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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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324 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

Blade Displacement Measurement Technique Applied to a Full-Scale Rotor Test

Blade displacement measurements using multi-camera photogrammetry were acquired during the full-scale wind tunnel test of the UH-60A Airloads rotor, conducted in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel. The objectives were to measure the blade displacement and deformation of the four rotor blades as they rotated through the entire rotor azimuth. These measurements are expected to provide a unique dataset to aid in the development and validation of rotorcraft prediction techniques. They are used to resolve the blade shape and position, including pitch, flap, lag and elastic deformation. Photogrammetric data encompass advance ratios from 0.15 to slowed rotor simulations of 1.0, thrust coefficient to rotor solidity ratios from 0.01 to 0.13, and rotor shaft angles from -10.0 to 8.0 degrees. An overview of the blade displacement measurement methodology and system development, descriptions of image processing, uncertainty considerations, preliminary results covering static and moderate advance ratio test conditions and future considerations are presented. Comparisons of experimental and computational results for a moderate advance ratio forward flight condition show good trend agreements, but also indicate significant mean discrepancies in lag and elastic twist. Blade displacement pitch measurements agree well with both the wind tunnel commanded and measured values.

Abrego, Anita I.↗
NASA NTRS2012

Evaluation of Rotor Structural and Aerodynamic Loads using Measured Blade Properties

The structural properties of Higher harmonic Aeroacoustic Rotor Test (HART I) blades have been measured using the original set of blades tested in the wind tunnel in 1994. A comprehensive rotor dynamics analysis is performed to address the effect of the measured blade properties on airloads, blade motions, and structural loads of the rotor. The measurements include bending and torsion stiffness, geometric offsets, and mass and inertia properties of the blade. The measured properties are correlated against the estimated values obtained initially by the manufacturer of the blades. The previously estimated blade properties showed consistently higher stiffnesses, up to 30% for the flap bending in the blade inboard root section. The measured offset between the center of gravity and the elastic axis is larger by about 5% chord length, as compared with the estimated value. The comprehensive rotor dynamics analysis was carried out using the measured blade property set for HART I rotor with and without HHC (Higher Harmonic Control) pitch inputs. A significant improvement on blade motions and structural loads is obtained with the measured blade properties.

Jung, Sung N.↗
NASA NTRS2013

Comparison of Computed and Measured Vortex Evolution for a UH-60A Rotor in Forward Flight

A Computational Fluid Dynamics (CFD) simulation using the Navier-Stokes equations was performed to determine the evolutionary and dynamical characteristics of the vortex flowfield for a highly flexible aeroelastic UH-60A rotor in forward flight. The experimental wake data were acquired using Particle Image Velocimetry (PIV) during a test of the fullscale UH-60A rotor in the National Full-Scale Aerodynamics Complex 40- by 80-Foot Wind Tunnel. The PIV measurements were made in a stationary cross-flow plane at 90 deg rotor azimuth. The CFD simulation was performed using the OVERFLOW CFD solver loosely coupled with the rotorcraft comprehensive code CAMRAD II. Characteristics of vortices captured in the PIV plane from different blades are compared with CFD calculations. The blade airloads were calculated using two different turbulence models. A limited spatial, temporal, and CFD/comprehensive-code coupling sensitivity analysis was performed in order to verify the unsteady helicopter simulations with a moving rotor grid system.

Evolution↗
NASA NTRS2014

Shake Test Results and Dynamic Calibration Efforts for the Large Rotor Test Apparatus

Prior to the full-scale wind tunnel test of the UH-60A Airloads rotor, a shake test was completed on the Large Rotor Test Apparatus. The goal of the shake test was to characterize the oscillatory response of the test rig and provide a dynamic calibration of the balance to accurately measure vibratory hub loads. This paper provides a summary of the shake test results, including balance, shaft bending gauge, and accelerometer measurements. Sensitivity to hub mass and angle of attack were investigated during the shake test. Hub mass was found to have an important impact on the vibratory forces and moments measured at the balance, especially near the UH-60A 4/rev frequency. Comparisons were made between the accelerometer data and an existing finite-element model, showing agreement on mode shapes, but not on natural frequencies. Finally, the results of a simple dynamic calibration are presented, showing the effects of changes in hub mass. The results show that the shake test data can be used to correct in-plane loads measurements up to 10 Hz and normal loads up to 30 Hz.

Large Rotor Test Apparatus↗
NASA NTRS2014

Measurement of the UH-60A Hub Large Rotor Test Apparatus Control System Stiffness

This purpose of this report is to provides details of the measurement of the control system stiffness of the UH-60A rotor hub mounted on the Large Rotor Test Apparatus (UH-60A/LRTA). The UH-60A/LRTA was used in the 40- by 80-Foot Wind Tunnel to complete the full-scale wind tunnel test portion of the NASA / ARMY UH-60A Airloads Program. This report describes the LRTA control system and highlights the differences between the LRTA and UH-60A aircraft. The test hardware, test setup, and test procedures are also described. Sample results are shown, including the azimuthal variation of the measured control system stiffness for three different loadings and two different dynamic actuator settings. Finally, the azimuthal stiffness is converted to fixed system values using multi-blade transformations for input to comprehensive rotorcraft prediction codes.

Large Rotor Test Apparatus↗
NASA NTRS2016

Modularization and Validation of FUN3D as a CREATE-AV Helios Near-Body Solver

Under a recent collaborative effort between the US Army Aeroflightdynamics Directorate (AFDD) and NASA Langley, NASA's general unstructured CFD solver, FUN3D, was modularized as a CREATE-AV Helios near-body unstructured grid solver. The strategies adopted in Helios/FUN3D integration effort are described. A validation study of the new capability is performed for rotorcraft cases spanning hover prediction, airloads prediction, coupling with computational structural dynamics, counter-rotating dual-rotor configurations, and free-flight trim. The integration of FUN3D, along with the previously integrated NASA OVERFLOW solver, lays the ground for future interaction opportunities where capabilities of one component could be leveraged with those of others in a relatively seamless fashion within CREATE-AV Helios.

Jain, Rohit↗
NASA NTRS2017

Parametric Investigation on the Use of Lateral and Logitudinal Rotor Trim Flapping for Tiltrotor Noise Reduction

This paper presents an acoustics parametric study of the effect of varying lateral and longitudinal rotor trim flapping angles (tip-path-plane tilt) on noise radiated by an isolated 26-ft diameter proprotor, similar to that of the AW609 tiltrotor, in edgewise flight. Three tip-path-plane angle of attack operating conditions of -9, 0 and 6 deg, at 80 knots, were investigated. Results showed that: 1) minimum noise was attained for the tip-path-plane angle of attack value of -9 deg, and 2) changing the cyclic trim state (i.e., controls) altered the airloads and produced noticeable changes to the low-frequency (LF) and blade-vortex interaction (BVI) radiated-noise magnitude and directionality. In particular, by trimming the rotor to a positive (inboard) lateral flapping angle of 4 deg, further reductions up to 3 dB in the low-frequency noise sound pressure level were attained without significantly impacting the BVI noise for longitudinal tip-path-plane angles of -9 and 6 deg.

Noise Reduction↗
NASA NTRS2017

Whirl Flutter Stability and Its Influence on the Design of the Distributed Electric Propeller Aircraft X- 57

This paper studies the whirl flutter stability of the NASA experimental electric propulsion aircraft designated the X-57 Maxwell. whirl flutter stability is studied at two flight conditions: sea level at 2700 RPM to represent take-off and landing and 8000 feet at 2250 RPM to represent cruise. Two multibody dynamics analyses are used: CAMRAD II and Dymore. The CAMRAD II model is a semi-span X-57 model with a modal representation for the wing/pylon system. The Dymore model is a semi-span wing with a propeller composed of beam elements for the wing/pylon system that airloads can be applied to. The two multibody dynamics analyses were verified by comparing structural properties between each other and the NASTRAN analysis. For whirl flutter, three design revisions of the wing and pylon mount system are studied. The predicted frequencies and damping ratio of the wing modes show good agreements between the two analyses. Dymore tended to predict a slightly lower damping ratio as velocity increased for all three dynamic modes presented. Whirl flutter for the semi-span model was not present up to 500 knots for the latest design, well above the operating range of the X-57.

Hoover, Christian B.↗
NASA NTRS2018

Shake Test Results and Dynamic Characterization of the Large Rotor Test Apparatus in the NFAC 40- by 80-Foot Wind Tunnel

Prior to the full-scale wind tunnel test of the UH-60A Airloads rotor, a shake test was completed on the Large Rotor Test Apparatus. The goal of the shake test was to characterize the oscillatory response of the test rig and provide a dynamic calibration of the balance to permit accurate measurement of vibratory hub loads. This paper provides a summary of the shake test results, including balance, shaft bending gauge, and accelerometer measurements. Sensitivity to hub mass and angle of attack were investigated during the shake test. Hub mass was found to have an important impact on the vibratory forces and moments measured at the balance, especially near the UH-60A 4/rev frequency. Comparisons were made between the accelerometer data and an existing finite-element model, showing agreement on mode shapes, but not on natural frequencies. The results suggest that the shake test data can be used to correct in-plane loads measurements up to 10 Hz and normal loads up to 30 Hz.

Shake Test↗
NASA NTRS2019

Extraction of Dynamic Inflow Models for Coaxial and Tandem Rotors from CFD Simulations

The dynamic inflow coupling with rotor/body dynamics is crucial in the analysis of stability and control law design for helicopters. Over the past several decades, finite-state inflow models for single rotor configurations in hover, forward flight, and maneuver have developed (Ref.1-3). By capturing the interference effects between rotors, the extension of pressure potential finite state inflow model has promising result for coaxial rotor configuration (Ref.4-6). Recently, the focus of the dynamic inflow modeling has shifted to tandem rotor configurations (Ref.7, 8). The development of the dynamic inflow models for tandem rotor configuration still have some limitations due to the lack of knowledge of rotor-to-rotor interference, and rotor-wake interference. Experimental methods, and computational fluid dynamics methods are commonly used to understand the rotor performance and rotor airload variations, and measure or predict inflow velocity distributions at the rotor desk. The inflow distributions are subsequently used to improve the dynamic inflow models. Tandem rotor configurations have been studied experimentally and computationally for several decades (Ref.9-12). Sweet (Ref.10) observed that a tandem rotor with 76-percent-radius overlap required 14% more induced power at hovering condition, relative to an isolated rotor of equivalent disk area. Sweet also found that, above a shaft-to-shaft distance of 1.03 diameter, the performance of the tandem rotor was nearly the same as two isolated rotors. The objective of the present study is to apply computational fluid dynamics simulations of tandem rotors for the extraction of dynamic inflow models. The extended methodology is first validated by comparing the computed induced power against test data. Subsequently inflow distributions and wake structures are analyzed.

Extraction of Dynamic Inflow Models↗
NASA NTRS2020

Computational Study of NASA's Quadrotor Urban Air Taxi Concept

High-fidelity computational fluid dynamics simulations have been carried out in order to analyze NASA's quadrotor urban air taxi concept for urban air mobility, also know as on-demand mobility applications. High-order accurate schemes, dual-time stepping, and the delayed detached-eddy simulation model have been employed. The ow solver has been loosely coupled with a rotorcraft comprehensive analysis code. The vehicle simulated is a six-passenger quadrotor for air taxi operations. A study of power reduction as a function of the rear-rotor to front-rotors vertical separation has been performed, for a quad-rotor without the airframe, in cruise flight conditions. Then, the quadrotor without the airframe has been simulated in hover. The airloads and wake geometries are analyzed. To finish the study the complete quadrotor vehicle is presented. NASA's quadrotor air taxi concept is one of the many concepts being developed by NASA in support of aircraft development for vertical take-o and landing air taxi operations.

Ventura Diaz, Patricia↗
NASA NTRSDate not supplied

Practical Conceptual Design of Quieter Urban VTOL Aircraft

A toolchain and process for conceptual design of VTOL rotorcraft, employing low- and mid-fidelity tools is presented. The approach is capable of providing more quantitatively-credible trades between noise, size, and cost metrics than the methods commonly used for conceptual design. In addition to a general conceptual design tool, the approach employs comprehensive analysis for trim, blade motion, and airloads; these are then used by acoustic analysis software to develop source sound, propagate it, and calculate noise metrics. A key aspect of the approach is flexibility to assess varied aircraft types and different technologies and design features. Vehicles are sized using a representative Urban Air Mobility design mission. Demonstration cases are presented for a single main rotor helicopter, quadrotor, side-by-side helicopter, and lift+cruise aircraft. Noise metrics used for demonstration are the FAA/EASA certification Effective Perceived Noise Levels for takeoff, flyover, and approach. The concept aircraft in this study are shown to achieve reductions in noise relative the initial design points, with changes in mission performance and cost as a consequence. Many of the designs are predicted to be tens of EPNdB quieter in the certification metrics than existing helicopters.

Conceptual Design↗
NASA NTRSDate not supplied

High-Fidelity Simulations of a Quadrotor Vehicle for Urban Air Mobility

High-fidelity computational fluid dynamics simulations have been carried out to analyze NASA’s quadrotor air taxi concept for urban air mobility. High-order accurate schemes, dual-time stepping, and the delayed detached-eddy simulation model have been employed. The flow solver has been loosely coupled with the rotorcraft comprehensive analysis code. The vehicle simulated is a six-passenger quadrotor for air taxi operations. The quadrotor has been simulated in hover and cruise, with flight conditions representative of an air taxi mission. Initially, the quadcopter vehicle is analyzed using low-fidelity tools. Then, a complete analysis using high-fidelity simulations of the quadcopter is performed in conjunction with collective pitch control. Airloads, wake geometry, and performance are studied and compared. A comparison between isolated rotors and complete vehicle simulations is presented. NASA’s quadrotor is one of NASA’s concept vehicles designed in support of aircraft development for vertical take-off and landing air taxi operations.

ARMD↗
NASA NTRSDate not supplied

Structural Design and Aeromechanical Analysis of Unconventional Blades for Future Mars Rotorcraft

The structural design for rotor blades with thin, unconventional airfoils for Earth-based testing is obtained using three-Dimensional (3D) aeromechanical analysis. This analysis is in support of the NASA ROAMX project. The outer mold was provided by NASA, but the internal structural design was developed at the University of Maryland and is presented here, along with a thorough aeromechanical analysis. The main objectives are to verify the structural integrity of the design and understand the unique aeroelastic behavior of the non-conventional airfoils designed for low-Reynolds number and high-Mach number flow. Six different blade models are considered, with the pitch axis varied from quarter-chord to mid-chord to determine the effect of C.G. offset on natural frequencies, blade deformations, root loads, and 3D stresses. All six blade designs are first studied under rotation in pure vacuum, and significant reductions in root loads and 3D stresses are achieved by moving the pitch axis closer to mid-chord to reduce the C.G. offset. Based on the vacuum analysis, the blade design with the pitch axis at 40% chord is selected for aerodynamic analysis. The blade control load, airloads, deformations, and 3D stresses are studied for steady hover. Dynamic control load and dynamic 3D stresses are studied for unsteady hover achieved using cyclic. Significant elastic twist is observed due to the trapeze effect and propeller moment, affecting the spanwise distribution of aerodynamic loads on the blades. However, the effect of aerodynamic loads on 3D stresses and the blade control load is found to be minimum. The dynamic control load is found to increase significantly due to inertial coupling from the C.G. offset. The dynamic stresses also increase, although still have factors of safety greater than two for both tensile and compressive stress.

Structural Design↗
NASA NTRS2023

Structural Design and Aeromechanical Analysis of Unconventional Blades for Future Mars Rotorcraft

The structural design for rotor blades with thin, unconventional airfoils for Earth-based testing is obtained using three-Dimensional (3D) aeromechanical analysis in support of the NASA ROAMX project. The outer mold line was provided by NASA, but the internal structural design was developed at the University of Maryland and is presented here along with a thorough aeromechanical analysis. The main objectives are to verify the structural integrity of the design and understand the unique aeroelastic behavior of the non-conventional airfoils designed for low-Reynolds number and high subsonic Mach number. Four different blade models are considered, with the pitch axis varied from quarter-chord to mid-chord to determine the effect of C.G. offset on natural frequencies, blade deformations, root loads, and 3D stresses. First, torsional stability is calculated for each of the designs – especially important due to the low Lock number on Mars. All four blade designs are studied under rotation in vacuum, and significant reductions in root loads and 3D stresses are achieved by moving the pitch axis closer to mid-chord to reduce the C.G. offset. Based on the vacuum analysis, the blade design with the pitch axis at 40% chord is selected for aeromechanical analysis. The blade control load, airloads, deformations, and 3D stresses are studied for steady hover. Dynamic control load and dynamic 3D stresses are studied for unsteady hover achieved using cyclic. Significant elastic twist is observed due to the trapeze effect and propeller moment, affecting the spanwise distribution of aerodynamic loads on the blades. The dynamic control load is found to increase significantly due to inertial coupling from the C.G. offset. The dynamic stresses also increase, although still have factors of safety greater than two for both tensile and compressive stress.

Structural Design↗
NASA NTRS2023

High-Fidelity Simulations of a Tiltwing Vehicle for Urban Air Mobility

NASA is playing an important role in the development of the urban air mobility ecosystem by identifying key research areas and establishing a fleet of conceptual reference vehicles for urban air mobility applications. This paper delves deeper into the study of NASA’s six-passenger tiltwing air taxi aerodynamics using high-fidelity computational fluid dynamics simulations. NASA’s OVERFLOW flow solver has been loosely-coupled with the rotorcraft comprehensive analysis code CAMRAD II. Dual-time stepping, high-order accurate schemes, and the delayed detached-eddy simulation are employed. The tiltwing configuration is analyzed in airplane and helicopter mode, with flight conditions representative of an air taxi mission. Airloads, wake geometry, and performance are studied to identify the unique flow features of this configuration. NASA’s tiltwing vehicle is one of the conceptual designs intended to focus and guide NASA’s research activities in support of aircraft development for vertical take-off and landing air taxi operations.

RVLT↗
NASA NTRSDate not supplied

Fundamental Test of a Hovering Rotor: Comprehensive Measurements for CFD Validation

A model-scale hover test of a 4-bladed, 11.08-ft diameter rotor was recently completed inside the National Full-Scale Aerodynamics Complex 80- by 120-Foot Wind Tunnel test section. The primary objective of the test was to acquire key experimental data for a hovering rotor of sufficient quality and quantity to allow validation of state-of-the-art analysis codes. A comprehensive measurement set has been acquired, including rotor performance, blade airloads, flow transition locations, blade deflections, and wake geometry for a range of tip Mach numbers and collective settings. The present paper provides an overview of the test, including detailed descriptions of the hardware, instrumentation, and measurement systems. In addition, the specific test objectives, approach, and sample results are presented. The full test database, as well as detailed rotor geometry information, will ultimately be shared openly on a NASA-sponsored website to serve as a benchmark validation dataset.

Hover↗
NASA NTRSDate not supplied

A Comparison of Rotor Disk Modeling and Blade-Resolved CFD Simulations for NASA's Tiltwing Air Taxi

A multi-fidelity computational fluid dynamics analysis is carried out for NASA’s tiltwing air taxi concept operating in airplane and helicopter mode. High-fidelity simulations are computationally expensive due to individual rotor blade modeling in a time-dependent computational domain with rotating grids. The mid-fidelity rotor disk option, in its source term implementation, is explored as a more affordable alternative. Computations are performed with NASA’s OVERFLOW flow solver loosely-coupled with the comprehensive code CAMRAD II for appropriate rotor trim. Detailed comparisons are shown for the trim solution, airloads, wake geometry, and rotor performance. While the rotor disk model is able to capture the flow field with satisfactory agreement in airplane mode, it faces difficulties in helicopter mode due to the three-dimensional effects of the wake. Although this study is limited to a specific vehicle geometry, it is expected that the results are somewhat generalizable to the analysis of multi-rotor configurations.

ARMD↗