A vortex lattice code, CAMRAD II, and a Reynolds-Averaged Navier-Stoke code, OVERFLOW-D2, were used to predict the aerodynamic performance of a two-bladed horizontal axis wind turbine. All computations were compared with experimental data that was collected at the NASA Ames Research Center 80- by 120-Foot Wind Tunnel. Computations were performed for both axial as well as yawed operating conditions. Various stall delay models and dynamics stall models were used by the CAMRAD II code. Comparisons between the experimental data and computed aerodynamic loads show that the OVERFLOW-D2 code can accurately predict the power and spanwise loading of a wind turbine rotor.

https://rotorcraft.arc.nasa.gov/publications/files/Duque_AIAA2003.pdf

Navier-Stokes and Comprehensive Analysis Performance Predictions of the NREL Phase VI Experiment

A computational fluid dynamics (CFD) code and rotorcraft computational structural dynamics (CSD) code are coupled to calculate helicopter rotor airloads across a range of flight conditions. An iterative loose (weak) coupling methodology is used to couple the CFD and CSD codes on a per revolution, periodic basis. The CFD code uses a high fidelity, Navier‐Stokes, overset grid methodology with first principles-based wake capturing. Modifications are made to the CFD code for the aeroelastic analysis. For a UH-60A Blackhawk helicopter, three challenging level flight conditions are computed: 1) high speed, μ = 0.37, with advancing blade negative lift, 2) low speed, μ = 0.15, with blade‐vortex interaction, and 3) high thrust with dynamic stall, μ = 0.24. Results are compared with UH-60A Airloads Program flight test data. For all cases the loose coupling methodology is shown to be stable, convergent, and robust with full coupling of normal force, pitching moment, and chord force. In comparison with flight test data, normal force and pitching moment phase and magnitude are in good agreement. The shapes of the airloads curves are well captured. Overall, the results are a noteworthy improvement over lifting line aerodynamics used in rotorcraft comprehensive codes.

https://rotorcraft.arc.nasa.gov/publications/files/Potsdam2_AHS04.pdf

Rotor Airloads Prediction Using Loose Aerodynamic/Structural Coupling

Nomenclature ADC Analog-to-Digital Converter BIB Battery Interface Board COTS Commerical Off-the-shelf CPU Central Processor Unit dof degrees-of-freedom ECM Electronics Core Module EDM Engineering Design Model FC Flight Controller FFB FPGA/Flight-Controller Board FPGA Field-Programmable Gate Array GPIO General Purpose Input/Ouput GPS Global Positioning System IC Integrated Circuit IMU Inertial Measurement Unit MCU Microcontroller Unit MEMS Microelectromechanical System NAV Navigation NSB Navigation/Servo Controller Board ROI Region of Interest RTE Return-to-Earth SEL Single-Event Latch-up SOM System On a Module SPI Serial Peripheral Interface TCB Telecommunications Board UART Universal Asynchronous Receiver/Transmitter

Mars Helicopter Technology Demonstrator

Concept vehicles are presented for air taxi operations, also known as urban air mobility or on-demand mobility applications. Considering the design-space dimensions of payload (passengers and pilot), range, aircraft type, and propulsion system, three aircraft are designed: a single passenger (250-lb payload), 50-nm range quadrotor with electric propulsion; a six-passenger (1200-lb payload), 4x50 = 200-nm range side-by-side helicopter with hybrid propulsion; and a fifteen-passenger (3000-lb payload), 8x50 = 400-nm range tiltwing with turbo-electric propulsion. These concept vehicles are intended to focus and guide NASA research activities in support of aircraft development for emerging aviation markets, in particular VTOL air taxi operations. Research areas are discussed, illustrated by results from the design of the concept vehicles.

/pdf/concept-vehicles-for-vtol-air-taxi-operations-4cxh36x2fp.pdf

Concept Vehicles for VTOL Air Taxi Operations

: Flight test measurements of the performance of the UH-60 Black Hawk helicopter with both standard and advanced rotors are compared with calculations obtained using the comprehensive helicopter analysis CAMRAD II In general, the calculated power coefficient shows good agreement with the flight test data However, the accuracy of the calculation degrades at high gross weight for all of the configurations The analysis shows fair to good correlation for collective and longitudinal cyclic angles and pitch attitude, and poor to fair correlation for the lateral trim quantities "lateral cyclic angle and roll attitude" The increased solidity of the wide chord blade appears to be a dominant factor in the performance improvement at high gross weight by reducing blade loading and thus delaying stall

https://rotorcraft.arc.nasa.gov/publications/files/Yeo_AHS2002.pdf

Performance Analysis of a Utility Helicopter with Standard and Advanced Rotors

Recent developments of the dynamics models for the comprehensive analysis CAMRAD II are described, specifically advanced models of the geometry and material for the beam component, and a force balance method for calculating section loads. Calculations are compared with measurements for beams undergoing large deflection. Bearingless rotor stability and bending loads calculations are compared with the results from a full-scale wind tunnel test. With a reasonable number of beam elements representing the rotor blade, any large deflection effects are captured by the rigid body motion (which is always exact), and a second-order model of the beam element elastic motion is adequate. The deflection method gives unacceptable results for the structural loads in practical cases, and even with uniform blade properties. The force balance method described here gives good results for blade load, without requiring a large number of nodes.

/pdf/rotorcraft-aerodynamics-models-for-a-comprehensive-analysis-4sm59o6xku.pdf

Wayne Johnson

Papers

Rotorcraft Aerodynamics Models for a Comprehensive Analysis