Effect of chord-wise flexibility in the lift generation of flapping MAV with membrane wing

Purpose The purpose of this study is to experimentally analyse the effect of flexible and stiffened membrane wings in the lift generation of flapping micro air vehicle (MAV). Design/methodology/approach This is analysed by the rectangle wing made up of polyethylene terephthalate sheets of 100 microns. MAV is tested for the free stream velocity of 2 m/s, 4 m/s, 6 m/s and k* of 0, 0.25, 1, 3, 8. This test is repeated for flapping MAV of the free flapping frequency of 2 Hz, 4 Hz, 6 Hz, 10 Hz and 12 Hz. Findings This study shows that the membrane wing with proper stiffeners can give better lift generation capacity than a flexible wing. Research limitations/implications Only a normal force component is measured, which is perpendicular to the longitudinal axis of the model. Practical implications In MAVs, the wing structures are thin and light, so the effect of fluid-structure interactions is important at low Reynold’s numbers. This data are useful for the MAV developments. Originality/value The effect of chord-wise flexibility in lift generation is the study of the effect of a flexible wing and rigid wing in MAV. It is analysed by the rectangle wing. The coefficient of normal force at different free stream conditions was analysed.

Three-dimensional numerical modeling of flow upstream of a symmetric streamlined body mounted over a flat plate with tip gap

In this research activity numerical simulations are carried out to investigate the flow field upstream of a symmetric streamlined body mounted perpendicular to a flat plate with and without clearance gap between the tip of the streamlined body and the flat plate with laminar boundary layer. The developed numerical model successfully predicted the three-dimensional horseshoe vortex system upstream of the streamlined body with and without the tip gap. The resulting vortex system for the configuration with tip gap contains multiple vortices with characteristics similar to that of end-wall-flows of surface-mounted obstacles. The effects of varying tip gap clearance for various values of free stream Reynolds number are also investigated. It was found that the introduction of a gap between the streamlined body tip and flat surface caused shifting of the vortex structure system in the upstream direction. Moreover, it is observed that the free stream Reynolds number and the tip gap between the streamlined body and the flat plate substantially influences the unsteady character of the flow field and the vortex system structure. Results obtained from the numerical simulations are compared with experimental measurements of a blunt body configuration and have been found in good agreement.

Investigating the Level of Fidelity of an Actuator Line Model in Predicting Loads and Deflections of Rotating Blades under Uniform Free-Stream Flow

In this paper, the accuracy of an in-house Actuator Line (AL) model is tested on aeroelastic simulations of a Wind Turbine (WT) rotor and a helicopter Main Rotor (MR) under uniform free-stream flow. For the scope of aeroelastic analyses, the AL model is coupled with an in-house multibody dynamics code in which the blades are modeled as beams. The advantage from the introduction of CFD analysis in rotorcraft aeroelasticity is related to its capability to account in detail for the interaction of the rotor wake with the boundary layer developed on the surrounding bodies. This has proven to be of great importance in order to accurately estimate the aerodynamic forces and thus the corresponding structural loads and deflections of the blades. In wind turbine applications, a good example of the above is the rotor/ground interaction. In helicopter configurations, the interaction of MR with the ground or the fuselage and the interaction of tail rotor with the duct in fenestron configurations are typical examples. Furthermore, CFD aerodynamic analysis is an obvious modeling option in which the above mentioned asset can be combined with the consideration of the mutual interaction of the rotor with the ambient turbulence. A WT rotor operating inside the atmospheric boundary layer under turbulent free-stream flow is such a case. In the paper, AL results are compared against Blade Element Momentum (BEM) and Lifting Line (LL) model results in the case of the WT, whereas LL and measured data are considered in the helicopter cases. Blade loads and deflections are mainly compared as azimuthal variations. In the helicopter MR cases, where comparison is made against experimental data, harmonic analysis of structural loads is shown as well. Overall, AL proves to be as reliable as LL in the canonical cases addressed in this paper in terms of loads and deflections predictions. Therefore, it can be trusted in more complex flow conditions where viscous effects are pronounced.

A CASE STUDY ON STABILISER FIN-HULL INTERACTION USING CFD AND MODEL EXPERIMENTS

A case study was conducted to investigate and quantify stabiliser fin-hull interaction using a combination of Computational Fluid Dynamics and physical model experiments. The fin-hull interaction was studied by comparing the lift and drag of a stabiliser fin in a free stream condition and when attached to a hull. The findings of this case study showed that using free stream fin characteristics to predict performance of a stabiliser fin fitted to the hull resulted in an over-prediction of drag by up to 46% and under-prediction of lift by up to 75% for the speeds and angle of attack analysed. These discrepancies are for this case study only and in practice will vary for different hull forms, fin types, fin location and angles of attack. However, the research highlights the limitations of using free stream fin characteristics to predict the performance of a fin fitted to a hull.