Full-scale Wind Tunnel Tests Research Articles

Determination of unsteady wing loading using tuft visualization

Unsteady separated flow affects the aerodynamic performance of many large-scale objects, posing challenges for accurate assessment through low-fidelity simulations. Full-scale wind tunnel testing is often impractical due to the object’s physical scale. Small-scale wind tunnel tests can approximate the aerodynamic loading, with tufts providing qualitative validation of surface flow patterns. This investigation demonstrates that tufts can quantitatively estimate unsteady integral aerodynamic lift and pitching moment loading on a wing. We present computational and experimental data for a NACA0012 wing, capturing unsteady surface flow and force coefficients beyond stall. Computational data for varying angles of attack and Reynolds numbers contain the lift coefficient and surface flow. Experimental data, including lift and moment coefficients for a tuft-equipped NACA0012 wing, were obtained at multiple angles of attack and constant Reynolds number. Our results show that a data-driven surrogate model can predict lift and pitching moment fluctuations from visual tuft observations.

Investigation of tyre rim protectors on the aerodynamics of a passenger vehicle

The wheels of a passenger vehicle contribute to a significant part of the vehicle’s aerodynamic drag. The previous research has shown that the flow is sensitive to small geometrical variations of the tyre, such as its shoulder profile and tread pattern. This work investigates the effect of altering the tyre profile in the transition region between the tyre and the rim by adding a so-called rim protector. Full-scale wind tunnel tests capturing forces, flow fields and surface pressures were conducted for three tyre variants in combination with two rim configurations on a crossover SUV. With a low rim protector, the forces and flow fields were similar to the reference tyre without a rim protector for both rims. With a wide, protruding, rim protector on the open rim, a larger and more outwashed front wheel wake was obtained with differences in the vortex structures, resulting in a drag penalty of 0.017CD\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$0.017~C_D$$\\end{document}. The altered front wheel wake reduced the shielding of the rear wheel, resulting in differences in the rear wheel wake and base pressure. With a closed rim, the differences with the wide rim protector were much smaller with only a slight drag increase compared to the reference, demonstrating that there can be a strong interaction between the tyre and rim design.

On the Effectiveness of Scale-Averaged RANS and Scale-Resolved IDDES Turbulence Simulation Approaches in Predicting the Pressure Field over a NASCAR Racecar

Racecar aerodynamic development requires well-correlated simulation data for rapid and incremental development cycles. Computational Fluid Dynamics (CFD) simulations and wind tunnel testing are industry-wide tools to perform such development, and the best use of these tools can define a race team’s ability to compete. With CFD usage being limited by the sanctioning bodies, large-scale mesh and large-time-step CFD simulations based on Reynolds-Averaged Navier–Stokes (RANS) approaches are popular. In order to provide the necessary aerodynamic performance advantages sought by CFD development, increasing confidence in the validity of CFD simulations is required. A previous study on a Scale-Averaged Simulation (SAS) approach using RANS simulations of a Gen-6 NASCAR, validated against moving-ground, open-jet wind tunnel data at multiple configurations, produced a framework with good wind tunnel correlation (within 2%) in aerodynamic coefficients of lift and drag predictions, but significant error in front-to-rear downforce balance (negative lift) predictions. A subsequent author’s publication on a Scale-Resolved Simulation (SRS) approach using Improved Delayed Detached Eddy Simulation (IDDES) for the same geometry showed a good correlation in front-to-rear downforce balance, but lift and drag were overpredicted relative to wind tunnel data. The current study compares the surface pressure distribution collected from a full-scale wind tunnel test on a Gen-6 NASCAR to the SAS and SRS predictions (both utilizing SST k−ω turbulence models). CFD simulations were performed with a finite-volume commercial CFD code, Star-CCM+ by Siemens, utilizing a high-resolution CAD model of the same vehicle. A direct comparison of the surface pressure distributions from the wind tunnel and CFD data clearly showed regions of high and low correlations. The associated flow features were studied to further explore the strengths and areas of improvement needed in the CFD predictions. While RANS was seen to be more accurate in terms of lift and drag, it was a result of the cancellation of positive and negative errors. Whereas IDDES overpredicted lift and drag and requires an order of magnitude more computational resources, it was able to capture the trend of surface pressure seen in the wind tunnel measurements.

Investigation of Tyre Pattern Effect on the Aerodynamics of a Passenger Vehicle

Abstract The wheels of a passenger vehicle are one of the major contributors to the total aerodynamic drag, making their aerodynamic performance a considerable factor for the overall energy efficiency of the vehicle. Previous studies have shown that the complex flow field created by the wheels is sensitive to small geometrical variations of the tyre and that features such as shoulder profile and tread pattern can have a significant impact on drag and lift. In this study, the DrivAer model is used to evaluate the flow fields and aerodynamics of four tyre tread patterns with two rim designs. Full-scale wind tunnel tests were conducted where forces, surface pressures and flow fields were measured. Numerical simulations were also performed to aid the analysis. Using a slick tyre as the reference, it was found that rain grooves typically reduced the drag, whereas the effect of lateral grooves was dependent on the rim configuration. For the lift forces, the largest lift variations were obtained for the front lift which, in general, was reduced by rain grooves and increased by lateral grooves, most notably for the closed rim. The importance of considering the parasitic lift force acting on the wheel drive units when comparing experiments and simulations was demonstrated.

System identification of cropped delta UAVs from flight test methods using particle Swarm-Optimisation-based estimation

AbstractIn the era of Unmanned Aerial Systems (UAS), an onboard autopilot occupies a prominent place and is inevitable for many of their modern applications. The efficacy of autopilot heavily relies upon the accuracy of the sensors employed and the capability of the onboard flight controller. In general, aerodynamic behaviour and flight dynamic capabilities of Unmanned Aerial Vehicles (UAVs) govern the selection and the design of flight controllers. Precise modeling of linear aerodynamic characteristics from flight data can be achieved using many of the existing classical parameter estimation techniques such as Output Error Method (OEM), Equation Error Method (EEM), and Filter Error Method (FEM). However, all the classical methods may not be readily applicable for aerodynamic modeling in nonlinear flight envelopes. The current manuscript is an attempt to exploit the capabilities of the Artificial Intelligence (AI) technique, named Particle Swarm Optimisation (PSO), in combination with Least Squares (LS) cost function to perform linear as well as nonlinear aerodynamic parameter estimation. The aforementioned task is accomplished by considering flight data from manoeuvers pertaining to linear angles of attack, moderate and near stall flight envelopes of two different UAVs with cropped delta planform geometry. Parameters estimated using the proposed LS-PSO method are consistent with minimum standard deviation and are on a par with OEM estimates. The proposed LS-PSO method enhances the capabilities of LS-based EEM while estimating stall characteristic parameters, which was not possible with LS alone. The longitudinal and lateral-directional static parameters estimated from the full-scale wind tunnel testing of the two UAVs were also used to corroborate the results obtained from the flight data using the LS-PSO method.

Development of scheme to evaluate the performance of parachute canopy fabrics under tensile impact

The present research is an extension of the earlier work wherein a wider scheme of small-scale tensile impact testing is proposed, to characterise the whole parachute canopy instead of full-scale wind tunnel testing. The drop height for equivalent tensile impact on the rectangular stitched specimens is chosen as 300 mm, and accordingly, the dimension (Length × Width) has been decided (300 mm × 100 mm). To evaluate the performance of stitched specimen (at 45° bias angle), ungripped width of 20 mm on both sides of the specimen has been worked out. In the work, the actual payload responsible for parachute inflation has been addressed for the calculation of the exact opening shock force. Subsequently, to apply impact load on the specimen, dead weights are predicted based on the different levels of opening shock forces of the C-9 parachute canopy under different aerodynamic conditions. Considering a specific case, the behaviour of the ripstop and plain-woven fabric sample in terms of load versus extension curve and work done at the time of impact have been analysed under different loads using a high-speed digital camera. This study revealed that the plain-woven fabric is to be preferred for human dropping because it has a higher extension and higher impact duration than ripstop fabric. As a result, the plain-woven fabric will produce a lower impact or shock force in the parachute canopy which is to be transferred to the skydiver. On the other hand, ripstop fabric possesses higher strength, therefore can be preferred for materials dropping.

Suction and Pulsed Blowing Applied to Local Separation Downstream of Slat Cutout

An experimental study on the application of active flow control (AFC) to a .4 scale model of a swept wing in a landing configuration was conducted. The wing is fitted with an ultrahigh bypass ratio (UHBR) engine nacelle. The highly efficient UHBR engines are characterized by a large diameter that interferes with the flow around the wing, especially with slats deflected, degrading its performance. An innovative AFC device, creating steady suction and pulsed blowing (PB), was installed in the leading-edge region of the wing, above the nacelle, and its performance was experimentally evaluated. The effects of the suction and PB mechanisms were examined individually and simultaneously using relevant normalized parameters to pave the way to a full-scale wind-tunnel test. It was shown that the AFC actuators increased lift by up to 3%, redirected the flow to the desired downstream direction, and reduced the size of the separation zone created due to the implementation of the UHBR nacelle. The next step is validating the small-scale results of this study in a full-scale wind-tunnel tests that would be the last step before the technology is flight test ready.

Extended Study of Full-Scale Wind Tunnel Test and Simulation Analysis Based on DrivAer Model

There is a great demand for car model series that can meet the needs of today’s research about vehicle aerodynamics due to the limitations of models used in the past. This paper focuses on the introduction of the extension of DrivAer model and discussions about the model’s experimental and simulation results. On the basis of DrivAer model, the upgrade and innovation of pickup styling back and concept of perception testing are added. Specifically, the SUV back and the Pickup back are redesigned in combination with Chinese aerodynamic design trend. The experiments were performed in a full-scale aero-acoustic wind tunnel with ground simulation system, consisting of boundary layer control system and five-belt system. Base on the wind tunnel experimental results, it can be found that the ground simulation has obviously influence on the drag coefficient, but has no influence on the distribution of surface pressure in upper body. The close state of the grilles, the absence of mirrors, and the fully enclosed of rims can significantly reduce the drag coefficient. Digital wind tunnel (DWT) simulation and open road (OR) simulation have been completed and verified with experimental results. It can be concluded that DWT simulation with the same geometry as the real wind tunnel performs better than the OR simulation. The maximum difference between the experimental results and the DWT simulation results does not exceed 2% and DWT simulation also performs well in the surface pressure simulation.

Prediction and Suppression of Vortex-Induced Vibration for Steel Tubes with Bolted Joints in Tubular Transmission Towers

In this paper, a series of full-scale wind tunnel tests are conducted to study the vortex-induced vibration (VIV) of the steel tubes connected with C-shaped bolted joints. The dynamic properties of VIV responses of the steel tubes are analyzed and discussed in terms of probability density functions (PDFs) and power spectral density (PSD) functions. Based on the wind tunnel test results, a new empirical formula is derived to estimate the VIV critical wind speed of the tube with C-shaped joints, and an improved model is developed to predict the maximum VIV response of the steel tube. The proposed models are further validated through an independent wind tunnel test. In order to suppress excessive VIV responses of steel tubes, a passive vibration control approach is employed by installing a discrete cross-fin spoiler (DCFS) in various designs on the testing tubes. Key design factors of the DCFS, which are related to the VIV suppression effectiveness, are studied through wind tunnel tests, and the relatively optimal design of DCFS is recommended for VIV mitigation.

Characterization of wind-induced pressure on membrane roofs based on full-scale wind tunnel testing

Flexible roofing systems (e.g., membrane roofs) are widely used in low-rise commercial and industrial buildings, accounting for over 60% of low-sloped building roofs in North America. Despite their wide usage, the effects of roof flexibility are neither thoroughly studied, nor accounted for in current building design codes and standards. To investigate such roof flexibility effects on wind-induced pressure, full-scale testing was conducted at the NHERI Wall of Wind (WOW) Experimental Facility (EF). The mechanically attached roof system (MARS) and partially adhered roof system (PARS), two of the most commonly used commercial roofing systems with different flexibility characteristics, were considered in this study. “U-shaped” pressure taps were used to measure the wind-induced pressure on the membrane roof, and the pressure coefficients were compared to those measured on a plywood roof. The effects of wind direction and wind speed on the wind-induced pressure coefficients of membrane roofs were studied. The results showed that the membrane deformation due to the membrane roof flexibility resulted in a reduction in the peak pressure coefficients as compared to those of rigid plywood roof. This reduction in wind loads is more significant for the MARS (27%) which has more flexibility than the PARS (19%). The membrane roof flexibility also modifies the non-Gaussian characteristic which results in a lower peak factor than the plywood roof. It was also observed that peak pressure coefficients on the flexible roof increase at higher wind speeds. This study provides an improved understanding of the effect of roof flexibility on wind-induced pressure coefficients. Further research is needed by testing more types and configurations of flexible roofs to formulate new code provisions for wind effects on flexible membrane roofs.

Wind-Tunnel Testing of Otto Lilienthal’s Production Aircraft from 1893

A full-scale wind-tunnel test of a replica of Otto Lilienthal’s Normalsegelapparat from 1893 was conducted in a closed low-speed wind tunnel. The goal was to determine the flight performance and characteristics of this glider for the first time. It is of particular interest to this investigation to resolve the open question about the design’s static stability and to clear up whether Lilienthal treated the cloth covering the wings. Therefore, tests were performed both with an impermeable, sealed cloth as well as with untreated, permeable wings. Forces and moments were measured at freestream velocities between 5 and at angles of attack from the linear lift interval up to fully stalled conditions. The recorded data are used to investigate the flight performance and characteristics of the glider with an emphasis on its static stability. The impact of the permeability of the cloth in comparison to the impermeable configuration is discussed.

Monitoring of wind effects on a super-tall building during multiple typhoons and validation of wind tunnel testing techniques

Wind effects on high-rise buildings have always been a major concern in structural engineering. This paper investigates the wind effects on a 420-meter-tall building located in Hong Kong by full-scale measurements and wind tunnel testing. Using a structural health monitoring system installed in the building, wind fields and structural responses were collected during 15 typhoons from 2008 to 2017 with a total record time length of 375 hours. In wind tunnel tests, both rigid and aeroelastic scaled models of the monitored building were employed to predict the wind-induced structural responses, and then these experimental results were compared with the field measurements for verification of the model test results. The objective of this research is to further understand the wind effects on super-tall buildings during typhoons, validate the wind tunnel testing techniques based on a large amount of field measurements obtained during multiple typhoons, and hence provide useful information for the wind-resistant design of future skyscrapers.

Field investigation of wind–rain induced pressure on a low-rise building during Typhoon Haikui

Due to the strike of wind-blown raindrops, the pressure caused by wind and rain on building facades is different from the action of wind-only. The wind–rain induced pressure during Typhoon Haikui (2012) was collected at three taps on the windward side of Tongji University experimental building which was located near the coast of East China Sea. The observed data during the storm was compared with both the data of normal wind events without rains and wind tunnel test. The results show that the presence of driving rains intensifies the wind effects acting on the windward side of the building. More specifically, the mean wind–rain induced pressure coefficients at the three locations of the experimental building are larger than those collected from the strong wind-only events and the wind tunnel test when the wind direction ranges from 110° to 130°. It was also found that the mean wind–rain induced pressure coefficients at each tap increase in magnitude with rainfall intensity and the distance between the pressure tap and the wall corner. Similarly, the fluctuating wind–rain induced pressure coefficients are larger in comparison to the wind-only pressure coefficients from the full-scale measurement and wind tunnel test. However, the coefficients decrease with the distance from the wall corner in the case of 80°–140° wind directions. In addition, it was found that Gamma distribution is a robust model to represent the probability distribution of the wind–rain induced pressure coefficients. High quality of pressure correlation was observed among three taps, regardless of the rainfall intensity. By contrast, the presence of driving rains slightly reduces the correlation of wind–rain induced pressure.

The design and validation of over/under turbine-based combined cycle inlet

The design constraints including capture area and mode transition point of turbine-based combined cycle (TBCC) inlet are determined by the performance analysis of combined cycle propulsion system. According to the mass flow and thrust requirement of the combined cycle engine, the capture area of 1.0 m2 and mode transition between Ma 2.2 and 2.5 are recommended. Based on these two quantities an over/under TBCC inlet which can operate from takeoff to Ma 4.0 is designed. The variable geometry scheme of TBCC inlet is shown at different flight Mach number. Three dimensional numerical simulations of full-scale model and wind tunnel test of 8-percent scale model are explored to verify this inlet design method. The results from the numerical simulations and experimental tests indicate that the TBCC inlet could work properly during this Mach number range. The mass flow captured by the inlet and total pressure recovery at turbine/ramjet aerodynamic interface planes (AIP) meet the requirement of the TBCC propulsion system.

Investigation of the Effect of Tire Deformation on Open-Wheel Aerodynamics

<div class="section abstract"><div class="htmlview paragraph">This paper introduces a finite element (FE) approach to determine tire deformation and its effect on open-wheeled racecar aerodynamics. In recent literature tire deformation was measured optically. Combined loads like accelerating at corner exit are difficult to reproduce in wind tunnels and requires several optical devices to measure the tire deformation. In contrast, an FE approach is capable of determining the tire deformation in combined load states accurately. The FE tire model was validated using computer tomography images, 3D scan measurements, contact patch measurements and stiffness measurements. The deformed shape of the FE model was used in a computational fluid dynamics (CFD) simulation. A sensitivity study was created to determine the effect of the tire deformation on aerodynamics for unloaded and loaded tires. In addition, the influence of these tire deformations was investigated in a CFD study using a full vehicle model. The CFD model was validated through full scale wind tunnel tests as well as on-road tests. Finally, a straight-line and a steady state cornering maneuver based on a vehicle dynamics simulation were simulated using this combined approach of FE and CFD. The tire deformation included proper wheel load, wheel speed and slip angle for each wheel. The CFD full vehicle model took chassis slip angle, body roll angle and wheel steering angle into account in order to match the real driving situation. The results show that realistic tire deformations provide better insight into the effect of rotating wheels on aerodynamics of full vehicles, especially that of race cars.</div></div>

Active Flow Control on Vertical Tail Models

Active flow control (AFC) subscale experiments were conducted at the Lucas Wind Tunnel of the California Institute of Technology. Tests were performed on a generic vertical tail model at low speeds. Fluidic oscillators were used at the trailing edge of the main element (vertical stabilizer) to redirect the flow over the rudder and delay or prevent flow separation. Side force increases in excess of 50% were achieved with a 2% momentum coefficient () input. The results indicated that a collective of about 1% could increase the side force by 30–50%. This result is achieved by reducing the spanwise flow on the swept back wings that contributes to early flow separation near their tips. These experiments provided the technical backdrop to test the full-scale Boeing 757 vertical tail model equipped with a fluidic oscillator system at the National Full-scale Aerodynamics Complex 40-by 80-foot Wind Tunnel, NASA Ames Research Center. The is shown to be an important parameter for scaling a fluidic oscillator AFC system from subscale to full-scale wind tunnel tests. The results of these tests provided the required rationale to use a fluidic oscillator AFC configuration for a follow-on flight test on the Boeing 757 ecoDemonstrator.

Elastic shape morphing of ultralight structures by programmable assembly

Ultralight materials present an opportunity to dramatically increase the efficiency of load-bearing aerostructures. To date, however, these ultralight materials have generally been confined to the laboratory bench-top, due to dimensional constraints of the manufacturing processes. We show a programmable material system applied as a large-scale, ultralight, and conformable aeroelastic structure. The use of a modular, lattice-based, ultralight material results in stiffness typical of an elastomer (2.6 MPa) at a mass density typical of an aerogel . This, combined with a building block based manufacturing and configuration strategy, enables the rapid realization of new adaptive structures and mechanisms. The heterogeneous design with programmable anisotropy allows for enhanced elastic and global shape deformation in response to external loading, making it useful for tuned fluid-structure interaction. We demonstrate an example application experiment using two building block types for the primary structure of a 4.27 m wingspan aircraft, where we spatially program elastic shape morphing to increase aerodynamic efficiency and improve roll control authority, demonstrated with full-scale wind tunnel testing.

The influence of reduced Reynolds number on the wake of the DrivAer estate vehicle

Experiments on vehicle aerodynamics were conducted in a low-speed water channel at a Reynolds number two orders of magnitude lower than that of typical full-scale studies. Particle Image Velocimetry (PIV) measurements, focused on the wake of a realistic estate passenger vehicle model, were obtained and compared with existing wake measurements from full-scale wind-tunnel tests. The combination of sharp and rounded trailing edges present on the geometry impacts properties of the separating shear layers, although the general wake structures are qualitatively similar. In both cases, the wake remains dominated by the upwash from the underbody exit diffuser outflow. Effects of the reduced Reynolds number on the spectral content of the wake velocity field downstream of the recirculation region are also documented.

Full-Scale Testing of Active Flow Control Applied to a Vertical Tail

Full-scale wind tunnel tests were carried out on a Boeing 757 vertical tail equipped with 37 sweeping jet actuators on the starboard side along the rudder hinge line. The tests were performed at the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel () at NASA Ames Research Center. The model was tested at a nominal airspeed of 100 knots across rudder deflections and sideslip angles that covered the airplane’s emergency single engine climb. Active flow control (AFC) was optimized at the maximum rudder deflection of 30° and sideslip angles of 0° and . A threshold success criterion of 20% increase in the maximum side force was exceeded at largest rudder deflection using 12 sweeping jet actuators in the absence of sideslip but barely reached it with 18 actuators at the maximum sideslip at a momentum coefficient input of approximately 0.5%; consequently, 31 actuators were selected for most tests. AFC caused significant increases in suction pressure and associated side force on the actuated side. The successful demonstration of this application cleared the way for a subsequent flight demonstration on the Boeing 757 ecoDemonstrator in 2015.

Aeroelastic analysis of a helicopter rotor in hover

The paper deals with the numerical analysis of a helicopter rotor in hover conditions, including aeroelastic effects. In existing literature the effects of an aircraft structural deformation on airloads distribution and performance are fairly well described but mainly for airplanes. The purpose of the presented work is to indicate the possible influence of blades elasticity on helicopter rotor loads and performance in hover. Additionally, it aims to validate a new computational method based on a set of experimental results for a UH-60A helicopter rotor. The method used combines a high fidelity Navier-Stokes aerodynamic model coupled with a low-order beam structural model. This approach made it possible to take into consideration blade deformations in simulations and revealed the high influence of aeroelastic effects on rotor loads and performance at hover conditions. To authenticate the results, the presented method was validated with experimental data from two different flight test programs, three small-scale wind tunnel tests and one full-scale wind tunnel test. They were conducted for the UH-60A helicopter rotor by different organizations. The comparison of results revealed that the created computational method has high accuracy.