccormack scheme to the study of aggradation-degradation in alluvial channels
    (Department of Water Resources Engineering, 1998-07) Mahbub Alam, Md.; Bhuiyan, Dr. Muhammed Ali
    Aggradation and degradation are ubiquitous phenomena that occur in most alluvial channels. The complete Saint Venant equations describe the unsteady open channel /low conditions. The continuity equation for the conservation of sediment mass needs to be solved along with the hydrodynamic equations to determine aggradation and/or degradation of channel bottom. In these viewpoints, a one-dimensional mathematical model has been developed that computes the aggradation-degradation of channel bed. The MacCormack explicit finite difference scheme has been used in the model. This scheme is second-order accurate, handles shocks and discontinuities in the solution without any special treatment, and allows simultaneous solution of the water and sediment equations, thereby obviating the need for iterations. The developed model has been applied to two different case studies. The first case is a laboratory investigation where experimental results were obtained due to imposing extra sediment load. The sediment overloading produces aggradation in the channel. It has been found that the model simulates most of the test runs with a reasonable accuracy. In order to verify the ability of the model to real field situation, it has been applied to simulate Jamuna river reach from Bahadurabad to Sirajgang. A test run for three years has been done using field data for that period. The agreement between the computed results and measured data is quite satisfactory. The successful application of the model strongly demonstrates that the model is valid in solving unsteady open channel flow problems in conjunction with sediment transport. The different problems just require incorporating the appropriate initial and boundary conditions .
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    Computational Study on the Control of Self-sustained Shock Oscillation around a Supercritical Airfoil in Transonic Flow
    (Department of Mechanical Engineering, 2012-10) Mahbub Alam, Md.; Hasan, Dr. A. B. M. Toufique
    Transonic flow around supercritical airfoil involves shock induced oscillation at certain free stream Mach number and angle of attack due to the interaction of shock wave with airfoil boundary layer. This interaction consequences fluctuating lift and drag coefficient, aero acoustic noise and vibration, intense drag rise, high cycle fatigue failure (HCF), buffeting and so on. Moreover, the unsteady pressure fluctuations generated by the shock motions are highly undesirable from structural integrity and aircraft maneuverability point of view. The aerodynamic characteristics of the present problem have been solved by numerical computation. A commercial finite volume CFD package has been used for this computation. The computational domain has been discretized into a structured mesh by using a commercial preprocessing tool. The transonic flow around a supercritical airfoil is governed by the unsteady compressible Reynolds-averaged Navier-Stokes equation together with the energy equation. Two additional equations of k-ω SST turbulence model have been included to model the turbulence in the flow field. The results obtained from the numerical computation have been validated with the experimental results. Maintaining same flow parameters computational analysis has been done at free stream Mach number 0.77 and angle of attack from 2° to 7°. Mach contour, lift and drag coefficient, pressure coefficient and pressure history at different points over the airfoil has been captured and analyzed. To suppress the self-excited shock oscillation effectiveness of bump based passive control technique around the airfoil in transonic interval flows has been numerically analyzed and found its effectiveness.