Full-scale Wind Tunnel Tests Research Articles

Flight Test of an Active Flow Control Enhanced Vertical Tail

The size of the vertical tail and rudder of a commercial aircraft is influenced by the requirement that the airplane must be controllable in the event of an engine failure. As a result, on twin-engine airplanes, it is typically larger than is required for lateral/directional stability and control under normal flight conditions. Despite the rarity of the need for this level of control, the airplane must carry this size vertical tail and rudder with it at all times. The primary impact of this is additional drag and weight that reduces the fuel efficiency of the airplane. Active flow control can be used to enhance the control authority of the rudder by mitigating flow separation on it at high rudder deflection and sideslip angles. This effect can be used to provide the required level of rudder control authority from a physically smaller vertical tail. As a result, fuel efficiency of the airplane may be increased due to the reduced size and drag of the smaller vertical tail throughout the operational envelope of the airplane. In April 2015, Boeing and NASA tested a pneumatic sweeping-jet-based active flow control system on the vertical tail of the modified Boeing 757 ecoDemonstrator. This test was the culmination of several years of development that included small-scale wind-tunnel testing, computational-fluid-dynamics simulations, a system-integration study, full-scale wind-tunnel testing, and the flight demonstration. The data from the flight test indicate that the flow control actuation may be able to provide an approximately 14% increase in side force at the maximum tested rudder deflection and at critical sideslip angles.

Online system identification of mini cropped delta UAVs using flight test methods

The current manuscript presents the longitudinal and lateral directional online parameter estimation of two unmanned aerial vehicles (UAVs) using sequential Least Squares formulation in frequency domain. The two fixed wing UAVs share a similar cropped delta planform and differ in their cross sectional geometries, one with a rectangular and the other being a reflex airfoil cross sections respectively. Recursive Fourier Transform algorithm has been used to convert the flight data in time domain to frequency domain which is measured by means of a dedicated on-board data acquisition system capable of on-board logging and telemetry to ground station. The combination of Sequential Least Squares with Recursive Fourier Transform (SLS-RFT) in frequency domain can be used to carry out online parameter estimation. An attempt has been made to check the applicability of the current method to estimate parameters from the generated flight data of the two UAVs using both conventional as well as random control inputs. Results showed that the parameters estimated, using SLS-RFT, from the linear flight data are consistent and in close agreement with the obtained parameters from full scale wind tunnel testing of UAVs. It was also observed that the estimates from the manoeuvres with multistep control inputs converged faster compared to the parameters obtained from the manoeuvres with slow varying control surface deflections. The time varying linear aerodynamic parametric model of SLS-RFT was able to capture the dynamics of the flights with nonlinear aerodynamics. Certain limitations of the current online system identification method were also observed with estimating parameters from the flight data of UAVs performing near stall manoeuvres. The estimated parameters using SLS-RFT are also compared with the results obtained from batch methods namely classical Maximum Likelihood (ML) and neural based Neural–Gauss–Newton (NGN) methods.

Lateral directional parameter estimation of a miniature unmanned aerial vehicle using maximum likelihood and Neural Gauss Newton methods

ABSTRACTThe current research paper describes the lateral-directional parameter estimation from flight data of a miniature Unmanned Aerial Vehicle (UAV) using Maximum Likelihood (ML), and Neural-Gauss-Newton (NGN) methods. An unmanned configuration with a cropped delta planform and thin rectangular cross-section has been designed, fabricated and instrumented. Exhaustive full-scale wind-tunnel tests were performed on the UAV to extract the form of aerodynamic model that has to be postulated a priori for parameter estimation. Rigorous flight tests have been performed to acquire the flight data for several prescribed manoeuvres. Four sets of compatible flight data have been used to carry out parameter estimation using classical ML and neural-network-based NGN methods. It is observed that the estimated parameters are consistent and the lower values of the Cramer-Rao bound for the corresponding estimates have shown significant confidence in the obtained parameters. Furthermore, to validate the aerodynamic model used and to enhance the confidence in the estimated parameters, a proof of match exercise has been carried out.

Aerodynamic effect of the aircraft carrier island on flight deck flow with cross wind

Regarding the importance of helicopter operations over aircraft carriers and the increment of the workload of the pilot during take-off and landing manoeuvres, it has been performed a study of the flow downstream the island of an aircraft carrier in cross-wind conditions. The main objective of this work is to characterize the aerodynamic flow in that critical area providing insight for future investigations directed to reduce the workload and improve safe operational conditions. Then, a wind tunnel test campaign was carried out using particle image velocimetry and laser Doppler anemometry techniques. Finally, wind tunnel results have been compared with on-board measurements showing a good agreement between full-scale and model-scale wind tunnel tests.

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...

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 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

Analysis of Rear Window Buffeting Characteristics Using a Production Sedan

In this paper rear left side window buffeting characteristics of a production sedan under different yaw angles and different window opening sizes are investigated through full-scale aeroacoustic wind tunnel tests. By yaw angle -10 degree, as driver position on the lee side, the resonance peak SPL is much less than that by yaw angle 0 or +10 degree and the corresponding frequency is also some lower than that by yaw angle 0 or +10 degree. As window opening size turns small, the resonance peak SPL decreases. By side window with 25% opening size, the peak SPL is much less than that by side window with 50% or 100% opening size. In addition, the corresponding frequency is also some lower than that by side window with 50% or 100% opening size. Different test positions at the front row or back row show very similar buffeting characteristics.

An Experimental Investigation of Sunroof Buffeting Characteristics of a Sedan

After a short introduction about vehicle wind buffeting noise generation mechanisms, sunroof buffeting characteristics of a production sedan under different wind speeds and operating modes are investigated through full-scale aeroacoustic wind tunnel tests. As sunroof fully open, the severest buffeting effect occurs at wind speed 50kph, with the peak SPL 122dB and the corresponding resonance frequency 18Hz for the test point at the front row. From ca. 60kph it seems that the buffeting effect disappeared. As sunroof tilt, the severest buffeting effect occurs at wind speed equal or less than 30kph, the resonance frequency equal or less than 15Hz. From ca. 40kph the buffeting effect almost disappeared. Whether sunroof fully open or tilt, the resonance frequency increases all along as wind speed goes up till the buffeting effect disappeared (less than 20Hz). Different test positions at the front row or back row show very similar buffeting characteristics.

Influence of Crosswind to Automobile Interior Aerodynamic Noise

After a brief introduction about aerodynamic noise generation and transmission mechanisms, the influence of crosswind to vehicle interior aerodynamic noise for a production automobile sedan was investigated through full-scale aeroacoustic wind tunnel tests. Through analysis of sound pressure level of vehicle interior driver ear position and pressure fluctuation level on vehicle side window glass under different yaw angles, the following results are obtained: The frequency characteristics of vehicle interior aerodynamic noise vary as yaw angle changes under one certain wind speed. Whether on the leeside or by windward, sound pressure level increases as yaw angle goes up. Under the same yaw angle, interior noise level on the leeside is higher than that by windward. Test results between pressure fluctuation level on side window glass and vehicle interior aerodynamic noise of driver ear position show good correlation

Measurement of high solidity vertical axis wind turbine aerodynamic loads under high vibration response conditions

A series of full-scale experimental wind tunnel tests were performed to determine the aerodynamic loading behaviour on the airfoils of a high solidity, H-type, vertical axis wind turbine. During the course of this investigation, high amplitude vibration of the turbine was observed over a wide range of test conditions. The primary vibration excitation mechanism was resonance of the dominant whirling mode of the turbine with the operating blade pass frequency. In addition, for a significant number of test cases, resonance of the airfoil support struts at higher frequencies was also observed. This large vibration response resulted in conditions that made it difficult or impossible to measure the underlying aerodynamic loading. As a result, in order to gain a greater understanding of the aerodynamic loading, a vibration isolation methodology was developed to remove the effect of vibration from the measured aerodynamic forces on the blades. This included tests with two different support shaft end conditions over a range of flow velocities from 8 to 11m/s, and the use of band-stop filtering to remove residual small amplitude vibrations. In this way, an accurate and complete measurement of the aerodynamic loading on the turbine blades could be obtained to better understand the effects of dynamic stall and validate the results of numerical model predictions.

Sail pressures from full-scale, wind-tunnel and numerical investigations

The main results of a two-year project aimed at comparing full-scale tests, wind tunnel tests, and numerical analysis predictions are presented. Pressure measurements were obtained from both full-scale tests and wind tunnel tests, in upwind and downwind conditions. The upwind wind tunnel test condition was modelled using a Vortex Lattice code, while the downwind wind tunnel test was modelled using a Navier–Stokes code. The pressures obtained from the three different methods are compared on three horizontal sections of the headsail, mainsail and asymmetric spinnaker. In general the pressure from the three experiments showed good agreement. In particular, very good agreement was obtained between the numerical computations and the wind tunnel test results. Conversely, the results from the downwind full-scale pressure measurements showed less similarity due to a slightly tightened trim being used for the spinnaker in the on-water tests. Full-scale tests allow the action of unsteadiness due to the wind, wave and yacht movements to affect the results. This unstable environment caused the asymmetric spinnaker to move around, and a tightened trim was required to prevent the spinnaker from collapsing.

Numerical Simulation of Wind Pressure Distribution on Structure Roofs with Suspension Solar Panels

This paper presents the results of full-scale numerical wind tunnel tests of wind pressure on structure roofs with suspension solar panels. Solar roof project is popularized in this century. Solar panels are suspended above the structure roof. So the wind load effect on the structure roof is varied. The wind tunnel experiments are often expensive. A 3D model is introduced and solved using ADINA. The wind pressure distribution coefficients are calculated.

Roll Contrial via Active Flow Control: From Concept to Flight

This paper describes a series of experiments that enabled a flight demonstration of roll control without moving control surfaces. That goal was achieved using a wing with a partial span Glauert-type airfoil, characterized by an upper-surface boundary-layer separation from the two-thirds chord location at all incidence angles. The flow over that region was proportionally controlled using zero-mass-flux unsteady excitation emanating from piezofluidic actuators. The control was applied to one wing at a time, resulting in gradual suppression of the boundary-layer separation, increased lift, and reduced drag, leading to a coordinated turning motion of the small electric drone. The extensive multidisciplinary study (starting from the actuator adaptation, the airfoil integration, and the two dimensional wind-tunnel tests) led to the selection of a configuration for the flight demonstrator. Further development of a lightweight wing and piezofluidic actuators, along with a compact, lightweight, energy-efficient electronic drive system, was followed by full-scale wind-tunnel tests and three successful flight tests. It was flight demonstrated that active flow control can induce roll moments that are sufficient to control the vehicle flight path during cruise, as well as during landing. A linear model was used to predict the roll motion of the active-flow controlled drone, with reasonable agreement to the flight-test data. The current study resulted in several pioneering (to the best of our knowledge)achievements that should pave the way to further integration of active-flow-control methods in flight vehicles for hingeless flight attitude and flight-path control, as well as improved performance and increased reliability with lower observability.

Air-Side Heat-Transfer Enhancement by a New Winglet-Type Vortex Generator Array in a Plain-Fin Round-Tube Heat Exchanger

The impact of a vortex-generation technique for air-side heat-transfer improvement is experimentally investigated through full-scale wind-tunnel testing of a plain-fin round-tube heat exchanger under dry-surface conditions. Inspired by the formation locomotion of animals in nature, a new vortex generator (VG) array deployed in a “V” is proposed in the present work, aiming to create constructive interference between vortices. The array is composed of two delta-winglet pairs and placed at an attack angle of 10 deg or 30 deg. Its effectiveness is compared with a baseline configuration and two conventional single-pair designs placed at 30 deg, a small pair with half the area of the array and a large pair with the same area as the array. The frontal air velocity considered ranges from 2.3 m/s to 5.5 m/s, corresponding to a Reynolds number range based on the hydraulic diameter of 1400–3400. The experimental results show little impact of the 10 deg array and a moderate heat-transfer improvement of up to 32% for the small pair, both introducing additional pressure loss of approximately 20–40%. For the 30 deg array and the large pair, similar augmentation of 25–55% in air-side heat-transfer coefficient is obtained accompanied by average pressure drop penalties of 90% and 140%, respectively. Performance evaluation using the criteria of the modified area goodness factor and the volume goodness factor indicates the superiority of the heat exchanger enhanced by the 30 deg array among all the investigated VGs. The VG array is found more effective at comparatively low Reynolds numbers, representative of many heating, ventilation, air-conditioning, and refrigeration applications and compact heat-exchanger designs.

Aerodynamic study of different cyclist positions: CFD analysis and full-scale wind-tunnel tests

Three different cyclist positions were evaluated with Computational Fluid Dynamics (CFD) and wind-tunnel experiments were used to provide reliable data to evaluate the accuracy of the CFD simulations. Specific features of this study are: (1) both steady Reynolds-averaged Navier–Stokes (RANS) and unsteady flow modelling, with more advanced turbulence modelling techniques (Large-Eddy Simulation – LES), were evaluated; (2) the boundary layer on the cyclist’s surface was resolved entirely with low-Reynolds number modelling, instead of modelling it with wall functions; (3) apart from drag measurements, also surface pressure measurements on the cyclist’s body were performed in the wind-tunnel experiment, which provided the basis for a more detailed evaluation of the predicted flow field by CFD. The results show that the simulated and measured drag areas differed about 11% (RANS) and 7% (LES), which is considered to be a close agreement in CFD studies. A fair agreement with wind-tunnel data was obtained for the predicted surface pressures, especially with LES. Despite the higher accuracy of LES, its much higher computational cost could make RANS more attractive for practical use in some situations. CFD is found to be a valuable tool to evaluate the drag of different cyclist positions and to investigate the influence of small adjustments in the cyclist’s position. A strong advantage of CFD is that detailed flow field information is obtained, which cannot easily be obtained from wind-tunnel tests. This detailed information allows more insight in the causes of the drag force and provides better guidance for position improvements.

Effect of wind direction on greenhouse ventilation rate, airflow patterns and temperature distributions

The effect of wind direction, relative to a multi-span naturally ventilated greenhouse, on the airflow patterns and air temperature distribution inside the house and at the openings is investigated in the present study, in a greenhouse with vertical roof openings. Experiments in a full-scale greenhouse, CFD (Computational Fluid Dynamics) full-scale simulations and wind tunnel tests on a small-scale model were carried out. The results showed a significant effect of the wind direction on the flow patterns both inside the house and at the roof openings. Furthermore, wind direction significantly affected the ventilation rate and the air and crop temperature distributions. A reasonable qualitative agreement was achieved between the experiments, numerical simulations and wind tunnel tests with respect to flow patterns through the openings. Quantitatively, the numerically predicted ventilation rates are in reasonable agreement with estimates of ventilation rates obtained by a model given in the literature. However, numerically predicted air velocities at the greenhouse openings differ from the measured values and possible reasons for the differences are highlighted and discussed.

Heat transfer enhancement by winglet-type vortex generator arrays in compact plain-fin-and-tube heat exchangers

The potential of winglet type vortex generator (VG) arrays for air-side heat transfer enhancement is experimentally evaluated by full-scale wind-tunnel testing of a compact plain-fin-and-tube heat exchanger. The effectiveness of a 3VG alternate-tube inline array of vortex generators is compared to a single-row vortex generator design and the baseline configuration. The winglets are placed in a common-flow-up orientation for improved tube wake management. The overall heat transfer and pressure drop performance are assessed under dry-surface conditions over a Reynolds number range based on hydraulic diameter of 220 ≤ Re ≤ 960. It is found that the air-side heat transfer coefficient increases from 16.5% to 44% for the single-row winglet arrangement with an increase in pressure drop of less than 12%. For the three-row vortex generator array, the enhancement in heat transfer coefficient increases with Reynolds number from 29.9% to 68.8% with a pressure drop penalty from 26% at Re = 960 to 87.5% at Re = 220. The results indicate that vortex generator arrays can significantly enhance the performance of fin-tube heat exchangers with flow depths and fin densities typical to those used in air-cooling and refrigeration applications.