Experimental Investigation of the Aerodynamic Flow in the Aircraft Carrier Ski-jump by means of PIV

Computational Fluid Dynamics （CFD） methods have opened a new field to perform aerodynamic studies saving money and time. The difficulties presented by this method to calculate complex flow field problems imply that CFD validation is needed to provide correct results. Experimental data have recently been used to validate the accuracy of CFD predictions. Particle Image Velocimetry （PIV） has shown to be a powerful tool in the investigation of complex flows. The aim of this paper is to present results from PIV experiments that would be interesting for CFD validation. Regarding aircraft operations, the short runway available implies the necessity of equipment which helps to take-off performances. Ski-jump ramp system improves aircraft performances by an increment of lift resulting in successful take-off operations. The ski-jump ramp presence generates a complex flow bounded by a turbulent shear layer and a low velocity recirculation bubble over the end of the flight deck. The adverse effects on the aircraft aerodynamics affect to pilot safe operations, so this region is an interesting problem to be studied by means of wind tunnel experimental tests.

EXPERIMENTAL STUDY OF HIGH SUBSONIC CAVITY FLOW OSCILLATION AND ITS SUPPRESSION BY ACOUSTIC EXCITATION

An experimental study of cavity oscillating flow carried out on subsonic wall jet facilities in an anechoic room is summarized. The jet exit Mach number range is from 0.2 to 0.8. The effects of the flow Mach number ( Ma ) and the cavity depth ( D ) on the oscillation are studied. It is found that for L/D =4, (shallow cavity), the oscillation is mainly due to the self exciting of the free shear layer above the cavity opening, for L/D =2, the acoustic resonance is responsible for the oscillation. Preliminary tests are performed to study the suppression effect of the leading edge tone excitation on cavity flow, and considerable reduction of oscillation has been achieved when Ma ≤0.6.

Static aeroelastic analysis of a high-aspect-ratio wing based on wind-tunnel experimental aerodynamic forces

The aeroelastic responses of a high-aspect-ratio wing are investigated based on nonlinear experimental aerodynamic forces. The influences of nonlinear experimental aerodynamic forces and dynamic pressures on the wing loads are studied in the longitudinal and lateral maneuver states. The flight loads of the wing fixed at the root are calculated at different angles of attack. The aileron efficiency with respect to the dynamic pressures and aileron deflections are also studied. The results indicate that the flight loads of the wings vary nonlinearly with the angle of attack and dynamic pressure. Due to the high-lift aerofoil, elastic components are a large portion of the wing loads, especially for small angles of attack and high dynamic pressure condi-tions. The aileron efficiency is significantly affected by aileron deflections, dynamic pressures and angles of attack when the nonlinear experimental aerodynamic forces are used for calculation. In states with high dynamic pressures and large aileron deflections, aileron reversal can occur. The aileron deflection and angle of attack have a nonlinear effect on the aileron efficiency. An efficient method for analyzing the flight loads and structural design of high-aspect-ratio wings is derived in this study, and the analysis can provide insight into the distribution of flight loads for high-aspect-ratio wings.

Aerodynamic load control on a dynamically pitching wind turbine airfoil using leading-edge protuberance method

The aerodynamic loads of wind turbine blades are substantially affected by dynamic stall induced by the variations of the angle of attack of local airfoil sections.The purpose of the present study is to explore the effect of leading-edge protuberances on the fluctuation of the aerodynamic performances for wind turbine airfoil during dynamic stall.An experimental investigation is carried out by a direct force measurement technique employing force balance at a Reynolds number Re=2×105.The phase-averaged and instantaneous aerodynamic loads of the pitching airfoil,including the baseline and the wavy airfoil,are presented and analyzed.The phase-averaged results indicate that the effects of dynamic stall for the wavy airfoil can be delayed or minimized compared to the baseline airfoil,and the negative damping area of the wavy airfoil is significant decreased in full-stall condition.These effects of leading-edge protuberances are more notable at a higher reduced frequency.For the instantaneous aerodynamic loads of the wavy airfoil,there is an observable reduction in fluctuations compared with baseline case.Furthermore,spectral analysis is applied to quantitatively undercover the nonstationary features of the instantaneous aerodynamic loads.It is found that the leading edge protuberances can reduce the harmonics of the aerodynamic force signal,and enhance the stability of the aerodynamic loads under different reduced frequencies.In conclusion,leading-edge protuberances are found effective to reduce the fluctuation characteristics of the aerodynamic loads during the dynamic stall process,and help to improve the stability and prolong the service life of the wind turbine blades.

Experimental investigations of a full model with adaptive elasto-flexible membrane wings

The morphing wing concept aims to constantly adapt the aerodynamics to different flight stages.The wing is able to adapt to different flight conditions by an adjustable Aspect Ratio(AR)and sweep.A high AR configuration provides high aerodynamic efficiency,while a low AR configuration,with highly swept wings offers a good maneuverability.Additionally,the flexible membrane allows the wing surface to stretch and contract in-plane as well as the airfoil to adapt to different aerodynamic loads.In the context of this work,the aerodynamic characteristics of a full model with form-adaptive elasto-flexible membrane wings are investigated experimentally.The focus is on the high-lift regime and on the analysis of the aerodynamic coefficients as well as their sensitivities.Especially,the lateral aerodynamic derivatives at asymmetric wing positions are of interest.

Aerodynamic design,analysis,and validation techniques for the Tianwen-1 entry module

The clear differences between the atmosphere of Mars and the Earth coupled with the lack of a domestic research basis were significant challenges for the aerodynamic prediction and verification of Tianwen-1.In addition,the Mars entry,descent,and landing(EDL)mission led to specific requirements for the accuracy of the aerodynamic deceleration performance,stability,aerothermal heating,and various complex aerodynamic coupling problems of the entry module.This study analyzes the key and difficult aerodynamic and aerothermodynamic problems related to the Mars EDL process.Then,the study process and results of the design and optimization of the entry module configuration are presented along with the calculations and experiments used to obtain the aerodynamic and aerothermodynamic characteristics in the Martian atmosphere.In addition,the simulation and verification of the low-frequency free oscillation characteristics under a large separation flow are described,and some special aerodynamic coupling problems such as the aeroelastic buffeting response of the trim tab are discussed.Finally,the atmospheric parameters and aerodynamic characteristics obtained from the flight data of the Tianwen-1 entry module are compared with the design data.The data obtained from the aerodynamic design,analysis,and verification of the Tianwen-1 entry module all meet the engineering requirements.In particular,the flight data results for the atmospheric parameters,trim angles of attack,and trim axial forces are within the envelopes of the prediction deviation zones.

A method for static aeroelastic analysis based on the high-order panel method and modal method

A method for static aeroelastic analysis based on the high-order panel method and modal method is presented. The static aeroelastic characteristics of flexible wings are investigated using this method. Three-dimensional aerodynamic models of flexible wings are constructed based on the geometry of wing configuration, and the modal method is adopted to achieve the fluid-structure coupling. The static aeroelastic characteristics of the AGARD445.6 wing and a low-aspect-ratio wing are investigated in this study. The influences of elastic structural deformation on aerodynamic forces are studied with an emphasis analyzing the aerodynamic coefficients, wing root loads, structural deformation and pressure distribution of different sections, and results are compared with the results from wind-tunnel tests and the elastic results based on experimental aerodynamic forces. It is concluded that aerodynamic forces can be accurately calculated with the high-order panel method. The method presented in this study is feasible, credible and efficient. Comprehensive static aeroelastic characteristics can be provided by the method for early phases of aircraft design.

Aeroelastic optimization design for wing with maneuver load uncertainties

An aeroelastic optimization design methodology for air vehicle considering the uncertainties in maneuver load conditions is presented and applied to a structural design process of low-aspect-ratio wing. An aerodynamic load correction model is developed and used to predict the critical load conditions with the perturbations of theoretical linear aerodynamic forces and experimental aerodynamic forces from wind-tunnel test, when concerning the uncertainties in use of theoretical linear and experimental aerodynamic forces. Three objective functions of critical loads are defined. The load evaluations for three wing sections are investigated in four characteristic maneuvers, and the most critical load conditions are confirmed by using the sequential quadratic programming method. On this basis, the aeroelastic optimization design employing the genetic-gradient hybrid algorithm is conducted, in which the objective is to minimize structural mass subject to the constraints of stress, deformation and flutter speed. The resulting optimal structure is heavier than the one simply based on the theoretical linear or experimental aerodynamic forces. However, it is more robust when encountering the critical load conditions in actual flight due to the consideration of uncertainties in aerodynamic forces in the early design phase, thereby, the risk of structural redesign can be reduced.

Flight dynamics modeling of a small ducted fan aerial vehicle based on parameter identifcation

This paper presents a simple and useful modeling method to acquire a dynamics model of an aerial vehicle containing unknown parameters using mechanism modeling,and then to design different identifcation experiments to identify the parameters based on the sources and features of its unknown parameters.Based on the mathematical model of the aerial vehicle acquired by modeling and identifcation,a design for the structural parameters of the attitude control system is carried out,and the results of the attitude control flaps are verifed by simulation experiments and flight tests of the aerial vehicle.Results of the mathematical simulation and flight tests show that the mathematical model acquired using parameter identifcation is comparatively accurate and of clear mechanics,and can be used as the reference and basis for the structural design.

Effects of wing locations on wing rock induced by forebody vortices

Previous studies have shown that asymmetric vortex wakes over slender bodies exhibit a multi-vortex structure with an alternate arrangement along a body axis at high angle of attack. In this investigation, the effects of wing locations along a body axis on wing rock induced by forebody vortices was studied experimentally at a subcritical Reynolds number based on a body diameter. An artificial perturbation was added onto the nose tip to fix the orientations of forebody vortices. Particle image velocimetry was used to identify flow patterns of forebody vortices in static situations, and time histories of wing rock were obtained using a free-to-roll rig. The results show that the wing locations can affect significantly the motion patterns of wing rock owing to the variation of multi- vortex patterns of forebody vortices. As the wing locations make the forebody vortices a two-vortex pattern, the wing body exhibits regularly divergence and fixed-point motion with azimuthal varia- tions of the tip perturbation. If a three-vortex pattern exists over the wing, however, the wing-rock patterns depend on the impact of the highest vortex and newborn vortex. As the three vortices together influence the wing flow, wing-rock patterns exhibit regularly fixed-points and limitcycled oscillations. With the wing moving backwards, the newborn vortex becomes stronger, and wing-rock patterns become fixed-points, chaotic oscillations, and limit-cycled oscillations. With fur- ther backward movement of wings, the vortices are far away from the upper surface of wings, and the motions exhibit divergence, limit-cycled oscillations and fixed-points. For the rearmost location of the wing, the wing body exhibits stochastic oscillations and fixed-points.