Browsing by Author "Aldheeb, Mohammed Abdulmalek"

This research investigates the effect of permeability on the aerodynamics of airfoils and wings. The aerodynamic performance of these airfoils and wings were studied experimentally in the IIUM-low speed wind tunnel. From the literature, it appears that a comprehensive experimental study on permeable wings and airfoils is needed. The research comprises two main objectives; the first of which is to investigate the aerodynamic performance of permeable wings and airfoils using experimental and simulation methods (CFD). The second objective is to investigate experimentally the effect of permeable wingtips on the flow field over the wingtip and its effect on the wake vortex flow downstream using particle image velocimetry (PIV). A permeable thin flat plate, representing a thin symmetric airfoil, as well as a finite wing of the same cross section is used. Permeability is introduced by using a honeycomb structure. The experiment was performed for a range of different porosity values. The results are presented in terms of lift slope versus permeability. The lift slope reduces as the permeability increases for both wings and airfoils. The behaviour/trend of the lift slope is similar to the analytical results available in the literature. The effect of permeability on the aerodynamic center is plotted as well. As the permeability increases the aerodynamic center moves towards the impermeable region. The investigation on the applicability of the standard equation for calculating the lift slope of a wing from an airfoil is applied to permeable wings and airfoils. The result shows that this equation is applicable to both conventional impermeable as well as permeable wings and airfoils. The CFD work is carried out on a thin symmetric airfoil using NACA008 as its cross section. The results of the variation of the lift slope with permeability show a similar behavior as in the experimental study. The results of permeability from CFD shows that a low value of permeability reduces the drag coefficients and thus increases the lift to drag ratio by a large amount. The effect of directional porosity of wing tips on the flow field on the wing surface and in the nearfield of the wing is investigated through PIV. The PIV experiment was performed on seven models of wingtips including the base model. An impermeable wing with a NACA 653218 section was used in this study. Directional porosity is used in five wing tip configurations and one wing tip was made of a honeycomb structure. Configurations 4 – 7 have the highest porosity and the porosity direction in configurations 4 and 5 is 90º, and configurations 6 and 7 have a directional porosity of 95º and 100º, respectively, the directional porosity angle is measured from the chord line., have the highest effect on flow vortex downstream and the reduction in vorticity can reach up to 90% and reduction in tangential velocity can reach up to 74%. These directional porosity wing tips have a great impact on the flow field over the wingtip surface as shown by studying the flow field over the upper surface of wingtips using PIV measurements. These configurations have a porosity perpendicular to the chord line. Configuration 5 has the highest impact as it has the highest porosity value. Configurations 2 and 3 result in a lesser effect on vorticity and tangential velocity as they have porosity inclinations of 30º and 45º respectively. The PIV results over the upper surface of the wingtip show a high disturbance of the flow on the upper surface which results in a reduction in wake vortex downstream. The aerodynamic performances of permeable wingtips were obtained as well and they show a negligible reduction in lift but increase in drag coefficients in some configurations can reach up to 18% at angles of attack [10º - 15º]. These permeable wing tip configurations can be used to alleviate the wake vortex as they are not add-on devices and they are easy to deploy. Thus, this research investigated the behavior of permeable airfoils and wings and compared their behavior with analytical results. It also verified the applicability of the standard equation of calculating lift slope of wing from airfoil lift slope for permeable wings and airfoils. The research also introduced new directionally permeable wingtips which have high impact on vorticity reduction downstream in the near wake field. Last, it investigated the flow behavior over the porous wingtip surface to investigate its role in wake vortex strength reduction downstream.

Air launch vehicles provide a prominent solution for low cost launch of micro and nano satellites with much less launching constraints as compared to ground launch. In this research, evolutionary optimization techniques is used to design a micro air launch vehicle (MALV) which is specifically designed for very small payloads. To perform the optimization, a two-step design optimization algorithm is developed. In the first step, a preliminary design optimization of the air launch vehicle is performed to determine its design and performance parameters. In the second step, a trajectory optimization is performed to determine optimal trajectory and estimate the velocity losses of the designed vehicle. For the first step, a preliminary design model is developed for air launch vehicles. This model is used to calculate the masses, dimensions and performance parameters of the air launch vehicle. The inputs for this model are the payload mass; launching velocity losses due to drag, steering and gravity; and initial guess values for the vehicle specific impulses and inert mass fractions. Given these values, mission analysis and preliminary design is performed to determine, for each stage of the vehicle, the geometric and performance parameters taking into consideration some important inputs such as thrust to weight ratio, length to diameter ratio, chamber pressure, type of propellant and structure materials. For the second step, a 3 degree-of-freedom trajectory simulation model is developed. The inputs of this model are the masses and performance parameters obtained from vehicle design and a predetermined set of angles of attack. Angles of attack are used to steer the vehicle along its trajectory using aerodynamic forces. The coefficients of lift and drag are obtained using Missile DATCOM, which calculates the aerodynamic coefficients within the flight envelope of the vehicle. Two evolutionary optimization techniques are used for the optimization of the air launch vehicle trajectory and design; namely particle swarm optimization (PSO) and differential evolution (DE). These techniques were selected for their ability to handle large design spaces with many dimensions while making no assumptions about the design problem itself. The optimization problem is formulated with the vehicle initial mass taken as the objective function. A set of design variables are used in vehicle design, which are thrust to weight ratio, length to diameter ration, exit area to rocket diameter ratio, chamber pressure and velocity fraction for each stage. The micro air launch vehicle is designed to launch a 20-kg payload into a 400-km circular polar orbit after release from mother plane at 12-km with initial velocity of 300 m/s. Realizing the important role of the fairing mass on vehicle performance, a geometric method is used to estimate the fairing mass for micro air launch vehicle. The estimation gives fairing mass between 8 kg and 12 kg. Using PSO, the optimal micro air launch vehicle initial mass achieved is 1287 kg and the maximum payload mass is 20.7 kg for 12-kg fairing mass. When the 8-kg fairing mass is assumed, the initial mass achieved is reduced to 1267 kg and the maximum payload mass is reduced to 20.64 kg. DE is used to solve the same optimization problem with 8-kg fairing mass for comparison with PSO. The initial mass obtained from DE using fairing mass of 8 kg is 1267 kg and payload mass is 20.61 kg. Therefore, both evolutionary techniques give very close optimal results for the same objective functions and same design variables.