Dynamic Wind Tunnel Tests Research Articles

A flow-field integrated flight control: dynamic wind tunnel testing and simulation

Abstract Abrupt changes in aircraft attitude due to encountering terrain turbulence or wind shear at low altitudes can directly lead to serious accidents. Therefore, a highly responsive and reliable active attitude stabiliser on board is necessary to counteract low-level severe atmospheric disturbances. However, gust environments caused by local terrain and structures are difficult to represent with typical models, such as the Dryden continuous gust model in free space. As a result, an optimal model-based control design cannot be applied. To address this problem, this paper introduces an adaptive mechanism for updating motion equations based on atmospheric conditions using in-flight surface pressure-field sensing. Additionally, a dynamic wind tunnel experiment system, which can be constructed at universities at a low cost, is developed and described in detail. The effectiveness of the proposed scheme is evaluated through wind tunnel experiments and numerical simulations using a large number of gust samples.

Quaternion-Based Attitude Estimation of an Aircraft Model Using Computer Vision.

Investigating aircraft flight dynamics often requires dynamic wind tunnel testing. This paper proposes a non-contact, off-board instrumentation method using vision-based techniques. The method utilises a sequential process of Harris corner detection, Kanade-Lucas-Tomasi tracking, and quaternions to identify the Euler angles from a pair of cameras, one with a side view and the other with a top view. The method validation involves simulating a 3D CAD model for rotational motion with a single degree-of-freedom. The numerical analysis quantifies the results, while the proposed approach is analysed analytically. This approach results in a 45.41% enhancement in accuracy over an earlier direction cosine matrix method. Specifically, the quaternion-based method achieves root mean square errors of 0.0101 rad/s, 0.0361 rad/s, and 0.0036 rad/s for the dynamic measurements of roll rate, pitch rate, and yaw rate, respectively. Notably, the method exhibits a 98.08% accuracy for the pitch rate. These results highlight the performance of quaternion-based attitude estimation in dynamic wind tunnel testing. Furthermore, an extended Kalman filter is applied to integrate the generated on-board instrumentation data (inertial measurement unit, potentiometer gimbal) and the results of the proposed vision-based method. The extended Kalman filter state estimation achieves root mean square errors of 0.0090 rad/s, 0.0262 rad/s, and 0.0034 rad/s for the dynamic measurements of roll rate, pitch rate, and yaw rate, respectively. This method exhibits an improved accuracy of 98.61% for the estimation of pitch rate, indicating its higher efficiency over the standalone implementation of the direction cosine method for dynamic wind tunnel testing.

Impact of marine atmospheric corrosion on the thermophysical properties of building coatings

Coastal structures are subjected to substantial thermal and solar loads, as well as relentless erosion from salt sprays originating from the ocean. This erosion poses a significant threat to the integrity of the surface coatings. However, the examination of the impact of salt spray on coatings from a heat-transfer perspective is limited. The objective of this study is to quantitatively evaluate the influence of ocean salt spray on the thermal properties of building coatings by investigating the modifications in surface thermal properties and heat transfer performance. Specifically, water-based polyurethane coatings, water-based acrylic coatings, and solvent-based coatings was subjected to corrosion through indoor accelerated aging tests and wind tunnel experiments. After a 30-day expose to ultraviolet ageing and salt spray corrosion, noticeable discoloration, and a substantial reduction in surface glossiness of up to 84 % are observed in the coating samples. The change in reflectance ratio before and after corrosion was measured using a spectrophotometer, indicating a maximum reduction of 9.4 %. To analyse the variations in the dynamic heat transfer performance of the samples before and after corrosion, this study employed the heat balance equation and conducted dynamic wind tunnel tests. The corrosion process appears to increase heat transfer along the coating's surface, evident from the consistent elevation in heat transfer capacity coefficients (CHTC) of the specimens after corrosion. Notably, these increases, particularly pronounced during nighttime, reveal substantial and consistent gaps in coefficients, reaching values of up to 10 W/m2 (WP1), 12.5 W/m2 (WA1), and 10 W/m2 (S2), respectively.

Effects of wind barriers on VIV performances of twin separated parallel decks for a long-span rail-cum-road bridge

Wind barriers are frequently used on the railway bridges to improve operational safety of high-speed trains. However, the effects of wind barriers along the railway on the separated decks' Vortex-induced vibration (VIV) for rail-cum-road bridges are not fully known, whose VIV characteristics are more complicated because of aerodynamic interference effect (AIE). A number of dynamic sectional model wind tunnel tests for VIV performance were carried out. Three different heights (H) varying from 2 m to 4 m and four different ventilation ratios (R) varying from 20% to 50% for wind barriers on railway decks were examined under two opposite incoming flow directions at a fixed spacing. Results indicated that twin separated decks' overall VIV performance are poor when the wind flows from the railway upstream to the highway downstream. The wind barrier on railway deck can weak the remarkable fluctuating wind pressure coefficients, change the correlation coefficients and reduce the contribution coefficients of local distribution aerodynamic forces to the overall aerodynamic forces. It was effective to suppress VIV of the railway deck, and it also had a greater impact on the adjacent highway deck. The VIV-suppress ability of wind barriers is determined by the parameters of H and R. The wind barriers with H = 3 m and R = 30% were recommended to satisfy the requirements of twin decks after a comprehensive evaluation.

Effect of ice accretion on aerodynamic characteristics of pipeline suspension bridges

Pipeline suspension bridges may confront the issue of ice accretion in areas prone to glaze ice or rime. Ice accretion is known to influence the wind-induced responses of various structures, while the effects on the wind-induced responses of pipeline suspension bridges received little attention. To this end, this paper investigated the effect of ice accretion on the aerodynamic characteristics of pipeline suspension bridges from a series of wind tunnel tests. The influences of the shape of cross-section, ice shape, ice class, and Reynolds number on mean aerodynamic force coefficients were examined through static wind tunnel tests. The galloping stability was further examined based on the quasi-steady galloping theory according to the mean aerodynamic force coefficients. Furthermore, the effects of ice class and ice shape on the aeroelastic stability and flutter derivatives of a pipeline suspension bridge were investigated through dynamic wind tunnel tests. The results comprehensively reveal how ice accretion affects the aerodynamic characteristics of the bridge. Ice accretion on the girder can increase the static aerodynamic force, probability of galloping, and leads to vortex-induced vibration. Research results can provide a basis for aerostatic and buffeting analyses and a reference for the wind-resistant design of similar bridges in cold regions.

Türbülans Yoğunluğunun Geçiş Yer Tahminine Etkisinin Bölgesel Korelasyon Geçiş Modeli ile İncelenmesi

Aerodynamic parameters are among the most important parameters in flight performance analyses of air/sea vehicles. Free stream turbulence intensity has significant importance on aerodynamic parameters obtained with computational fluid dynamic analyses and wind tunnel tests measurements. In this study, the effect of free stream turbulence intensity on the transition locations of spheroid geometry using with the widely accepted local correlation transition model. The computations are performed at 6.5 x 106 Reynolds number with 0 and 5 degree angle of attacks. The computations at 5 degree angle of attack are compared with an available experimental study. The effect of free stream turbulence intensity is investigated with axial force coefficient, normal force coefficient, and surface friction coefficient distributions. It is seen that axial and normal force coefficients increase with increasing free stream turbulence intensity. The differences in force coefficients obtained with the free stream intensity range used in the study shall create noteworthy effects in flight performance analyses. When surface friction coefficients are investigated, the transition model estimates the transition locations earlier while free stream turbulence intensity increases as expected. However, the transition front geometry is obtained significantly different with respect to the experimental results.

Objective comparison of numerical spin study with aircraft model free-flight spin tests

This paper reports on the results of a research project that investigated the spin and recovery characteristics of a multirole fighter aircraft. In the first phase, numerical/computational methods were used to predict full scale aircraft spin and recovery characteristics. The aerodynamic data used in the numerical study was obtained from rotary balance steady coning and oscillatory coning motion dynamic wind tunnel tests conducted on 1/13th scale aircraft dynamic model. All the possible steady spin modes were numerically computed, a complete set of dynamic modes of the spinning aircraft were evaluated and six degree of freedom simulations of predicted flat spins were performed to investigate their dynamic stability and recovery characteristics. In the second phase, free-flight spin trials were conducted using 1/5th scale dynamic model of the understudy aircraft to validate the results of the analytical spin studies. Dynamic characteristics of the analytically predicted flat spins were objectively compared with flat spins found in free-flight spin trials as a validation process. Our results reveal that the numerically predicted full scale aircraft spin and recovery dynamic characteristics correlate well with those estimated from model test flights. The present study is an important step toward objective comparison of numerical spin studies based on dynamic wind tunnel tests data with free-flight spin trials, yielding important guidelines and results for future aircraft spin studies.

Self-Induced Roll–Yaw Oscillations of an Aircraft Model in a Wind Tunnel

Wind tunnel oscillatory testing is a technique conventionally used for the measurement of dynamic aerodynamic loads on subscale aircraft models. Oscillatory testing is commonly used for identification of dynamic stability derivatives for flight mechanics models. Model oscillation is normally driven by a rig drive mechanism, or with the use of its control surfaces. This paper presents a new test technique in which self-induced coupled roll and yaw oscillations are driven purely by the aircraft’s natural modes of motion when constrained in translation and in pitch rotation. This method does not require external mechanisms to drive the motion, nor the use of aircraft control surface inputs to sustain the oscillation. Without these sources of error, it is potentially advantageous for identification of dynamic stability derivatives using parameter estimation techniques. The mechanics of and requirements for this self-induced oscillation are discussed. Computational simulation and dynamic wind tunnel tests of a subscale BAe Hawk model are used to demonstrate the self-induced roll–yaw oscillations and their results are compared. Effects of varying parameters such as wind tunnel speed and the addition of spring stiffness onto the aircraft rotation axes on the frequency and stability of the oscillation are investigated.

Experimental Study on Directional Stability of Tumbling Plate

This paper describes the directional stability of the tumbling plate by measuring the trajectory of a paper piece that is shaped systematically. The tumbling phenomenon is considered to be an important phenomenon for aircraft flight safety because of the possibility of falling objects from the aircraft reaching far away. Therefore, this paper presents the result of measuring the trajectory of six configurations which shows that Concave configurations have directional stability while the Convex and Rectangular configurations are unstable. For generalization, the experimental result deducted using generalized equations into dimensionless values. Qualitative consideration is given to the relationship between the stall delay caused by sudden pitch motion and the phenomenon of the increase in the maximum vertical force coefficient (so-called Dynamic Lift), and the consistency with the dynamic lift wind tunnel test is shown.

Post-stall flight dynamics of commercial transport aircraft configuration: A nonlinear bifurcation analysis and validation

Loss-of-control has become the largest fatal accident category for worldwide commercial jet accidents, and any initiative aimed at preventing such events requires an understanding of the fundamental aircraft behavior, especially the flight dynamics at post-stall region at which loss-of-control usually occurred. A series of low-speed static and dynamic wind tunnel tests of the Common Research Model over a large angle of attack/sideslip envelope was conducted and a non-linear aerodynamic model was developed. The bifurcation analysis, complemented by time-history simulation was used to understand the post-stall flight dynamics and the numerical analysis results were preliminary validated by wind tunnel virtual flight test. Several representative post-stall behaviors for the transport aircraft have been identified, including departure, periodic oscillation, post-stall gyration and steep spiral, etc. Furthermore, the predicted periodic oscillation in pitch motion has been perfectly duplicated in wind tunnel virtual flight test. The approach used in this work shows a promising way to uncover the flight dynamics of transport aircraft at extreme and loss-of-control flight conditions, as well as to apply to nonlinear unsteady aerodynamics modeling and validation, flight accident investigation, advanced flight control law design or studying initiative for loss-of-control prevention or mitigation.

Effect of countermeasures on the galloping instability of a long-span suspension footbridge

The aeroelastic stability of a long-span suspension footbridge with a bluff deck (prototype section) was examined through static and dynamic wind tunnel tests using a 1:10 scale sectional model of the main girder, and the corresponding aerodynamic countermeasures were proposed in order to improve the stability. First, dynamic tests of the prototype sectional model in vertical and torsional motions were carried out at three attack angles (α= 3°, 0°, -3°). The results show that the galloping instability of the sectional model occurs at α = 3° and 0°, an observation that has never been made before. Then, the various aerodynamic countermeasures were examined through the dynamic model tests. It was found that the openings set on the vertical web of the prototype section (web-opening section) mitigate the galloping completely for all three attack angles. Finally, static tests of both the prototype and web-opening sectional models were performed to obtain the aerodynamic coefficients, which were further used to investigate the galloping mechanism by applying the Den Hartog criterion. The total damping of the prototype and web-opening models were obtained with consideration of the structural and aerodynamic damping. The total damping of the prototype model was negative for α = 0° to 7°, with the minimum value being -1.07%, suggesting the occurrence of galloping, while that of the web-opening model was positive for all investigated attack angles of α = -12° to 12°.

Non-across-wind galloping of a square-section cylinder

This paper presents new insights on the galloping instability phenomenon of square-section prisms. The role of the orientation of the structural axes on the galloping response is studied through wind tunnel tests and quasi-steady theory. A new series of dynamic wind tunnel tests on a square section model were conducted to evaluate non-across-wind galloping vibrations, as well as conventional across-wind galloping. The results are then compared with theoretical predictions to evaluate the reliability of quasi-steady theory in assessing the galloping phenomenon. It is found that for a given angle of attack, the structure has different aeroelastic behaviour for different orientations of the principal axis. At an angle of attack close to the critical angle of attack of square prisms, the quasi-steady theory well predicts the critical wind velocity for the onset of non-across-wind galloping but it is not successful for the case of across-wind galloping.

Investigating pitching moment stall through dynamic wind tunnel test

Experimental characterisation of aircraft dynamic stall can be a challenging and complex system identification activity. In this article, the authors present a method that combines dynamic wind tunnel testing with parameter estimation techniques to study the nonlinear pitching moment dynamics of a 1/12 scale Hawk model undergoing moment stall. The instrumentation setup allows direct calculation of angular acceleration terms, such as pitch acceleration, and avoids post-processing steps involving differentiation of signals. Data collected from tests, carried out at 20 m/s and 30 m/s, are used for a brief aerodynamic analysis of the observed stall hysteresis. Then an output-error-based parameter estimation process is used to parameterise dynamic stall models and furthermore, illustrate that in a scenario where the model's heave motion is constrained. The observed nonlinear behaviour arises from the nonlinear angle of attack and linear pitch rate components.

Magnetic Suspension of a Moving Aircraft Model at High Angles of Attack

The magnetic suspension and balance system (MSBS) suspends a model without physical support systems. With the use of a pair of two-dimensional CMOS image sensors, a position sensing system that detects the position of the model by dynamically tracking the model attitude was developed with the aim of applying an MSBS for high angles of attack (AOAs). The position sensing system developed in this study was able to detect the position and attitude of the model within the range of AOAs of -40 to 40 degrees. The position sensing system was installed to an existing 60 cm MSBS at JAXA, and static and dynamic wind tunnel tests were conducted to investigate the ability of the MSBS and the dynamic characteristics of a delta wing aircraft model at various AOAs. The MSBS could suspend and oscillate the model in pitch direction at AOA of 15 degrees with the amplitude of 6 degrees in the wind. The delta wing model was dynamically stable at each tested AOAs.

Gust Alleviation Control using Prior Gust Information: Wind Tunnel Test Results

Abstract This paper reports dynamic wind tunnel test results of gust alleviation using preview control. The wind tunnel tests are conducted as a part of validation of gust alleviation control using an onboard Doppler LIDAR (Light Detection and Ranging) system, which was developed by JAXA (Japan Aerospace Exploration Agency) and can measure wind velocities in front of an aircraft. The wind tunnel system is composed of a gust wind generator, a half-span rigid aircraft model, a model support system and a digital controller unit. The aircraft model is allowed to move pitch direction by the support system. It is equipped with two control surfaces, which are controlled by commands from the controller unit. Since the LIDAR system cannot be used in the wind tunnel system, the LIDAR information is emulated using the predetermined timeseries of the gust wind generator and used for the preview control law. The wind tunnel tests are conducted with 1-cosine shape gust generation commands and the proposed preview control law is compared with a conventional feedback control law. The results show that the proposed control law is effective in alleviating vertical load caused by gust wind.

Parameters estimation methodology for the nonlinear rolling motion of finned cylindrical body

Identification of nonlinear roll dynamics of finned cylindrical bodies is a critical step when assessing free motion stability and trajectories of aerially dispensed munitions or decoys. In this paper the authors present a parameter estimation process that focuses on identifying nonlinear aerodynamic models that characterize the roll dynamics of a cylindrical body with wrap around fins using data from a series of dynamic wind tunnel tests. This is a three step approach that combines ordinary least squares, stepwise regression and the augmented output-error method, and it is initially tested using simulation data corrupted by white Gaussian noise and then applied to the wind tunnel data. Roll and roll rate dynamics were captured through a series of high angle of attack free-to-roll tests carried out at an airspeed of 35m/s corresponding to a Reynolds number of 800,000. The results and discussion in this paper demonstrate how simulation can be used to develop and mature a system identification routine followed by its assessment through wind tunnel test data. It is shown that high order nonlinear models with up to 14 terms can be parameterized to provide high levels of agreement with roll and roll rate dynamics observed in the dynamic wind tunnel tests.

UAV aerodynamic design involving genetic algorithm and artificial neural network for wing preliminary computation

In this paper, the aerodynamic design procedure of a mini unmanned aerial vehicle, intended to perform aerial reconnaissance at low altitude and low Reynolds number, was summarized. Design process was divided into two major parts: conceptual design phase and preliminary design phase. During the conceptual design, classical procedures and data from similar unmanned aerial vehicles already designed were employed to define the requirements related to unmanned aerial vehicle design. The preliminary design was performed using panel method where the emphasis was given on the design of the UAV wing, fuselage design and empennage. The wing planform parameters were determined through an aerodynamic optimization process using both genetic algorithms and artificial neural networks. Finally an aerodynamic analysis using panel method, Computational Fluid Dynamic simulations and wind tunnel testing was carried out. Unmanned aerial vehicle full configuration design process was consistent, where a comparison between the final obtained results was carried out and showed an agreement in terms of lift, drag and pitch moment coefficients.

RESEARCH ON DYNAMIC TEST TECHNOLOGY FOR WIND TURBINE BLADE AIRFOIL

The dynamic oscillation process of wind turbine blades is usually accompanied by pitching and yaw. Due to the unclear understanding of many dynamic problems previously, a safer design is adopted at the expense of increasing the weight of the blade structure in engineering, usually neglecting the influence of the yaw oscillation. The design of large wind turbines has put forward higher requirements for obtaining more comprehensive and accurate dynamic loads of airfoils. It is of great significance to study the influence of yaw oscillation on the dynamic aerodynamic characteristics of airfoil. In view of this, the dynamic wind tunnel test on yaw oscillation of airfoil is carried out in this paper for the first time. The “electronic cam” technology is used instead of the mechanical cam to realize the stepless adjustment of oscillation frequency and oscillation angle. Based on the designed electronic external trigger device, the real-time measurement of the dynamic flow field is realized. Meanwhile, the synchronous acquisition of wind tunnel flow, model angular displacement and dynamic pressure data is realized. Furthermore, the static pressure measurement, pitching / yaw dynamic pressure measurement, PIV and fluorescent wire test are carried out respectively. The accuracy of the test results is high, and the regular pattern is reasonable. Besides, the influence mechanism of wall interference in dynamic test is analyzed. Research shows that: there is also obvious hysteresis effect on the dynamic aerodynamic parameters of yaw oscillation airfoil with the changing of the angle of attack. And with the increase of oscillation frequency, the aerodynamic hysteresis characteristics of the airfoil under pitching and yaw oscillation are all enhanced. The dynamic stall vortex at the positive stroke is delayed due to the pitching oscillation. The pressure distribution of the airfoil is greatly influenced by the strong three-dimensional effect at the intersection of the wind tunnel wall and the model tip. Overall, the dynamic test technique of yaw oscillation established in this paper can provide technical support for the study of the dynamic swept effect of the wind turbines.

Testing of a Hinged Wingtip Device for Gust Loads Alleviation

Recent aircraft designs have considered higher-aspect-ratio wings to reduce induced drag for improved fuel efficiency; however, to remain compliant with airport gate requirements, folding wingtips have been introduced as a solution to the increased wingspan. Recent numerical studies suggest that a folding wingtip solution may be incorporated with spring devices to provide an additional gust loads alleviation ability in flight as well. In this work, a series of low-speed steady and dynamic wind tunnel tests was conducted using a prototype of such a concept. It was found that a folding wingtip with a nonzero relative angle of the folding hinge axis to the streamwise direction could provide gust loads alleviation. The level of load alleviation varied with hinge spring stiffness and lifting condition, with the best performance achieving a 56% reduction in peak loading.

Comparison of Static Aerodynamic Data Obtained in Dynamic Wind Tunnel Tests and Numerical Simulation Research

Comparison of Static Aerodynamic Data Obtained in Dynamic Wind Tunnel Tests and Numerical Simulation Research