Aerodynamic Force Data Research Articles

A physics-based digital twin for model predictive control of autonomous unmanned aerial vehicle landing

This paper proposes a two-level, data-driven, digital twin concept for the autonomous landing of aircraft, under some assumptions. It features a digital twin instance (DTI) for model predictive control (MPC); and an innovative, real-time, digital twin prototype for fluid-structure interaction and flight dynamics to inform it. The latter digital twin is based on the linearization about a pre-designed glideslope trajectory of a high-fidelity, viscous, nonlinear computational model for flight dynamics; and its projection onto a low-dimensional approximation subspace to achieve real-time performance, while maintaining accuracy. Its main purpose is to predict in realtime, during flight, the state of an aircraft and the aerodynamic forces and moments acting on it. Unlike static lookup tables or regression-based surrogate models based on steady-state wind tunnel data, the aforementioned real-time digital twin prototype allows the DTI for MPC to be informed by a truly dynamic flight model, rather than a less accurate set of steady-state aerodynamic force and moment data points. The paper describes in detail the construction of the proposed two-level digital twin concept and its verification by numerical simulation. It also reports on its preliminary flight validation in autonomous mode for an off-the-shelf unmanned aerial vehicle instrumented at Stanford University. This article is part of the theme issue 'Data-driven prediction in dynamical systems'.

Multi-Fidelity Surrogate Models for VPP Aerodynamic Input Data

Predicting the performance of a sail design is important for optimising the performance of a yacht, and Velocity Prediction Programs (VPPs) are commonly used for this purpose. The aerodynamic force data for a VPP is often calculated using Computational Fluid Dynamics (CFD) models, but these can be computationally expensive. A full VPP analysis for sail design is therefore usually restricted to high-budget design projects or research activities and is not practical for many industry projects. This work presents a method to reduce the computational cost of creating lift and drag force coefficient curves for input into a VPP using both multi-fidelity kriging surrogate modelling and data from existing sail designs. This method is shown to reduce the number of CFD simulations required for a desired accuracy when compared to a single-fidelity model. A maximum reduction in the required computational effort of 57% was achieved for model-scale symmetric spinnaker sails. For the same number of simulations, the accuracy of the model predictions was improved by up to 72% for scale-symmetric spinnaker sails, and 90% for asymmetric spinnakers.

A Fast Correction Method of Model Deformation Effects in Wind Tunnel Tests

The influence of model deformation needs to be corrected before the aerodynamic force data measured in the wind tunnel is applied to aircraft design. In order to obtain the aerodynamic forces on rigid model shape, this paper presents a fast correction method by establishing a mathematical modelling method connecting aerodynamic forces and wing section torsion. The aerodynamic force coefficients on rigid model shape can then be calculated quickly just by setting section torsion to zero. A 25-point simulation dataset of the High Reynolds Number Aero-Structural Dynamics (HIRENASD) model generated by Computational Fluid Dynamics (CFD) and Static Computational Aeroelasticity (CAE) approach is used to investigate the influence of section locations, basis function type, support radius, and deformation perturbation on the prediction accuracy. Finally, the present correction method is applied to predict the aerodynamic forces on the rigid shape of a NASA common research model. The results of parametric analysis and application show that the present correction method with the Wendland’s C6 function and a support radius of 1.0 can provide a reasonable prediction of aerodynamic forces on the rigid model shape.

An experimental study on the aerodynamic performance degradation of a wind turbine blade model induced by ice accretion process

Abstract An experimental study was conducted to characterize aerodynamic performance degradation of wind turbine blades induced by dynamic ice accretion process. The experimental study was performed in an Icing Research Tunnel with a turbine blade model under a typical glaze icing condition. Ice structures were found to accrete rapidly over both the upper and lower surfaces of the blade model after starting the ice accretion experiment. Irregular-shaped ice structures were found to disturb the airflow around the blade model greatly, resulting in large-scale flow separations and shedding of unsteady vortex structures from the ice accreting surface. The aerodynamic performance of the blade model was found to degrade significantly. The performance degradation induced by the ice accretion was found to be a strong function of the angle of attack of the blade model with more significant degradations at lower angles of attack. For the test case at the angle of attack of 5.0°, while the lift decreases to only ∼12% of its original value after 600 s of the ice accretion experiment, the drag was found to increase 4.5 times correspondingly. The detailed flow field measurements were correlated with the aerodynamic force data to elucidate the underlying physics.

An experimental study on the aerodynamic performances and wake characteristics of an innovative dual-rotor wind turbine

A novel dual-rotor wind turbine (DRWT) concept with an auxiliary upwind rotor and a bigger downwind rotor was introduced for improved turbine performance. An experimental study was performed in an Atmospheric Boundary Layer (ABL) wind tunnel with scaled turbine models to investigate the aerodynamic performances and wake characteristics of DRWTs in either co-rotating or counter-rotating configuration (i.e., CR-DRWT or CO-DRWT), in comparison to those of a conventional single-rotor wind turbine (SRWT). In additional to measuring the aerodynamic forces and power outputs, the wake flow characteristics behind DRWTs and SRWT were also quantified by using a high-resolution Particle Image Velocimetry (PIV) system. In comparison to those of SRWT, while the aerodynamic force acting on the CR-DRWT was found to increase 13.3%, the power coefficient of the CR-DRWT design was improved by 7.2%. Faster wake recovery behind the DRWT designs was confirmed from both the measured power outputs of the same turbine model sited in the turbine wakes and the measured flow velocity at various downstream locations. The wake flow measurements were correlated with the aerodynamic force and power output data to elucidate underlying physics for the higher efficiency of DRWT designs in either isolation or wind farm settings.

Towards efficient flight: insights on proper morphing-wing modulation in a bat-like robot

In this article, we address the question of how the flight efficiency of Micro Aerial Vehicles with variable wing geometry can be inspired by the biomechanics of bats. We use a bat-like drone with highly articulated wings using shape memory alloys (SMA) as artificial muscle-like actuators. The possibility of actively changing the wing shape by controlling the SMA actuators, let us study the effects of different wing modulation patterns on lift generation, drag reduction, and the energy cost of a wingbeat cycle. To this purpose, we present an energy-model for estimating the energy cost required by the wings during a wingbeat cycle, using experimental aerodynamic and inertial force data as inputs to the energy-model. Results allowed us determining that faster contraction of the wings during the upstroke, and slower extension during the downstroke enables to reduce the energy cost of flapping in our prototype.

Development of the In Situ Load System for Internal Wind-Tunnel Balances

Results from the Facility Analysis Verification and Operational Reliability project revealed a critical gap in capability in ground-based aeronautics-research applications. Without a standardized process for check loading the wind-tunnel balance or the model system, the quality of the aerodynamic force data collected varied significantly between facilities. The In Situ Load System was developed to provide a standard for facilities in the check-loading process. The system includes both the hardware and a statistically rigorous process that facilitates the ability for the user to make defendable decisions on the performance of the system. The compactness and simplicity of the system reduce customer costs unrelated to achieving the research objectives, while simultaneously improving the knowledge about the accuracy of the test data collected. While the focus is on the check-load process, the hardware and methods are also applicable to the in situ calibration of a balance or wind-tunnel model system.

An Analysis Method of Static Aeroelastic Response with Nonlinear Aerodynamic Data on 3D Bodysurface Panel Element

A static aeroelastic responses analysis method based on mapping external nonlinear aerodynamic forces onto 3D body surface panel elements is proposed. The external nonlinear aerodynamic force data can be obtained by Euler solver, Navier-Stokes solver and wind tunnel tests. In this paper, the method is applied to obtain static aeroelastic responses of a flexible aircraft, and the emphasis is placed on the change of aerodynamic coefficient, aerodynamic pressure distribution and flight load. The results are compared with static aeroelastic responses calculated by high-order panel method. It is concluded that the method presented in this study is feasible, credible and efficient, and can provide an assessment of static aeroelastic response characteristics for the detailed stage of aircraft design.

An Analysis Method of Static Aeroelastic Response with Nonlinear Aerodynamic Data on 3D Bodysurface Panel Element

A static aeroelastic responses analysis method based on mapping external nonlinear aerodynamic forces onto 3D body surface panel elements is proposed. The external nonlinear aerodynamic force data can be obtained by Euler solver, Navier-Stokes solver and wind tunnel tests. In this paper, the method is applied to obtain static aeroelastic responses of a flexible aircraft, and the emphasis is placed on the change of aerodynamic coefficient, aerodynamic pressure distribution and flight load. The results are compared with static aeroelastic responses calculated by high-order panel method. It is concluded that the method presented in this study is feasible, credible and efficient, and can provide an assessment of static aeroelastic response characteristics for the detailed stage of aircraft design.

Air Flow Analyses in an Ultra-Thin Hard Disk Drive

Turbulent air flow analysis is carried out in an ultra-thin hard disk drive using the large eddy simulation (LES). Aerodynamic force acting on various structural components is obtained for about 40 ms and analyzed in detail. Using one set of full scale simulation data, aerodynamic force data for other different sets of operating conditions is obtained using scaling methods thus minimizing the computational time significantly. Validation of the scaling methods is discussed and concluded.

Aerodynamic behavior of a discus

To determine the flight path of a discus when it is thrown, it is essential to know what aerodynamic forces are acting on it. However, little data on this is available. Employing a full-size model in a wind tunnel, we have measured the aerodynamic forces acting on a discus spinning on its transverse axis, as well as on a ‘non-spinning’ discus. The aerodynamic force data (drag, lift and pitching moment) were obtained to create an ‘aerodynamic database’. These forces are given as functions over practical ranges of the angle of attack, the spin rate and the wind speed. It was found that the stalling angle was about 30°C, and that the lift coefficient increased linearly with increasing angle of attack up to the stalling angle. The estimated lift coefficient obtained by the vortex lattice method agrees with the experimental data within a standard deviation of 0.08. It was observed by oil flow and smoke observation methods that a pair of longitudinal vortexes occur from the ‘pressure side’ to the ‘suction side’, similar to wing-tip vortices. These longitudinal vortexes prevent flow-separation up to a high angle of attack, around 30°C. The drag coefficient increases with increasing angle of attack up to the stalling angle, and it decreases slightly around the stalling angle, corresponding to a significant and abrupt decrease in lift at the same angle. The coefficient of the pitching moment is almost positive, which is the case with ‘nose-up’ rotation. There is little difference between the aerodynamic coefficients whether the discus is spinning or not.

전투기 외부 연료 탱크의 종방향 정안정성 및 투하 궤적 해석

The present work is to analyze the longitudinal static stability and the drop trajectory of fighter aircraft's external fuel tank, of which horizontal fin is modified as the 20% scale down size compared with the original one. The analytical results to the pitching stability of external fuel tank using a thin airfoil's aerodynamic force data show the corresponding tendency to results of wind tunnel experiment. Results of trajectory simulation by the 6 degree of freedom equations of motion, comparing with drop trajectories of wind tunnel experiment, are shown that aircraft's attitude affects strongly on horizontal movement but not on the vertical movement. Those results give the reliability to aircraft safety when the external fuel tank with the 20% reduced horizontal fins is released from aircraft based on the flight manual.

1811 高速度カメラによるスキージャンパーに働く空気力の測定(S18 スポーツ流体工学,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

We measured aerodynamic forces acting on real jumping flights in the take-off phase as well as a quasi-steady flight phase. The frame rate was 250 frames/s. It is concluded that the present aerodynamic force data derived from the image analysis are found to be in fair agreement with existing wind tunnel data for the cases of jumping flights in the quasi-steady flight phase. The aerodynamic data in the cases of relatively large forward leaning angle, which is typical in the initial phase of a jumping, could also be obtained. The lift in the take-off phase is relatively larger when compared with the quasi-steady flight phase.

B30 高速度ビデオカメラの画像解析を用いたスキージャンプの空力解析(スキー・リュージュ)

A ski jumping flight analysis was attempted on the basis of the high-speed digital video image taken at Hakuba Ski Jumping Stadium in Japan. Initial 40m of flights of 120-m jumping after take-off were recorded by a fixed high-speed video camera at a frame rate of 250 frames/s. After some corrections, a number of time series data were extracted for the loci of key parts of a jumper such as the waist, the ski boots and the ski tip as well as for key angles representing a jumper posture such as the ski angle and the forward leaning angle. It is demonstrated that the aerodynamic force data during real jumping flights, in particular in the early phase of a flight can be derived from video image.

Evaluation of a Three Degree of Freedom Test Rig for Stability Derivative Estimation

This paper details a quantitative investigation into a cost-effective, three degree-of-freedom test rig to determine aircraft static and dynamic stability derivatives. The technique used a specifically designed three degree-of-freedom gimbaled mechanism to connect an actively controlled model to a vertical support strut. The support strut was also mounted on a six-component piezoelectric balance to obtain aerodynamic force and moment data simultaneously with the model motion. With only minor modifications to the overall setup, a comprehensive set of static and dynamic stability derivatives were obtained which showed reasonable to good agreement with other, independently obtained, data.

A17 高速度ビデオカメラの画像解析を基にしたスキージャンプの空力特性の研究(サッカー・流れ)

A ski jumping flight analysis was attempted on the basis of the high-speed digital video image taken at Hakuba Ski Jumping Stadium in Japan. Initial 40m of flights of 120-m jumping after take-off were recorded by a fixed high-speed video camera at a frame rate of 250 frames/s. After some corrections, a number of time series data were extracted for the loci of key parts of a jumper such as the waist, the ski boots and the ski tip as well as for key angles representing a jumper posture such as the ski angle and the forward leaning (ski-body) angle. The primary purpose of the present study is to derive the aerodynamic force data during real jumping flights, in particular in the early phase of a flight.

Aerodynamic force data for a V-style ski jumping flight

To determine the flight of a ski jumper it is essential to know what aerodynamic forces are acting on the ski jumper. However, few data on this are available, especially for a V-style ski jumping flight. We have measured the aerodynamic forces during the free flight phase for a V-style, as well as a parallel-style, ski jump by employing a full-size model in a wind tunnel. The aerodynamic force data, (drag, lift and pitching moment) were obtained to create an aerodynamic database. These forces are given in polynomial form as functions of the angle of attack, the body-ski (forward leaning) angle and the ski-opening (V-style) angle. Using the polynomial form database is a convenient way of obtaining the aerodynamic forces. Moreover, the wind tunnel was equipped with a ground effect plate to measure the aerodynamic forces during the landing phase. It was found that the difference between the lift with and without the ground effect plate increases with the ski-opening angle. The longitudinal stability in the pitching motion of a body-ski combination is also discussed on the basis of the pitching moment data. This indicates that a stable pitching oscillation of the body-ski combination may arise around an equilibrium point in the angle of attack, the trim angle of attack, during flight.

Unsteady aerodynamic loads on high speed trains passing by each other

In order to study unsteady aerodynamic loads on high speed trains passing by each other 350km/h, three-dimensional flow fields around trains during the crossing event are numerically simulated using three-dimensional Euler equations. Roe’s FDS with MUSCL interpolation is employed to simulate wave phenomena. An efficient moving grid system based on domain decomposition techniques is developed to analyze the unsteady flow field induced by the restricted motion of a train on a rail. Numerical simulations of the strain passing by on the double-track are carried out to study the effect of the train nose-shape, length and the existence of a tunnel on the crossing event. Unsteady aerodynamic loads-a side force and a drag force-acting on the train during the crossing are numerically predicted and analyzed. The side force mainly depends on the nose-shape, and the drag force depends on tunnel existence. Also. a push-pull (i.e. impluse force) force successively acts on each car and acts in different directions between the neighborhood cars. The maximum change of the impulsive force reaches about 3 tons. These aerodynamic force data are absolutely necessary to evaluate the stability of high speed multi-car trains. The results also indicate the effectiveness of the present numerical method for simulating the unsteady flow fields induced by bodies in relative motion.

Desirable Gliding Styles and Techniques in Ski Jumping

Desirable flight styles and techniques in ski jumping were calculated on the basis of the new aerodynamic force data for three styles: classic style, V style, and flat V style. In the V style and flat V style two skis are in a herringbone position in the frontal plane, whereas in the classic style the skis are parallel Flat V style is more flat in the sagittal plane than V Style. The most effective style was the flat V style if a ski jumper model did not change style during the gliding phase, which was the late part of flight phase (distance was 110 m). If the model changed flight style, the model that changed from classic style to V style at 1.3 s after takeoff or from flat V style to V style at 1.6 s could achieve 112.5 m. In addition, forward initial angular velocity was a positive factor to increase distance; in particular, the distance for the V style was sensitive to initial angular velocity.

Shuttle entry aerothermodynamic flight research - The Orbiter Experiments program

Results of the OEX program are summarized with emphasis on the information on entry aerothermodynamic phenomena derived from Space Shuttle operations. The discussion focuses on OEX experiment complement and operational history, freestream environment and vehicle attitude data, aerodynamic force and moment data, aerodynamic surface data, and vehicle configuration data. Attention is also given to orbiter aerodynamic performance, stability and control, high-altitude atmospheric density variability, direct simulation Monte Carlo validation, orbital drag variation, and computational fluid dynamic technique validation.