Wind Tunnel Test Results Research Articles

Wind Tunnel Study of a Grid Fin Stabilized Guided Projectile

There is a need for methods/techniques to analyze the aerodynamics of grid fins at high angle of attack. The existing methods to predict or compute the aerodynamic parameters for grid fins are inadequate at high angles of attack. The present study attempts to extend the understanding of the complex aerodynamics associated with grid fins. The analysis draws its conclusion from wind tunnel test results of five basic grid fin configurations. A vortex lattice solution was used to model the aerodynamics of the chosen grid fins. Next the analytical and empirical relations as discussed in open literature were applied to model grid fin aerodynamics at high angle of attack. The aerodynamic coefficients were computed. These coefficients were then compared with the experimental results obtained using the five grid fin configurations. To improve the matching at high angle of attack a proposed approach using Kirchoff’s theory along with vortex lattice method was applied. The results show that this approach can be a starting tool to model lattice/grid fin aerodynamics.

Uncertainty analysis method of internal drag measurement for flow-through model in high-speed wind tunnel

For aircraft with complex air intake and exhaust systems, the flow-through model simulating the internal flow passage is generally used to reduce the interference of internal and external flow fields when carrying out high-speed wind tunnel tests. The drag generated by the internal flow passage needs to be accurately measured and deducted from the full-model aerodynamic force, so as to obtain the aerodynamic characteristics of the aircraft to be tested. However, the existing internal drag measurement methods do not evaluate the uncertainty of the measurement results, which leads to the failure to evaluate the reliability of the flow-through model high-speed wind tunnel test results. This paper introduces the device and measurement method of internal drag of flow-through model. Based on GUM uncertainty analysis method, the analysis method of internal drag measurement uncertainty is established through strict mathematical derivation, which provides technical support for the evaluation of internal drag measurement uncertainty.

Intelligent Identification and Verification of Flutter Derivatives and Critical Velocity of Closed-Box Girders Using Gradient Boosting Decision Tree

Flutter derivatives (FDs) of the bridge deck are basic aerodynamic parameters by which flutter analysis determines critical flutter velocity (CFV), and they are traditionally identified by sectional model wind tunnel tests or computational fluid dynamics (CFD) numerical simulation. Based on some wind tunnel testing results and numerical simulation data, the machine learning models for identifying FDs of closed-box girders are trained and developed via a gradient boosting decision tree in this study. The models can explore the underlying input–output transfer relationship of datasets and realize rapid intelligent identification of FDs without wind tunnel tests or numerical simulation. This method also provides a convenient and feasible option for expanding datasets of FDs, and the distribution of FDs can be analyzed through the post-interpretation of trained models. Combined with FD sensitivity analysis, the models can be verified by the calculation error of CFV. In addition, the proposed method can help determine the appropriate shape of the box girder cross-section in the preliminary design stage of long-span bridges and provide the necessary reference for aerodynamic shape optimization by modifying the local geometric features of the cross-section.

Design and dry wind tunnel test of progressive flexible variable bending wing

AbstractThe deformable wing structure can change its aerodynamic shape according to the change of flight mission and flight environment, so as to obtain better lift-drag, stability and control characteristics, which is considered as one of the future research directions of aviation technology. Considering the current technology maturity and reliability, a gradient corrugated fin is designed to realise the bending deformation of the wing. The structure of the skin is optimised to keep the skin smooth during deformation. In addition, a progressive push and pull rod is proposed to drive the wing deformation, and the fluid-structure interaction simulation is carried out for the wing deformation. At the same time, the changes of wing aerodynamic characteristics under different angles of leading and trailing edges and different push rod action schemes are analysed. Finally, a dry wind tunnel simulation test of the designed progressive flexible variable bending wing is carried out. The results of fluid-structure interaction simulation and dry wind tunnel test show that the progressive flexible variable bending wing proposed in this paper has a simple and reliable structure and remarkable deformation effect. It has advantages in increasing lift and reducing drag, ensuring high lift-drag ratio and providing wing trim moment. The deformable wing dry wind tunnel test platform designed by this method is structurally reliable, easy to operate, and can accurately reflect the influence of wing deformation on its aerodynamic force, which provides a verification means for the development of the design method and the design of practical aircraft in the future.

Ablation Behavior of Rudder Wing Structure in Hypersonic Environment

In the flight process of a rudder wing structure in a hypersonic environment, a large temperature gradient is generated due to severe aerodynamic heating, leading to structural strength failure or ablation failure under the coupling effect of thermal stress aerodynamic force. Therefore, this paper proposes a method to study the ablation behavior of the hypersonic rudder wing structure. Based on the basic theories of hypersonic aerodynamics and structural mechanics, a fluid–solid–thermal coupling model of the rudder wing structure in a hypersonic environment is established. The temperature distribution and deformation of the rudder wing structure in the service state are obtained. In addition, the finite element analysis method based on automatic remeshing simulates the ablation of the rudder wing structure in a hypersonic environment. Under inflow conditions, the leading edge of the rudder has high temperatures and large deformation. The ablation simulation results are compared with the wind tunnel test results, and the results show that the proposed method can be applied to the study of service behavior in a hypersonic environment.

Experimental and numerical investigation of different wing profiles

Computational Fluid Dynamics (CFD) techniques are widely used in product development processes due to efficient algorithms to solve Navier Stokes equations. In this study, the coordinates of the NACA 1412 and NACA 2415 sections selected from the standard wing sections of the National Aviation Advisory Committee (NACA) have been implemented with specific procedures to create new geometries and a new wing profile design using the coordinate method. The wing profile geometry is created from the coordinates available in the literature. Fixed two-dimensional viscous flows around the generated wing profiles are simulated using commercially available ANSYS-Fluent software. The mesh structure used was created using the C type and rectangular structure. CFD and wind tunnel analysis of attack angles ranging from certain degrees. The aerodynamic coefficients of the related statuses, i.e. the lift and drag coefficients obtained from the analysis, have been compared with the wind tunnel test results. Aerodynamic research in recent years focuses on active flow control concepts, laminar flow control, fuel economy and higher transport/drag force ratio. This is designed to understand and analyze flow behavior around airfoils using the CFD method.

Aerodynamic modelling of a tilt-wing transition corridor

With the recent rapid evolution of the UAM class concepts in past years, the re-emerged interest in VTOL concepts and their aerodynamics arises. The tilt-wing is one of the possible solutions for such a vehicle. Recent decades of tilt-wing aerodynamic research point to the importance of the understanding transition regime from cruise to hover. Especially the wing stall phenomena which affect descent capabilities and control during the landing phase. Understanding such a regime is crucial for optimal wing design. This paper presents several approaches to the modelling of aerodynamic forces during the critical phase of transition. Computations are aimed particularly to the edge of the flight envelope. The low to high fidelity methods are employed and compared with the results of low-speed wind tunnel testing. The results from high fidelity methods match well with experimental results but the proposed simple analytical model fails in prediction of the transition corridor in the most critical regimes.

Identification of the High-Order Rational Function of Bridge Decks by SDOF Forced Vibration Testing

The high-order rational function provides an accurate and effective model of self-excited forces for flutter analysis of bridges. This study proposes a direct identification method for the rational function of a bridge deck, which enables high-order modeling. In this method, the single degree of freedom (SDOF) forced vibration test is first carried out on the sectional model of the bridge deck. The tested results are then processed by a harmonic function-based filter, yielding force time histories with high signal-to-noise ratios. Formulas are derived to identify parameters of the high-order rational function from these time histories. To deal with the numerical difficulties of the formulas, two practical optimal nonlinear fitting procedures were proposed, which simplify the identification but at the same time maintain a reasonable accuracy. A thin flat plate and a streamlined box section under various wind angles of attack were used as examples to elucidate the effectiveness and feasibility of the proposed identification method. Results showed that the identified high-order rational function could accurately replicate the self-excited force. In contrast, a significant deviation was observed if the first-order rational function was utilized as an alternative. Finally, the high-order rational function model identified was applied in the flutter analysis by a state-space method. The yielded critical flutter wind speed matched satisfactorily with the free-vibration wind tunnel test results, confirming the advantage of the proposed model.

Prediction of aerodynamic coefficients of iced conductors based on composite image and convolutional neural network

The aerodynamic force of iced conductors is a key factor in the galloping study of transmission lines. At present, it is less efficient to obtain the aerodynamic coefficients of iced conductors by wind tunnel tests or numerical simulations. In this paper, an efficient method is proposed to predict the aerodynamic coefficients of iced conductors based on a convolutional neural network. The linear mapping relationships are constructed between the wind flow parameters and the shape image RGB matrix to generate composite images. Then the composite image and the convolutional neural network (CI–CNN) model is proposed. Due to the aerodynamic coefficients having a strong nonlinearity, the Fourier fitting function is used to describe the nonlinear characteristics of the aerodynamic coefficients changing with the attack angles. Then the Fourier composite image and convolutional neural network (FCI–CNN) model is proposed. The 1443 aerodynamic coefficients of crescent-shaped iced conductors from the wind tunnel test are taken as an example. The results show that both the FCI–CNN model and the CI–CNN model perform well during the estimation of the drag coefficient, especially the R2 calculated as 0.986 and 0.977, with MAE as 0.087 and 0.066, proving that the proposed method is effective. When predicting the lift coefficient, the R2 of the FCI–CNN model and the CI–CNN model are 0.931 and 0.838, respectively. So do the result in the prediction of the torque coefficient. Through the Den Hartog coefficient, the FCI–CNN model reflects the most important range of 170°–185° galloping wind attack angle compared to the wind tunnel test results. The FCI–CNN model gives better predictions than the CI–CNN model.

Numerical Simulation of the Aerodynamic Performance of A U-Shaped Sail

For a U-shaped sail that has been applied on real ships, we establish a three-dimensional sail geometry model using SolidWorks, and obtain its numerical simulation results under 10 different angles of attack using Fluent to numerically simulate its aerodynamic performance. By comparing the calculated results with the wind tunnel test results, the simulation model proved to be effective. Then the interference effects between the twin sails of the U-shaped sail were investigated by using the sail simulation model.

Semiempirical Models of Speedup Effect for Downburst Wind Field over 3-D Hills

Downbursts occur frequently in mountainous regions, such as the southwest of China, and causing extensive damage to engineering structures. While some researchers have developed semiempirical models for the speedup effect, most are based on the wind field in the boundary layer over the hill, and there is a lack of semiempirical models for the downburst wind field over the hill. This study employs three RANS (Reynolds Average Navier-Stokes) turbulence models to numerically simulate the downburst wind field over a quadratic curved hill. The realizable k-ε model is selected as the optimal model for the subsequent numerical simulations based on comparison with wind tunnel test results. Then, a semiempirical model of the speedup effect of the downburst wind field over the hill is constructed by numerically simulating the downburst wind field over the hill with different radial locations and different slopes. Finally, the constructed semiempirical model is validated and demonstrates good accuracy.

Effects of damping and helical fillets on galloping vibration of stay cable installed with a rectangular lamp

Lamps attached on the stay cable can change the stable circular cross-section of the stay cable, which is easy to cause galloping vibration. Stay cables of the Kuipu bridge in the Fuzhou City of China were equipped with damper and helical fillets. After the installation of rectangular lamps on this bridge, no obvious vibration of the stay cables was observed. This is totally different from another bridge, the Kuimen bridge in the Chongqing City of China, which has been recently reported by the authors. The purpose of this study is to clarify the effects of the helical fillets and the structural damping on galloping vibration. The features of galloping vibration of the stay cable attached to a rectangular lamp were carefully studied, and the effectiveness of damping and helical fillets in reducing the galloping vibration was evaluated. First, the force measurement wind tunnel tests on the segmental test model were carried out, and the lift and drag coefficients of the stay cable attached to the rectangular lamp were measured. The dangerous wind attack angle of galloping vibration was predicted by the galloping force coefficient. Second, 3-dimensional vibration measurement wind tunnel tests were carried out to measure the wind-induced response of the cable-lamp test models. The variation of wind-induced response of stay cable with yaw angle and wind velocity was measured for test models with and without helical fillets. In the test, the features of wind-induced vibration were studied at the damping level of 0.1%, 0.6%, 0.7%, 0.8%, and 1.0%. According to Den Hartog’s theory, the minimum coefficient of galloping force is about −9.8. The experimental results of 3-dimensional vibration measurement wind tunnel tests show that the helical fillets wrapped on the cable surface can enhance the critical wind velocity to a certain extent, but the critical wind velocity is still far lower than the design wind velocity. When the damping ratio of the stay cable is up to 1.0% ( SC = 35.1), the galloping vibration of the stay cable attached to a rectangular lamp on the Kuipu Bridge can be effectively mitigated.

Evaluation of Spray Drift of Plant Protection Drone Nozzles Based on Wind Tunnel Test

The use of drones in agriculture is expanding at a brisk pace in crop production due to the superiority in precision, efficiency, and safety of their applicators. However, their potential drift risk also raises concern for users and regulatory authorities. The method of wind tunnel research can effectively evaluate the weighted influence of each drift factor, especially the drift characteristics of the nozzle and spray solution. Based on the wind tunnel test results, centrifugal nozzles have a higher drift risk than hydraulic nozzles, even with a similar DV50. The cumulative drift rate of the centrifugal nozzle at 2 m downwind was 90.1% compared to the LU12001 nozzle’s 40.6% under the wind speed of 3.5 m/s. Compared with the same coding as the flat fan hydraulic nozzle, the IDK nozzle can effectively reduce the drift rate. For the tested nozzles, DV50 and wind speed had a linear relationship with drift rate, and the sampling location had an exponential or logarithmic relationship with drift rate. Spray adjuvants, especially modified vegetable oils, had a significant effect on reducing the amount of drift. The results of this experiment provide a reference for the selection of nozzles and the addition of spray adjuvants. Further clarifying the spray drift characteristics of drones until a drift prediction model is available is still the focus of research.

Simulation of a ground-mounted prism in ABL flow using LES: on overview of error metrics and distribution

The accuracy of wind loading predictions using Large Eddy Simulation (LES) is usually influenced by numerous model parameters, which can influence the obtained results. The validation of numerical simulations with traditional Wind Tunnel Test (WTT) is still an important task, necessary to increase our a priori knowledge of possible inaccuracies and set up mitigation strategies. In this study, LES is used to simulate the wind fields around an isolated model high-rise building, under seven wind attack angles and validated with WTT results. The influence of various settings and parameters on the model performance is studied. For the angle of attack showing higher inaccuracy, different mesh refinement strategies and turbulence models are tested. Results indicate that LES can accurately predict the mean and local maxima of the pressure coefficients for both perpendicular and skew wind attack angles, as well as reproduce global forces and their envelopes with very good accuracy. Conversely, pronounced errors are found in the prediction of the pressure coefficient standard deviation and the local minima. The highest deviations between LES and WTT are found close to the leading edge in correspondence of flow separations which are observed in WTT and not in LES for skew flows. The addition of boundary layer cells and the use of different subgrid models have very limited effectiveness in modifying the obtained results for the analysed case.

Research on turbulence model for simulation of wind flow in mountain areas of micro-topography

The accuracy of wind flow simulation in mountain area in micro-topography is related to discrete scheme, turbulence model and wall function. In this paper, the standard hill model is adopt to analyze the calculation accuracy of different turbulence models. Four turbulence models, including RNG k-ε, k-ω, SST k-ω and TSST k-ω, were used in the calculation, and were compared with the result of wind tunnel test. The calculation results with the second-order upwind scheme, the SST or TSST turbulence model and the scalable wall function are basically consistent with results of wind tunnel test.

Study on the influence of aerodynamic configuration on vortex vibration of steel pipe

In this paper, for steel pipe members with a slenderness ratio of 120, spoilers with different numbers and spacings are arranged to test the vibration reduction effect. Wind tunnel test results show that 7 sets of spoilers with a size of 1D×0.5D can basically suppress the vibration of the steel pipe member. When the spoiler spacing is 1D~4D, the reduction of the maximum amplitude is more than 90%.

Aerodynamic characterisation of delta wing unmanned aerial vehicle using non-gradient-based estimator

AbstractAerodynamic characterisation from flight testing is an integral subroutine for evaluating a new flight vehicle’s aerodynamic performance, stability and controllability. The estimation of aerodynamic parameters from flight test data has extensively been explored, in the past, using estimation methods such as the equation error method, output error method and filter error method. However, in the current era, non-gradient-based estimation techniques are gaining attention from researchers due to their inherent data-driven optimisation capability to find the global best solution. In this paper, a novel non-gradient-based estimation method is proposed for the aerodynamic characterisation of unmanned aerial vehicles from flight data, which relies on the maximum likelihood method augmented with particle swarm optimisation. Flight data sets of a wing-alone unmanned aerial vehicle are used to demonstrate the capabilities of the proposed method in estimating aerodynamic derivatives. Estimates from the proposed method are corroborated with the wind tunnel test and output error method results. It has been observed that simulated flight vehicle responses using estimated parameters are in good agreement with measured data in most of the manoeuvers considered. Confidence in the estimates of linear and nonlinear aerodynamic parameters is well established with the lower limit of Cramer-Rao bounds, which are minimal. The proposed method also demonstrates good predictability of the quasi-steady stall aerodynamic model by estimating stall characteristic parameters such as aerofoil static stall characteristics parameter, hysteresis time constant and breakpoint. The overall performance of the proposed estimation method is on par with the output error method and is validated with the proof-of-match exercise.

Derivation and validation of a similarity law for free-flight wind tunnel tests of parallel stage separation

Aiming at the safety problem of the stage separation of parallel reusable high-speed air vehicles, this paper studies the unsteady test method and focuses on deriving a similarity law of parallel stage separation free-flight wind tunnel tests. The new similarity law considers the influences of aerodynamic force and gravity on the motions of the two stages, as well as the influence of aerodynamic interference between the two stages on each other’s motion. From the perspective of multi-angle physical equations, the conditions to ensure that the two-stage separation trajectory of a wind tunnel test is similar to that of a real air vehicle are derived innovatively, so as to ensure the authenticity and credibility of wind tunnel test results. The similarity law is verified by an HIFiRE-5 air vehicle, and the separation trajectories of wind tunnel tests and the real air vehicle are obtained by numerical simulation. The research shows that the similarity law derived in this paper can ensure that wind tunnel free-flight tests have the ability to predict the two-stage separation characteristics of real parallel vehicles. By analyzing the separation trajectory curve of the typical state, it is found that the new method can ensure that the trajectory error of a wind tunnel test does not exceed 1%, which indicates that this method is credible. The establishment of the new method lays the foundation for subsequent wind tunnel tests and provides support for research on the safety of the stage separation of parallel reusable air vehicles.

Effect of Wind Load on Milad Tower and Adjacent Buildings Case study: Shed Adjacent to Tower

Tall buildings are subject to wind loads as one of the effective lateral loads. An analysis of the effect of wind on Milad Tower is presented in this research. The wind tunnel testing results and numerical modelling implemented in computational fluid dynamics (CFD) using ANSYS software. For the numerical simulation, the K-epsilon model has been used. The study evaluated the flow around the tower in several deformation states and compared it with a model where the tower is modeled rigidly in the wind tunnel. The maximum coefficient of negative pressure (suction) at the top of the tower structure equals to -1.95, which occurs at q =90o, and the maximum coefficient of the positive pressure equals +1. Since the buildings near the tower are located a short distance from the tower, the shed's structure, which is located near the tower, has also been investigated. With the aid of Tecplot software. The wind pressure coefficients obtained from the wind tunnel test were plotted. As part of the wind loading analysis in the single-span and two-span shed models, the model is rotated with a step of 5o relative to the direction of wind application, and wind pressure is recorded.

Installation error calibration for MEMS angular measurement system in hypersonic wind tunnel

The accuracy of model attitude measurement has an important impact on wind tunnel test results. Microelectromechanical System Inertial Measurement Unit (MEMS IMU) provides a feasible way to measure model attitudes with high accuracy. However, the installation error between MEMS IMU coordinate system and the body coordinate system of test models can make the accuracy of the model attitude measurement decrease. In wind tunnel tests, the installation error depends on the relationship between the IMU and the model mechanism before tests. Therefore, in-field calibration in wind tunnel tests is necessary to reduce installation errors. To improve attitude measurement accuracy, the least squares quaternion calibration method based on MEMS IMU and six-position calibration procedure are proposed. High-precision three-axis turntable tests are performed. The pitch accuracy after calibration is higher than that before calibration in the angle of attack sweeping tests. The Root-Mean-Square Errors (RMSE) in the roll and yaw are within 0.01°, which are smaller than those before calibration. In the roll sweeping tests, RMSE of three attitude angles decrease significantly. In hypersonic wind tunnel tests, the pitch errors before and after calibration are within 0.05° and 0.02° in the angle of attack sweeping tests without wind. In five angle of attack sweeping tests with wind, the deviation between the mean of the pitch and the pitch after the elastic angle correction is within 0.03° and the standard deviation of five tests is within 0.01°. The proposed method is confirmed to enhance the accuracy of attitude measurement effectively, which is convenient for engineering applications.