Shuanghou Deng

Experimental Investigation on the Aerodynamics of a Bio-inspired Flexible Flapping Wing Micro Air Vehicle

An experimental investigation on a 10 cm bio-inspired flexible Flapping-Wing Micro Air Vehicle (FWMAV) was conducted in both hovering and forward-flight conditions with the objective to characterize its aerodynamic performance. The measurements in hovering conditions were performed with the particular objective to explore the effect of different wing configurations (i.e. different aspect ratios and wing flexibilities), whereas forward flight tests in a wind tunnel were carried out to assess the aerodynamic performance of the FWMAV as a function of flow speed, flapping frequency and body angle. The cyclic variation of forces (lift and thrust) generated as a result of the wing flapping was captured by means of a high-resolution force sensor, in combination with high-speed imaging to track the wing motion. Results of measurements in hover show that the flapping frequency, aspect ratio and wing flexibility have a crucial impact on the efficiency and the force generation during the flapping cycle. An estimated flight envelop for the MAVs operation is defined from the data obtained in the wind tunnel measurements. Furthermore, additional tests on several brushless DC motors provide a feasible option in future engine selection and design.

Experimental Investigation of Aerodynamics of Flapping-Wing Micro-Air-Vehicle by Force and Flow-Field Measurements

This study explores the aerodynamic characteristics of a flapping-wing micro aerial vehicle (MAV) in hovering configuration by means of force and flowfield measurements. The effects of flapping frequency and wing geometry on force generation were examined using a miniature six-component force sensor. Additional high-speed imaging allowed identification of the notable different deformation characteristics of the flexible wings under vacuum condition in comparison to their behavior in air, illustrating the relevance of aeroelastic effects. Flow visualization around the flapping wing by means of planar particle image velocimetry (PIV) measurements revealed the formation, development, and shedding of the vortical structures by the wings during flapping motion, with particular emphasis on the clap-and-fling phase. Further stereoscopic PIV measurements performed in the wake showed a momentum surplus wake induced by the clap-and-fling, indicative of thrust generation. The vortical structures in the wake formed d...

Numerical Simulation of a Flexible X-Wing Flapping-Wing Micro Air Vehicle

Numerical simulations were performed to investigate the flowfield around a flexible flapping-wing micro air vehicle using an in-house-developed computational fluid dynamics solver. To include the d...

A Computational Study on the Aerodynamic Influence of a Propeller on an MAV by Unstructured Overset Grid Technique and Low Mach Number Preconditioning

The influence of a propeller on the aerodynamic performance of an MAV is investigated using an unstructured overset grid technique. The flow regime of a fixed-wing MAV powered by a propeller contains both incompressible regions due to the low flight speed, as well as compressible flow areas near the propeller-tip region. In order to simulate all speed flow efficiently, a dual-time preconditioning method is employed in the present study. The methodology in this paper is verified as providing a reliable numerical simulation tool for all flow regimes, in the additional presence of moving boundaries, which is treated with an overset grid approach.

Numerical simulation of an X-wing flapping wing MAV by means of a deforming overset grid method

A numerical study was conducted to investigate the flexible wing aerodynamics of a flapping wing MAV with a four-wing configuration by means of an in-house developed computational fluid dynamic URANS solver. The wing deformation pattern is derived from a stereo-vision experiment and subsequently imposed in the simulation to mimic realistic flexible wing kinematics. In order to implement the wing kinematics, a deforming overset grid strategy was developed to deal with flow field simulations involving large displacements and multiple-body movements. The computational results provide a quantitative prediction of the unsteady aerodynamics of the flapping wing MAV under stucy in terms of vortex structures.

Effect of flexion on the propulsive performance of a flexible flapping wing

A numerical study was carried out to investigate the effect of chordwise flexion on the propulsive performance of a two-dimensional flexible flapping wing. The wing undergoes a prescribed sinusoidal heaving motion with a local deflection. A deformable overset grid dynamic mesh method was employed to implement the motion of the grid instantaneously. The effect of flexural pattern, flexural amplitude and flapping frequency in terms of Strouhal number are evaluated. Unsteady flow around the wing is computed using an in-house developed Unsteady Reynolds-Averaged Navier-Stokes (URANS) solver. The results show that the different flexural patterns will create different flow fields, and thus the thrust generation will be significantly varied. The thrust and propulsive efficiency do not increase monotonically with the flexure amplitude while a peak value is revealed. It is found that the wake vortices after the flapping motion assembly behave as a reverse von-Karman vortex street, which can principally create thrust. The thrust is found to increase with increasing Strouhal number. Propulsive efficiency is beneficial from the chordwise flexibility and peaks within the range of 0.2 < St < 0.4, which is evidenced by natural flyers.

Numerical study on the flow characteristics of micro air vehicle wings at low Reynolds numbers

The aerodynamic characteristics around a micro air vehicle wing with an inverse-Zimmerman configuration are numerically investigated by an in-house programmed solver particularly dedicated for aircrafts operating in low Reynolds number regime. The complex three-dimensional aerodynamic performance was investigated in terms of force generation and flow structures visualization. Results show that the flow around the low aspect ratio MAV wing is characterized by complex three-dimensional separation-dominated flow. The flow fields exhibit separation, reattachment, secondary separation, secondary reattachment, and strong interaction between the separated boundary layer and wingtip vortices. In addition, the effect of tip-attached vertical stabilizers on flow structure and aerodynamic forces is addressed in this paper. The stabilizers significantly influence both the flow structure and aerodynamic forces via reducing the strength of wingtip vortices and shedding and interacting of wingtip vortices. Eventually, the unsteadiness of the aerodynamics revealed that higher angle of attack will result in stronger unsteady phenomena as demonstrated by the oscillating forces.

Numerical Investigation on the Propulsive Performance of Biplane Counter-Flapping Wings

A numerical investigation is performed to address the flexing effect on the propulsion performance of flapping wing particularly on the counter-flapping wings of the biplane configuration. A Reynolds number of 10,000 is considered in the present study which corresponds to the flight regime of most existing flapping wing micro air vehicles. The computation involves solving the compressible unsteady Reynolds- averaged Native-Stokes equation using an inhouse developed code. The flapping motion is incorporated by an efficient deforming overset grid technique which allows multiple flexible bodies to be embedded into the flow field. Results show that the biplane wing with counter-flapping configuration has a better propulsive performance in comparison to a single flapping wing. A low-pressure regime between the two wings during the outstroke produces more thrust, while the counter-flapping motion can also generate a surfeit momentum rushing in to the wake. The more flexible wing can produce more thrust while less power is required thus owning a better propulsive performance.

Deformable Overset Grid for Unsteady Aerodynamic Simulation

A deformable overset grid method was proposed to simulate the unsteady aerodynamic problems with multiple flexible moving bodies. This method uses an unstructured overset grid locally coupled with mesh deformation to achieve both robustness and efficiency. The overset grid hierarchically organizes the sub-grids into CLUSTERs and LAYERs, allowing for overlapping/ embedding of different type meshes, of which the mesh quality and resolution can be independently controlled. At each time step, mesh deformation is locally applied to the sub-grids associated with deforming bodies by an improved Delaunay graph mapping method which uses a very coarse mesh as the background graph. The graph is moved and deformed by a spring analogy according the specified motion and then the computational meshes are relocated by a simple one-to-one mapping. An efficient implicit hole-cutting and inter-grid boundary definition procedure is fully automatically implemented for both cell-centered and cell-vertex schemes based on wall distance and an alternative digital tree (ADT) data search algorithm. This method was successfully applied to several complex multi-body unsteady aerodynamic simulations and the results demonstrated the robustness and efficiency of the proposed method for complex unsteady flow problems, particularly for those perform large relative motion and self-deformation simultaneously.