A Laser Inertial Fusion Energy (LIFE) target’s flight through a low Reynolds number and high Mach number regime was analyzed with computational fluid dynamics software. This regime consisted of xenon gas at 1,050 K and approximately 6,670 Pa. Simulations with similar flow conditions were performed over a sphere and compared with experimental data and published correlations for validation purposes. Transient considerations of the developing flow around the target were explored. Simulations of the target at different velocities were used to determine correlations for the drag coefficient and Nusselt number as functions of the Reynolds number. Simulations with different target angles of attack were used to determine the aerodynamic coefficients of drag, lift, Magnus moment, and overturning moment as well as target stability. The drag force, lift force, and overturning moment changed minimally with spin. Above an angle of attack of 15°, the overturning moment would be destabilizing. At angles of attack less than 15°, the overturning moment would tend to decrease the target’s angle of attack, indicating the lack of a need for spin for stability at these small angles. This stabilizing moment would cause the target to move in a mildly damped oscillation about the axis parallel to the free-stream velocity vector through the target’s center of gravity.

The aerodynamic performance of any airborne vehicle is an important characteristic to be considered during the concept development process. Lift and drag forces are the two most important aspects of aerodynamics that dictates vehicle efficiency. As these forces depend on various conditions, evaluating the performance at the intended flight condition is necessary. As the experimental investigations are extremely expensive, computational methods are used to find the performance characteristics of a vehicle in the early design stages. The main focus of this thesis is to find the aerodynamic parameters of an UAV, lift coefficient (Cl) and drag coefficient (Cd) at a predefined flight state and further investigate the trim performance in turn flight state. Two types of computational methods were used namely Panel Methods i.e., Vortex Lattice Method (VLM) and Computational Fluid Dynamics (CFD). These methods differ by computational time and accuracy. Investigations were performed to two UAV models namely UAV1 andUAV2 where both models have minor differences in design. Both VLM and CFDwere used to investigate the performance of UAV1. This was done to find the maximum capability of VLM, which is computationally cheaper. A trim analysis was also performed to find additional parameters to aid the comparison of VLM and CFD. Apart from investigating UAV1 at the required flight states, investigation was also performed at near stall to find the performance of UAV1 in worse flight condition. A comparison of UAV1 and UAV2 was then made to find the best flight states where an UAV can fly fulfilling the designer requirements. UAV2 was then simulated to find the trim condition of a level flight by deflecting the elevator control surfaces in turn flight state. The results from the analysis showed that VLM provides reasonable results within its limitations. From the CFD results, both the UAV’s have sufficient Cl, but the Cd of UAV1 is approximately twice the Cd of UAV2. The turn analysis of the UAV2 showed that at a higher angle of attack, UAV2 can bank at a large bankangle without losing the level flight condition.

<p>The use of drones, also called unmanned aerial vehicles (UAVs), is increasing every day. These aircraft are piloted either remotely by a human pilot or completely autonomously by an on-board computer. UAVs are typically equipped with a video camera providing a live video feed to the operator. While they were originally developed mainly for military purposes, many civil applications start to emerge as they become more affordable.<p><p><p>Micro air vehicles are a subgroup of UAVs with a size and weight limitation; many are designed also for indoor use. Designs with rotary wings are generally preferred over fixed wings as they can take off vertically and operate at low speeds or even hover. At small scales, designs with flapping wings are being explored to try to mimic the exceptional flight capabilities of birds and insects. <p><p><p>The objective of this thesis is to develop a control mechanism for a robotic hummingbird, a bio-inspired tail-less hovering flapping wing MAV. The mechanism should generate moments necessary for flight stabilization and steering by an independent control of flapping motion of each wing.<p><p><p>The theoretical part of this work uses a quasi-steady modelling approach to approximate the flapping wing aerodynamics. The model is linearised and further reduced to study the flight stability near hovering, identify the wing motion parameters suitable for control and finally design a flight controller. Validity of this approach is demonstrated by simulations with the original, non-linear mathematical model.<p><p><p>A robotic hummingbird prototype is developed in the second, practical part. Details are given on the flapping linkage mechanism and wing design, together with tests performed on a custom built force balance and with a high speed camera. Finally, two possible control mechanisms are proposed: the first one is based on wing twist modulation via wing root bars flexing; the second modulates the flapping amplitude and offset via flapping mechanism joint displacements. The performance of the control mechanism prototypes is demonstrated experimentally. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished