Laurent Dala

Generalized Formulation and Review of Piston Theory for Airfoils

The present work presents a brief review of some of the notable contributions to piston theory and of its theoretical basis. A generalized formulation of piston theory is given, applicable to both local and classical piston theory. A consistent generalized formulation of the downwash equation is given, accounting for arbitrary motion in the plane of the airfoil. The formulation reduces to established downwash equations through appropriate definition of the cylinder orientation. The theoretical range of validity of classical piston theory is examined, and the relative accuracy of a number of approximate theories encapsulated by the formulation as applied to a planar wedge is considered. The relative importance of higher order terms in piston theory is examined, with the significance of recent literature extending the fidelity of the first-order term highlighted. It is subsequently suggested that current implementations of local piston theory may be improved through the use of a first-order term of suitable...

Quadrotors trajectory tracking using a differential flatness-quaternion based approach

A quadrotors is a type of Unmanned Aerial Vehicles (UAV) systems that attract the researchers in the control field since its a highly nonlinear, underactuated system. In this paper, a non-linear dynamic model based on quaternions is developed. Differential flatness is an approach that enables the optimization to occur within the output space and therefore simplifies the problem of the trajectory tracking. This work aim to combine both methods in order to create a differential flatness-quaternion based approach that enables the quadrotors to follow a desired optimal path and avoid any singularities that can occur. The trajectory tracking is assured by a double loop control structure based on the LQR controller.

Time-Averaged Behavior of Gap Flow Between Two Side-by-Side Circular Cylinders

The time-averaged behavior of gap flow between two stationary side-by-side circular cylinders immersed in the subcritical Reynolds number regime and its variation with gap spacing are presented. A series of experiments and numerical simulations are performed. Results reveal that gap flow, which is the flow passing between the cylinders, can be classified broadly into pressure- and momentum-driven regimes, depending on the spacing ratio (T/D), where T is the transverse center-to-center spacing between the cylinders and D is the cylinder diameter. The pressure-driven regime occurs for roughly T/D 1.25. Within the pressure-driven regime, subtransitions of the gap flow are further classified, based on distinct changes in the circumferential static pressure distribution, as well as the velocity profile, ...

An Engineering Method for Very Low Aspect Ratio Cruciform Wing-Body Configurations

An engineering method (called the free vortex model or FVM), based on the Allen and Perkins concept and utilising a 2D unsteady potential formulation, has been developed that can predict normal force, centre-of-pressure and vortex positions for cruciform wingbody configurations with very low aspect ratio wings (AR ≤ 0.1) and taper ratios ≈ 1 at supersonic speeds in the ’+’ orientation. The method utilises the modified Newtonian impact theory to calculate the 2D cross sectional loads and a cross flow Mach number dependency is modeled using experimental data. The rolled up shed vortex sheet is modeled as a single idealised vortex whose predicted positions are strictly applicable where no symmetric vortex shedding occurs.