Search NASA⌕ Search

SEARCH · Search NASA

Results for “Rotor Aerodynamics”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1987

Ground and air resonance of bearingless rotors in hover

A finite element formulation is used to investigate ground and air resistence in hover for a bearingless rotor. Aerodynamic forces are studied using quasi-steady strip theory, and unsteady aerodynamic effects are introduced through an inflow dynamics model. Reasonable correlation was found between predicted ground and air resonance results and data obtained from measurements using a 1/8th Froude-scaled dynamic model. Systematic parametric studies of the effects of various design parameters were performed, and lag frequency was found to significantly influence ground resonance stability, whereas pitch-lag coupling, blade sweep and pitch link stiffness had powerful effects on air resonance stability.

Jang, Jinseok↗
NASA NTRS1988

Comprehensive rotorcraft analysis methods

The development and application of comprehensive rotorcraft analysis methods in the field of rotorcraft technology are described. These large scale analyses and the resulting computer programs are intended to treat the complex aeromechanical phenomena that describe the behavior of rotorcraft. They may be used to predict rotor aerodynamics, acoustic, performance, stability and control, handling qualities, loads and vibrations, structures, dynamics, and aeroelastic stability characteristics for a variety of applications including research, preliminary and detail design, and evaluation and treatment of field problems. The principal comprehensive methods developed or under development in recent years and generally available to the rotorcraft community because of US Army Aviation Research and Technology Activity (ARTA) sponsorship of all or part of the software systems are the Rotorcraft Flight Simulation (C81), Dynamic System Coupler (DYSCO), Coupled Rotor/Airframe Vibration Analysis Program (SIMVIB), Comprehensive Analytical Model of Rotorcraft Aerodynamics and Dynamics (CAMRAD), General Rotorcraft Aeromechanical Stability Program (GRASP), and Second Generation Comprehensive Helicopter Analysis System (2GCHAS).

Stephens, Wendell B.↗
NASA NTRS1988

Recent Sikorsky R and D progress

The recent activities and progress in four specific areas of Sikorsky's research and development program are summarized. Since the beginning of the S-76 design in 1974, Sikorsky has been aggressively developing the technology for using composite materials in helicopter design. Four specific topics are covered: advanced cockpit/controller efforts, fly-by-wire controls on RSRA/X-Wing, vibration control via higher harmonic control, and main rotor aerodynamic improvements.

Source record↗
NASA NTRS1995

Effect of wake structure on blade-vortex interaction phenomena: Acoustic prediction and validation

During the Higher Harmonic Control Aeroacoustic Rotor Test, extensive measurements of the rotor aerodynamics, the far-field acoustics, the wake geometry, and the blade motion for powered, descent, flight conditions were made. These measurements have been used to validate and improve the prediction of blade-vortex interaction (BVI) noise. The improvements made to the BVI modeling after the evaluation of the test data are discussed. The effects of these improvements on the acoustic-pressure predictions are shown. These improvements include restructuring the wake, modifying the core size, incorporating the measured blade motion into the calculations, and attempting to improve the dynamic blade response. A comparison of four different implementations of the Ffowcs Williams and Hawkings equation is presented. A common set of aerodynamic input has been used for this comparison.

Gallman, Judith M.↗
NASA NTRS1959

A Wind-Tunnel Investigation of Rotor Behavior Under Extreme Operating Conditions with a Description of Blade Oscillations Attributed to Pitch-Lag Coupling

A wind-tunnel investigation was made to study the behavior of a model helicopter rotor under extreme operating conditions. A 1/8-scale model of the front rotor of a tandem helicopter was built and tested to obtaining blade motion and rotor aerodynamic characteristics for conditions that could be encountered in high-speed pullout maneuvers. The data are presented without analysis. A description is given in an appendix of blade oscillations that were experienced during the course of the investigation and of the part that blade pitch-lag coupling played in contributing to the oscillatory condition.

McKee, John W.↗
NASA NTRS2009

UH-60 Airloads Program Tutorial

From the fall of 1993 to late winter of 1994, NASA Ames and the U.S. Army flew a flight test program using a UH-60A helicopter with extensive instrumentation on the rotor and blades, including 242 pressure transducers. Over this period, approximately 30 flights were made, and data were obtained in level flight, maneuver, ascents, and descents. Coordinated acoustic measurements were obtained with a ground-acoustic array in cooperation with NASA Langley, and in-flight acoustic measurements with a YO-3A aircraft. NASA has sponsored the creation of a "tutorial' which covers the depth and breadth of the flight test program with a mixture of text and graphics. The primary purpose of this tutorial is to introduce the student to what is known about rotor aerodynamics based on the UH-60A measurements. The tutorial will also be useful to anyone interested in helicopters who would like to have more detailed knowledge about helicopter aerodynamics.

Bousman, William G.↗
NASA NTRS2010

Aeroelastic Computations of a Compressor Stage Using the Harmonic Balance Method

The aeroelastic characteristics of a compressor stage were analyzed using a computational fluid dynamic (CFD) solver that uses the harmonic balance method to solve the governing equations. The three dimensional solver models the unsteady flow field due to blade vibration using the Reynolds-Averaged Navier-Stokes equations. The formulation enables the study of the effect of blade row interaction through the inclusion of coupling modes between blade rows. It also enables the study of nonlinear effects of high amplitude blade vibration by the inclusion of higher harmonics of the fundamental blade vibration frequency. In the present work, the solver is applied to study in detail the aeroelastic characteristics of a transonic compressor stage. Various parameters were included in the study: number of coupling modes, blade row axial spacing, and operating speeds. Only the first vibration mode is considered with amplitude of oscillation in the linear range. Both aeroelastic stability (flutter) of rotor blade and unsteady loading on the stator are calculated. The study showed that for the stage considered, the rotor aerodynamic damping is not influenced by the presence of the stator even when the axial spacing is reduced by nearly 25 percent. However, the study showed that blade row interaction effects become important for the unsteady loading on the stator when the axial spacing is reduced by the same amount.

Reddy, T. S. R.↗
NASA NTRS2020

Recent Efforts Enabling Martian Rotorcraft Missions

The Mars Helicopter (MH), launching as a part of the Mars 2020 mission, will begin a new era of planetary exploration. Mars research has historically been conducted through landers, rovers, and satellites. As both government and private industries prepare for human exploration of the Martian surface within two decades, more in depth knowledge of what awaits on the surface is critical. Planetary aerial vehicles increase the range of terrain that can be examined, compared to traditional landers and rovers and have more near surface capability than orbiters. The Jet Propulsion Laboratory (JPL) and NASA Ames are currently exploring possibilities for a Mars Science Helicopter (MSH), a second-generation Mars rotorcraft with the capability of conducting science investigations independently of a lander or rover (although this type of vehicle could also be used assist rovers or landers in future missions). Preliminary designs of coaxial-helicopter and hexacopter configurations have targeted the minimum capability of lifting a payload in the range of two to three kilograms with an overall vehicle mass of approximately twenty kilograms. These MSH designs’ sizes are constrained by the aeroshell dimensions(currently focused on employing legacy Pathfinder or MSL aeroshells), rather than vehicle structural or aeroperformance limitations. Feasibility of the MSH configurations has been investigated considering packaging/deployment, rotor aerodynamics, and structural analysis studies. Initial findings suggest not only the overall feasibility of MSH configurations but also indicate that improvements up to 11.1 times increase in range or 1.3 times increase in hover time might be achievable, even with an additional science payload, compared to the current design of the MH.

Withrow-Maser, Shannah↗
NASA NTRSDate not supplied

Modeling Shed Vorticity from Coaxial Blade Interactions

Coaxial counter-rotating rotors operate in a flowfield different from single rotors. Aerodynamic interactions such as blade crossing and shed vorticity result in potential sources of noise and impulsive blade loads. In previous research, the authors simulated two trains of airfoils traveling in opposite directions for specified speeds, airfoil thickness and vertical separation distances, using the compressible Navier-Stokes solver OVERFLOW. Previously, the effects of circulation, thickness, and compressibility were explored. This work continues the previous research by exploring downwash and shed vorticity effects. These phenomena are explored by simulating two trains of eight airfoils vertically separated traveling in opposite directions. The effects of downwash are simulated by introducing a vertical flow. Vorticity shed from the upper train of airfoils is shown to interact with the lower train, affecting the loading on the lower airfoils. Furthermore, viscid and inviscid calculations are performed to further understand the behavior of shed vorticity.

Natasha L Schatzman↗
NASA NTRS2023

Blade-Wake Interaction Noise for Small Hovering Rotors, Part I: Characterization Study

This work illustrates the use of artificial neural network modeling to study and characterize broadband blade-wake interaction noise from hovering small unmanned aerial systems rotors subject to varying airfoil geometries, rotor geometries, and operating conditions. Design of experiments was used to create input feature spaces, and a high-fidelity strategy was implemented at the discrete data points defined by the input feature spaces to design airfoils and rotor blades, predict the unsteady rotor aerodynamics and aeroacoustics, and isolate the blade-wake interaction noise from the acoustic broadband noise. A metric for the blade-wake interaction noise was developed, and the ANOPP2 Artificial Neural Network Tool was used to identify an optimal prediction model for the nonlinear relationship between the input features and the metric for blade-wake interaction noise. This optimal artificial neural network was then validated over training/test data and exhibited prediction accuracy over 91% for data previously unseen by the model. A sensitivity analysis was conducted, which showed that input features that directly modify the thrust coefficient had a dominant effect over blade-wake interaction noise. The optimal prediction model along with aerodynamic simulations were used to further study the effect of varying input features on blade-wake interaction noise, and three types of blade-wake interaction noise were identified

Christopher S. Thurman↗
NASA NTRS1974

Aerodynamic design of a rotor blade for minimum noise radiation

An analysis of the aerodynamic design of a hovering rotor blade for obtaining minimum aerodynamic rotor noise has been carried out. In this analysis, which is based on both acoustical and aerodynamic considerations, attention is given only to the rotational noise due to the pressure fluctuations on the blade surfaces. The lift distribution obtained in this analysis has different characteristics from those of the conventional distribution. The present distribution shows negative lift values over a quarter of the span from the blade tip, and a maximum lift at about the midspan. Results are presented to show that the noise field is considerably affected by the shape of the lift distribution along the blade and that noise reduction of about 5 dB may be obtained by designing the rotor blade to yield minimum noise.

Karamcheti, K.↗
NASA NTRS1977

An investigation of rotor noise generation by aerodynamic disturbance

An open rotor was considered as a process for converting an unsteady velocity inflow into sound radiation. With the aid of crude assumptions, aero-acoustic transfer functions were defined theoretically for both discrete frequency and broad band noise. A study of the validity of these transfer functions yielded results which show good agreement at discrete frequencies though slightly less good for broad band noise. Agreement in both cases holds over three or more decades of the relevant parameters. A rotating hot wire anemometry system consisting of a single hot wire probe mounted in the nose cone of the rotor was used to quantify fluctuations in the airflow onto a single rotor blade for the transfer function results. Further theoretical analysis revealed that the sound field can be expressed in terms of blade-to-blade correlations in the airflow, and results from two probes rotating simultaneously were modelled mathematically and inserted in the theory. Preliminary results snow encouraging agreement with experimental data.

Whitfield, C. E.↗
NASA NTRS1988

Effect of aerodynamic detuning on supersonic rotor discrete frequency noise generation

A mathematical model was developed to predict the effect of alternate blade circumferential aerodynamic detuning on the discrete frequency noise generation of a supersonic rotor. Aerodynamic detuning was shown to have a small beneficial effect on the noise generation for reduced frequencies less than 3. For reduced frequencies greater than 3, however, the aerodynamic detuning either increased or decreased the noise generated, depending on the value of the reduced frequency.

Hoyniak, D.↗
NASA NTRS1990

Estimation of UH-60 blade aerodynamic loads and rotor impedance using generalized strain pattern/Kalman filter approach

The purpose of the study is to develop and verify a methodology capable of predicting the vibration levels and estimating the aerodynamic loads and rotor impedance of a rotorcraft blade. Simulated flight test data is generated, blade airloads and elastic hub motions are estimated from the simulated data through the use of the Kalman filter/smoother, simulation upgrading and parameter identification are performed, and the ability to identify rotor impedance from a simulation by isolating the rotor model and providing a prescribed motion for the hub as rotor excitation is demonstrated. It is pointed out that the statistical estimation procedure utilized in the proposed methodology minimizes the impact of sensor noise, truncation error, and instrumentation bias on the results.

Bruhis, Ofer↗
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 NTRS1985

Forced response analysis of an aerodynamically detuned supersonic turbomachine rotor

High performance aircraft-engine fan and compressor blades are vulnerable to aerodynamically forced vibrations generated by inlet flow distortions due to wakes from upstream blade and vane rows, atmospheric gusts, and maldistributions in inlet ducts. In this report, an analysis is developed to predict the flow-induced forced response of an aerodynamically detuned rotor operating in a supersonic flow with a subsonic axial component. The aerodynamic detuning is achieved by alternating the circumferential spacing of adjacent rotor blades. The total unsteady aerodynamic loading acting on the blading, as a result of the convection of the transverse gust past the airfoil cascade and the resulting motion of the cascade, is developed in terms of influence coefficients. This analysis is used to investigate the effect of aerodynamic detuning on the forced response of a 12-blade rotor, with Verdon's Cascade B flow geometry as a uniformly spaced baseline configuration. The results of this study indicate that, for forward traveling wave gust excitations, aerodynamic detuning is very beneficial, resulting in significantly decreased maximum-amplitude blade responses for many interblade phase angles.

Hoyniak, D.↗
NASA NTRS1981

The influence of unsteady aerodynamics on hingeless rotor ground resonance

Calculations of the model frequency and damping for a hingeless rotor on a gimballed support in hover are compared with measured results for two configurations (differing in blade flap stiffness). Good correlation is obtaned when an inflow dynamics model is used to account for the influence of the unsteady aerodynamics. The effect of the unsteady aerodynamics is significant for this rotor system. The inflow dynamics model introduces additional states corresponding to perturbations of the wake-induced velocity at the rotor disk. The calculations confirm the experimental observation that the inflow mode introduced by these additional states is measurable for one configuration but not for the other.

Johnson, W.↗
NASA NTRS1991

Aerodynamic detuning for aeroelastic control of stability and forced response of supersonic rotors

An unsteady aerodynamic model is developed to analyze flutter and aerodynamically forced response of aerodynamically detuned supersonic axial flow rotors. Alternate blade aerodynamic detuning is considered, accomplished by alternating the circumferential spacing of adjacent blades as small solidity variations which do not have a dominant effect on the steady performance of a rotor. The unsteady aerodynamics are determined by developing an influence coefficient technique which is appropriate for both aerodynamically tuned and detuned rotor configurations. Torsion mode rotor stability and aerodynamically forced response are then analyzed with this unsteady aerodynamic model by combining it with a single-degree-of-freedom structural model. The effects of this detuning on the flutter and forced response characteristics of supersonic axial flow rotors is then demonstrated by considering baseline twelve bladed rotors.

Spara, Karen M.↗