Wind Tunnel Model Research Articles

Application of a Numerical Simulation to the Estimation of Wind Loads on Photovoltaic Panels Installed Parallel to Sloped Roofs of Residential Houses

Many residential houses with sloped roofs are equipped with photovoltaic (PV) systems. In Japan, PV systems are generally designed based on JIS C 8955, which specifies wind force coefficients for designing PV panels. However, no specification is provided to the PV panels installed near the roof edges where high suctions are induced. When installing PV panels in such high-suction zones, we need to evaluate the wind loads on the PV panels appropriately, usually by performing a wind tunnel experiment. However, it is difficult to make wind tunnel models of PV panels with the same geometric scale as that for the building, e.g., 1/100, because the thickness of PV panels and the distance between PV panels and a roof are both several centimeters. Therefore, in the present paper a numerical simulation is applied to the estimation of pressures in the space between the lower surface of PV panels and the roof surface, called “layer pressures”, using the unsteady Bernoulli equation and the time histories of external pressure coefficients obtained from a wind tunnel experiment. An assumption of the weak compressibility of the air and an adiabatic condition is made for predicting the layer pressures from the flow speed through the gaps. The simulation method is validated by a wind tunnel experiment using a model of square-roof building.

Study of the Behavior of a Vertical Axis Eolic Turbine with Articulated Blades

This work presents the results of the development of a vertical axis wind turbine composed of variable geometry, plane blades, applied in operations with low wind speeds. The new concept of vertical axis wind turbine with variable opening blades is presented as an innovative prototype where mechanical details are important for the natural control of the openings of the blades. Theoretical, numerical and experimental analyzes are performed in the turbine called DEC® with the aim of determining the aerodynamic characteristics. An analysis of the behavior of the DEC® turbine consists of a numerical study carried out to calculate or drag coefficient, considering a range of opening positions of the opening at each moment to determine the power coefficient. A second numerical approach is to analyze the moment caused by the interaction between all the turbine blades, in which the effects of energy dissipation caused by the flow mats are considered. Then, the theoretical, numerical results are validated by tests performed using a model in the open wind tunnel, where the prototype is subjected to different wind speeds while maintaining rotation control. Suggestions are made to improve the mechanical and aerodynamic design of the innovative prototype. Finally, the DEC® turbine is expected to serve as an inspiration for creating other mechanical forms of passive or active control to improve variable aerodynamics applied in low-speed conditions.

Wind-induced tension and deflection of multi-span bundled transmission conductors using aeroelastic model wind tunnel test

An aeroelastic model of the two-span six-bundled conductors is fabricated without distortion of conductors, to investigate the performance of wind-excited multi-span transmission conductors. The wind tunnel test is conducted in a wind tunnel with a big size of cross-section to contain the large aeroelastic model of multi-span transmission conductors and measure wind-induced tension and deflection of the insulator. The effects of wind direction, wind speed, and length of insulator on the wind-induced tension and swing angle of the insulator are then investigated based on the wind tunnel measurement. Results show that the mean transverse tension increases with wind direction θ and follows the law of sin2θ when θ > 40°, but is not proportional to the square of mean wind speed VH when VH < 35 m/s. The force coefficient of the tension decreases with increasing θ and wind speed, and is close to 1.0 when θ = 90° and VH > 35 m/s. Swing angle of the insulator increases with θ and VH, and follows the law of sinθ when θ > 40°. The dynamic response component of the insulator’s swing angle is insignificant when VH > 30 m/s. The length of insulator tends to increase the transverse tension while decrease the swing angle of the insulator. In addition, the wind force coefficient from the aeroelastic model of the two-span conductors is smaller than that specified in GB50545 and GB50655, indicating that these two might overestimate the wind loads on multi-span multi-bundled conductors.

Manufacturing, Assembly and Integration of a Large Scale Composite Wing Wind Tunnel Model and the Design and Implementation of an associated Measurement System

Building a wind tunnel model with an innovative aerodynamic design including a laminar airfoil concept and morphing parts requires a suitable manufacturing and assembly plan to transfer the virtual model to concrete reality.The contribution of the INVENT GmbH within the GRETEL consortium is the manufacturing of the main structural components of the Wing and the integration of the Wind Tunnel Model. To realize such a precise projection, the main approach is to implement a high overall accuracy of the later model by realizing a low percentage of geometry deviation already on piece part level. Beginning with a material dedicated tool design concerning cure cycle parameters and induced strain effects, for aspects of geometrical manufacturing accuracy, also suitable inspection techniques, regarding the verification of structural requirements and material conditions are implemented in the integration process at specified steps.A further part of the integration process of the GRETEL Wind Tunnel Model is the installation of application-related measurement equipment. The Institute of Composite Structures and Adaptive Systems of the German Aerospace Center (DLR) is responsible for the design and realization of such a project customized measurement concept. For the measurement of the pressure distribution along the profile contour with various angles of attack and wing configurations during the testing, the wing is equipped with several pressure taps. Further, the measurement equipment spectrum covers also the registration of acceleration forces and mechanical loads of the inner wing structure components. This concept creates a holistic picture of the coherences between aerodynamical and mechanical dimensions for each tested configuration.The implementation of all aforementioned aspects into the large-scale model is elucidated and discussed in the light of morphing parts of the model being delivered by another project. The integrated equipment is described and the impact of the integration into the design and assembly of the overall model is illustrated.

Virtual manipulation of tail postures of a gliding barn owl (Tyto alba) demonstrates drag minimization when gliding.

Aerodynamic functions of the avian tail have been studied previously using observations of bird flight, physical models in wind tunnels, theoretical modelling and flow visualization. However, none of these approaches has provided rigorous, quantitative evidence concerning tail functions because (i) appropriate manipulation and controls cannot be achieved using live animals and (ii) the aerodynamic interplay between the wings and body challenges reductive theoretical or physical modelling approaches. Here, we have developed a comprehensive analytical drag model, calibrated by high-fidelity computational fluid dynamics (CFD), and used it to investigate the aerodynamic action of the tail by virtually manipulating its posture. The bird geometry used for CFD was reconstructed previously using stereo-photogrammetry of a freely gliding barn owl (Tyto alba) and we validated the CFD simulations against wake measurements. Using this CFD-calibrated drag model, we predicted the drag production for 16 gliding flights with a range of tail postures. These observed postures are set in the context of a wider parameter sweep of theoretical postures, where the tail spread and elevation angles were manipulated independently. The observed postures of our gliding bird corresponded to near minimal total drag.

Standing waves in the plenum of an open jet wind tunnel: Resonance and self-excited oscillation

The low-frequency pressure pulsations in a large low-speed open jet wind tunnel were studied using a 1:20 scaled model wind tunnel. It was found that plane pressure standing waves existed in all three directions of the wind tunnel’s plenum. It was confirmed that the large pressure pulsations in the transverse direction of the plenum were caused by the resonance of the plane pressure standing waves in that direction with the edgetone feedback (vortex-sound feedback between the nozzle and the collector). The analysis of the standing waves in the vertical direction of the plenum suggested that they might come from self-excited oscillations. For the model wind tunnel with a 1:20 strictly scaled collector, the standing waves in the transverse direction of the plenum were much stronger than those in the other two directions. By increasing the width of the collector, the intensity of the standing waves in the transverse direction was significantly reduced to a level similar to that of the standing waves in the vertical direction. It was also found that the standing waves in the transverse direction were significantly enhanced after a floor was added to the test section.

Instrumentation and Ground Testing of a Composite Elastic Wing Wind Tunnel Model

The Goal of the Project GRETEL is to build a composite elastic wing wind tunnel model. This model incorporates morphing aerodynamical structures and is to be delivered for testing in the Large Low speed Facility (LLF) wind tunnel of DNW. In order to be allowed to be tested in a wind tunnel, a ground test is required to assure the integrity of the design of the wing. In this paper a short introduction to the overall setup of the model is given including an overview of integrated sensors. A short introduction into the different configurations of the wing to be tested is given as well as the rationale for the derived test-matrix of the ground tests. The mechanical setup for the ground tests is described. There are two main tests done, on the one hand the static tests of the wingbox, on the other hand the dynamic tests for determination of modal parameters of the model in its different configurations. The static tests are done to identify mechanical responses of the model as built and compare them to the predictions of the Finite Element simulations. The method to derive the boundary conditions, i.e. loads and deformations, for the static tests from the simulation is documented and discussed. The static tests are also used to calibrate the integrated strain gauges to enable load monitoring in the wind tunnel tests. First experimental results from the ground tests are shown and discussed, comparing them to predictions from the simulation.

An accurate RANS-based transition prediction approach (part II)

We present a CFD analysis of a wind tunnel model of the new laminar turbo-prop aircraft designed in the frame of the European Clean Sky 2 programme. The work presents the numerical results of the aerodynamic performance of a scaled model of the innovative laminar turboprop A/C wing by using a CFD approach that includes the transition prediction. Numerical results will be compared by considering two different procedures: a) CFD analyses in which the transition location is imposed and b) CFD analyses in which the position of the transition is evaluated. The prediction of the transition location and the laminar flow extension is based on a numerical framework based on the coupling between a high-fidelity RANS tool and a Linear Stability (LNS) solver. According to this method, boundary layer equations are written in the conical formulation and the solution of RANS equations and transition onset is obtained through an eN method based on the LNS calculations.

Optimization of long-span suspension bridge erection procedure considering flutter risk in mixed extreme wind events

During the erection stage of the suspension bridge, its critical flutter wind speed is continuously varying due to changing structural dynamic properties including mass and stiffness. On the other hand, the wind climate is also varying greatly seasonally or even monthly during the bridge erection procedure. This work proposes an analytical framework to optimize the deck erection timeline under complex wind climate attacks. Xihoumen Bridge built at Chinese southeastern coast is taken as a calculation example. Full-bridge aeroelastic model wind tunnel test was conducted to examine the critical flutter speed at different erection stages. Extreme wind speed for tropical cyclones and synoptic wind are analyzed by tropical cyclone simulation and meteorological records respectively. Results show that the optimal timeline for Xihoumen Bridge is starting in August if a one-month duration is required for each stage. However, if the worst timeline is selected, the flutter risk will be increased 40 times larger. If the construction timeline is flexible for the construction schedule, this research proves that timeline optimization is a more economical and safe approach than structural approaches like storm ropes.

Low-Interference Wind Tunnel Measurement Technique for Pitch Damping Coefficients at Transonic and Low Supersonic Mach Numbers

An experimental method for the determination of the pitch damping moment coefficient sum Cmq+Cmα˙ in a wind tunnel at transonic and low supersonic Mach numbers is developed. With support interference being a major issue for dynamic tests at these velocities, a minimum interference wire suspension approach is used. The motion of the wind tunnel model is restricted to a single-degree of freedom pitching oscillation through the geometry of the support system. A statistical evaluation procedure allows the simultaneous evaluation of multiple tests to increase confidence in the results. The influence of the wires as well as nonlinear effects are accounted for. The method is validated in an extensive test series at Mach numbers ranging from 0.6 to 2.0. Two reference missile models—the Basic Finner and the Army-Navy Spinner Rocket (ANSR)—are used. The results agree very well with CFD calculations throughout the transonic range. In comparison to free-flight tests the accuracy is significantly improved and result uncertainties are reduced by an order of magnitude.

Cross-flow transition model predictions of hypersonic transition research vehicle

Hypersonic transition research vehicle (HyTRV) is a customized lifting body for studying hypersonic three-dimensional boundary-layer transition on a complex geometry. In this study, the transition model of an HyTRV lifting body at relatively high angles of attacks is investigated. A hypersonic cross-flow transition correlation is embedded in the γ-Re˜θt transition model on the Chant2.0 computing platform, called the C-γ-Reθ transition model. The transition model is validated in a series of typical three-dimensional aerodynamic configurations. HyTRV's flow characteristics and transition phenomenon are investigated. The model predictions are in good agreement with the stability analysis results and shockwave wind tunnel flow visualizations, exhibiting the model potential for hypersonic cross-flow transition prediction. The results of wind tunnel experiments, stability analysis, and model predictions confirm that transition regions on the upper/lower surface of HyTRV are dominated by cross-flow instabilities. With an increase in the angle of attack, the circumferential pressure gradient on the lower surface decreases and cross-flow intensity reduces; the transition onset location recesses until finally disappears. 2–3 pairs of isolated cross-flow transition zones exist on the surface of the HyTRV at a low angle of attack, which guarantees the HyTRV to be a typical validation case for cross-flow transition modeling.

TO THE PROBLEM OF MODELING THE AERODYNAMICS OF SURFACE TRANSPORTATION VEHICLES

The article deals with the problems of modeling the aerodynamics of surface high-speed vehicles of winged layout moving at a short distance from the water surface. To support them in the air, the screen effect formed under the influence of proximity to the water surface should be used. The effect of ground proximity is observed in air transport in the takeoff and landing modes of aircraft. The proximity of the ground affects the formation of the aerodynamic characteristics of vehicles. Today, the study of the aerodynamics of advanced vehicles moving near the underlying surface is possible using the following approaches: full-scale tests; modeling on special tracks; wind tunnel modeling. Full-scale tests are usually used at the final stages of vehicle development. simulation on special tracks is associated with the complexity of obtaining aerodynamic characteristics and is not widely used. The most suitable is modeling using wind tunnels. The current level of equipment of experimental laboratories allows for correct aerodynamic studies of aircraft. However, when modeling aerodynamic processes around vehicles moving near the interface, complex problems arise with reproducing the conditions of motion dynamics. The paper describes in detail the methods of studying the influence of the proximity of the ground on the formation of aerodynamic characteristics of vehicles in wind tunnels. These include: a method using a fixed plate; a method of mirroring the model; a method of suction or blowing the boundary layer; a method using a moving belt. The possibility of their use for modeling the aerodynamics of high-speed surface vehicles of winged layout is evaluated. When modeling the flow of high-speed vehicles moving near the water surface, a number of difficulties arise due to the realization of real flow conditions, namely, taking into account the dynamics of the water surface. Ideally, relative motion is realized between the vehicle and the water surface. The review of methods used in modeling the aerodynamics of vehicles over a solid screen proved to be of little use for high-speed winged vehicles moving at a short distance from the water surface. Ensuring the similarity of relative motion is an extremely difficult task. It requires a reasonable analysis of physical processes and the search for ways to develop physical and mathematical models suitable for use in the design of high-speed surface vehicles with wing arrangement. These models should range from simple engineering techniques to techniques based on the full and averaged Navier-Stokes equations.

Experimental Research on the Flow in the Steam Turbine Axial Exhaust Hood

There is the still remaining task to increase the efficiency of power plants and steam turbines. One possibility to increase the thermodynamic efficiency is to apply a suitable exhaust hood. Axial exhaust hoods are mainly designed for small turbines up to 180 MW. They are a very important part of steam turbines and its main purpose is to take away the steam from the last stage outlet to a condenser with minimal loss or even with pressure compression and an increase in the last stage enthalpy drop. This paper concerns experimental measurements on the axial exhaust hood wind tunnel model. The main goal of this paper is to determine how given geometrical and flow parameters affect the resulting pressure recovery coefficient. Main observed parameters are velocity and circumferential angle profiles at the diffuser inlet along with a number, shape and geometrical configuration of internal struts. Several geometrical variants are measured for two types of circumferential angles at the diffuser inlet and for two values of Mach number in the presented work. Multi-hole pneumatic probes and pressure taps are used for flow parameters measurement. The proposed experimental model, along with corresponding CFD (computational fluid dynamics) simulations, will help to optimize the flow parameters in the exhaust hood and allow a decrease in pressure losses in this part.

Establishment of a Coupling Model for the Prediction of Heat Dissipation of the Internal Combustion Engine Based on Finite Element

The aerodynamics and heat transfer performance in the rear-mounted automobile cabin have an important influence on the engine's safety and the operational stability of the automobile. The article uses STAR-CCM and GT-COOL software to establish the 3D wind tunnel model and engine cooling system model of the internal combustion engine. At the same time, we established a 3D artificial coupling model through parameter transfer. The research results show that the heat transfer coefficient decreases with the increase of the comprehensive drag coefficient of the nacelle. This shows that the cabin flow field has an important influence on the heat transfer coefficient. The mainstream temperature rise of the engine room increases with the increase of the engine load. It is proved that vehicle speed affects the amount of heat dissipation of the engine room internal combustion engine under certain load conditions. The article provides a more effective and fast calculation method for the research on the heat dissipation of the internal combustion engine and the optimization of the cooling system equipment.

Wind tunnel modeling experiments on airflow characteristics of underground metro station with sunken squares

Building airflow characteristics can affect the indoor air environment, thereby affecting indoor air quality and building energy consumption. In recent years, the sunken square has increasingly designed and applied to underground transportation hub systems, because of their special advantages, such as improving the ventilation and lighting of the underground space, blurring the feeling of the ground and underground and improving the quality of the space. However, at present, there are few systematic and comprehensive researches on the airflow characteristics of the sunken squares to the underground metro station. In this study, the wind tunnel modeling experiment and the particle image velocity (PIV) technology are comprehensively used to study the influence of the sunken square on the airflow characteristics of the underground metro station, the influence of the sunken square on the flow field distribution and air exchange rate of underground metro station are obtained. The dimensionless average wind velocity at the large openings of the sunken square is 0.053-0.18, and the air exchange rate of the underground metro station is changed with the number and the relative positions of sunken squares. Conclusions of this research could provide useful reference to the design of airflow characteristics for underground buildings.

USM3D Simulations for the Third AIAA Sonic Boom Prediction Workshop

The NASA USM3D flow solver was used to compute test cases for the Third AIAA Sonic Boom Prediction Workshop (SBPW3). The test cases included a near-field biconvex shock–plume interaction wind tunnel model and the C608 low boom flight demonstrator. Numerical simulations were conducted on the mixed-element and tetrahedral grids provided by the workshop committee, as well as a family of grids generated by an in-house approach known as BoomGrid. The near-field pressure signatures were extracted and propagated to the ground, and the perceived loudness levels on the ground were computed. The USM3D near-field pressure signatures, corresponding ground signatures, and loudness levels on the ground were compared with that of mean values from other workshop participants. The effect of three flux-limiters on the accuracy of near-field pressure signature prediction was investigated and results were compared with that of mean values from other workshop participants. The effect of using wall-function models for predicting near-field pressure signatures was also evaluated. Results showed that the overpressure signatures extracted from the wall-modeled simulations and the wall-resolved simulations are in good agreement. The use of wall functions (wall-modeled simulations) allowed for approximately 23% savings in the time to solution and yielded comparable perceived loudness levels on the ground to the wall-resolved Reynolds-averaged Navier–Stokes simulations.

General model derivation and verification of free-drop testing of aircraft in wind tunnel

A variety of models of the wind tunnel test with different masses and inertias are needed when the Mach number and altitude of the object in flight change in the traditional light model method. This limits the characteristics of mass of the free-drop wind tunnel test model, increases the duration of such projects as well as their cost of processing, and renders the relevant tests inflexible to cause a significant waste of human and material resources. To solve these problems, this study improves the equation for the constraint on the mass in free-drop testing in the wind tunnel model by simplifying it. This is done according to the parameters of the separation conditions by using only one general test model and adjusting the separation velocity. We used the wing-pylon generic store for a computational fluid dynamics simulation. The results show little difference between the proposed and simplified testing method that uses a store test model, and the traditional method that uses a variety of test models. The difference between the general model design and the ideal wind tunnel test was less than 1.0% and 1.5% in terms of errors in the linear and angular displacements, respectively. The proposed method can thus ensure similarity between the results of the improved wind tunnel test and the store trajectory. It can shorten the test cycle while reducing the cost and increasing the flexibility of testing.

Experimental Study of Mitigation of Wind-Induced Vibration in Asymmetric Cable-Stayed Bridge Using Sharp Wind Fairings

This paper investigated the aerodynamic response features of an asymmetric cable-stayed bridge. The wind resistance design parameters for judging the response were first determined, afterwards the bridge dynamic characteristics were analyzed for subsequent aerodynamic analysis. The vortex-induced vibrations (VIV) and flutter response at various wind fairing angles were then examined by using a 1:50 sectional model in the wind tunnel test. Finally, a 1:150 full bridge aeroelastic model was employed to explore the aerodynamic stability and characteristics of the whole asymmetric bridge under different wind attack angles in various flow fields. The results show that the sharp wind fairings could reduce the VIV amplitude of the steel box girder cable-stayed bridge to some extent, and the example bridge has examined to have enough flutter stability through sectional and full bridge aeroelastic model wind tunnel tests. Unlike symmetric bridges, the bridge’s maximum displacement of first torsion mode shape is at the closure rather than the mid-span, which is the essential reason to lead this unique vibration feature. The results from the present study could highlight the important effect of structural asymmetry and fairing shape to the wind-induced bridge vibration and hence may facilitate more appropriate wind design of asymmetric cable-stayed bridges.

Case study of vortex-induced vibration and mitigation mechanism for a long-span suspension bridge

The wind-induced vibration of long-span bridges mainly manifests as flutter, galloping, vortex-induced vibrations (VIVs), buffeting, etc. Among these, VIVs cause vertical or torsional single-mode vibrations of the main girder; these affect the comfort of drivers or pedestrians on the bridge when vortex-induced resonance occurs. In this study, field measurements, numerical simulations, and wind tunnel tests were used to systematically investigate triggering mechanism during the sudden first and secondary VIV phenomena of Humen Bridge, along with the structural mode and damping characteristics and VIV aerodynamic mitigation effects, etc. The results show that the sudden first VIV was caused by the temporary installation of water-filled barriers, as these changed the aerodynamic configuration of the box girder; the decisive removal of these water-filled barriers can effectively suppress the VIV amplitude to some extent. The succedent secondary VIV was caused by the reduction of the structural damping; therefore, aerodynamic control and damping control measures are proposed. The aerodynamic control measures include the implementation of suppressor plates on the top of handrails and removal of the maintenance rails under the girder, whereas the structural damping control measures involve the successive installation of tuned-mass damper (TMD) to compensate for the reduced damping owing to the former large-amplitude VIV performance. After verification based on reduced-scale model wind tunnel tests, the aerodynamic control measures and structural damping control measures are successfully adopted and applied to Humen Bridge. These measures are shown to effectively suppress VIVs, as confirmed via succedent long-term on-the-spot observations.

Experimental investigation of hybrid laminar flow control by a modular flat plate model in the DNW-NWB

To determine the characteristics of new suction concepts for hybrid laminar flow control (HLFC) a modular flat plate wind tunnel model is investigated in the DNW-NWB wind tunnel facility. This approach allows detailed examination of suction characteristics in consideration of realistic boundary layer flow conditions. The following evaluation reveals the effects of joining methods between successive panels and other surface disturbances of porous materials and underlying chambers on HLFC techniques. After successful measurements with and without suction panels, this paper compares experimental results with theoretical and numerical approaches and draws conclusions from N-factor results and boundary layer (BL) measurements.