This dissertation studies the drag reduction of passenger cars with pushed-in rear door and rear bumper to improve aerodynamics and thus fuel efficiency. Drag reduction was focused on modifications of the surface at the bottom rear side profile of a passenger car in order to maintain attached flow across the sides of the body and a smaller wake size at the rear of the car. A simplified car model was used to represent a typical passenger car. The flow over the car model was simulated in Computational Fluid Dynamics (CFD) software Star-CCM+ to obtain the drag coefficient. Parametric studies were performed in order to determine the best drag reduction configuration. Significant reduction of drag by 4.7% was achieved with the combination of a pushed-in rear door and rear bumper. Combination of both strategies should be made carefully so that early flow separation will not occur on the side rear bumper.

The aerodynamic parameters of a conventional wingless airship and a preliminary winged-hull airship design are investigated. The research methodology involved the use of numerical simulation and wind tunnel testing. The aerodynamic parameters of the designs are first computed using a commercial CFD code. The force and moment coefficients are then measured on a scaled model in the IIUM low speed wind tunnel. The experimental results were used to validate the reliability of CFD results in order to predict the full scale airship models. It is found out that the experimental results generally agree with the CFD predicted data. Addition of a wing to conventional airship increases the lift substantially with a reasonable increase in drag. In general, winged airship has three times the lifting force at positive angle of attack compare to wingless airship whereas the drag increases in the range of 16% to 58%. The conventional airship and the hybrid airship were found to be statically stable for both longitudinal and directional stability motions; however, they have poor rolling stability. Winged airship has slightly more stable longitudinal motion than wingless airship. The wingless airship has better directional stability than the winged airship. However, the wings contribution to directional stability is found to be negligible. The wingless airship only possesses static rolling stability at the range of yaw angle of -5° to 5°. On the contrary, the winged airship does not possess rolling stability at all. CFD simulations show that modifications to the wing placement and its dihedral have strong positive effect on the rolling stability. Raising the wings on the center of gravity and introducing dihedral angle of 5° stabilize the rolling motion of the winged airship.

Gust load due to atmospheric turbulence is mandatory to be considered in the aircraft analysis as part of airworthiness requirement. The gust load alleviation plays an important role to effectively utilize the wing structural flexibility without ignoring the safety issue. In the present work, a method to alleviate the wing gust load is proposed by considering the structural flexibility of the wing and proper arrangement of composite material layers. The approach takes into account the wing planform, wing composite thickness and material direction, wing structural dynamic frequencies and modes, steady and unsteady aerodynamics of the wing surface. The objective of the study is to minimize the wing root bending moment power spectral density. The constraint of the study includes the wing material requirement, wing configuration, and the aerodynamic wing performance. The gust load analysis of the present structural model will be compared to the literature for the validation purpose. A finite element approach is used to simulate the wing structure in combination with the doublet lattice method to model the wing aerodynamics. The gust load profile, according to aviation regulations, is used. The proposed method gives a contribution to the gust load alleviation of large transport aircraft and unmanned air vehicles. It is clearly seen that the best configuration for reducing the bending moment power spectral density is swept back wing then swept forward. The swept-back configuration (45 degrees) showed an average decrease of the bending moment by 12% for a frequency range of 0 to 100 Hz. The present work also shows that the wing composite thickness and material direction affects the aerodynamic stability derivatives as function of Mach number which are important for the design of the aircraft flight dynamic and performance.

Birds and insects are creatures with complex flying capabilities. Trying to emulate their flying technique meets challenges of high degree of difficulties. Birds and insects flap their wings to generate lift and thrust for forward motion as well as for hovering motion. This work involves in modeling the beetle-mimicking ornithopter using mixed Unscented Kalman Filter (UKF) and Differential Evolution (DE) method. The research plans to model the beetle mimicking ornithopter aerodynamically and mathematically. An experiment in the IIUM closed loop low speed wind tunnel to determine the aerodynamics coefficients and stability derivatives produced by the beetle mimicking ornithopter is proposed and then the values can be used in the mathematical modeling using mixed UKF and DE algorithm. The data will be inputted into the coding as initial and guessing values. Unfortunately, the work cannot be continued due to the constraints that the wind tunnel has broken down. Therefore, the modeling is halted at the mathematical algorithm and the simulation using MATLAB is not preceded. Flow visualization experiments on the flapping wing are done in the open loop TE54 subsonic wind tunnel to investigate the vortex generation in the ornithopter. The existence of vortices can be seen mostly during both peaks of upstroke cycle and downstroke cycle. The verification of the accuracy of the proposed mixed UKF and DE method is provided in this work. The modeling using the proposed method of mixed UKF and DE proves to be efficient and reliable as the result shows small error differences.

In this work, aerodynamics investigation of the flow around the circular planform unmanned aerial vehicle (CP-UAV) was carried out numerically and validated with existencing published experimental data. The aircraft uses NACA 4412 airfoil. CD-Adapco STARCCM+ CFD software was used to simulate the flow. The simulations were carried out for three dimensional flows around CP-UAV to analysze the viscous flow behavior and aerodynamics coefficients such as boundary layer thickness, velocity vector contour, pressure distribution, streamlines, lift and drag coefficients. Three dimensional simulation was started with generating CATIA 3Ddrawing and exported to STAR-CCM+ for meshing. The numerical results of lift drag and moments coefficients were compared to experimental data. The qualitative comparison has shown acceptable good agreement. Finally, the study has shown that the CP-UAV is more stable and better aerodynamic characteristics than the conventional aircraft.