Full-scale Wind Tunnel Research Articles

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)

Power-Curve Corrections for Horizontal-Axis Wind Turbine by an Improved Blade Element Momentum Theory

AbstractThis paper proposes a correction method to improve the accuracy of traditional blade element momentum theory (BEMT) in predicting the mechanical power and power coefficient of horizontal-axis wind turbine (HAWT) blade. In this paper, the traditional BEMT incorporated with the Viterna-Corrigan (VC) stall/stall-delay model is proposed to improve the accuracy of power-curve prediction, by which its applicability is thus enhanced. For verification of the proposed method, three distinct types of geometries of HAWT blades subjected to different operations are studied with outcomes compared with experimental data. Two different wind turbines developed by National Renewable Energy Laboratory (NREL) were tested at constant rotational speeds in a full-scale wind tunnel to acquire performance data. As a comparative platform, another wind turbine designed by BEMT for this study was also experimented in identical environment but at variable rotational speeds. As expected, the results clearly indicate that the power-curve prediction is effectively improved by the proposed method especially in the stall region when compared with experimental data. Indeed, this study shows that the improved BEMT is an ideal means to accurately predict the power-curve used for designing an optimal HAWT rotor.

Advanced Aeroacoustic Vehicle Development in a Full-Scale Wind Tunnel

Advanced Aeroacoustic Vehicle Development in a Full-Scale Wind Tunnel

Parameter Estimation of Unmanned Flight Vehicle Using Wind Tunnel Testing and Real Flight Data

AbstractThe work presented in this paper addresses the longitudinal parameter estimation of an unmanned configuration using wind tunnel testing and flight data. For this purpose, an unmanned aerial vehicle has been designed with a cropped delta planform and rectangular cross-section. Exhaustive full-scale wind tunnel tests were carried out on the designed unmanned flight vehicle to capture the linear and nonlinear variation of aerodynamic force and moment coefficients. The measured wind tunnel test data, in the form of signals, have been processed to forces and moments about the desired reference point of the designed unmanned platform. A comprehensive discussion on the obtained results from wind tunnel testing has been presented. In order to enhance the confidence in the generated aerodynamic database from wind tunnel testing and also to estimate the dynamic derivatives, two sets of real flight data pertaining to longitudinal dynamics (acquired during the flight tests) have been used. The parameter estim...

Wind effects on a cable-suspended roof: Full-scale measurements and wind tunnel based predictions

Full-scale measurements of wind effects on a long-span cable-suspended roof were carried out. The wind-induced response data were analyzed in the time-frequency domain based on the wavelet transformation, and modal frequencies and amplitude-dependent damping ratios were identified with the random decrement technique. The damping ratios were noted larger with increasing response amplitude especially in the fundamental mode. The identified modal frequencies from the full-scale measurements were lower than those from the original finite element model (FE model). The identified modal parameters were then used to update the FE model with an artificial neural networks (ANNs) based scheme. The dynamic response from the roof was computed from the updated FE model of the structure where the wind loads input was obtained from simultaneous pressure measurement in wind tunnel tests. In view of the uncertainties surrounding both full scale measurements and wind tunnel based predictions, these comparisons show good agreements at least at two locations. Both the dynamic response from full-scale measurements and numerically predicted analyses demonstrated significant contributions from multi-mode effects. The computed response spectra at selected locations were similar to those from the full-scale measurements, suggesting a validation of the predictions.

Experiments on the Performance of Small Horizontal Axis Wind Turbine with Passive Pitch Control by Disk Pulley

The present work is to design a passive pitch-control mechanism for small horizontal axis wind turbine (HAWT) to generate stable power at high wind speeds. The mechanism uses a disk pulley as an actuator to passively adjust the pitch angle of blades by centrifugal force. For this design, aerodynamic braking is caused by the adjustment of pitch angles at high wind speeds. As a marked advantage, this does not require mechanical brakes that would incur electrical burn-out and structural failure under high speed rotation. This can ensure the survival of blades and generator in sever operation environments. In this paper, the analysis uses blade element momentum theory (BEMT) to develop graphical user interface software to facilitate the performance assessment of the small-scale HAWT using passive pitch control (PPC). For verification, the HAWT system was tested in a full-scale wind tunnel for its aerodynamic performance. At low wind speeds, this system performed the same as usual, yet at high wind speeds, the equipped PPC system can effectively reduce the rotational speed to generate stable power.

A time-dependent Eulerian model of droplet diffusion in turbulent flow

Industrial sprays are common in many operations where liquid application to surfaces is required. Maximization of the spray process efficacy depends on accurate simulation of spray characteristics and surrounding flow conditions. Traditionally, droplet modeling has been performed using a Lagrangian approach which requires tracking a sufficient number of droplets to form statistical estimates of droplet deposition. Alternatively for this study, an Eulerian-based flow and droplet transport model using the Direct Quadrature Method of Moments (DQMOM) is applied to spray modeling and is coupled with the Reynolds Averaged Navier Stokes (RANS) equations and Shear Stress Transport (SST) turbulence model. A new turbulent diffusion model is developed for droplet transport which accounts for inertia and time-limit effects and covers a wide range of operational parameters associated with aerial spraying. The model is based on a full parametric study using Lagrangian particle tracking in a uniform, homogeneous and isotropic turbulent flow field and is subsequently implemented within the Eulerian DQMOM framework and compared to: 1) Lagrangian tracking predictions of a log-normal particle size distribution injected into a homogeneous, isotropic turbulent flow field, and 2) full-scale experimental wind tunnel measurements in the anisotropic, non-homogeneous wake of a hollow cone hydraulic nozzle.

Turbulent airflow above a full-scale macroporous material: Boundary layer characterization and conditional statistical analysis

Convective drying of macroporous materials is governed by the complex interaction between airflow above and into the material, the roughness of the air–material interface and the characteristics of the material pore system. In this study, we experimentally investigate this interplay in detail and at full-scale, using porous asphalt (PA) as a model material. The characteristics of the turbulent flow in the immediate vicinity of the material surface are studied with full-scale wind tunnel experiments at three flow speeds over two types of PA with different surface porosities and surface pore sizes, and are compared to similar measurements over a smooth and impermeable reference material. It is shown that, above a certain wall-normal distance, turbulence profiles can be scaled to make them independent of the flow speed. However, at low speed, the scaling breaks down due to a combination of organized turbulent structures of high intensity and a low turbulence background. No generally valid scaling applicable at all tested air speeds is found close to the surface, where drying occurs. Hence, realistic drying experiments must be performed at full scale and for the entire range of velocities of interest.

Wind Speed and Direction Detection by Means of Solid-state Anemometers Embedded on Small Quadcopters

This work describes the application of a compact, MEMS-based, 2D anemometer to the estimation of a quadrotor's airspeed. Correcting for the vehicle's ground speed provided by internal GPS and inertial units allows this low cost, mobile platform to provide local wind speed estimates. A series of initial, bench-top tests were performed to characterize and calibrate the sensor, which is an improved version of a recently proposed and novel device. Additional full-scale wind tunnel experiments were performed with the sensor mounted on a fixed quadrotor to test the effect of the propellers on the sensor's performance.

Large Eddy Simulation of Flows Around a Kite Used as an Auxiliary Propulsion System

The aerodynamic forces acting on a kite proposed for propelling marine shipping are investigated using computational and experimental means. Attention is given to the kite's positions as perpendicular or nearly perpendicular to the air flow that still possess potential for thrust generation but cannot be analysed using finite wing models applicable for kites at low angles of attack. Good agreement is achieved in the prediction of the time-averaged drag coefficient between the large eddy simulations (LESs) of a full scale kite and wind tunnel measurements of a small scale kite model. At zero-yaw conditions both the time-averaged drag and lift (side) forces show behavior similar to the literature-reported empirical relations for flat plates of the same aspect ratio (AR), but with differences of up to 20% in the coefficients’ values. Thus, the plate’s known empirical formulae for aerodynamic forces at zero yaw angles may be used as fast low-accuracy prediction tools before engaging with the more costly turbulent flow computations and wind tunnel tests. Yawing moderately the kite can actually increase mildly the drag but further yawing or pitching it reduces the dominant drag force. Both the drag and lift show unsteady components that are related to the large turbulent wake behind the kite and vortical shedding from the kite's ends. Power spectra of the aerodynamic forces’ coefficients are presented and analysed.

New FKFS Technology at the Full-Scale Aeroacoustic Wind Tunnel of University of Stuttgart

New FKFS Technology at the Full-Scale Aeroacoustic Wind Tunnel of University of Stuttgart

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.

High speed driving stability of passenger car under crosswind effects

The driving stability of a passenger car at high-speed and under crosswind conditions is affected by aerodynamic characteristics as well as their dynamic characteristics, suspension, and weight distribution. In this study, the total measuring system was thought up to understand the transient vehicle dynamics and aerodynamics with driver’s control inputs all together. The test results were taken from a full-scale wind tunnel test, a crosswind generator test and an on-road test. We investigated major aerodynamic parameters that affect the driving stability of passenger cars under crosswind effects such as overtaking, passing each other, natural crosswind, etc. The reaction rate of high-speed stability will be improved when we minimize the total lift, side force and especially the yawing moment.

The influence of unsealing on the wind resistance of asphalt shingles

This paper addresses the wind-induced tearing and blow-off of asphalt roofing shingles, which are the most frequently observed forms of residential building damage in hurricanes. Field surveys indicate that in-service asphalt shingle sealant strips can lose adhesion along their leading edge over time, leaving the shingle partially unsealed and susceptible to wind uplift. Two interrelated studies presented in this paper show that unsealing is a naturally occurring process and that unsealed shingles are a contributing cause of shingle roof cover damage in high winds. The first study quantified the number, location, and failure mode of laminate and three-tab style shingle systems installed on residential buildings at 30 sites in Florida and Texas. Systematic patterns of partially unsealed field shingles found on 22 of the 30 roofs resembled spatial patterns of wind-induced shingle damage observed in post-hurricane building performance assessments. As expected, older roofs generally contained more unsealed shingles than newer roofs. The results of the second study link blow-off to partially unsealed shingles. Seventeen ASTM D7158 Class H asphalt shingle roofs were aged outside for nominally one year at the Insurance Institute for Business & Home Safety Research Center and then evaluated in full-scale wind tunnel tests. Partially unsealed field and hip shingles frequently exhibited damage during wind testing, while fully sealed shingles were not damaged unless adjacent, unsealed shingles failed first.

Development of Full-Scale Wind Tunnel for Enhancement of Vehicle Aerodynamic and Aero-Acoustic Performance

Development of Full-Scale Wind Tunnel for Enhancement of Vehicle Aerodynamic and Aero-Acoustic Performance

Years devoted to development of aerodynamics in Siberia

April 29, 2014 is the 100th anniversary of Vladimir V. Struminskii. He was born in Orenburg in a family of a school teacher Vasilii Ya. Struminskii (1880–1967) and his wife Mariya F. Dmitrovskaya (1884−1972). After studying at school for seven years, he worked as a turner at a factory in Kazan and then at the Dinamo plant in Moscow. In 1933, without leaving his work, Vladimir Struminskii graduated from the school for working youth and entered the Physical Faculty of the Lomonosov Moscow State University. After graduating from the university cum laude, V.V. Struminskii became a post-graduate student at the Institute of Physics at the Moscow State University; in 1941, he defended the candidate’s thesis entitled “Electron theory of solids,” where he presented a solution of the Schroedinger equation for the crystal lattice of alloys. On the eve of the Great Patriotic War, Vladimir V. Struminskii was appointed to the Central Aerohydrodynamic Institute named after Academician N.E. Zhukovskii (TsAGI), where he started to study some problems new for him: aerodynamic investigations of finitespan wings. Several years later, he developed a method for calculating the maximum lift force of the wing and the distribution of stall zones over the wing span. A series of experiments with finite-span wings in the full-scale wind tunnel based at TsAGI at high Reynolds numbers confirmed the efficiency of the proposed method of aerodynamic design of the wing. In 1947, Struminskii together with other TsAGI researchers was awarded with the State Prize for the development of new wings for high-velocity airplanes and preparation for their batch production. V. V. Struminskii made a significant contribution to the progress in aeronautics by developing a method of aerodynamic design of the wing from a set of airfoils with a nonseparated flow at the wing tip, which ensured high reliability and safety of flight at high angles of attack; this method was developed during the Great Patriotic War. Before that, a large amount of theoretical activities were performed. Exact solutions of three-dimensional boundary layer equations

The influence of model surface roughness on wind loads of the RC chimney by comparing the full-scale measurements and wind tunnel simulations

A wind tunnel test of a scaled-down model and field measurement were effective methods for elucidating the aerodynamic behavior of a chimney under a wind load. Therefore, the relationship between the results of the wind tunnel test and the field measurement had to be determined. Accordingly, the set-up and testing method in the wind tunnel had to be modified from the field measurement to simulate the real behavior of a chimney under the wind flow with a larger Reynolds number. It enabled the results of the wind tunnel tests to be correlated with the field measurement. The model surface roughness and different turbulence intensity flows were added to the test. The simulated results of the wind tunnel test agreed with the full-scale measurements in the mean surface pressure distribution behavior.

Experimentally Simulating Wind Driven Firebrand Showers in Wildland-urban Interface (WUI) Fires: Overview of the NIST Firebrand Generator (NIST Dragon) Technology

Evidence suggests that wind driven firebrand showers are a major cause of structural ignition in Wildland-Urban Interface (WUI) fires. While firebrands have been researched for over four decades, prior studies have focused mainly on how far firebrands fly and are of limited use to design firebrand resistant structures. The NIST Firebrand Generator (NIST Dragon) is an experimental device that can generate a firebrand shower in a safe and repeatable fashion. Since wind plays a critical role in the spread of WUI fires in the USA and urban fires in Japan, NIST has established collaboration with the Building Research Institute (BRI) in Japan. BRI maintains one of the only full scale wind tunnel facilities in the world designed specifically for fire experimentation; the Fire Research Wind Tunnel Facility (FRWTF). The coupling of the NIST Firebrand Generator and BRI's FRWTF is leading to progress in assessing vulnerabilities of structures to a firebrand attack. A brief summary of key results to date using the NIST Dragon installed in the FRWTF are provided in this paper as well as a description of the NIST Dragon's LAIR (Lofting and Ignition Research) facility. The Dragon's LAIR is the only experimental facility capable of simulating continuous wind driven firebrand showers at bench scale. In addition, a detailed description of a new experimental apparatus is presented here for the first time. This device is known as the NIST full scale continuous feed Firebrand Generator (the NIST continuous feed Dragon).When installed inside BRI's FRWTF, the full scale continuous feed Dragon, an improvement of the NIST Dragon, is the first and only experimental apparatus capable of generating, continuous wind driven, controlled firebrand showers that may be directed onto full scale building elements. This paper closes with a discussion of future research needs and opportunities for collaboration.

Design for Wind Tunnel Testing of Scaled Model by CFD Method

The numerical investigations presented in this paper deal with wind tunnel testing scheme design for 1/4 scaled MIRA model including supporting system. Based on the structure of aerodynamic and aero-acoustic full scale wind tunnel, using computational fluid dynamics (CFD), focus on MIRA model and supporting system, the drag force of scaled models and supporting system were calculated. By comparing with the wind tunnel testing results and drag force coefficient of reference, it is certain that the wind tunnel testing scheme is available and effective and that the value calculated by CFD is in good agreement with experiments.

Development and Operation of an Automatic Rotor Trim Control System for the UH-60 Individual Blade Control Wind Tunnel Test

A full-scale wind tunnel test to evaluate the effects of Individual Blade Control (IBC) on the performance, vibration, noise and loads of a UH-60A rotor was recently completed in the National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel [1]. A key component of this wind tunnel test was an automatic rotor trim control system that allowed the rotor trim state to be set more precisely, quickly and repeatably than was possible with the rotor operator setting the trim condition manually. The trim control system was also able to maintain the desired trim condition through changes in IBC actuation both in open- and closed-loop IBC modes, and through long-period transients in wind tunnel flow. This ability of the trim control system to automatically set and maintain a steady rotor trim enabled the effects of different IBC inputs to be compared at common trim conditions and to perform these tests quickly without requiring the rotor operator to re-trim the rotor. The trim control system described in this paper was developed specifically for use during the IBC wind tunnel test