Papers by Keyword: Low Reynolds Number

Abstract: This paper aims to estimate the effect of turbulent inlet flow to vortices on Delta wing with four different turbulence intensity from 0.5% to 15% and the effect of taper ratios to aerodynamic characteristics of Delta wings with four taper ratios: 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7. The main purpose of this paper is to find out the formation, development, and breakdown of vortices on Delta wings when changing taper ratios and turbulence intensity thence determining the center of vortices with the range of attack angles from 5o to 40o in low velocities about 2.5 m/s. This research uses Delta wing models with a 40o swept-back leading edge, the root chord length 150 mm, and a thickness 5 mm. The problem is simulated by using ANSYS fluent and experiment in the subsonic wind tunnel to compare and validate results. The Delta wing models are meshed by using ICEM to improve the mesh quality and using the turbulence model for low Reynolds number flows Transition SST (4 equations) to calculate aerodynamic characteristics such as lift coefficient, drag coefficient, pressure coefficient... find the paths which connect centers of the vortices, and show the contours of pressures and velocities to evaluate the change of centers of the vortices. The results showed that the two vortices grow up and tend to move inward when the attack angle increase, the vortices are broken strongly in high attack angles, the aerodynamic quality of Delta wings change insignificantly when changing turbulent intensity at inlet. This research also carried out that the stall angle increase when increasing the taper ratio.

Abstract: This paper assesses the performance of three two-equation turbulence models viz. the SST k-ω, the RNG and realizable k-ε for the simulations of a rotating blade in a wind tunnel experiment where k, ε and ω are turbulent kinetic energy, dissipation rate and specific dissipation respectively. The experiments showed the stall-delay phenomenon at the inboard of the rotating blade at a Reynolds number of 4800. This trend of suction peaks was captured by all three turbulence models albeit not matching the experimental coefficient of pressure accurately. All three models also showed radial flow at the inboard which is consistent with the experiments while the SST predicted the least k at low wall values.

Abstract: To avoid broadband noise from a slat cove, the deployed slat contour is usually modified by filling cove, but the design is sensitive to aerodynamic performance. In the paper, a bionic slat without a cove is built on the basis of a bionic airfoil (i.e. stowed bionic multi-element airfoil), which is extracted from a long-eared owl wing. The quasi-two-dimensional models with a deployed bionic slat and a stowed bionic slat are manufactured by rapid manufacturing and prototyping system, respectively, and measured in a low-turbulence wind tunnel. The results are used to characterize high-lift effect: the lift coefficients of the model with a stowed slat are larger at less than 4°angle of attack, but the model with a deployed slat has the larger lift coefficients at greater than 4°angle of attack. Furthermore, the deployed bionic slat can increase stall angle and maximum lift coefficient, but also delay the decline of the lift coefficient curve slope meaning that the leading-edge separation is postponed within a certain range of angle of attack. At the same time, the flow field around the models is visualized by smoke wire method. The leading-edge separation of the model with a stowed slat is shown at low Reynolds number and angle of attack. However, the finding does not occur in the flow field of the model with a deployed slat at the same conditions, probably because the gap between the bionic slat and the main wing results in favorable pressure gradient, the deployed bionic slat decreases the peak of adverse pressure gradient by increasing the chord of the bionic multi-element model, and the bionic slat wake excites transition to the boundary layer on upper surface of the main wing. This superiority may be used as reference in the design of the leading-edge slat without a cove.

Abstract: In this paper, a low Reynolds number airfoil (S1223) is the objective of the study. The Navier-Stokes equations were established to simulate the complex flow around a low Reynolds number airfoil, in which the turbulence model was used. The complex flow around the airfoil was simulated at 2x10⁵ Reynolds number and its aerodynamic characteristics were analyzed. The relationship among lift coefficient, drag coefficient and angle of attack was studied.

Abstract: This paper presents a methodology to design the optimum proprotor for tilt-body micro-air-vehicles (TB-MAV) with efficient global propulsion system and long flight endurance in both cruise and hover modes. The TB-MAV developed at ISAE, which is called MAVion, was used as a baseline in the design process. To acquire maximum performance of TB-MAV’s global propulsion system, an efficient optimization process of the proprotor propulsion system was carried out. The optimization process consists of two-step inverse design methods. The first step determines the optimal operating conditions in terms of power and rotational speed of proprotor and the second step designs the optimal blade geometry in terms of twist angle distribution. The optimal blade twist distribution along the blade was computed using the Glauert’s strip theory for minimum energy loss condition. Meanwhile, the optimal operating conditions were determined by the motor outputs corresponding to high motor efficiency. A comparison of performance in terms of total efficiency and flight endurance between the optimized flexible proprotor, the optimized rigid proprotor, optimized propeller and optimized rotor is presented.

Abstract: As a new conceptual micro air vehicle, biomimetic flapping-wing robots have the advantages of small sizes, light weights, high maneuverability, and perfect aerodynamic performance. Flapping-wing robot can produce more effective aerodynamic force than traditional fixed-wing or rotary-wing aircrafts. Unsteady aerodynamics at low Reynolds number is the main theory applied to micro air vehicle analysis. In this paper, the flight parameters for a flapping-wing robot are designed with geometric similarity firstly. Then an improved aerodynamic model with optimized parameters is established. Lastly, some simulation and analysis are presented to illustrate and verify the feasibility and effectiveness of the models.

Abstract: Micro Air Vehicles (MAVs) are catching more and more attentions for their broad application in civilian and military fields. Since the theories on the aerodynamics of low Reynolds number are not maturely presented and the wind-tunnel experiments cost long periods and great expenses. The numerical simulation based on computational fluid dynamics (CFD) is a good method to choose. Through three-dimensional simulation of the wings, the aerodynamic characteristics of the flows around MAVs can be easily obtained. The tip vortices produced around low-Reynolds-number and low-aspect-ratio wings can increase the lift and stall angles. The result of numerical simulation can be used as references of theory analysis and wind-tunnel experiments.