Spanwise structures in a two-dimensional reattaching separated flow were studied using multisensor hot-wire anemometry techniques. The results of these measurements strongly support the existence and importance of large-scale vortices in both the separated and reattached regions of this flow. Upstream of reattachment, vortex pairings are indicated and the spanwise structures attain correlation scales closely comparable to previously measured mixing-layer vortices. These large-scale vortices retain their organization far downstream of the reattachment region. However, pairing interactions appear to be strongly inhibited in this region. It is suggested that large-scale vortex dynamics are primarily responsible for some of the important time-averaged features of this flow. Notably, the reduction of turbulence energy in the reattachment region and the slow transition of the mean flow downstream of reattachment are attributed to effects associated with these vortices.

This paper describes and analyzes the measurements from a full-scale, slowed revolutions per minute (rpm), UH-60A rotor tested at the National Full-Scale Aerodynamics Complex 40-by 80-ft wind tunnel up to an advance ratio of 1.0. A comprehensive set of measurements that includes performance, blade loads, hub loads, and pressures/airloads makes this data set unique. The measurements reveal new and rich aeromechanical phenomena that are unique to this exotic regime. These include reverse chord dynamic stall, retreating side impulse in torsion load, large inboard-outboard elastic twist differential, diminishing rotor forces and yet a dramatic buildup of blade loads, and high blade loads and yet benign levels of vibratory hub loads. The objective of this research is the fundamental understanding of these unique aeromechanical phenomena. The intent is to provide useful knowledge for the design of high-speed, high-efficiency, slowed rpm rotors of the future and a database for validation of advanced analyses. Nomenclature

ABTRACTA full-scale four-bladed UH-60 rotor system was tested in the NASA Ames 80-by 120-Foot Wind Tunnel. A quality data set at low forward speed, 0 to 80 knots, has been obtained to support future rotor developments and analysis improvements. To evaluate the NASA Ames 80-by 120-Foot Wind Tunnel as a hover testing facility, rotor performance data were compared with predictions, UH-60 aircraft flight test data, and UH-60 model-scale data from other test facilities. Results indicate that valid hover data for this size rotor can be obtained from this facility at low to medium thrust conditions. Comparisons with flight test and model-scale data demonstrate the variability between existing data sets. Predictions show good agreement with full-scale data. To evaluate the analytical modeling in the 0 to 80 knot speed range, forward flight rotor performance data were acquired and compared with predictions. Comparisons were also made with existing model-scale and flight test data. Power calculations show fair to good agreement with full-scale wind tunnel data at advance ratios between 0.10 to 0.19 and poor agreement at advance ratios below 0.10. Comparisons with flight test and model-scale data show good agreement at all advance ratios tested. Propulsive force calculations show good correlation with full-scale wind tunnel data at advance ratios of 0.10 to 0.19. Report Documentation PageForm Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. DESCRIPTION OF THE TESTThe following section provides a brief description of the test, including the model, the primary measurement system and the test conditions. A more detailed description of the test and the facility can be found in Ref. 23. ModelThe experiment was conducted in the NASA Ames 80-by 120-Foot Wind Tunnel using a production Sikorsky Aircraft UH-60A rotor system mounted on NASA's Large Rotor Test Apparatus (LRTA). Figure 1 shows the model installed in the wind tunnel.The rotor system, including the hub, spindles, blades, and swashplate, is identical to the one used on the production aircraft. The rotor is four-bladed with coincident flap and lag articulation provided at the blade root by elastomeric bearings. The elastomeric bearing, through the rotor spindle, also allows blade pitch motion. No bifilars were ...

Wind tunnel measurements of performance, loads, and vibration of a full-scale UH-60A Black Hawk main rotor with an individual blade control (IBC) system are compared with calculations obtained using the comprehensive helicopter analysis CAMRAD II and a coupled CAMRAD II/OVERFLOW 2 analysis. Measured data show a 5.1% rotor power reduction (8.6% rotor lift to effective-drag ratio increase) using 2/rev IBC actuation with 2.0• amplitude at µ = 0.4. At the optimum IBC phase for rotor performance, IBC actuator force (pitch link force) decreased, and neither flap nor chord bending moments changed significantly. CAMRAD II predicts the rotor power variations with IBC phase reasonably well at µ = 0.35. However, the correlation degrades at µ = 0.4. Coupled CAMRAD II/OVERFLOW 2 shows excellent correlation with the measured rotor power variations with IBC phase at both µ = 0.35 and µ = 0.4. Maximum reduction of IBC actuator force is better predicted with CAMRAD II, but general trends are better captured with the coupled analysis. The correlation of vibratory hub loads is generally poor by both methods, although the coupled analysis somewhat captures general trends.

i Rotor Hp vortex geometry data have been acquired using the wide-field shadowgraph technique. Shadowgraphs were taken of the wakes of two model main.rotor systems in hover. These shadowgraphs provided detailed tip vortex trajectories from which axial and radial vortex coordinates were measured. Another result of the experimental work was the development of a method to predict the degree of visibility of rotor tip vortices on shadowgraphs. Using this method, the ability of the shadowgraph technique to visualize tip vortices in the rotor wake was quantified.