Wind Tunnel Test on a Slowed Mach-Scaled Hingeless Rotor with Lift Compounding

2021 ◽  
Author(s):  
Shashank Maurya ◽  
Xing Wang ◽  
Inderjit Chopra
Keyword(s):  
Wind Tunnel ◽  
Reverse Flow ◽  
Wind Tunnel Test ◽  
Bending Moment ◽  
Flow Region ◽  
Dynamic Stall ◽  
Rolling Moment ◽  
Slowing Down ◽  
Slowed Rotor ◽  
Compressibility Effects

A single main rotor helicopter's maximum forward speed is limited due to the compressibility effects on the advancing side and reverse flow and dynamic stall on the retreating side. Compound helicopters can address these issues with a slowed rotor and lift compounding. There is a scarcity of test data on compound helicopters, and the present research focuses on a systematic wind tunnel test on lift compounding. Slowing down the rotor increases the advance ratio and, hence, the reverse flow region, which does not produce much lift. The lift is augmented with a wing on the retreating side. A hingeless rotor hub helps to balance the rolling moment with lift offset. Wind tunnel tests were carried out on this configuration up to advance ratios of 0.7 at two different wing incidence angles. Rotor performance, controls, blade structural loads, and hub vibratory loads were measured and compared with in-house comprehensive analysis, UMARC. A comparison between different wing incidences at constant total lift provided many insights into the lift compounding. It increased the vehicle efficiency and reduced peak-to-peak lag bending moment and in-plane 4/rev hub vibratory loads. The only trade-off was steady rotor hub loads and rolling moment at the wing root carried by the fuselage.

Wind Tunnel Test of a Rotorcraft with Lift Compounding

2021 ◽  
Vol 66 (1) ◽  
pp. 1-16
Author(s):  
Andŕe Bauknecht ◽  
Xing Wang ◽  
Jan-Arun Faust ◽  
Inderjit Chopra
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
Reverse Flow ◽  
Lift Coefficient ◽  
Wind Tunnel Test ◽  
Flow Region ◽  
Field Analysis ◽  
Rolling Moment ◽  
The Impact ◽  
Side Flow

Rotorcraft flight speed is limited by compressibility effects on the advancing blade side and decreasing lift potential on the retreating blade side. It may thus be beneficial to employ a hingeless rotor to generate additional lift with the advancing blade and compensate the resulting rolling moment with a fixed wing on the retreating blade side. This concept is a form of "lift compounding" that appears to show enormous potential. The present paper presents results of a wind tunnel test with a slowed, hingeless rotor and single fixed wing on the retreating blade side. Based on rotor test stand data and flow field measurements, the impact of operational and rotor parameters on system performance and aerodynamics is examined, mutual interaction effects between rotor and fixed wing are analyzed, and dominant flow structures are characterized in the reverse flow region on the retreating blade side. Flow field analysis reveals a reverse flow entrance vortex that freely convects through the reverse flow region and rivals the blade tip vortices in strength. Contrary to previous beliefs, this vortex originates from upstream of the reverse flow region and only its detachment from the rotor blade is related to entering this region. The combination of finite rolling moment trim and aft shaft tilt significantly increases rotor lift coefficient and corresponding peak lift-to-drag ratio of the compound rotorcraft. Results are compared with predictions from a comprehensive rotor analysis that is expanded to cover the main effects of the added fixed wing and is able to reproduce general performance trends of the rotorcraft. The present study highlights that adding a single fixed wing and hingeless rotor to a high-speed rotorcraft could significantly improve its performance.

Refined Performance Results on a Slowed Mach-Scaled Rotor at High Advance Ratios

2020 ◽  
Vol 65 (1) ◽  
pp. 1-13
Author(s):  
Xing Wang ◽  
Lauren Trollinger ◽  
Inderjit Chopra
Keyword(s):  
Wind Tunnel ◽  
High Speed ◽  
Reverse Flow ◽  
Flow Region ◽  
Comprehensive Analysis ◽  
Compressibility Effect ◽  
Inflow Condition ◽  
Advance Ratio ◽  
Slowed Rotor ◽  
Performance Results

Owing to its ability to alleviate the compressibility effect on the advancing side, the slowed rotor operating at high advance ratios is a key feature in high-speed compound rotorcraft. A series of wind tunnel tests were conducted in the Glenn L. Martin Wind Tunnel with a four-bladed Mach-scaled articulated rotor. The objective of the tests was to gain a basic understanding of unique features of high-advance-ratio aerodynamic phenomena, such as thrust reversal and dynamic stall in the reverse flow region. In this study, high-advance-ratio tests were carried out with highly similar, noninstrumented blades and on-hub control angle measurements, to minimize possible error due to blade structural dissimilarity and pitch angle discrepancy. The tests were conducted at 900 and 1200 RPM, advance ratios of 0.3–0.9, and a shaft tilt study was conducted at±4°. Pitch and flap motion at the blade roots, rotor performance, and vibratory hub loads were investigated during the test. The test data were then compared with those of previous tests and with predictions from comprehensive analysis. The airload results were investigated using comprehensive analysis to gain insights into the influences of advance ratio and shaft tilt angle on rotor performance and hub vibratory loads. Results indicate that the thrust benefit from backward shaft tilt is dependent on the change in the inflow condition and the induced angle of attack increment, and the reverse flow region at high advance ratios is the major contributor to changes in shaft torque and horizontal force.

Blade Structural Load/Airload Correlation on a Slowed Mach-Scaled Rotor at High Advance Ratios

2020 ◽  
Vol 65 (4) ◽  
pp. 1-14
Author(s):  
Xing Wang ◽  
Yong Su Jung ◽  
James Baeder ◽  
Inderjit Chopra
Keyword(s):  
Wind Tunnel ◽  
Structural Model ◽  
Reverse Flow ◽  
Pressure Sensors ◽  
Wind Tunnel Test ◽  
Design Feature ◽  
Flow Region ◽  
Rotor Blades ◽  
Data Correlation ◽  
Advance Ratio

To expand the cruise speed of a compound helicopter, alleviating the compressibility effects on the advancing side with reduced rotor RPM is proved to be an effective design feature, which results in high advance ratio flight regime. To investigate the aerodynamic phenomena at high advance ratios and provide data for the validation of analytical tools, a series of wind tunnel tests were conducted progressively in the Glenn L. Martin Wind Tunnel with a 33.5-inch radius fourbladed articulated rotor. In a recent wind tunnel test, the rotor blades were instrumented with pressure sensors and strain gauges at 30% radius, and pressure data were acquired to calculate the sectional airloads by surface integration up to an advance ratio of 0.8. The experimental results of rotor performance, control angles, blade airloads, and structural loads were compared with the predictions of comprehensive analysis and computational fluid dynamics (CFD) analysis coupled with computational structural dynamics (CSD) structural model. The paper focuses on the data correlation between experimental pressure, airload, and structural load data and the CFD/CSD predicted results at various collective and shaft tilt angles. Overall, the data correlation was found satisfactory, and the study provided some insights into the aerodynamic mechanisms that affect the rotor airload and performance, in particular the mechanisms of backward shaft tilt, the effect of hub/shaft wake, and the formation of dynamic stall in the reverse flow region.

Homogeneous, Isotropic Flow in Grid Generated Turbulence

1999 ◽  
Vol 122 (1) ◽  
pp. 51-56 ◽  
Author(s):  
Riccardo Tresso ◽  
David R. Munoz
Keyword(s):  
Wind Tunnel ◽  
Three Dimensional ◽  
Wind Tunnel Test ◽  
Flow Region ◽  
Hot Wire ◽  
Spatial Homogeneity ◽  
One Dimensional ◽  
Streamwise Location ◽  
Dimensional Measurements ◽  
Approach Zero

Detailed grid generated turbulent analysis has been completed using a three-dimensional hot-wire anemometer and traversing mechanism to identify a homogeneous, isotropic flow region downstream of a square mesh. The three-dimensional fluctuating velocity measurements were recorded along the centerline of a wind tunnel test section and spatially over the entire wind tunnel cross section downstream of the square mesh. Turbulent intensities for various grid sizes and Reynolds numbers ranged from a minimum of 0.2 percent to a maximum of 2.2 percent in each of the three principal velocity directions. Spatial homogeneity and isotropy were determined for several turbulent flow conditions and downstream positions using the method of covariances. Covariances, in theory, should approach zero asymptotically; however, in practice, this was not achievable. A subjective judgment is required to determine downstream location where the variance of the three covariances reaches a value close to zero. The average standard deviation provides an estimate for defining the limit or subjective threshold needed to determine the onset of homogeneous, isotropic flow. Implementing this threshold, a quantitative method was developed for predicting the streamwise location for the onset of the homogeneous, isotropic flow region downstream of a 25.4 mm square grid as a function of Reynolds number. A comparison of skewness, determined from one-dimensional hot wire anemometer measurements, and covariances, determined from three dimensional hot wire anemometer measurements, indicates a need for caution when relying solely on one-dimensional measurements for determination of turbulence isotropy. The comprehensive three-dimensional characterization also provides an improved understanding of spatial distribution of fundamental turbulence quantities generated by the grid within a low-speed wind tunnel. [S0098-2202(00)02501-3]

scholarly journals Numerical investigation of the effect of airfoil thickness on onset of dynamic stall

2019 ◽  
Vol 870 ◽  
pp. 870-900 ◽  
Author(s):  
Anupam Sharma ◽  
Miguel Visbal
Keyword(s):  
Reverse Flow ◽  
Separation Bubble ◽  
Time Integration ◽  
Angle Of Attack ◽  
Leading Edge ◽  
Flow Region ◽  
Dynamic Stall ◽  
Implicit Time ◽  
Gradual Change ◽  
Dynamic Simulations

Effect of airfoil thickness on onset of dynamic stall is investigated using large eddy simulations at chord-based Reynolds number of 200 000. Four symmetric NACA airfoils of thickness-to-chord ratios of 9 %, 12 %, 15 % and 18 % are studied. The three-dimensional Navier–Stokes solver, FDL3DI is used with a sixth-order compact finite difference scheme for spatial discretization, second-order implicit time integration and discriminating filters to remove unresolved wavenumbers. A constant-rate pitch-up manoeuver is studied with the pitching axis located at the airfoil quarter chord. Simulations are performed in two steps. In the first step, the airfoil is kept static at a prescribed angle of attack ($=4^{\circ }$). In the second step, a ramp function is used to smoothly increase the pitch rate from zero to the selected value and then the pitch rate is held constant until the angle of attack goes past the lift-stall point. The solver is verified against experiments for flow over a static NACA 0012 airfoil. Static simulation results of all airfoil geometries are also compared against XFOIL predictions with a generally favourable agreement. FDL3DI predicts two-stage transition for thin airfoils (9 % and 12 %), which is not observed in the XFOIL results. The dynamic simulations show that the onset of dynamic stall is marked by the bursting of the laminar separation bubble (LSB) in all the cases. However, for the thickest airfoil tested, the reverse flow region spreads over most of the airfoil and reaches the LSB location immediately before the LSB bursts and dynamic stall begins, suggesting that the stall could be triggered by the separated turbulent boundary layer. The results suggest that the boundary between different classifications of dynamic stall, particularly leading edge stall versus trailing edge stall, is blurred. The dynamic-stall onset mechanism changes gradually from one to the other with a gradual change in some parameters, in this case, airfoil thickness.

Investigating pitching moment stall through dynamic wind tunnel test

2019 ◽  
Vol 234 (2) ◽  
pp. 267-279
Author(s):  
Alessandro Pontillo ◽  
Sezsy Yusuf ◽  
Guillermo Lopez ◽  
Dominic Rennie ◽  
Mudassir Lone
Keyword(s):  
Parameter Estimation ◽  
Wind Tunnel ◽  
Wind Tunnel Test ◽  
Angular Acceleration ◽  
Direct Calculation ◽  
Dynamic Stall ◽  
Nonlinear Behaviour ◽  
Wind Tunnel Testing ◽  
Pitching Moment ◽  
Heave Motion

Experimental characterisation of aircraft dynamic stall can be a challenging and complex system identification activity. In this article, the authors present a method that combines dynamic wind tunnel testing with parameter estimation techniques to study the nonlinear pitching moment dynamics of a 1/12 scale Hawk model undergoing moment stall. The instrumentation setup allows direct calculation of angular acceleration terms, such as pitch acceleration, and avoids post-processing steps involving differentiation of signals. Data collected from tests, carried out at 20 m/s and 30 m/s, are used for a brief aerodynamic analysis of the observed stall hysteresis. Then an output-error-based parameter estimation process is used to parameterise dynamic stall models and furthermore, illustrate that in a scenario where the model's heave motion is constrained. The observed nonlinear behaviour arises from the nonlinear angle of attack and linear pitch rate components.

scholarly journals Dynamic Stall Model for Tower Shadow Effects on Downwind Turbines and Its Scale Effects

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5237
Author(s):  
Shigeo Yoshida
Keyword(s):  
Wind Speed ◽  
Wind Tunnel ◽  
Scale Effects ◽  
Wind Tunnel Test ◽  
Dynamic Stall ◽  
Test Model ◽  
Wind Speed Profile ◽  
Empirical Parameter ◽  
Wake Model ◽  
Tower Shadow

A dynamic stall model for tower shadow effects is developed for downwind turbines. Although Munduate’s model shows good agreement with a 1.0 m wind tunnel test model, two problems exist: (1) it does not express load increase before the entrance of the tower wake, and (2) it uses the empirical tower wake model to determine the wind speed profile behind the tower. The present research solves these problems by combining Moriarty’s tower wake model and the entrance condition of the tower wake. Moriarty’s model does not require any empirical parameter other than tower drag coefficient and it expresses positive wind speed around the tower also. Positive wind speed change is also allowed as the tower wake entrance condition in addition to the negative change observed in the previous model. It demonstrates better agreement with a wind tunnel test and contributes to the accuracy of the fatigue load, as it expresses a slight increase in load around the entrance of the tower wake. Furthermore, the scale effects are also evaluated; lift deviation becomes smaller as the scale increases, i.e., lower rotor speed.

Numerical Simulation and Wind Tunnel Studies of the Wind Load on Wind Turbine Structures

2011 ◽  
Vol 250-253 ◽  
pp. 3811-3814
Author(s):  
Cheng Hsin Chang ◽  
Jen Mu Wang ◽  
Chii Ming Cheng
Keyword(s):  
Numerical Simulation ◽  
Wind Tunnel ◽  
Wind Turbine ◽  
Wind Tunnel Test ◽  
Bending Moment ◽  
Dynamic Mesh ◽  
Base Shear ◽  
Structural Responses ◽  
Simulation Results ◽  
Rng Turbulence Model

This paper investigated the structural responses of the wind turbine due to wind loads by performing the wind tunnel test and the Computational Fluid Dynamics, (CFD). The base shear force and the base moment of the wind turbine measured by the wind tunnel test were compared with the numerical simulation results. Both the numerical dynamic mesh and sliding mesh models were selected for the numerical simulations. The results showed that the dynamic mesh model was better than the sliding model by comparing to the wind tunnel test result. In the case of the k-epsilon RNG turbulence model, the prediction of the bending moment affecting by acrossswind was more than 50%, and the prediction of the force affecting by acrosswind was less than 3%. The both simulation results of the prototype and the full scale wind turbine were obtained by CFD model. The comparisons of the result showed that the error of Fxwas about 15% and Mywas about 13.5%.

scholarly journals Effect of propeller-induced flow on the performance of biplane micro air vehicle dynamics

2019 ◽  
Vol 234 (3) ◽  
pp. 716-728 ◽  
Author(s):  
Shuvrangshu Jana ◽  
Harikumar Kandath ◽  
Mayur Shewale ◽  
M Seetharama Bhat
Keyword(s):  
Wind Tunnel ◽  
Vehicle Dynamics ◽  
Wind Tunnel Test ◽  
Micro Air Vehicle ◽  
Aerodynamic Parameter ◽  
Rolling Moment ◽  
Air Vehicle ◽  
Induced Flow ◽  
Flow Effects ◽  
Force Range

This paper presents the analysis of propeller-induced flow effects on the dynamics of a fixed wing biplane micro air vehicle. The analysis is based on wind tunnel tests and mathematical modeling. This analysis plays a pivotal role because the propeller-induced flow has significant effects on the dynamics of fixed wing micro air vehicle due to submergence of a large portion of the wing in propeller slipstream. Although the effect of the propeller-induced flow on the various aerodynamic parameter is reported in the literature; however, its effects on overall forces, moments and vehicle dynamics are not quantified so far. In this paper, propeller-induced flow effects are modeled as a function of motor rotation speed and mathematical analysis is performed to quantify their effects. The wind tunnel test is conducted at different propeller speeds on a biplane micro air vehicle “Skylark”, having wingspan and chord length of 150 mm and 140 mm, respectively. Analysis of results shows that the propeller slipstream increases the overall lift, drag, side force, range, and endurance significantly. Propeller flow also contributes to the rolling moment and the pitching moment, while it has negligible effects on the yawing moment. It is shown that the trim angle of attack is lower when the propeller flow is considered in computing the trim conditions.

Improvement of Aircraft Aerodynamic Performance Using Piezoelectric Actuators

2005 ◽  
Vol 888 ◽  
Author(s):  
Li Min ◽  
Chen Wei-min ◽  
Li Wei
Keyword(s):  
Wind Tunnel ◽  
High Speed ◽  
Dynamic Pressure ◽  
Bending Moment ◽  
Piezoelectric Actuators ◽  
Aerodynamic Performance ◽  
Control Surface ◽  
Flight Vehicle ◽  
Rolling Moment ◽  
Induced Drag

AbstractTo flight vehicle designer, the ability to adapt air vehicle aerodynamic shape so as to increase the optimum flight envelope is highly desirable. In this work, by distributing piezoelectric actuators on the top and bottom surfaces of a rectangular wing, the improvement of aerodynamic performance of flight vehicle is studied. The approach of the Fictitious Control Surface (FCS) is evaluated at a group of dynamic pressure and wing stiffness, through examining four aspects including the improvement of rolling power, the increase of lift, the decrease of the induced drag and the decrease of the bending moment at root of wing. Then an experimental model of high-speed wind tunnel is designed in order to validate the results of theoretical analysis. The ground tests and wind tunnel tests demonstrate that the lift and rolling moment can be increased by using the favorable aeroelastic effect. And quantificationally the experimental results agree well with the analytical results.

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