Flap Angle Research Articles

Numerical analysis on hydrodynamic performance and hydrofoil optimization for amphibious vehicles

A numerical approach is established to study the hydrodynamic performance using an amphibious transport vehicle (ATV) as a research object. Numerical calculation based on the Reynolds average Navier–Stokes method is studied in terms of first layer grid height, surface meshing partition scale, and prismatic layer coefficient. Through uncertainty analysis, the correctness and convergence of the numerical approach are verified. Towing tests are conducted to compare the experimental data with the simulation results, which validated the reliability of the numerical approach under all working conditions. Results show that the numerical approach will affect the simulated results, with an average error of 3.91% for the resistance and 4.21% for the trim, meeting the requirements for analysis accuracy. Based on the proposed numerical approach, an optimization design is carried out to improve the hydrodynamic performance of the ATV. Effects of bow plate angle, stern flap angle, and stern flap install height are studied. Latin hypercube is used for sampling in optimization design, and the Kriging method is applied to establish an approximate model. The cross-validation is carried out using the leave-one-out method. Particle swarm optimization is used for parameter optimization, and the optimized configuration is verified using the numerical approach. Results indicate that the combination of bow plate and stern flap shows excellent improvement in the hydrodynamic performance of amphibious vehicles. Numerical error of the approximate model is only 0.292%, which fully verifies its accuracy and effectiveness. The optimized ATV configuration shows the best drag reduction performance of 38.81% compared to the original model.

NumericalStudy of Turbulent Flows over a NACA 0012 Airfoil: Insights into Its Performance and the Addition of a Slotted Flap

This work provides a comprehensive overview of various aspects of airfoil CFD simulations. The airflow around a 2D NACA 0012 airfoil at various angles of attack is simulated using the RANS SST turbulent flow model and compared to experimental data. The airfoil is then modified with a slotted flap and additionally the angle of the flap is altered. The flow model is subsequently coupled to a heat transfer model to compare the isothermal versus non-isothermal performance. The airfoil with the slotted flap shows increased CL and CD values compared to the standard NACA 0012. Larger flap angles further increase the CL and CD. The lift and drag coefficients show no difference in the non-isothermal model compared to the isothermal model, indicating the isothermal model is sufficient for this system. The 3D model without wingtips shows a similar CL to the 2D model as it effectively has an infinite span. Adding a wingtip reduces the lift coefficient, as the air can flow around the wingtip, increasing the pressure on top of the wing. Overall, these results match the behavior expected from wing theory well, showing how CFD can be effectively applied in the development and optimization of wings, flaps, and wingtips.

Fourth AIAA High-Lift Prediction Workshop: Fixed-Grid Reynolds-Averaged Navier–Stokes Summary

The current state-of-the-practice technology for high-lift aerodynamic simulations is to solve the Reynolds-averaged Navier–Stokes (RANS) equations on a fixed grid or a refinement sequence of fixed grids. The Fixed-Grid Reynolds-Averaged Navier–Stokes Technology Focus Group set out to determine meshing requirements and best practices, whether RANS can accurately predict the change in aerodynamic performance with changes in flap deflection, whether RANS modeling can produce accurate results near CLmax, and the effects of underconvergence and solution strategy on computed results. Eighteen groups of participants submitted over 100 datasets. Challenges with grid convergence and iterative convergence made it impossible to definitively answer all the questions we had posed. Despite this, we can conclude that meshes with at least half a billion cells (more than one billion degrees of freedom) are required for grid convergence away from stall; that RANS simulations cannot currently be reliably used to predict aerodynamic coefficients near stall, nor changes in coefficients with changes in flap angle; that iterative underconvergence remains a significant source of uncertainty in outputs; and that solution initialization can have an important effect on solution behavior, including flow separation patterns.

Investigation of the effect of hidden vortex generator-flap integrated mechanism revealed in low velocities on wind turbine blade flow

In this study, the flap and vortex generator (VG) mechanisms which were employed separately in aircraft were used as integrated first in literature. In this mechanism, the flap motion triggered and activated the VGs when it was needed at low speeds. Thus, this flap mechanism eliminated the unnecessary drag force generation when VGs were not needed. Numerical simulations which were validated with experimental data were employed in the study. In the first step, the flow characteristics formed on the S809 airfoil with 4 different flap angles (β = 30°, 20°, 10°, 0°) were investigated without the VG. Then, those flow structures formed on the S809 airfoil with both flap and VG were examined under the same conditions. According to the results, utilizing flap and VGs together had a positive impact at low wind speeds. Moreover, due to the flap and vortex generator integrated mechanism closed up to be not unnecessary drag formation at high wind speeds, thus those structures increased further to the positive effect with the increasing wind velocity. In terms of energy output, it was shown that this novel idea provided more energy output in this study.

Trajectory planning and prescribed performance tracking control based on fractional-order observers for unmanned helicopters with unmeasurable states

The trajectory planning and tracking control problem is studied in this paper based on prescribed performance method (PPM) for the small-scale unmanned autonomous helicopter (UAH) with wind-gust disturbances (WGDs) and unmeasurable states. For the purpose, the nonlinear model with flapping dynamics is established, and the transformation performance function is used to ensure that the errors of trajectory tracking satisfy the corresponding performance. A fractional-order observer is designed for unmeasurable states to estimate the flapping angles in actual flight, and the fractional-order extended state observer (ESO) is constructed to estimate the WGDs, respectively. On the basis of PPM and the designed observers, the fractional-order theory-based backstepping trajectory tracking control scheme is developed for the UAH system, and the three-dimensional trajectory is planned by the improved wolf pack algorithm. Then the stability of the entire system is proven through strict theoretical analysis. Finally, the simulation analysis on the UAH is presented to demonstrate the efficiency of the designed method.

Optimum design of morphing flaps for improving horizontal axis wind turbine performance

AbstractThis study presents a conceptual design of optimum deformable blades as a function of wind speed. In this design, at any speed of wind flow, the blade sections have their optimal shape. Accordingly, the wind turbine performance will increase at different speeds. The WindPACT 1.5‐MW wind turbine is used as the base turbine, which has three different sections at the root, middle, and tip of the blade. The proposed deformation method, due to its simplicity, is suitable for the use of actuators. Different deflection angles are obtained at various wind speeds for each section through a controllable flap deformation method. The blade element momentum theory is used to calculate the performance of the morphing flaps. The results of this design are then validated by computational fluid dynamics (CFD) simulations using three‐dimensional Reynolds averaged Navier–Stokes equations together with the k–w turbulence model. The CFD results show that using optimum flap angles between 2° and 8° in the root, middle, and tip parts of the blade leads to a promising power increase of about 1.2%, 3.7%, and 13.5% at wind speeds of 4, 8, and 11.5 m/s.

The effect of different endplate geometries on the hydrodynamic and acoustic performance of the tip-loaded propeller

The tip-loaded propeller design is one of the new methods for improving propellers' hydrodynamic and acoustic performance. This study investigates the effects of different endplate geometries on the performance of a 5-blade B-series propeller with normal skew and rake using the RANSE numerical method. For each of the different geometries, hydrodynamic coefficients, cavitation volume, and propeller noise are calculated. Using an endplate, this research aims to reduce cavitation, tip vortex, and propeller noise. As a result of the research, propellers with a contraction of 0.95R and a flap angle of 60°, as well as propellers with a contraction of 0.9R and a flap angle of 60°, showed better acoustic performance than other propellers, resulting in approximately 7 dB and 5 dB reductions in overall noise for the initial propeller. In terms of hydrodynamic efficiency, these propellers have a reduction of 0.2 and 0.8%, respectively. It can be stated that both propellers are generally optimal both in terms of acoustics and hydrodynamics.

Protection of the marginal mandibular branches of the facial nerves by different surgical procedures in comprehensive cervical lymphadenectomy for locally advanced oral and oropharyngeal cancer: a multicenter experience

ObjectiveAccording to the different characteristics of patients and cervical lymph node metastasis of oral and oropharyngeal cancer, the marginal mandibular branches of facial nerves were treated by different surgical procedures, and the safety and protective effects of different surgical procedures were investigated.MethodsOne hundred ninety-seven patients with oral and oropharyngeal cancer satisfying the inclusion criteria were selected. According to the different characteristics of patients and cervical metastatic lymph nodes, three different surgical procedures were used to treat the marginal mandibular branches of the facial nerve: finding and exposing the marginal mandibular branches of the facial nerves at the mandibular angles of the platysma flaps, finding and exposing the marginal mandibular branches of facial nerves at the intersections of the distal ends of facial arteries and veins with the mandible, and not exposing the marginal mandibular branches of the facial nerves. The anatomical position, injury, and complications of the marginal mandibular branches of the facial nerves were observed.ResultsThe marginal mandibular branches of the facial nerves were found and exposed at the mandibular angles of the platysma flaps in 102 patients; the marginal mandibular branches of facial nerves were found and exposed at the intersections of the distal ends of the facial arteries and veins with the mandibles in 64 patients; the marginal mandibular branches of facial nerves were not exposed in 31 patients; among them, four patients had permanent injury of the marginal mandibular branches of the facial nerves, and temporary injury occurred in seven patients. There were statistically significant differences in the protection of the mandibular marginal branch of the facial nerve among the three different surgical methods (P = 0.0184). The best protective effect was to find and expose the mandibular marginal branch of the facial nerve at the mandibular angle of the platysma muscle flap, and the injury rate was only 2.94%.ConclusionThe three different surgical procedures were all safe and effective in treating the marginal mandibular branches of the facial nerves, the best protective effect was to find and expose the mandibular marginal branch of the facial nerve at the mandibular angle of the platysma muscle flap.

Numerical study on flow characteristics of shroud with and without flap for wind turbine applications

Shrouded wind turbines have the shroud added to the rotor’s circumference, enhancing wind power compared to conventional wind turbines. This article aims to design a shorter aerofoil cross-sectional enclosure for the wind turbine that improves average velocity and reduces drag, duct material volume, and tower load. Numerical simulations were performed to understand the characteristics of shroud alone and shroud with flap using ANSYS Fluent in the operating regime of the small wind turbine. The influence of the shroud’s length-to-diameter L/ D ratio and angle on the performance was analyzed using a one-factor-at-a-time (OFAT) approach, and the optimum values were found. Then the analysis was performed by including the flap at the exit of an optimized shroud. The shroud with flap results showed enhanced average velocity, increased mass flow rate, and higher drag forces than a single long shroud. In order to reduce the drag coefficient, the enclosure geometrical parameters were analyzed using the Design of Experiments (DOE) approach. The results show that the shroud L/ D ratio significantly affects the average velocity. Moreover, the optimum combination was found as shroud L/ D ratio=0.4, shroud angle=9°, flap L/ D ratio=0.2, flap angle=16°, and radial distance of 0.2 R. The proposed combination helps to get an acceleration factor of 1.78, a drag coefficient of 1.84, and a material volume of 0.7×10−3 m3. It was found that the optimal ratio of shroud L/ D could be between 0.3 and 0.6, resulting in a higher acceleration factor, lower material volume, and shorter length. The drag forces acting in the shroud alone and shroud with flap were studied by analyzing the forces in every section. The results show that the negative drag force acts in the shroud’s inner leading edge.

Investigation of Improvement Design on Aileron Surface Flow State of High Lift Configuration in BWB

The aileron is one of the most important tools for adjusting the roll attitude of the aircraft, but the surface flow state of the aileron is likely to be affected by high-lift devices. In this paper, by using computational fluid dynamics (CFD) simulations and wind tunnel tests, the Krueger flap effects on the surface flow state of ailerons in a typical blended wing body civil aircraft were investigated. In order to increase the lift, deflecting the Krueger flap makes the flow separation occur on the aileron surface of BWB civil aircraft. This way of the surface stall that the flow separation in the aileron zone first appears at the wing tip rather than at the wing root is unreasonable for civil aircraft. For the above problem, a sensitivity analysis of the design parameters of the Krueger flaps was carried out. The results indicate that the angle of the outboard Krueger flap mainly affects the flow separation of the ailerons. Its length affects the pitch moment tremendously, while its width slot affects the pitch moment slightly. Finally, the design principles of the BWB Krueger flap for the improvement aileron surface flow state were proposed, and the redesign of the BWB high lift configuration significantly improved the flow state of the aileron zone at a minimal cost of aerodynamic characteristics without losing the existing great aerodynamic performance.

Aeroacoustic Benchmarking of Trailing-Edge Noise from NACA Airfoil with Trailing-Edge Serrations

Experimental results on trailing-edge (TE) noise from a NACA airfoil are presented for a chord-based Reynolds number range between and . Far-field TE noise from the baseline airfoil with a straight TE and TE serrations is measured with varying , angle of attack, and serration shape and flap angle. Additionally, aerodynamic coefficients and boundary-layer parameters at the TE are also reported. To cover such a broad range, two NACA airfoil models were tested in two different wind tunnels. The measurements include the emitted noise with natural and forced transition locations. For the straight TE, the forced transition location results in up to 5 dB increase of the far-field TE noise level, compared to the natural one. Scaling of the far-field noise spectra from the baseline TE shows that the Strouhal numbers at which the peak noise level is measured reduce as increases. TE noise spectra for the cases with the TE serrations are found to be dependent on the airfoil lift and . The present data are to be included in the framework of the Benchmark Problems for Airframe Noise Computations category I and are publicly available in a repository with the following digital object identifier (DOI): https://doi.org/10.4121/20940646.

Experimental Investigation of the Effect of Passive Flap Configuration on the Performance of the Darrieus Hydrokinetic Turbine at Low TSR

The finite supply of fossil fuels has forced scientists to explore sustainable energy alternatives. One of the alternatives is using a hydrokinetic turbine to generate energy from the water current. Vertical axis hydrokinetic turbine Darrieus type has a range operation in medium to high TSR. In this study, a Darrieus hydrokinetic turbine was tested experimentally in lower TSR to observe the behavior of the attached passive flap on the turbine's blade with different placement configurations, i.e., inner flap, outer flap, and combined flap. The passive flap movements were limited to a maximum opening angle of 45° and 90° for each flap position compared to NACA 0018 (Clean) without a flap. The test was demonstrated inside the racetrack flume under Re 14500. All the tests were recorded using a video camera to give clear information regarding the flap's behavior. The turbine torque was measured using a rope brake dynamometer by gradually adding weights to create resistance between the rope and the turbine's rotation. As a result, the inner flap configuration with a maximum opening angle of 90° positively affects the turbine performance compared to all configurations. Attaching a passive flap outside the blade rotation will reduce the turbine performance. The smaller the opening angle of the outer flap, the higher the turbine performance and vice versa. It indicates that the outer flap for Darrieus hydrokinetic turbine is not recommended. Furthermore, the inner flap improves the operation range in lower TSR than the original NACA 0018.

CFD based prediction on hydrodynamic effects of Interceptor and flap combination on planing hull

It has been a continuous effort for long years by high-speed vessel designers to achieve its optimal hydrodynamic performance. Few studies were made on the impact of interceptor and flap combination on high speed hulls in recent years. Interceptors are blades which extend vertically downwards at the transom of the vessel and a flap is attached to its end. The installation of interceptor near the vessel transom a change in pressure distribution around the hull and more significantly observed at the transom. The present study investigates on the hydrodynamic quality of 20deg deadrise high-speed planing hull mounted with interceptor-flap combination using computational fluid dynamics (CFD). Planing hull model was analyzedusing CFD based Finite Volume method with dynamic mesh. The height of the interceptor and angle of flap plays an important role on the efficiency of the vessel. Experiments were carried out in the towing tank at Indian Institute of Technology Madras for the planing hull and CFD studies were extended with interceptor-flap. The validation studies serve to authenticate the use of the interceptor on the basis of comparison with simulations using model tests. The pressure variation that is caused due to integrated interceptor-flap has an effect on the resistance of the vessel which further showed better control of trim. The numerical study on planing hull with interceptor-flap showed an increased waterline length which leads to reduced Froude number. The hydrodynamically improved underwater form was observed leading to resistance reduction of upto 25% on the vessel and significant reduction of trim upto 57% at the design speed.

Experimental Investigation of Flow Separation Control over Airfoil by Upper Surface Flap with a Gap

This paper focused on the effects of the flap with a tiny gap on the flow separation over the NPU-WA-180 airfoil. The effects of the geometric parameters of the flaps, such as the flap gap height, angle, and position, were investigated. The study showed that the flap can significantly improve the stall features of airfoil in a limited phase of angle of attack (AoA), and increase lift and reduce drag at a high AoA. It can increase the lift coefficient and drag coefficient in the case of high AoAs, and the angle range of the lift augmentation and drag reduction can reach more than 9°. Furthermore, an excessively large gap is not conducive to the improvement of the airfoil stall performance. The flap angle plays a key role in the airfoil stall characteristic. As the flap angle decreases, the angle range of improving airfoil stall characteristics becomes larger, the pitching moment increment becomes smaller. However, the maximum lift increment and the effect of the drag reduction will decrease. And the effects of the position of the flap on the airfoil performance were also studied. Considering the maximum lift coefficient and drag coefficients in large AoA, the Type1 installed at the 0.7c position has the best effect; from the perspective of delayed stall, the Type1 installed at the 0.6c position has the best delay effect. These results can provide the data and theoretical support for the flap application in engineering.

Time–frequency characteristics of noise generated from different slat and flap geometrical configurations of the high-lift device

High-lift device installed on modern large aircraft is a major noise source during the approach and landing phases. For high-lift device, slat and flap parameters such as gap, overlap and deflection angle have strong effect on aerodynamic and aeroacoustic characteristics. However, the research about time–frequency characteristics of high-lift device noise affected by slat and flap parameters is lacking. This paper presents an investigation on 30P30N model to reveal the effect of different slat and flap geometrical configurations on the aeroacoustic time–frequency characteristics with experimental measurement and wavelet analysis. The results show that the multiple tones at small flap and slat deflection angles are mainly generated from the flap gap region. The time–frequency characteristic of the tones is satisfied with the amplitude modulation phenomenon, namely that the acoustic energy concentrates on the primary tone and the other tones are generated from the modulation process of the primary tone. While the multiple tones at large slat deflection angles are generated from the slat cove and slat gap regions. The time–frequency characteristic of the tones is satisfied with the mode switching phenomenon, namely that the dominant noise energy temporally switches from one mode to another in time and these multiple tones cannot coexist independent of one another.

Optimisation of Trailing Edge Flaps on the Base Cavity of a Vehicle for Improved Performance at Yaw

Regulations to reduce greenhouse gas emissions of passenger vehicles are becoming increasingly stringent. The aerodynamic drag is a major contributor to the vehicle’s total energy consumption where a large portion is attributed to the base wake. This paper optimises the angles of small trailing edge flaps on a base cavity of a full-scale sports utility vehicle placed in a wind tunnel. The trailing edge flaps are controlled using servos mounted inside the cavity. The flap angles are optimised using a surrogate model based optimisation algorithm with the objective of reducing the aerodynamic drag at different yaw angles and to create a yaw-insensitive geometry by considering several weighted yaw angles to form the driving cycle averaged drag. Low drag designs are further investigated using base pressures and wake measurements. The results show that the base pressures are symmetrised by reducing the crossflow in the wake. As the model is yawed the wake becomes increasingly downwash dominated by a large rotating windward structure which is reduced by the optimised flaps. The cycle averaged drag optimised design has a smaller increase in drag when yawed compared to a design optimised without considering yaw.

Whirl Tower Demonstration of an SMA Blade Twist System

This paper focuses on the development and demonstration of a novel blade morphing system within a whirl tower facility. The scope is to investigate the behavior of the proposed architecture under representative loads, demonstrating its capability to alter the blade original shape in operation under centrifugal, aerodynamic, and internal forces. The morphing concept was developed inside the European project “Shape Adaptive Blades for Rotorcraft Efficiency”, SABRE, and consists of a shape memory alloy system able to change the original twist law and, in this way, enhance rotor performance at certain specific regimes, such as hover and vertical flight. These phases, indeed, are generally penalized with respect to other more extended flight regimes (cruise). The work starts with an overview of the research in the field of morphing, with specific reference to the researches envisaging rotary wing demonstrations. Then, an overview of the morphing twist concept is provided, with particular attention paid to those features particularly suited for the whirl tower representative test environment. The laboratory characterization and commissioning operations are illustrated. Then, the task of the installation of the prototype on the whirl tower facility is described together with the testing modality adopted. Finally, the results of the test campaign are illustrated and critically discussed, providing the reader with insights and possible future steps to be taken in further research. The impact on the morphing capability of the following different parameters was investigated: the number of the prototype segments switched on, the speed and thus the centrifugal actions, and the angles of attack. The stiffening effect due to centrifugal actions was quantified through the measurement of the actual twist and the internal deformation. The link between speed, angle of attack at root, and twist and flap angles was also tracked, building a database useful for the comprehension of the phenomenon, and for the assessment of numerical predictive models. The achieved results highlighted the capability of the system to produce a twist angle matching the target of 8° per blade radius; this figure is related to a potential power saving of 10% in hover and vertical flight and an improvement of about 1% on the over-all efficiency of the rotorcraft.

Criterion for the transition of the fan control system to the mode of dynamic performance control

An algorithm for the transition of the automatic control system from the fan performance stabilization mode to the dynamic control mode is presented. The algorithm makes it possible to use the change in the closing angle of the air distribution regulator flaps and the regulation of the fan shaft speed to reduce the power required for ventilation of the subway.

Numerical Study using RANS model to Predict Loading of a Wind Turbine Blade with a Trailing Edge Flap

A numerical study was conducted with a 3D steady state Computational Fluid Dynamics (CFD) model using k-ω SST at SATP conditions for air. The mesh geometry is based on a S833 airfoil with a trailing edge flap to predict the lift and moment loads. This airfoil is representative of a wind turbine blade. A set of static CFD simulation cases were conducted with a free stream velocity of 29 m/s at an angle of attack (α) between -4° and 20°. A trailing edge flap is also present on the airfoil which was operated between an angle (αf) of -20° and 20°. The airfoil has a chord of 178 mm with the trailing edge flap covering 20% of the length and chord-based Reynolds number of 350,000. The CFD results were compared against an experimental study performed in a closed-loop wind tunnel at the University of Waterloo. The wind tunnel has a contraction ratio of 9:1 and a cross section of 0.61 m square. The experimental data showed that lift forces increased at a larger angle of attack and larger downward flap angle up until stall. Moment on the blade is relatively constant regardless of the angle of attack, however, increases significantly with upward flap angle. The CFD results showed very similar results in both the lift and moment coefficient, with all angle configurations having over 90% agreeability excluding α near +/- 20°.

Thermal-hydraulic performance enhancement of solar receiver channel by flapped V-baffles

Thermal-hydraulic performance investigation in a solar receiver channel equipped with a vortex flow generator, namely, flapped V-shaped baffle (FVB) on the absorber has been experimentally carried out. The purpose of using the square flaps on the V-baffle was to decline the pressure drag by directing the impact air to the absorber surface. The working fluid was air flowing into the uniform heat-fluxed channel at Reynolds number (Re) between 5300 and 23,600. The FVBs with 45°attack angle (α) were placed periodically on the absorber with the upstream V-apex arrangement. The FVB characteristics included three relative baffle-pitches (RP) and four flap angles (β)at one relative baffle height (RB=0.5) and flap length (b1/b = 0.4) were examined to obtain the optimum RP and β values. The present investigation has revealed that the FVB gives a considerable decrease in friction loss when compared with the solid V-baffle (β = 0) while the heat transfer rate reduces a little. The FVB with β = 45°, RP = 1.5 yields the greatest thermal performance around 2.5 as a result of the injecting air flows from the flap opening aside from the reduced friction loss. For the current experimental data, the Nusselt number and friction factor correlations were determined in the form of a function of the geometric FVB parameters and Re.