Wind Tunnel Balance Research Articles

Design of an external six-component wind tunnel balance with floating frame

Design of an external six-component wind tunnel balance with floating frame

Design of an external six-component wind tunnel balance with floating frame

This paper details the design procedure of a wind tunnel aerodynamic balance. It is the six-component external balance with floating frame used in our main Eiffel-type wind tunnel. This balance has the unique feature of being able to receive full and half wind tunnel models. Firstly, a set of design requirements and specifications is defined. Then the conceptual and detailed design of the mechanism is deeply explained. Finally, an analytical model of the balance is developed and used in order to study the effect of the design loads: this allowed sizing of the load cells and the counterweights of the balance.

Wind Tunnel Measurement Systems for Unsteady Aerodynamic Forces on Bluff Bodies: Review and New Perspective.

Wind tunnel tests have become one of the most effective ways to evaluate aerodynamics and aeroelasticity in bluff bodies. This paper has firstly overviewed the development of conventional wind tunnel test techniques, including high frequency base balance technique, static synchronous multi-pressure sensing system test technique and aeroelastic test, and summarized their advantages and shortcomings. Subsequently, two advanced test approaches, a forced vibration test technique and hybrid aeroelastic- force balance wind tunnel test technique have been comprehensively reviewed. Then the characteristics and calculation procedure of the conventional and advanced wind tunnel test techniques were discussed and summarized. The results indicated that the conventional wind tunnel test techniques ignored the effect of structural oscillation on the measured aerodynamics as the test model is rigid. A forced vibration test can include that effect. Unfortunately, a test model in a forced vibration test cannot respond like a structure in the real world; it only includes the effect of structural oscillation on the surrounding flow and cannot consider the feedback from the surrounding flow to the oscillation test model. A hybrid aeroelastic-pressure/force balance test technique that can observe unsteady aerodynamics of a test model during its aeroelastic oscillation completely takes the effect of structural oscillation into consideration and is, therefore, effective in evaluation of aerodynamics and aeroelasticity in bluff bodies. This paper has not only advanced our understanding for aerodynamics and aeroelasticity in bluff bodies, but also provided a new perspective for advanced wind tunnel test techniques that can be used for fundamental studies and engineering applications.

Additively Manufactured Wind-Tunnel Balance

One specialized application of a force transducer is a wind-tunnel force balance: a device used to measure the forces and moments exerted on a wind-tunnel model when subject to wind flow. In this study, a balance is manufactured from 17-4PH powder using selective laser melting. The performance of the balance is assessed relative to a conventionally manufactured balance. The additively manufactured balance exhibited accuracies and spring quality comparable to the conventionally manufactured balance; however, sensitivities were lower for the additively manufactured balance due to oversizing of almost all flexural members. Taken together, these results suggest that additive manufacturing can be used to manufacture balances for many wind-tunnel applications, which are expected to decrease the manufacturing time of balances by six to nine months and offer the potential to manufacture new balance design geometries.

Wind interference effects of a ventilated supertall building on its neighboring supertall building—A case study

SummaryOpening ventilating holes on a supertall building is an effective way to reduce its wind‐induced structural response and enhance its wind‐resistant performance. However, its interference effect on the neighboring supertall buildings has seldom been studied yet. Taking two actual neighboring buildings, the Guangdong International Financial Center (IFC) and the Guangzhou Chow Tai Fook Finance Centre (CTF) as examples, this study carried out high‐frequency force balance wind tunnel tests to investigate the interference effect of the IFC's ventilating openings on the wind‐induced response of CTF. Results show that when CTF is located in the downstream area of IFC, the ventilating openings on IFC make the high‐energy frequency band of the power spectral density (PSD) of CTF's crosswind aerodynamic load offset obviously towards the lower frequency interval. Consequently, the wind‐induced response of CTF can be significantly magnified or minified depending on the reduced structural natural frequencies. Since the reduced natural frequency for the structural base bending moment computation is usually smaller than that for the acceleration response computation, ventilation openings on IFC can be advantageous to the crosswind base bending moment response relevant to structural safety design, and disadvantageous to the acceleration response relevant to occupant comfort assessment.

High-accuracy fully automatic calibration systemfor impulse balance

<p indent="0mm">Long-test duration shock tunnel JF-12 has been built in 2012 in the Institute of Mechanics, Chinese Academy of Sciences. Its performance tests demonstrated that the facility is capable of reproducing the pure airflow with longer than 100 ms test time. In order to develop and improve the force test capability in JF-12, a high-accuracy fully automatic calibration system (AiBCS) for the large-load wind tunnel balances was designed and built, based on the characteristics of impulse-type balance. The design process and some key techniques of the AiBCS are shown and analyzed in detail in this paper. The strain-gauge balance with the maximum loads of <sc>15 kN</sc> can be calibrated automatically with high-accuracy in this balance calibration system. In this paper, the calibration data of an impulse-type balance by two calibration equipments are also compared and analyzed, where the performance of AiBCS is more excellent. Therefore, AiBCS provides an equipment foundation and technical supports for the development of force measurement in the impulse facilities, like a high-enthalpy shock tunnel.

Accuracy assessment of the Ring of Fire system for on-site aerodynamic drag measurements

: Nowadays, professional and ambitious amateur athletes are seeking small aerodynamic improvements relying on wind tunnel balance measurements, velodrome tests, and outdoor i¬eld tests. Many new companies have specialized in offering such testing days, which underlines the growing importance and demand on improving the aerodynamic efi¬ciency. However, one of the big drawbacks of these traditional testing methods is that they act as a black box, as only overall drag data can be extracted, without visualizing the i¬‚ow structures around the cyclist, which could be used to identify the region that offers the greatest potential. In order to gain further insight into the i¬‚ow around the cyclist, other approaches need to be employed. One of the methods is CFD (Computational Fluid Dynamics) which allows simulating the airi¬‚ow around the cyclist numerically. Even though this method shows the capability of simulating complex i¬‚ows in sports, as shown in Gardan et al. (2017), it is often limited to an idealized environment without modelling the transiting behaviour occurring in most sports, like the pedalling motion of a cyclist. Recently a new testing method has been developed  that quantifies the on-road aerodynamic drag of athletes in motion and visualizes the flow field in its wake (Spoelstra et al., 2019). The measurement system is based on large-scale stereoscopic particle image velocimetry (PIV) measurements over a plane crossed by the cyclist. The measurement concept is referred with the name Ring of Fire (RoF) as the vehicle crosses a region of intense light.

Development and characterization of a low-cost wind tunnel balance for aerodynamic drag measurements

Drag force measurement is one of the most important data that can be obtained in wind tunnel tests. Drag force is directly related to the energy that a vehicle needs to move, and, therefore, to the fuel costs associated with it. For vehicles, drag forces are usually measured in wind tunnels. The typical instruments for drag measurement are the force balances, which are usually complex and expensive instruments. The aim of this investigation is to study the development of a low-cost in-house balance for drag measurements in a wind tunnel. Based on a commercial available load cell XFTC300 Series in combination with simple elements designed and manufactured at INTA, a balance capable of measuring the drag force to models in a considerably wide adjustable range has been developed and characterized. The balance has been calibrated and used in a wind tunnel. Tests were carried out on a truck model, a simplified frigate shape and an Ahmed Body to obtain the resistance coefficient and evaluate the operation of the balance.

SIMULATION OF 2D FLOW AROUND OF AIRFOILS AT LOW-SPEED WIND TUNNEL WITH OPEN JET TEST-SECTION

At present, there is a great interest in the development of new airfoils for wind turbines and high-lift wings of unmanned aerial vehicles (UAV). The requirements for such airfoils differ from conventional aircraft airfoils, because of structural reasons and extreme operating conditions. So, wind turbine airfoils operate frequently under fully separated flow when stall is used for power regulation at high wind speeds. At the same time design of airfoils for wings UAV poses the problem of availability of high-lift at low Reynolds number. Modern airfoils are to a large extent developed from numerical methods. However, the complex flow conditions such as separation at high angles of attack, laminar separation bubbles and the transition from laminar to turbulent flow are difficult to predict accurately. Hence, testing of airfoils at a two-dimensional condition is an important phase in airfoil design. The development and validation of a 2D testing facility for investigation of single and multi-element airfoils in the wind tunnel Т-102 with open test section are considered in this article. T-102 is a continuous-operation, closed-layout wind tunnel with two reverse channels. The test section has an elliptical cross-section of 4 ×2,33 m and a length of 4 m. Two big flat panels of the L × H=3 ×3,9 m size installed upright on balance frame aligned with the free stream are used for simulating two-dimensional flow in the tunnel test section. The airfoil section in the layout of a rectangular wing is mounted horizontally between flat panels with minimum gaps to ensure 2D flow conditions. The aerodynamic forces and pitch moment acting on the model were measured by wind tunnel balance. To determine boundary corrections for a new test section of wind tunnel, the experimental investigation of three geometrically similar models has been executed. The use of boundary corrections has provided good correlation of the test data of airfoil NACA 6712 with the results obtained from the wind tunnel except for lift and drag coefficient values at high angles of attack.

Evaluation of Cryogenic Force Balance Calibration Methodologies Relative to Wind Tunnel Results

Independent tests of the NASA Common Research Model at NASA’s National Transonic Facility and the European Transonic Windtunnel reveal differences at low operating temperatures and high Reynolds numbers that warrant further investigation. Since each facility used their own wind tunnel balance for their tunnel entry, one suggestion for the differences was the temperature compensation methodology developed and applied for each balance. This hypothesis is explored through simulation and experiment. Independent calibrations of NASA’s NTF-118A balance at NASA Langley Research Center and European Transonic Windtunnel reveal differences in the thermal compensation of the normal force and pitching moment primary sensitivities with temperature, while the axial force primary sensitivities are in good agreement. The application of the balance calibrations performed at NASA and European Transonic Windtunnel to the prior wind tunnel data suggests that the thermal compensation differences are an order of magnitude lower than the differences observed between the wind tunnel aerodynamic coefficients. Thus, the balance temperature compensation methodologies used by NASA and European Transonic Windtunnel are not a major contributor to the wind tunnel differences.

Fusing wind-tunnel measurements and CFD data using constrained gappy proper orthogonal decomposition

In this article gappy proper orthogonal decomposition (POD) is used to fuse wind-tunnel measurements and computational fluid dynamics (CFD) data to provide a consistent and more comprehensive output of greater utility. The technique is used to fuse a very limited and ‘gappy’ set of wind-tunnel surface pressure measurements with computational surface pressure and friction data. By integrating the resulting fused surface data over a complete aerodynamic surface, the corresponding aerodynamic coefficients are obtained. A comparison between these integrated aerodynamic coefficients and the wind-tunnel balance measurements show a better agreement than that obtained between CFD and the wind-tunnel experiment. In addition, the original gappy POD algorithm is modified and extended to provide an accurate and consistent match between the integrated coefficients evaluated from the fused data set and the wind-tunnel balance measurements, thus producing a set of data distributed over the entire aerodynamic surface that conforms to experiment. This is achieved by considering the wind-tunnel balance measurements as equality constraints in the gappy POD least-squares problem formulation. The technique is demonstrated for steady flow around an RAE 2822 airfoil and an industrial wing-body aircraft configuration. Also, an important feature of the methodology that is essential for its use in an industrial environment, namely regularization, is discussed.

Accuracy of the parallel reset mechanism in a wind tunnel balance calibration system

Accuracy of the parallel reset mechanism in a wind tunnel balance calibration system

Hypersonic force measurements using internal balance based on optical micromachined Fabry-Perot interferometry

Force measurements using wind tunnel balance are necessary for determining a variety of aerodynamic performance parameters, while the harsh environment in hypersonic flows requires that the measurement instrument should be reliable and robust, in against strong electromagnetic interference, high vacuum, or metal (oxide) dusts. In this paper, we demonstrated a three-component internal balance for hypersonic aerodynamic force measurements, using novel optical micromachined Fabry-Perot interferometric (FPI) strain gauges as sensing elements. The FPI gauges were fabricated using Micro-Opto-Electro-Mechanical Systems (MOEMS) surface and bulk fabrication techniques. High-reflectivity coatings are used to form a high-finesse Fabry-Perot cavity, which benefits a high resolution. Antireflective and passivation coatings are used to reduce unwanted interferences. The FPI strain gauge based balance has been calibrated and evaluated in a Mach 5 hypersonic flow. The results are compared with the traditional technique using the foil resistive strain gauge balance, indicating that the proposed balance based on the MOEMS FPI strain gauge is reliable and robust and is potentially suitable for the hypersonic wind tunnel harsh environment.

Plasma Streamwise Vortex Generators for Flow Separation Control on Trucks

An experimental study of the effect of Dielectric Barrier Discharge plasma actuators on the flow separation on the A-pillar of a modern truck under cross-wind conditions has been carried out. The experiments were done in a wind tunnel with a 1:6 scale model of a tractor-trailer combination. The actuators were used as vortex generators positioned on the A-pillar on the leeward side of the tractor and the drag force was measured with a wind-tunnel balance. The results show that the effect at the largest yaw angle (9 degrees) can give a drag reduction of about 20% and that it results in a net power reduction. At lower yaw angles the reduction was smaller. The present results were obtained at a lower Reynolds number and a lower speed than for real driving conditions so it is still not yet confirmed if a similar positive result can be obtained in full scale.

Investigation of wind load on 1,000 m-high super-tall buildings based on HFFB tests

This paper studies the wind load on 1,000 m-high super-tall buildings and provides basic reference for design, including the utilization of passive and active control devices. High-frequency force balance wind tunnel tests of super-tall buildings with different height are carried out to investigate the effects of building height and wind flow on the wind load. Both monsoon and typhoon climate wind flows are simulated based on target models suggested in literatures. The simulation of typhoon climate wind flows is carried out by a newly developed technique. The analysis of the experimental results confirms that the aerodynamic force is very sensitive to both building height and wind flow. In monsoon climate, the turbulence intensity decreases on increasing the height above ground. Thus, on increasing the building height, vortex shedding becomes increasingly intense and excites stronger structural vibrations in the across-wind direction, though the across-wind fluctuating overturning moment coefficient is almost the same. In typhoon climate, both the mean and the fluctuating overturning moment coefficients increase with the building height. This is mainly caused by the decreasing mean wind speed. The vortex excitation becomes weaker on increasing the building height, and this phenomenon is different from that observed in the monsoon climate. In order to better explain vortex-shedding excitation, a new parameter referred to as the characteristic turbulence intensity is defined herein as a weighted mean value of the turbulence intensity in the range of the building height. It provides a robust interpretation of the vortex excitation of super-tall buildings located in different wind flow and climate conditions.

Influence of flight control law on spin dynamics of aerodynamically asymmetric aircraft

In this paper, we analyze the spin dynamics of an aerodynamically asymmetric aircraft in open-loop configuration and also evaluate the performance of gain scheduled flight control law in improving dynamic characteristics of aircraft spin. A look-up tables based aerodynamic model is developed from static, coning and oscillatory coning rotary balance wind tunnel test data. As a starting point, all possible steady spin modes are identified by solving the aircraft dynamic model comprising moment equations. The influence of high-alpha yawing moment asymmetry on predicted right and left spin modes is discussed. Six degree of freedom simulations of left and right flat spins are performed in open-loop and closed-loop configurations with the flight control law. Our studies reveal that large amplitude oscillations in the angle of attack and sideslip observed in the open-loop configuration are significantly damped by the control law. The control law reduces the recovery time of the left flat spin. However, the aircraft natural tendency to rotate rightwards due to yawing moment asymmetry at high angles of attack renders flight control law ineffective in aiding the recovery of the right flat spin.

Aircraft spin characteristics with high-alpha yawing moment asymmetry

This paper analyzes the open-loop spin dynamics of a fighter configuration that exhibits yawing moment asymmetry at high angles of attack. High-fidelity aerodynamic model, in a look-up-tables form, is developed using the experimental data from static, coning, and oscillatory coning rotary balance wind tunnel tests. As a first step, all attainable equilibrium spin modes along with their sensitivity to control settings are predicted. Investigation of the dynamic characteristics of the predicted spin modes is performed using six degrees-of-freedom time history simulations, which showed that both, right and left flat spins are oscillatory and divergent. Influence of high-alpha yawing moment asymmetry on the spin recovery piloting strategies with control inputs is also studied with six degrees-of-freedom time history simulations. Our studies reveal that the proposed spin recovery strategies effectively reduce the recovery time for the left flat spins. However, aircraft’s inherent tendency to yaw rightwards due to high-alpha yawing moment asymmetry renders proposed spin recovery strategies ineffective in accelerating the recovery of the right flat spins.

Measurement of the Aerodynamic Ventilation Drag of Passenger Car Wheels

The ventilation drag is proportional to an aerodynamic torque around the wheels’ axis. It results from the rotation of the wheels and is caused by surface friction and uneven pressure distribution at the spokes, Figure 1. It is an additional resistance to the aerodynamic drag referred to by the usual drag coefficient, cD. The ventilation drag coefficient is defined as Eq. 1: Open image in new window The extended aerodynamic drag coefficient is defined as Eq. 2 [5]: Open image in new window In full scale wind tunnels with a five-belt-system, the four belts of the wheel drive units (WDU) are mounted on the balance and are a part of the weighted system. The rotation of the wheels results in an aerodynamic ventilation torque, MVent, requiring a certain amount of force FVent at the belts to overcome this resistance. The ventilation drag FVent is superimposed with the rolling resistance and frictional losses, FX,Fric, defining the wheel resistance, Eq. 3: Open image in new window FX,Wheel is an internal force and cannot be measured by the wind tunnel balance. At the wind tunnels at BMW, FKFS and Porsche, load cells have been installed in order to measure these wheel resistances. Open image in new window Figure 1 The relevant aerodynamic forces acting on the balance and the wheel rotation units (© IVK | FKFS)

Long-Term Quantitative Study of Wind-Tunnel Balance Calibrations Across Multiple Calibration Systems

Long-Term Quantitative Study of Wind-Tunnel Balance Calibrations Across Multiple Calibration Systems

Mitigation of wind-induced accelerations using Tuned Liquid Column Dampers: Experimental and numerical studies

During the early design stages of a relatively slender 42-storey high-end residential building located in the Middle East, a series of High Frequency Force Balance wind tunnel tests highlighted that the highest occupied floors could experience wind-induced motion which – depending on the inherent damping of the finished structure – had the potential to exceed standard industry occupant comfort criteria. In order to mitigate these excessive vibrations, a Tuned Liquid Column Damper solution was proposed for this building. The performance prediction and validation of the behaviour of such device involved: an initial campaign of full scale measurements to validate frequencies and inherent damping of the structure near completion; a series of shake table tests employing a 1:20 scale physical model; and a final full scale extrapolation study using Computational Fluid Dynamics. The damper study, which this technical paper is focused on, was part of a wider range of wind engineering consultancy services which included: wind climate study; pedestrian and terrace / balcony level wind microclimate study; overall wind loading study and façade pressure study.