Development of the flapping wing for ornithopters: a numerical modelling

We designed a X-type wing of flapping-wing Micro Air Vehicles (MAV) and doing some aerodynamic force testing by the flapping-wing MAV aerodynamic force testing device which designed by ourselves. In order to study the relationship of aerodynamic force on the flapping-wing models, we do these tests of different flapping-wing models in different angles of attack and flapping frequency. Found that X-wings flapping wing MAV rely mainly on aerodynamic wings folded back when the compressed gas emitted and received; increase the X-wings flapping wing MAV flapping frequency can significantly increase aerodynamic wings; and X-flapping wing MAV Aerodynamic wing root shoot ratio and aspect ratio with the decrease, inversely proportional to the relationship.

Micro air vehicles are gaining attention due to their wide range of applications in civilian and defense fields. The wings of these vehicles generate a particular flow regime which is to be explored further. Since the theories on the aerodynamics of all affects are still to be investigated, simulation based computational fluid dynamics is a good approach rather than wind tunnel experiments which involves cost and long periods of experimentation. This study mainly emphasize on the lift, lift coefficient, drag and drag coefficient with respect to Reynold’s number and angle of attack, by modelling and analyzing the fixed wing of a micro air vehicle. The analysis has been done selecting NACA25411 air foil. Modelling has been done in Gambit and analysis is taken up using Fluent. Angle of attack and Reynold’s number have been optimized to increase the lift and decrease the drag.

The aim of the paper is to investigate the wind effect on vehicle aerodynamic properties. Two-dimensional Ahmed body is examined with Computational Fluid Dynamics (CFD) method. During the analysis, two different studies were carried out. First, the simplified vehicle shape was examined in standing position, only the force from the wind velocity affected the body. The drag coefficient change was examined in case of different wind velocities and angles of attack. After that, the effect of wind while driving was investigated. The body was defined as a moving object and at another inlet the wind was defined. Different travelling and wind velocities with different angles of attack were studied. Based on the results of the simulations, a comprehensive impact of the wind can be measured on the drag coefficient. This proves that the wind has a measurable effect on vehicle aerodynamic properties and must be taken into account when investigating the effect of weather conditions on vehicle aerodynamic properties.

Natural fliers like bats exploit the complex fluid–structure interaction between their flexible membrane wings and the air with great ease. Yet, replicating and scaling the balance between the structural and fluid-dynamical parameters of unsteady membrane wings for engineering applications remains challenging. In this study, we introduce a novel bio-inspired membrane wing design and systematically investigate the fluid–structure interactions of flapping membrane wings. The membrane wing can passively camber, and its leading and trailing edges rotate with respect to the stroke plane. We find optimal combinations of the membrane properties and flapping kinematics that out-perform their rigid counterparts both in terms of increased stroke-average lift and efficiency, but the improvements are not persistent over the entire input parameter space. The lift and efficiency optima occur at different angles of attack and effective membrane stiffnesses which we characterise with the aeroelastic number. At optimal aeroelastic numbers, the membrane has a moderate camber between 15% and 20% and its leading and trailing edges align favourably with the flow. Higher camber at lower aeroelastic numbers leads to reduced aerodynamic performance due to negative angles of attack at the leading edge and an over-rotation of the trailing edge. Most of the performance gain of the membrane wings with respect to rigid wings is achieved in the second half of the stroke when the wing is decelerating. The stroke-maximum camber is reached around mid-stroke but is sustained during most of the remainder of the stroke which leads to an increase in lift and a reduction in power. Our results show that combining the effect of variable stiffness and angle of attack variation can significantly enhance the aerodynamic performance of membrane wings and has the potential to improve the control capabilities of micro air vehicles.

In this paper, a bio-mimic approach was used to help characterise a flapping wing for the design of a Micro Air Vehicle (MAV). The main objective of this study is to characterise the lift performance of a flapping wing inspired by bat wings at different angle of attack (AoA), advance ratio (J) and wing camber. A series of flapping bat wings with different wing camber (flat, 6% camber, 9% camber, 12% camber, and 15% camber) was tested for its time averaged lift (CLavg) at AoA of 0⁰ to 50⁰ and at three different advance ratios which are; 0.88 (unsteady state regime), 1.76 (steady state regime), 3.09 (steady state regime). The result shows that as the advance ratio increases, the generated CLavg begins to decay but the enhancement of CLavg between increasing camber increases. This shows that wing camber begins to have a bigger role at higher advance ratio and hold the key to overcoming the adverse effect of high steady state flight regime on a flapping wing. Â

MAVs (micro air vehicles) with a maximal dimension of 15 cm and nominal flight speeds of around 10 m s−1, operate in a Reynolds number regime of 105 or lower, in which most natural flyers including insects, bats and birds fly. Furthermore, due to their light weight and low flight speed, the MAVs' flight characteristics are substantially affected by environmental factors such as wind gust. Like natural flyers, the wing structures of MAVs are often flexible and tend to deform during flight. Consequently, the aero/fluid and structural dynamics of these flyers are closely linked to each other, making the entire flight vehicle difficult to analyze. We have recently developed a hummingbird-inspired, flapping flexible wing MAV with a weight of 2.4–3.0 g and a wingspan of 10–12 cm. In this study, we carry out an integrated study of the flexible wing aerodynamics of this flapping MAV by combining an in-house computational fluid dynamic (CFD) method and wind tunnel experiments. A CFD model that has a realistic wing planform and can mimic realistic flexible wing kinematics is established, which provides a quantitative prediction of unsteady aerodynamics of the four-winged MAV in terms of vortex and wake structures and their relationship with aerodynamic force generation. Wind tunnel experiments further confirm the effectiveness of the clap and fling mechanism employed in this bio-inspired MAV as well as the importance of the wing flexibility in designing small flapping-wing MAVs.

The paper presents the fluid flow analysis of a symmetric airfoil having circular cavities on its suction surface at three different chordwise locations from leading to trailing edges. The leading edge cavity shapes were distorted using Bezier polynomial so that vortex trapping pattern in the cavities can be captured. Structured meshing scheme via a multi-block strategy was employed. Unsteady simulations were performed by a Reynolds averaged Navier-Stokes (RANS) solver. Lift, drag, pressure and skin friction coefficients were monitored at Reynolds number (Re) = 15 × 104 and 6 × 105 and different angles of attack. Cavity placed at the trailing edge produced better lift to drag ratio as compared to that of the other cavities. The distorted cavities performed badly in terms of lift and drag coefficients. The elliptical cavity shape showed better results at the angles of attack up to 10°.

Ice accretion on aircraft wings poses a critical safety challenge during operational flights as it alters the aerodynamic performance the wing profile and increases structural loads acting on it. Therefore, it has become crucial to understand the thermodynamic and fluid dynamic behavior of ice formation over the airfoil surface to address this issue. This study investigates the heat and mass transfer characteristics of a two-dimensional NACA0012 airfoil during in-flight icing under various flow conditions. The research aims to model the ice accretion process, analyze its impact on aerodynamic performance, and assess the heating requirements for ice mitigation. Throughout the study, a numerical approach was employed using the FENSAP-ICE simulation suite in ANSYS Fluent, which integrates the Reynold’s-Averaged Navier-Stokes equations with the K-ω SST turbulence model to model airflow and ice formation. Additionally, the study investigated icing at airflow velocities of 80, 102, 150, and 200 m/s, analyzing the resulting ice formation as a result of varying flow speeds, its influence on lift and drag coefficients across different angles of attack, and the heating loads necessary for ice removal using thermal balance calculations. The results of the study showed strong consistency between the simulated ice accretion patterns and droplet collection efficiency and the experimental findings reported in literature. Therefore, validating the use if FENSAP-ICE for such analyses. Furthermore, it was also found that the ice build-up over the airfoil significantly degrades its aerodynamic performance with reductions in lift and increases in drag coefficients. The obtained findings provide valuable insights for expanding the numerical analysis performed in this study to design effective ice protection systems for aircrafts under diverse operational conditions.

The primary goal in development of MAVs is to develop a flying body that weigh as less as 90 grams, with a span of 15cm [1]. Since it is challenging to meet these design characteristics of a MAVs with current technology, there has been a lot of research going on in this direction. This paper is also a continuation of the same quest. In this research a delta wing micro air vehicle was analyzed at low sub sonic speed at different angles of attack for determining lift, drag force, stall angle and L/D ratio. CFD and XFLR have been used as computational tools. For CFD analysis, a far field technique was used to calculate the lift and drag coefficients. Rectangular domain was created around the body with a size 10 times greater than body so that flow behavior can be captured accurately. Inflation layers were created around the body to capture boundary layer. Fine mesh was created at the regions of higher gradients. In fluent flow was analyzed using two turbulent models (SA and k-e). A potential flow solver (XFLR) was also used to compare results from RANS methodology with vortex lattice method (VLM). Validation of computational results was carried out by comparing with earlier research concerning wind tunnel testing of MAV [2] at 100,000 Re. This research will help the aero dynamists to understand the complete procedure of computational and XFLR analysis of MAVs. It was found that XFLR predicts higher values of lift coefficient and lower values of drag coefficient at all angles of attack. Consequently, lift to drag ratio as predicted by XFLR was found greater than RANS models. Further no appreciable difference was noticed between lift and drag characteristics predicted by SA and k-e models.

This study examines the aerodynamic performance of a NACA 4412 airfoil that is covered with denticles, comparing it to a smooth NACA 4412 airfoil. The aim was to assess the lift-to-drag ratio of the airfoil utilizing biomimetic surfaces inspired by the dermal denticles of Isurus oxyrinchus. To achieve this, the airfoils were subjected to testing in a wind tunnel. Both the denticles-covered and smooth airfoils, measuring 355 by 184 mm, were equipped with 27 pressure taps distributed across three spanwise sections: the leading edge, upper surface, and lower surface. Nine flexible tubes were connected to pressure sensors for each row of static taps. Wind tunnel tests were conducted at various angles of attack (AOAs), ranging from −10.8° to 16.2° with an increment of 1.8°. Testing was carried out at wind speeds of 3, 6, and 9 m/s. Computational fluid dynamics (CFD) simulations were conducted on the smooth airfoil under identical conditions to validate the wind tunnel testing setup. The lift and drag coefficients were derived from the recorded static pressures. A comparison between the aerodynamic coefficients obtained from experiments and CFD simulations indicated that higher wind speeds are preferable for wind tunnel testing as they yield more consistent results. When examining the aerodynamic coefficients of the smooth airfoil compared to the denticle-covered airfoil, it was found that the latter generally produced higher lift and drag, resulting in a lower lift-to-drag ratio across different angles of attack and wind speeds. Specifically, at 3 m/s, the denticle-covered airfoil exhibited better lift at most AOAs, higher drag at certain AOAs, and improved lift-to-drag ratios. At wind speeds of 6 and 9 m/s, the denticle-covered airfoil demonstrated higher lift for all tested AOAs and increased drag for several AOAs, yet it consistently had lower lift-to-drag ratios. These findings point to the potential benefits of utilizing the denticle-covered NACA 4412 airfoil due to its enhanced lift characteristics at lower wind speeds. Further research is warranted to quantify the differences between the airfoil types.

Powered autonomous aircraft can fly under an automatic control system without intervention from a pilot, which is significant for firefighting applications in today’s world. Small, capable, and cost-effective, they can be used to survey an area in more detail and closer to the ground than traditional aircraft and can even deliver humanitarian or fire-suppression payloads. In this work, a small-scale powered autonomous aircraft employing a KFm2 modified NACA 2412 airfoil is designed and analyzed. The conventional airfoils generally follow a teardrop shape, with the interior structure drastically increasing weight. A flat plate design reduces the weight, however, it drastically increases the parasitic drag from exposed avionics components on the surface and does not produce useful lift. The KFm2 airfoil modification is a hybrid of a flat plate and a conventional airfoil (NACA 2412), reducing the weight while maintaining the lift capability of the original airfoil. The KFm2 modified airfoil has a stepped profile where the step is located at the 50% chord length, and the height of the step is 7% of the chord length. The flow field characteristics and aerodynamic performance of this powered autonomous airplane are investigated numerically at different angles of attack (0°, 3°, 5°, 7°, 9°, and 11°) and velocities (6.1 m/s, 12.2 m/s, and 18.3 m/s). A similar study is performed on a small-scale aircraft with an unmodified NACA2412 airfoil to compare the effect of airfoil design at different velocities and angles of attack. For numerical modeling, ANSYS Fluent is employed and the SST K-Omega turbulence model is used for turbulence modeling. A grid independence study is performed and validation study is conducted against experimental data in literature. The results indicate the advantage of the hybrid geometry of the airfoil by increasing the lift force while reducing weight, making it a prime candidate for small powered autonomous aerial vehicles.

A numerical study is carried out to bring the boundaries of cavitating flow features on S-blade with and without the ultrasound field. The monitor points of pressure and vapor fraction are created on the upper and lower surface of the blade. Strouhal number is obtained from the time variation of monitor points of pressure and vapor fraction for different cavitation number and angle of attack. The effect of ultrasound with a different frequency is applied on the cavity in the wake and its effect on drag, and a lift is explored for different angles of attack. It is found that cavity dynamics for the upper and lower surface are significantly influenced by imposed ultrasound. At lower frequency range, it enhances the cavitation activity.

Investigations have been made adopting experiments and computations on an ogive-nosed slender body at different angles of attack and Reynolds number of 29,000 based on the model base diameter diameter. The results indicated an increase in the side force at large angles of attack, which is mainly due to the presence of asymmetric vortices in the leeward of the body. The inclusion of a rectangular cross-sectioned ring in the initial portion of the body reduced the side force at higher angles of attack. However, significant side force was experienced at lower angles of attack (30° < α < 40°). Use of a ring of 3% height was found to be suitable for reducing the side force at a higher angle of attack. From the results obtained it was observed that a ring if placed at a different axial location alters the flow field and changes the side force at higher angles of attack. Further studies indicated that placing of rings pair at an axial location of 3.5 and 4.5 times the base diameter reduced the side force to a very low value at all the angles of attack for the present shape of body and flow conditions.

CFD study of section characteristics of Formula Mazda race car wings

The otter board is one of the main components of single boat trawl fisheries. An oval cambered double slotted otter board was developed for improving the expansion performance of trawl net in bottom trawl fisheries. A flume model experiment was conducted to measure the lift coefficient (CL), drag coefficient (CD), and lift to drag ratio (K) in different angles of attack (α). The experimental results are as follows : (1) The CL and K value show a trend of increasing at the beginning and then decreasing with the increase of angle of attack, the CD value reflects an upward trend as the angle of attack increases; (2) The D3 otter board (front flow deflector angle at 29°) showed a better hydrodynamic performance. When α=30°, the max lift coefficient (CLmax) was 1.464, in this case CD = 0.554 and K=2.643. When α=15°, the max lift to drag ratio (Kmax) was 4.165, CL =0.633, and CD = 0.152. This suggests that the best working scope for the angle of attack is between 15°~30°, in which case, CL>0.633 and K>2.643. The mean value of the lift coefficient was 1.071 and the mean of the lift to drag ratio was 3.482. Comparative analysis of the hydrodynamic performance of different types of otter boards showed that the D3 otter board both had good expansion performance and efficiency, which can provide a reference basis for further optimization of the bottom trawl otter board.