Showing papers in "Journal of The American Helicopter Society in 2013"

Experimental investigation of dynamic stall performance for the EDI-M109 and EDI-M112 airfoils

Abstract: An experimental investigation of the dynamic performance of two new rotor blade airfoils was undertaken in a transonic wind tunnel. The EDI-M109 and EDI-M112 airfoils were tested at 0.3

Influence of rotation on dynamic stall

Abstract: A computational investigation of the effect of rotation on two-dimensional (2D) deep dynamic stall has been undertaken, showing that the effect of rotation is to reduce the severity of the pitching moment peak and cause earlier reattachment of the flow. A generic single blade rotor geometry was investigated, which had a pitching oscillation around the quarter chord axis while in hover, causing angle-driven dynamic stall. The results at the midpoint of the blade have the same Mach number (0.31), Reynolds number (1.15×106), and pitching motion (α =13◦±7◦) as a dynamic stall test case for which significant experimental wind tunnel data and 2D computations exist. The rotating blade is compared with 2D computations and computations using the same blade without rotation at Mach 0.31 and with the same pitching motion. All test cases involve geometries propagating into undisturbed flow with no downwash. The three-dimensional (3D) grid computed without rotation had lower lift at the reference section than for a 2D computation with the same geometric angle of attack time history, and the lift overshoot classically observed for Spalart–Allmaras turbulence models during 2D dynamic stall was significantly reduced in the 3D case. Rotation reduced the strength of the dynamic stall vortex, which reduced the accompanying pitching moment peak by 25%.

An Exploration of Radial Flow on a Rotating Blade in Retreating Blade Stall

Abstract: The nature of radial flow during retreating blade stall on a two-bladed teetering rotor with cyclic pitch variation is investigated using laser sheet visualization and particle image velocimetry in a low-speed wind tunnel. The velocity field above the retreating blade at 270◦ azimuth shows the expected development of a radially directed jet layer close to the blade surface in the otherwise separated flow region. This jet is observed to break up into discrete structures, limiting the spanwise growth of the radial velocity in the jet layer. The discrete structures are shown to derive their vorticity from the “radial jet” layer near the surface, rather than from the freestream at the edge of the separated region. The separation line determined using velocity data shows the expected spanwise variation. The results of this study are also correlated in a limited range of extrapolation to the phenomena encountered on a full-scale horizontal axis wind turbine in yaw.

Experimental Investigation of Air Jets for the Control of Compressible Dynamic Stall

Abstract: The experimental investigation of constant blowing air jets as fluidic control devices for helicopter dynamic stall control is described. A carbon fiber airfoil of constant OA209 cross section was fitted with a pneumatic system to deliver dry compressed air as jets for flow control at total pressures of up to 10 bar. The experiment used porthole jets of radius 1% chord, positioned at 10% chord and with spacing 6.7% chord. The positive dynamic stall control effects were demonstrated at Mach 0.3, 0.4, and 0.5 for deep dynamic stall test cases with the best test cases reducing the pitching moment peak after the main stall by 83% while increasing the mean lift over one pitching cycle by 30%. The conclusions from the experiments are supported by three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) computations of the pitching airfoil with flow control using the DLR-TAU code.

Deployable Vortex Generator Dynamic Stall Alleviation through Experimental and Numerical Investigations

Abstract: The flow over an OA209 airfoil subjected to a sinusoidal pitching motion under dynamic stall conditions and equipped with an innovative Deployable Vortex Generator actuator inducing stall control is experimentally and numerically investigated. Pressure and TR-PIV measurements allow a detailed comparison to be performed between clean and controlled cases, including separation point detection and Proper Orthogonal Decomposition analysis. Along with wind tunnel testing, numerical simulations are performed by solving the Unsteady RANS equations with the ONERA elsA code. Computations are successfully compared to the experimental reference and bring further understanding of the Deployable Vortex Generator actuation.

Loads Correlation of a Full-Scale UH-60A Airloads Rotor in a Wind Tunnel

Abstract: Wind tunnel measurements of the rotor trim, blade airloads, and structural loads of a full-scale UH-60A Black Hawk main rotor are compared with calculations obtained using the comprehensive rotorcraft analysis CAMRAD II and a coupled CAMRAD II/OVERFLOW 2 analysis. A speed sweep at constant lift up to an advance ratio of 0.4 and a thrust sweep at constant speed into deep stall are investigated. The coupled analysis shows significant improvement over comprehensive analysis. Normal force phase is better captured and pitching moment magnitudes are better predicted including the magnitude and phase of the two stall events in the fourth quadrant at the deeply stalled condition. Structural loads are, in general, improved with the coupled analysis, but the magnitude of chord bending moment is still significantly underpredicted. As there are three modes around 4 and 5/rev frequencies, the structural responses to the 5/rev airloads due to dynamic stall are magnified and thus care must be taken in the analysis of the deeply stalled condition.

Flight Testing the ADS-33E Cargo Helicopter Handling Qualities Requirements Using a CH-53G

Abstract: Flight testswith a German Army SikorskyCH-53G helicopter were performed to evaluate the applicability and repeatability of the U.S. Army’s Aeronautical Design Standard (ADS)-33E-PRF cargo helicopter handling qualities requirements. The objectives were to corroborate earlier findings and to propose modifications if deemed necessary. The CH-53G was chosen because it is the largest helicopter operated by the German Army, and its dedicated role is cargo and troop transport. The quantitative criteria and the associated boundaries as specified in the standard were largely confirmed. Several flight test maneuvers were revised and tailored. Generally, the heights for performing the near-earth maneuvers were increased. The time/tolerances experienced were borderline desired/adequate or adequate.

中央構造線沿いは熱いか？;中央構造線沿いは熱いか？;Is the zone along the Median Tectonic Line hot?

Abstract: The seismogenic layer in the zone on the southern side of the Median Tectonic Line that runs in the east-west direction crossing the Kii Peninsula and Shikoku is abnormally shallow. It is “abnormal” because the shallowness of the depth is not concordant with the generally observed feature that the higher the altitude of the area, the shallower the seismogenic layer. The depth of the seismogenic layer is as shallow as that in the mountainous zone along the Volcanic Front in northeastern Japan, nevertheless such low altitude areas as Wakayama and Tokushima plains exist in the zone on the southern side of the Median Tectonic Line. If it is postulated that the depth of the seismogenic layer is regulated by the brittle-ductile transition temperature of the crustal materials, the shallowness of the seismogenic layer means that the temperature in the crust is relatively high. Then, why is the temperature in the zone along the Median Tectonic Line high? We think it is not unreasonable to consider that thermal fluids are rising from the subducted slab there, if it is reminded that hot waters are estimated to exist beneath the Wakayama swarm region that belongs to the zone.