Lifting Surface Research Articles

Aerodynamic analysis of wings in Chevron and V formation flights

In this paper, numerical analysis is conducted using a local camber correction approach called “decambering” to predict pre and post-stall aerodynamic characteristics of multiple lifting surfaces operating in formation. A three wings Chevron formation and five and nine wings V-formation are studied. NACA2412 wing section is used and experimental validation is provided with Cessna 172 aircrafts flying in Chevron formation. Effect of wing incidence and shifting of stall angles is looked at along with changes in geometric offsets between the wings in formation. The spanwise distribution of coefficients of lift and induced drag at different angles of attack, including high and post-stall angles of attack is studied for all the wings. The span efficiency factor, which represents the correction in drag due to change in lift as compared to that of an ideal wing of the same aspect ratio but with elliptical lift distribution is calculated. The maximum possible efficiency is then used to estimate the maximum reduction in drag possible for individual wings in different formations. The change in efficiency with number of lifting surfaces in a formation is also estimated.

Simulation and Optimization of Takeoff Maneuvers of Very Flexible Aircraft

A generic framework for the simulation of transient dynamics in nonlinear aeroelasticity is presented that is suitable for flexible aircraft maneuver optimization. Aircraft are modeled using a flexible multibody dynamics approach built on geometrically nonlinear composite beam elements, and the unsteady aerodynamics on their lifting surfaces is modeled using vortex lattices with free or prescribed wakes. The open loop response to commanded inputs and external constraints is then fed into a Bayesian optimization framework, which adaptively samples the configuration space to identify optimal maneuvers. As a representative example, the proposed approach is demonstrated on a catapult-assisted takeoff. The specific modeling challenges associated to that problem are first discussed, including the effect of aircraft flexibility. An optimality measure based on ground clearance and wing root loads is then defined. It is finally shown that the link that ramp-length constraints introduce between acceleration, release speed, and wing root loads is the main driver in the optimal solution.

The double‐tree method: An O(n) unsteady aerodynamic lifting surface method

SummaryTwo new methods for reducing the computational cost of the unsteady vortex lattice method are developed. These methods use agglomeration to construct time‐saving tree structures by approximating the effect of either a group of vortex rings or query points. A case study shows that combining the two new O(n·log n) tree methods together results in an O(n) method, called the double‐tree method. Other case studies show that the trade‐off between accuracy and speed can be easily and reliably controlled by the agglomeration cutoff distance. For a flat plate with 5 × 200 panels analyzed over 20 time steps, the double‐tree method is 7 times faster than the unsteady vortex lattice method with a <5% difference in the force distribution and total lift coefficient. The case studies suggest that the computational benefit will increase for the same level of accuracy if the size of the problem is increased, making the method beneficial for full‐aircraft analysis within optimization or dynamic load analysis, where the computational cost of the unsteady vortex lattice method can be large.

On the theory of thin lifting surface with winglets

On the theory of thin lifting surface with winglets

Numerical and experimental studies on the hydrodynamic damping of a zero-thrust propeller

Fluid added mass and damping are significant parameters when predicting the dynamic response of a submerged structure. The hydrodynamic damping of underwater rotating machinery is numerically and experimentally investigated by a zero-thrust propeller in this paper. The lifting surface method(LSM) combined with forced vibration was introduced as the numerical method to compute the corresponding unsteady thrust, while the experimental method of measuring added damping was accomplished by a propeller undergoing rotation combined heave motion. Results of the theoretical method are in good agreement with the experimental results before cavitation occurs, as cavitation is regarded to weaken the unsteady response of the propeller partly. The calculation results also show that both the frequency ratio(vibration frequency divided by rotation frequency) and the blade angle have a significant influence on the hydrodynamic damping. Therefore, the effect of blade angle on hydrodynamic damping should be considered during the design phase.

Inclination angle influence on noise of cavitating marine propeller

In this study, the effects of inclined shaft angle on the hydro-acoustic performance of cavitating marine propellers are investigated by a numerical method developed before and Brown\'s empirical formula. The cavitating blades are represented by source and vortex elements. The cavity characteristics of the blades such as cavitation form, cavity volume, cavity length etc., are computed at a given cavitation number and at a set advance coefficient. A lifting surface method is applied for these calculations. The numerical lifting surface method is validated with experimental results of DTMB 4119 model benchmark propeller. After calculation of hydrodynamic characteristics of the cavitating propeller, noise spectrum and overall sound pressure level (OASPL) are computed by Brown\'s equation. This empirical equation is also validated with another numerical results found in the literature. The effects of inclined shaft angle on thrust coefficient, torque coefficient, efficiency and OASPL values are examined by a parametric study. By modifying the inclination angles of propeller, the thrust, torque, efficiency and OASPL are computed and compared with each other. The influence of the inclined shaft angle on cavity patterns on the blades are also discussed.

A novel lift-off diameter model for boiling bubbles in natural gas liquids transmission pipelines

The pipeline is a convenient and safe way to transport natural gas liquids (NGLs). However, the NGL is easy to boil due to the variations of pressures and temperatures along the pipeline. The bubble lift-off diameter is an essential parameter to calculate the mass and heat transfer rates between vapor and liquid phases for the NGL two-phase saturated boiling flow. This paper proposed a novel bubble lift-off diameter model based on the force-balance principle of bubbles, which considers the effects of the pressure, shear lift force, unstable drag force, surface tension, gravity force, buoyancy force, gas-phase density, bubble volume, bubble flow velocity, and bubble growth time on the bubble’s lift-off diameters at various pipe inclination angles. A total of 136 experimental data points are applied to validate the new model. Results demonstrate that the average relative deviation (ARD) between the experimental bubble’s lift-off diameters and calculated values based on the new model is in the range from 5.75% to 29.95%. In contrast, for horizontal and vertical pipes, the minimum ARDs of seven existing models (Fritz, Kocamustaf, Zeng, Lee, Situ, Hamzekhani, Chen models) are in the range from 19.42% to 42.58%, respectively. Moreover, the in-depth force analysis results reveal that the shear lift force, buoyancy force, drag force and surface tension force are dominant factors affecting the bubble lift-off diameters in inclined pipes. The new model provides an effective method to calculate the bubble lift-off diameter in the pipe at various inclination angles, overcoming the deficiencies of most existing models that only can be applied to either horizontal or vertical pipes.

Design and benchmarking of a robust strain-based 3D shape sensing system

Shape sensing can provide insight into the structural health and operating conditions of slender engineered lifting and control surfaces in aerospace and maritime applications. Shape sensing often relies upon digital image correlation, inertial measurement, or inverse finite element methods, which can be impractical in applications involving real-time reconstructions, static and dynamic deformations, or dynamic mode shape identification, especially outside of controlled laboratory environments. This work describes ongoing efforts to design, build, and validate a low-cost and robust tool for real-time shape sensing. The sensor consists of a simple aluminum spar, instrumented with strategically placed strain gauges. A kinematic model is used to reconstruct bi-axial bending and torsional displacements along the spar. The model is validated against FEM simulations and canonical analytical solutions. A prototype of the spar is benchmarked using a motion capture system. The pre-calibrated errors are correlated with the direction of bending, permitting a directionally compensative calibration scheme. After calibration of the spar and kinematic model, validation errors are 2.18% in bending magnitude and 0.97° in bending direction. This work addresses the emerging need for new low-cost sensors for structural health monitoring in environments where other sensing methods do not perform well.

A study of aerodynamic sound generated from an airfoil placed in a flow with turbulence (2<sup>nd</sup> Report: In the case of airfoil subjected to circular-cylinder wake)

To clarify the mechanism for aerodynamic sound to be generated from a lifting surface placed in a flow with turbulence, wind-tunnel experiments and numerical simulations have been carried out for a flow around an airfoil subjected to the wake of a circular cylinder. The test airfoil has the NACA0012 profile with a chord length of 150 mm and a spanwise length of 500 mm, and it is set in a flow with the cylinder wake at angles of attack of 0 degree and 9 degrees. The wind velocity is set to 30 m/s, which results in an airfoil Reynolds number of 3.0×105. The circular cylinder is set 100 mm upstream of the leading edge of the airfoil, and its diameter as well as installation position in the transverse direction are varied. The numerical simulations are composed of large eddy simulation (LES) and aeroacoustical simulations that solves the Lighthill equation in the frequency domain with the Lighthill tensor computed by the above-mentioned LES as the acoustical source terms. The sound pressure level is also computed by the Curle’s equation with the fluctuation in the airfoil lift force computed by the LES as the acoustical source and compared with the experiments. The computed static-pressure distributions on the airfoil surfaces and aerodynamic sound spectra are in good agreement with the measured equivalents. The pressure fluctuation near the leading edge of the airfoil is remarkably high when the circular cylinder is placed upstream. When they flow near the leading edge of the airfoil, the vortices in the cylinder wake are stretched due to the acceleration of the main flow, form strong source of sound, and radiate intense sound in the upstream direction.

NUMERICAL INVESTIGATIONS OF THE AERODYNAMIC CHARACTERISTICS FOR AN IMPROVED AIRFOIL WITH A CONTROL SURFACE

Numerical investigations of the two-dimensional flow around a lifting surface with a modified symmetrical NACA 0015 cross section and an aerodynamically balanced control surface were carried out at zero deflection angles in order to reduce the aerodynamic drag. Increased effectiveness of the deflected control surface at the modified lifting surface was achieved.

Re-treatment in LASIK: To Flap Lift or Perform Surface Ablation.

To review safety and efficacy outcomes following re-treatment for residual refractive errors in eyes with prior laser in situ keratomileusis (LASIK) and determine the most appropriate course of action for patients. A review of all patients undergoing LASIK enhancement at a single refractive surgery center between 2012 and 2017 was undertaken. Refraction and biomicroscopy results before and after enhancement were collated and analyzed according to the method of enhancement (flap lift or surface ablation). A total of 108 eyes were included in the analysis; 58 eyes underwent flap lift and 50 underwent surface ablation retreatment with mean times to enhancement of 22.3 and 53.2 months, respectively. The mean spherical equivalent prior to enhancement was -0.43 ± 0.69 and -1.03 ± 1.01 diopters (D) for the flap lift and surface ablation groups, respectively. The absolute difference from intended refraction was statistically significant (lift 0.16 ± 0.24 versus surface ablation 0.31 ± 0.35 D; P = .01). The difference was more pronounced for eyes with prior hyperopia (P = .041). The incidence of haze following re-treatment was 3.4% in the flap lift group versus 10.0% in the surface ablation group, and 8.6% of the flap lift group had evidence of epithelial ingrowth, with 1 eye requiring washout. There was no correlation between time to enhancement, refraction, and incidence of complications following the enhancement procedure. There has been a trend toward treating residual LASIK refractive error through surface ablation. This review suggests that flap lift may result in a more accurate refractive outcome, albeit with an expected greater risk of epithelial ingrowth. [J Refract Surg. 2020;36(1):6-11.].

Stability Analysis of a Subsonic Aircraft with Flight Control System Including Structural Damage

This paper aims to study a modeling technique for flutter analysis of subsonic aircraft by using finite element analysis including flight control failures. By applying distribution of stiffness of dynamic characteristics model as a beam element and distribution of mass as a concentrated mass, the configuration of aircraft idealized. The aerodynamic force model includes all lifting surfaces, fuselage and utilized doublet lattice method in consideration of mutual interference effect between lifting surface and lifting face and lifting surface and fuselage, in empty fuel condition, to 1.74 Vd and in full fuel condition, to 1.71 Vd. There has been no aeroelastic instability on the subsonic aircraft. As a result of flutter analysis based on hinge damage of control surface, it has been proved that it is safe to damages. However, it is required to observe carefully whether the hinge of rudder has been damaged, since the flutter seed decreases significantly when there is one. The control system that has major impact on the aeroelastic characteristic of subsonic aircraft has been modelled to represent the rotational mode of rigid body and elasticity. The flutter analysis has been conducted on empty fuel condition, full fuel condition, changes in volume of mass balance, cases of hinge damage and its results.

Aerodynamic characteristics analysis of electrically controlled rotor based on viscous vortex particle method

An electrically controlled rotor (ECR), also called as swashplateless rotor, replaces a swashplate with a trailing edge flap system to implement primary rotor control. To investigate the aerodynamic characteristics of the ECR, an analysis model based on the viscous vortex particle method, ECR blade pitch equation and Weissinger-L lifting surface model is established. In this model, the ECR wake flow field vorticity is discretized as multiple vortex particles, and the vorticity-velocity form Navier-Stokes equation is solved to simulate the transport diffusion of the vorticity. The impact of flap deflection on the blade bound vortex circulation is calculated via the equivalent incidence angle. The flap deflection induced blade pitch movement is obtained by solving the ECR blade pitch movement equation via the Runge-Kutta fourth-order method. On this basis, to address the low computing efficiency of the viscous vortex wake model, a “relaxation difference”-based trim strategy is developed to reduce the calculation times of the viscous vortex wake model during trim iteration. Based on this model, the aerodynamic characteristics of a sample ECR in hovering and forward flight conditions are analysed. The results show that in hovering and forward flight conditions, when the rotor trim requires large flap deflection, in the rotor wake vorticity field, apart from blade tip vortex, there are intense vortices at both ends of the flap. This additional intense vortex results in an ECR wake vorticity distribution that is more complex than that of a conventional rotor, significantly impacting the distribution of the rotor disc inflow and load. Additionally, in the forward flight condition, the ECR flap collective deflection results in cyclic blade pitch movement, while flap cyclic deflection results in a significant portion of the 2Ω harmonic component in the blade pitch movement when the advance ratio is high.

Airfoil Optimization of Land-Yacht Robot Based on Hybrid PSO and GA

Airfoil optimization algorithm is studied and a hybrid PSO and GA method is proposed in this paper. After function test, it shows that algorithm is well in convergence performance, fast speed, and optimization capability. Then, the airfoil parametric expression theory is analyzed. A new airfoil is obtained after combining CFD and PSO-GA optimization. The aerodynamic of new airfoil is compared with the airfoil optimized by GA-PSO and basic airfoil NACA0018. The results indicate that new airfoil is better than the other two airfoils in lift coefficient, lift-drag ratio, and surface pressure. At last, wing-sail of new airfoil and NACA0018 wing-sail are designed and manufactured. Both of them are applied in land-yacht robot linear motion and steering motion experiment. For the linear motion, in the situation of wind speed being 15[Formula: see text]m/s and angle of attack being 5, running speed of robot with optimized new wing-sail is 1.853[Formula: see text]m/s. In steering motion, trajectory with new wing-sail is closer to the real situation and it gets more thrust. The experiments data verify that the simulation results are correct and PSO-GA algorithm is effective.

The hydroelastic response of a surface-piercing hydrofoil in multiphase flows. Part 2. Modal parameters and generalized fluid forces

The fluid–structure interactions (FSI) of compliant lifting surfaces is complicated by free-surface and multiphase flows such as cavitation and ventilation. This paper describes the dynamic FSI response of a flexible surface-piercing hydrofoil in dry, wetted, ventilating and cavitating conditions. Experimental modal analysis is used to quantify the resonant frequencies and damping ratios of the fluid–structure system in each flow regime. The generalized hydrodynamic stiffness, fluid damping and fluid added mass are also determined as ratios to the corresponding structural modal forces. Added mass increases with increasing partial immersion of the hydrofoil and decreases in the presence of gaseous cavities. In particular, modal frequencies were observed to increase significantly in fully ventilated flow compared to fully wetted flow. The modal frequencies varied non-monotonically with speed in fully wetted flow. Gaseous cavities reduced the modal added mass and reduced the fluid disturbing force. Modal damping increases non-monotonically with increasing immersion depth. Forward speed causes the fluid damping force to increase with an approximately quadratic functional behaviour, consistent with a series expansion of the Morison equation, although damping identification became increasingly difficult at high flow speeds. The results indicate that fluid damping is greater than the associated structural damping in a quiescent liquid, and increasingly so with increasing immersion, suggesting viscous dissipation as a dominant mechanism. A preliminary investigation of modal vibration as a means of controlling the size and stability of ventilated cavities indicates that low-order modes encourage the formation of ventilation, while higher-order modes encourage the washout and elimination of ventilation.

Blade Section Profile Array Lifting Surface Design Method for Marine Screw Propeller Blade

Abstract The lifting surface model is widely used in screw propeller design and analysis applications. It serves as a reliable tool for determination of the propeller blade mean line and pitch distribution. The main idea of this application was to determine the blade shape that would satisfy the kinematic boundary condition on its surface with the prescribed bound circulation distribution over it. In this paper a simplified lifting surface method is presented – in which the 3D task for the entire blade is replaced by a set of 2D tasks for subsequent blade section profiles.

Aerodynamic analysis of a generic wing featuring an elasto-flexible lifting surface

A three-dimensional-membrane-type wing is investigated applying fluid-structure-interaction computations and complementary experiments. An analysis for three Reynolds numbers is conducted at various angles of attack. The computations are performed by means of the TAU-Code and the FEM Carat++ solver. Wind-tunnel tests are carried out for performance analysis and to estimate the accuracy of the computations. In the results, the advantages of an elasto-flexible-lifting-surface concept are highlighted by comparing the formvariable surface to its rigid counterpart. The flexibility of the material and its adaptivity to the freestream allow the membrane to adjust its shape to the pressure distribution. For positive angles of attack, the airfoil’s camber increases resulting in an increase in the wing lifting capacity. Furthermore, the stall onset is postponed to higher angles of attack and the abrupt decrease in the lift is replaced by a gradual loss of it.

Modelling and Structural Analysis of Three-Dimensional Wing

This paper attempts to discover the structural behavior of the wing imperiled to flowing loads through the voyage. The study uses a method in the form of finite element analysis of wing flexure distortion. As a first step, two wing models are established by captivating factual features, wing assembly, and plan principles into consideration. The gathering wing prototypical entails of tinny membrane, two poles, and multi-ribs. Two spars which consist of primary and secondary spars. NACA 23015 is chosen as the baseline aerofoil as this is identical alike to the tailored aerofoil being castoff in Airbus A320. Two rods mostly endure the twisting moment and trim strength, which is finished of titanium contaminant to ensure enough inflexibility. The covering and wing spars are made of aluminum amalgam to lessen the structural heaviness. Later, a static structural investigation is smeared, and the overall distortion, comparable elastic strain, and corresponding Von-Mises tension are obtained to analyze the mechanical behavior of the wing. Furthermore, modal investigation is being supported out to determine the natural rate of recurrence, as well as the modal shape of the three orders, which are acquired through the pre-stress modal analysis. The outcomes of the modal scrutiny aid engineers decrease excitation on the natural occurrences and avert the wing from the flurry. In view of the results obtained from the study, designers can emphasize consolidation and analysis the stress attentiveness range and huge distortion area. In conclusion, the recreation consequences indicate that the arrangement is possible and improves the information grade of the lifting surface.

Suppressing tip vortex cavitation by winglets

Despite the numerous remedies prescribed so far, tip vortex cavitation (TVC) remains a major issue in design and operation of diverse applications. In this paper, we experimentally investigate the effectiveness of winglets in suppressing TVC. An elliptical hydrofoil is selected as the baseline geometry and various winglets are realized by bending the last 5 or 10% of the span at ± 45° and ± 90° dihedral angles. To better focus on the physics of the problem, we have intentionally avoided any optimization on the geometries and our winglets are only smooth non-planar extensions of the original cross-section. Modifying no more than 3.7% of the lifting surface, lift-and-drag force measurements demonstrate that the hydrodynamic performances of the winglet-equipped hydrofoils are not substantially different from the baseline. Nevertheless, cavitation inception–desinence tests reveal that undeniable advantages are achieved by the winglets in TVC alleviation. It is found that the 10%-bent 90° winglets are more effective than the 45° cases, with − 90° (bent down toward the pressure side) performing superior to + 90°. For instance, the 90°-bent-downward winglet reduces the TVC inception index from 2.5 for the baseline down to 0.8 (a reduction of 68%) at 15 m/s freestream velocity and 14° incidence angle. In addition, the study on the bending length effect conducted for the 90° configurations shows that the 5%-bent winglets are not as striking as the 10% ones. Employing Stereo-PIV technique, the influence of winglets on non-cavitating flow structures is examined. For the most effective winglet (10%-bent 90°-downward), we observe that the maximum tangential velocity of the tip vortex falls to almost half of the baseline and the vortex core size increases significantly (by almost 70%). These effects are accompanied by a tangible reduction in the axial velocity at the vortex core leading to further mitigation of TVC.

Steady and dynamic hydroelastic behavior of composite lifting surfaces

We compare the steady-state and dynamic response of composite lifting surfaces in air and in water. Steady results predict lower (resp. higher) load coefficients when the fibers are oriented toward the leading (resp. trailing) edge, as nose-down (resp. nose-up) twist decreases (resp. increases) the effective angle-of-attack, both in air and in water. Natural frequencies are lower, and damping coefficients are higher, in water compared to in air. The natural frequencies and damping coefficients vary with speed. The speed and frequency dependency of the fluid loads lead to an emergence of a new mode. The vibration frequency of this new mode could be near zero and much significantly than the fundamental system frequency in quiescent water. Static divergence occurs when the frequency and damping value of the new mode goes to zero, while the frequencies of the original structural modes are nonzero. Unlike conventional coupled-mode flutter that involves frequency coalescence of two adjacent modes, composite plates in water tend to experience single-mode flutter, when the damping of the new low-frequency mode vanishes. In general, static-divergence governs when material bend-twist coupling leads to nose-up twist, and flutter governs otherwise. Dynamic load amplification is more severe in water because of higher fluid added mass.