Scale Wind Tunnel Model Research Articles

Design and construction of aeroelastic wind tunnel models

AbstractThe design and building of accurately scaled aeroelastic wind-tunnel models is difficult, time consuming and very costly. With the increasing usefulness of computational methods for predicting aeroelastic phenomena, few complex models have been built in recent years. New fighter aircraft projects are also becoming more and more scarce, and transport aircraft have essentially the same configuration since half a decade. This also significantly reduces the need for aeroelastic wind-tunnel models. However, there still is an interest in the results from aeroelastic testing. In some cases new and radical configurations may warrant wind-tunnel testing and in other cases complex phenomena arising in fight testing may need carefully performed experiments to resolve problems. However, there is definitely a trend towards building models and performing testing in the support of the development of computational methods.The developments in computer technology do not only improve the computational methods for aeroelasticity. Modern Computer Aided Design and Manufacturing techniques can significantly improve the quality and efficiency of the design and build process for aeroelastic models. There have also been some recent improvements in measurement techniques which have proven very useful for testing of aeroelastic wind-tunnel models. The paper will present some new design and build techniques developed for the manufacturing of a large scale wind-tunnel model of a canard delta wing fighter aircraft configuration. In the build process fiber-reinforced composites will be used, hence, challenges and possible solutions concerning the ability to produce a model with well defined material properties and fiber angles will be discussed. Further challenges arise when both measurement equipment and adjustable control surfaces should be attached inside the model using techniques that are possible to describe with computational methods. In addition, equipment, such as pressure taps, and control surface mechanics need to fit and function in a flexible structure. As a result, the above requirements will lead to necessary compromises in the design, hence, the paper will present the choices taken during the build process and for which reasons. The use of an optical positioning measurement system will also be discussed for both the validation of model properties and non-contact measurement of model deformations during wind-tunnel testing.

An experimental study of pressure distributions within an air-permeable, double-layer roof system in regions of separated flow

This paper is concerned with the pressure distributions on the external and internal surfaces of the outer layer of an air-permeable, double-layer roof system placed on a low-rise building in a region of separated flow. In particular, the effects of the gaps between panels (G), cavity depth between layers (H), and the panel size (L) on the pressures and panel loads are examined. Wind tunnel-based experimental data from the model of a low-rise building in an open country terrain were used. In total, 39 configurations were examined for the range 1/30≤G/H≤30 and 0.53≤t/G≤16, where t is the panel thickness. It was found that the cavity pressure distributions are significantly affected by the geometric parameters. Values of the non-dimensional parameter, ϕ=[G/H]2[(fHLc/H)/(2(CL+ftt/G))] >~1 are associated with the cavity flow resistance controlling the pressure drops, leading to reduced-magnitude peak panel loads. The implications of the results for model-scale wind tunnel testing are discussed.

On-Blade Control of Rotor Vibration, Noise, and Performance: Just Around the Corner? The 33rd Alexander Nikolsky Honorary Lecture

A concise review of the active control approaches for vibration reduction in rotorcraft is presented. Next, the evolution and status of higher harmonic control and pitch link actuated individual blade control is presented since these serve as the foundations of on blade control. Despite the success of these approaches, demonstrated by both full-scale wind tunnel and flight tests, higher harmonic control and pitch link actuated individual blade control have not managed to earn their way onto a production helicopter. An alternative, on blade control, is defined as a special implementation of individual blade control, where the control surfaces are located on the rotating blade and each blade has its own controller. A concise description of four on blade devices: (1) the actively controlled flap, (2) the active twist rotor, (3) the active tip rotor, and the (4) deployable Gurney flap, or microflap, is presented. An outline of an aeroelastic response modeling capability used to simulate active vibration and noise reduction using flaps or microflaps is presented. The simulation is a thread that links the various parts of the paper. Next, selected results from simulations and scale wind tunnel model tests on active flaps are used to provide insight on the operational and modeling aspects of these systems. Full-scale wind tunnel and flight tests are presented as culmination of the research effort invested in active flap rotors. Then, the evolution and application of the active twist rotor, and deployable Gurney flaps, or microflaps, is presented. The paper concludes with lessons learned and speculation about the potential implementation of on blade control on production rotorcraft.

Measurement and simulation of the flow field around the FINO 3 triangular lattice meteorological mast

A numerical and experimental simulation of flow around a complex, three-dimensional triangular lattice meteorological mast and accompanying anemometer booms has been carried out using the open source CFD code OpenFOAM. The simulation has been compared with results using a 1/20th scale wind tunnel model using 3D hot-wire anemometry probes and satisfactory agreement with the CFD has been found. Three turbulence models commonly applied in numerical external aerodynamics were employed with the one-equation Spalart–Almaras model compared with its more sophisticated two-equation counter parts k–ε and k–ω–SST. The differences in the results for the velocity field around the mast were found to be marginal and recommendations for the overall suitability of any individual RANS-based turbulence model for such flows were inconclusive. The predicted flow distortion surrounding the lattice mast differed from previously published data using the method suggested in International Electrotechnical Committee (IEC) standards based on the results specifically for the FINO 3 mast. Using the CFD simulation data it was possible to calculate the optimum boom length to place the anemometers outside of any flow distortion field for this mast. Shorter boom lengths than those suggested by the current IEC standard could potentially be used to place the anemometers beyond the flow distortion zone generated by the met mast. The results highlight the potential of using open-source CFD for the assessment of interference effects on masts with intricate, three-dimensional structural patterns.

Multi-disciplinary constrained optimization of wind turbines

We describe procedures for the multi-disciplinary design optimization of wind turbines, where design parameters are optimized by maximizing a merit function, subjected to constraints that translate all relevant design requirements. Evaluation of merit function and constraints is performed by running simulations with a parametric high-fidelity aero-servo-elastic model; a detailed cross-sectional structural model is used for the minimum weight constrained sizing of the rotor blade. To reduce the computational cost, the multi-disciplinary optimization is performed by a multi-stage process that first alternates between an aerodynamic shape optimization step and a structural blade optimization one, and then combines the two to yield the final optimum solution. A complete design loop can be performed using the proposed algorithm using standard desktop computing hardware in one-two days. The design procedures are implemented in a computer program and demonstrated on the optimization of multi-MW horizontal axis wind turbines and on the design of an aero-elastically scaled wind tunnel model.

Database-assisted design methodology to predict wind-induced structural behavior of a light-framed wood building

This study investigates the applicability of the database-assisted design (DAD) methodology to predict structural reactions in a light-framed wood structure subjected to fluctuating wind pressures. Structural influence functions were determined on a 1/3-scale light-frame wood structure, which was then subjected to a wind flow, while the surface pressures and structural reactions at roof-to-wall and wall-to-foundation connections were simultaneously recorded. There was a good agreement between the DAD-predicted structural reactions and experimentally measured reactions, confirming that the DAD method is suitable for predicting the structural reactions in light-frame wood buildings. Subsequently structural reaction time histories at several connections within the building were generated using a 1:50 scale wind tunnel model of the structure and the peak structural reactions determined using the DAD method and previously obtained influence functions. When the DAD-estimated reactions were compared with reactions predicted by the ASCE 7-05 main wind force resisting system (MWFRS) method, they showed the ASCE 7 reactions were highly non-conservative(i.e. smaller than the DAD method predictions), by as much as 39% at the gable end truss. The components and cladding method showed reasonable agreement with the DAD method for the gable end and first interior truss reactions but it too underestimated the reaction loads at the second and third interior trusses by 30% and 12% respectively.

The Influence of Viscous Effects and Physical Scale on Cavitation Tunnel Contraction Performance

The general performance of an asymmetric cavitation tunnel contraction is investigated using computational fluid dynamics (CFD) including the effects of fluid viscosity and physical scale. The horizontal and vertical profiles of the contraction geometry were chosen from a family of four-term sixth-order polynomials based on results from a CFD analysis and a consideration of the wall curvature distribution and its anticipated influence on boundary layer behavior. Inviscid and viscous CFD analyses were performed. The viscous predictions were validated against boundary layer measurements on existing full-scale cavitation tunnel test section ceiling and floor and for the chosen contraction geometry against model-scale wind tunnel tests. The viscous analysis showed the displacement effect of boundary layers to have a fairing effect on the contraction profile that reduced the magnitude of local pressure extrema at the entrance and exit. The maximum pressure gradients and minimum achievable test section cavitation numbers predicted by the viscous analysis are correspondingly less than those predicted by the inviscid analysis. The prediction of cavitation onset is discussed in detail. The minimum cavitation number is shown to be a function of the Froude number based on the test section velocity and height that incorporate the effects of physical scale on cavitation tunnel performance.

Structurally Effective Static Wind Loads for Roof Panels

A detailed comparison of the recent full-scale tests conducted at Mississippi State University (MSU) using simulated wind loads on a portion of a standing seam metal roof and model-scale wind tunnel tests carried out at the University of Western Ontario of an aeroelastic “failure” model of the same roof system is presented. In spite of the significantly different approaches, the results obtained were remarkably consistent. The tests suggest that, at the roof corner, the E1592 uniform pressure test contains conservatism of about 50% for the roof system tested by both approaches; and up to about 80% for the other roof systems tested only at MSU. This conservatism arises if the roof system is required to withstand the code-recommended pressure applied as uniform pressure in the E1592 test, without accounting for the reality of the dynamic spatially varying properties of the wind-induced pressures. In general, the tests also suggest that influence surface approaches together with experimentally measured press...

Transonic Computational Fluid Dynamics Calculations on Preproduction F/A-18E for Stability and Control

Computational fluid dynamics was used to predict the longitudinal and lateral/directional stability and control characteristics of an 8%-scale wind tunnel model of the preproduction F/A-18E Super Hornet at two transonic Mach numbers without any prior knowledge of existing wind tunnel or flight test data. The tetrahedral unstructured software system was used to generate and analyze grids during this computational study. The longitudinal stability and control characteristics of the aircraft were evaluated using three different horizontal tail deflections. Before evaluating nonzero horizontal tail deflections, coarse, medium and fine grids of the preproduction F/A-18E with a horizontal tail deflection of 0 deg were used in a grid resolution study to determine the grid density that was required to accurately calculate the forces and moments of the aircraft. The grid resolution study indicated that the medium grid was adequate at Mach 0.8 whereas the fine grid was necessary at Mach 0.9. The medium and fine grids with tail deflections of -6 and 6 deg were then generated and analyzed at Mach 0.8 and Mach 0.9, respectively, to determine the longitudinal stability and control characteristics of the aircraft. The lateral/ directional stability and control characteristics of the preproduction F/A-18E were evaluated using a range of sideslip angles for several different angles of attack at Mach 0.8 and 0.9. The computational results compared very favorably to the existing wind tunnel data.

Active Store Trajectory Control in Supersonic Cavities Using Microjets and Low-Order Modeling

Recently, there has been a concerted effort in controlling the trajectory of a store departing from a cavity in a supersonic flow so as to ensure safe separation. The candidate actuator that has achieved a safe departure in model-scale wind tunnel tests using minimum flow rate is a tandem array of microjets placed in the spanwise direction near the leading edge of the cavity. In this paper, a low-order model is derived that captures the dominant mechanisms that govern the store trajectory with and without microjets and conditions under which unsafe and safe departures occur are predicted. This model includes separate components to predict the pitch and plunge motion of the store when it is is inside the cavity, when it is passing through the shear layer at the mouth of the cavity and when it is completely outside the cavity. The model derivations are based on the assumptions of store ejection from the cavity middle, slender axisymmetric body aerodynamics, thin shear layer at the cavity mouth, high Reynolds number external crossflow, plane shock waves associated with the microjet actuators, and quiescent cavity. The model predictions are compared to the results of store drop experiments performed under the HIFEX Program at Mach 2.0 and 2.46 using a generic subscale weapons bay for different control inputs

Design, Fabrication, and Testing of a Scaled Wind Tunnel Model for the Smart Wing Project

Building on the research performed during the DARPA/AFRL/NASA Smart Wing Phase 1 program (Kudva, J.N. et al. (July 1999). Overview of the DARPA/AFRL/NASA Smart Wing Program, SPIE Symposium on Smart Structures and Materials, Newport Beach, CA, Vol. 3674, pp. 230 6; Martin, C.A. et al. (1999). Smart Materials and Structures Smart Wing Phase 1 Final Report, AFRL-ML-WP-TR-1999-4162, Air Vehicles Directorate, Air Force Research Laboratory, Wright-Patterson Air Force Base, OH.) sought to improve vehicle aerodynamic efficiency using control surfaces actuated by smart materials, the goal of the Phase 2 effort was to develop larger scale, smart hingeless control surfaces capable of high-rate actuation and quantify their performance benefits at test conditions representative of operational flight environments. To achieve this goal, a 30-percent geometric scale, full-span wind tunnel model of a proposed Northrop Grumman Corporation (NGC) Uninhabited Combat Air Vehicle (UCAV) was designed and tested. The model incorporated conventional, hinged control surfaces on the left side and smart, hingeless control surfaces on the right to allow incremental aerodynamic performance comparisons; including lift increment due to unit control surface deflection (CL), and roll moment due to unit control surface deflection (Cld). This paper describes the design, fabrication, system integration, and ground test results of the Smart Wing Phase 2 model. Topics that are covered include: (1) wind tunnel model selection; (2) analysis and design procedure; (3) smart control surface integration; (4) model instrumentation; and (5) static load and Ground Vibration Test (GVT) results and correlation.

Personal Perspective of Aeroelasticity During the Years 1953-1993

A brief review is given of the author’ s personal impressions of the development of aeroelasticity during the sixth to ninth decades of e ight. It is not intended to be all-inclusive, but rather a brief look at the e eld as the author saw it, from his own personal viewpoint as a worker in this area. It is limited to aircraft problems and does not embrace the parallel and large e eld of aeroelastic problems in helicopters. The e eld of aeroelasticity encompasses the interaction of aerodynamic, elastic, and inertia forces acting on a e ight vehicle. This was evident in the early days of e ight, even at low speeds, because aircraft structures were relatively e exible. As aircraft speeds increased and knowledge of aeroelasticity became more widespread, aircraft structures were made stiffer and were better designed to avoid these aeroelastic interaction problems. During World War II, with the advent of high speeds and slender-wing aircraft, a number of signie cant aeroelastic problems began to appear, ranging from loss of aileron power and control reversal, to wing and control surface e utter. The postwar period, with the emergence of highspeed jet transports with swept wings and engine nacelles, led to careful studies of the effects of aeroelasticity in the initial design of these aircraft. The basic approach to aeroelastic effects became centered around four general areas: 1) the development of effective analytic and numerical studies for e utter and aeroelasticity, 2) wind-tunnel testing of dynamically scaled wind tunnel models, 3) ground vibration tests to check the natural frequencies and stiffness properties of the actual aircraft, and 4) careful techniques for e ight testing the actual aircraft. By the mid-1950s, aeroelasticity had become recognized as an important part of the aircraft design process. An excellent historical review of developments in aeroelasticity up to this period, may be found by Garrick and Reed. 1 A seminal paper that marked the emergence of the e eld was given by Collar 2 in 1946. Another notable review emphasizing the British efforts in aeroelasticity up to this period was also given by Collar. 3

NOVEL WATER FACILITIES FOR CREATION OF COMFORTABLE URBAN MICROMETEOROLOGY

The cooling effects of artificial water facilities – fountains, waterfalls and urban canals – have not received much attention. To improve the meso-space thermal environment in an urban area, especially that during the midsummer, we propose using novel artificial water facilities to alter the temperature and humidity, so as to improve pedestrian comfort. To study this, we have carried out field measurements and wind tunnel tests, and we report the results in this paper. At first we made measurements of wind velocity, temperature and humidity around such artificial water facilities in Tennoji Park in Osaka city (a typical Japanese large city). The results showed reduced temperatures on the leeward side, and demonstrated the usefulness of water facilities in improving the thermal environment. Also, we constructed an insulated 1/400 scale wind tunnel model of the situation and measured, by means of X-type hot wire anemometer, the air currents on the wind tunnel surfaces in urban, suburban and rural terrains. We also measured, using fine-gauge T-type thermocouples, the air temperature distribution in front of and behind the model of the water facility. The results confirmed the qualitative ranges of the cooling effect provided by the actual water facilities. In particular, the cooling effect produced by a 1.0 mm diameter nozzle fountain was found to extend a distance downstream equal to ten times the height of spout.

Deposition of large particles from warehouse fire plumes—a small-scale wind tunnel model study

The report describes measurements of the deposition of large particles from a small scale wind tunnel model of a chemical warehouse fire plume. A common feature of such fires is the discharge of relatively large particles with falling speeds of the order of m s −1, partly generated by mechanical damage, which can fall out of the fire plume in a different pattern to that of the gases and fine particles. These large particles may also contain toxic components, so it is desirable to know their fallout pattern. The deposition of large particles from fire plumes has therefore been modelled directly as an adjunct to earlier small scale wind tunnel experiment on gaseous plume dispersion [1]using the same experimental conditions, so that the relative behaviour of gas plume and heavy particle dispersion could be compared. As far as we are aware, this is the first experiment of this type to be carried out. There are constraints on the range of deposition conditions that can be modelled, due to scaling problems. However, it proved possible to develop a viable technique and some useful data was obtained over a range of particle and plume conditions of interest. Nonetheless, the work should be regarded mainly as a proving trial of the technique and an indicator of the significant parameters as the measurements made were too few in number (essentially of three particle deposition conditions) to provide a broad-based indication of large particle deposition. Experiments were carried out for two gas plumes, buoyant and non-buoyant, both with and without a building shell around the source. Large particle concentrations near the surface proved markedly different to those for a gaseous plume, showing a much more rapid reduction in concentration with increasing distance. Both particle falling angle and particle inertia affected the particle plume dispersion, the highest concentrations at the ground occurring for the case with small falling angle and inertia, the lowest concentrations for the case with large falling angle and moderate inertia. Concentrations for the remaining condition, with large falling angle and high inertia, fell between these two, probably because the high inertia constrained the rate of lateral dispersion of the particles. Compared with the effects of particle falling angle and inertia, the effects of a building shell around the source were relatively limited. This was greatest for the non-buoyant plume where the building shell tended to act as a trap for large particles. The buoyant plume tended to carry particles beyond the building shell, so that in this case its effects were quite limited.

On the use of large scale windtunnel models

Abstract The use of large scale windtunnel models offers considerable advantages to an experimenter1. the possibility of obtaining high Reynolds number, certainly significant and sometimes equal to that in flight, for moderate stagnation pressures2. an accurate representation of geometric elements, i.e. good form similitude (it is necessary to emphasise the importance of being very thorough in this area)3. large internal volumes which enable numerous transducers to be implanted, ambitious experimental devices and means of remote control of model motorisation4. test conditions remain those corresponding to industrial manufacturing methods and so avoid problems related to extreme miniaturisation.Additionally, there exist some test conditions for which scale reduction is limited or even impossible; for example, because of physical phenomena, limitation in industrial methods of miniaturisation, or quite simply because the subject is itself the flying object. These conditions are applicable to all tests whether industrial or research. They are especially true for industrial tests where these concern important decisions. They are also true for research tests whenever they need to be sufficiently close to flight reality. Wind-tunnels are always a means to reduce the costs and risks of aeronautical project developments. The risk taken in extrapolating from windtunnel tests to flight are lower when the test is more realistic and this gives a clear advantage to tests on large sized models.

The aerodynamic tuning of a group sports racing car

This paper describes a wind-tunnel test program designed to optimise and validate some aerodynamic features on the Tiga GC83 sports racing car which won four races in the Group C2 category in the following season (1983). Particular attention was paid to the underbody venturi shape, the placing of the rear aerofoil, and the vehicle attitude. The experiments were conducted on a 1 8 scale wind-tunnel model at the Hatfield Polytechnic, and the results are compared with those obtained from wind-tunnel tests on a full-size similar vehicle undertaken at the Lockheed Georgia test facility. Despite the small scale of the model, good agreement was found in corresponding cases. The Group C regulations, which require an area of flat floor, imposed considerable problems in the design of a suitable underbody venturi, but it was found that the use of such a venturi was well worthwhile. The lift and drag coefficients were found to be sensitive to vehicle attitude, and the implications are discussed.

Extraction of power from a tornado wind energy system (TWES)

Vortex flow and power extraction from a vortex have been studied both experimentally and theoretically by an analytical approach. The measurements were first performed with a small scale wind tunnel model of logarithmic spiral shape. Power estimates have been derived from measurements with grid simulated turbines. For this basic configuration power output is small due to generation of radial equilibrium within the turbine flow. The performance of the system can be improved if interaction between vortex and top stream is avoided. Further improvements are obtained if advantage is taken of the axial pressure gradient within the tower flow. The power coefficient for a typical model with tower aspect ratio 3.6 increases from 2 to 10 per cent if these improvements are included. The corresponding augmentation ratio reaches a value of c A ≈ 2.

An approach to the determination of wind load effects on low-rise buildings

A covariance integration method for the determination of fluctuating overall structural loads due to wind and their effects on low-rise buildings is described. The required aerodynamic information can be obtained from boundary-layer wind tunnel tests; static structural-influence coefficients are also required. The method is an alternative to the direct on-line weighting technique, but is less demanding on wind tunnel instrumentation and data acquisition facilities. To obtain peak values, Gaussian probability distributions have been assumed for the loads or their effects. Use of the method is demonstrated by calculations of gust factors and peak values for various structural loads on the central bay of a single-storey house, using aerodynamic data obtained from a 1 50 - scale wind tunnel model.

Comparison of tower influence on wind velocity for NASA's 150-meter meteorological tower and a wind tunnel model of the tower

Tower influence of wind speed and direction measurements, comparing 150 meter meteorological tower and scale wind tunnel model