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At least 631 records · Page 35

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NASA NTRS1996

Solutions to Three-Dimensional Thin-Layer Navier-Stokes Equations in Rotating Coordinates for Flow Through Turbomachinery

The viscous, Navier-Stokes solver for turbomachinery applications, MSUTC has been modified to include the rotating frame formulation. The three-dimensional thin-layer Navier-Stokes equations have been cast in a rotating Cartesian frame enabling the freezing of grid motion. This also allows the flow-field associated with an isolated rotor to be viewed as a steady-state problem. Consequently, local time stepping can be used to accelerate convergence. The formulation is validated by running NASA's Rotor 67 as the test case. results are compared between the rotating frame code and the absolute frame code. The use of the rotating frame approach greatly enhances the performance of the code with respect to savings in computing time, without degradation of the solution.

Ghosh, Amrit Raj↗

NASA NTRS2001

An Experimental Evaluation of Generalized Predictive Control for Tiltrotor Aeroelastic Stability Augmentation in Airplane Mode of Flight

The results of a joint NASA/Army/Bell Helicopter Textron wind-tunnel test to assess the potential of Generalized Predictive Control (GPC) for actively controlling the swashplate of tiltrotor aircraft to enhance aeroelastic stability in the airplane mode of flight are presented. GPC is an adaptive time-domain predictive control method that uses a linear difference equation to describe the input-output relationship of the system and to design the controller. The test was conducted in the Langley Transonic Dynamics Tunnel using an unpowered 1/5-scale semispan aeroelastic model of the V-22 that was modified to incorporate a GPC-based multi-input multi-output control algorithm to individually control each of the three swashplate actuators. Wing responses were used for feedback. The GPC-based control system was highly effective in increasing the stability of the critical wing mode for all of the conditions tested, without measurable degradation of the damping in the other modes. The algorithm was also robust with respect to its performance in adjusting to rapid changes in both the rotor speed and the tunnel airspeed.

Kvaternik, Raymond G.↗

NASA NTRS2001

Airloads and Wake Geometry Calculations for an Isolated Tiltrotor Model in a Wind Tunnel

Comparisons of measured and calculated aerodynamic behavior of a tiltrotor model are presented. The test of the Tilt Rotor Aeroacoustic Model (TRAM) with a single, 0.25-scale V-22 rotor in the German-Dutch Wind Tunnel (DNW) provides an extensive set of aeroacoustic, performance, and structural loads data. The calculations were performed using the rotorcraft comprehensive analysis CAMRAD II. Presented are comparisons of measured and calculated performance for hover and helicopter mode operation, and airloads for helicopter mode. Calculated induced power, profile power, and wake geometry provide additional information about the aerodynamic behavior. An aerodynamic and wake model and calculation procedure that reflects the unique geometry and phenomena of tiltrotors has been developed. There are major differences between this model and the corresponding aerodynamic and wake model that has been established for helicopter rotors. In general, good correlation between measured and calculated performance and airloads behavior has been shown. Two aspects of the analysis that clearly need improvement are the stall delay model and the trailed vortex formation model.

Johnson, Wayne↗

NASA NTRS1984

Performance of a high-work low aspect ration turbine tested with a realistic inlet radial temperature profile

Experimental results are presented for a 0.767 scale model of the first stage of a two-stage turbine designed for a high by-pass ratio engine. The turbine was tested with both uniform inlet conditions and with an inlet radial temperature profile simulating engine conditions. The inlet temperature profile was essentially mixed-out in the rotor. There was also substantial underturning of the exit flow at the mean diameter. Both of these effects were attributed to strong secondary flows in the rotor blading. There were no significant differences in the stage performance with either inlet condition when differences in tip clearance were considered. Performance was very close to design intent in both cases.

Stabe, R. G.↗

NASA NTRS1984

Performance of a high-work low aspect ratio turbine tested with a realistic inlet radial temperature profile

Stabe, R. G.↗

NASA NTRS2012

Further Evaluation of Scaling Methods for Rotorcraft Icing

The paper will present experimental results from two recent icing tests in the NASA Glenn Icing Research Tunnel (IRT). The first test, conducted in February 2009, was to evaluate the current recommended scaling methods for fixed wing on representative rotor airfoils at fixed angle of attack. For this test, scaling was based on the modified Ruff method with scale velocity determined by constant Weber number and water film Weber number. Models were un-swept NACA 0012 wing sections. The reference model had a chord of 91.4 cm and scale model had a chord of 35.6 cm. Reference tests were conducted with velocity of 100 kt (52 m/s), droplet medium volume diameter (MVD) 195 m, and stagnation-point freezing fractions of 0.3 and 0.5 at angle of attack of 5deg and 7deg . It was shown that good ice shape scaling was achieved with constant Weber number for NACA 0012 airfoils with angle of attack up to 7deg . The second test, completed in May 2010, was primarily focused on obtaining transient and steady-state iced aerodynamics, ice accretion and shedding, and thermal icing validation data from an oscillating airfoil section over some selected ranges of icing conditions and blade assembly operational configurations. The model used was a 38.1-cm chord Sikorsky SC2110 airfoil section installed on an airfoil test apparatus with oscillating capability in the IRT. For two test conditions, size and condition scaling were performed. It was shown that good ice shape scaling was achieved for SC2110 airfoil at dynamic pitching motion. The data obtained will be applicable for future main rotor blade and tail rotor blade applications.

Tsao, Jen-Ching↗

NASA NTRS1996

Predicted Turbine Heat Transfer for a Range of Test Conditions

Comparisons are shown between predictions and experimental data for blade and endwall heat transfer. The comparisons of computational domain parisons are given for both vane and rotor geometries over an extensive range of Reynolds and Mach numbers. Comparisons are made with experimental data from a variety of sources. A number of turbulence models are available for predicting blade surface heat transfer, as well as aerodynamic performance. The results of an investigation to determine the turbulence model which gives the best agreement with experimental data over a wide range of test conditions are presented.

Boyle, R. J.↗

NASA NTRS1980

A comprehensive analytical model of rotorcraft aerodynamics and dynamics. Part 3: Program manual

The computer program for a comprehensive analytical model of rotorcraft aerodynamics and dynamics is described. This analysis is designed to calculate rotor performance, loads, and noise; the helicopter vibration and gust response; the flight dynamics and handling qualities; and the system aeroelastic stability. The analysis is a combination of structural, inertial, and aerodynamic models that is applicable to a wide range of problems and a wide class of vehicles. The analysis is intended for use in the design, testing, and evaluation of rotors and rotorcraft and to be a basis for further development of rotary wing theories.

Johnson, W.↗

DOE OSTI2024

Accelerated Lifetime Testing of Main Shaft Seals for Tidal Turbine Rotors

This document will briefly discuss the observations and results from an NREL conducted accelerated lifetime testing of the main shaft seal for the Verdant Power fifth generation Gen5 underwater Tidal Energy Converter (TEC) turbine, which successfully performed at the RITE project in 2020-2021. In order to evaluate a 5-year Service Interval ( SI) for this component, testing at NREL operated the main shaft seal nearly continuously for over 135 (text says 130 days on page 5 and 125 days on page 7 and 137 days on page 11) days at a rotational velocity of 160 rpm while the test stand recorded water pressure, barrier fluid pressure, temperature, and number of cycles., representing ~ 40% of the SI. An additional separate test was conducted to measure the aging behavior of the rubber drive rings. The water pressure reservoir was held constant as 29 psi. Barrier fluid pressure remained relatively constant throughout the duration of the test but was seen to sink to as low as 10.1 psi. No barrier fluid leakage was observed throughout the test. A sudden failure occurred within the seal after the power to test machine was interrupted for a scheduled building maintenance procedure. Upon restarting, the main shaft seal lost all ability to prevent water ingress. The exact cause is not known but is believed to be either a seal assembly issue or a change in the alignment of the seal components during or following the power outage. Following seal disassembly, significant wear was seen on one of the graphite sealing rings. Based on these results it is recommended that a follow-on TEAMER be conducted to rectify protocol and assembly issues to further evaluate SI of this component. The support and participation of Verdant Power Inc, Dovetail Solutions LLC and Garlock Manufacturing Inc were instrumental in understanding the results. NREL thanks them for their significant effort.

13 HYDRO ENERGY↗

NASA NTRS1980

Wind-tunnel tests of the XV-15 tilt rotor aircraft

The XV-15 aircraft was tested in the Ames 40 by 80 Foot Wind Tunnel for preliminary evaluation of aerodynamic and aeroelastic characteristics prior to flight. The tests were undertaken to investigate the aircraft performance, stability, control and structural loads for flight modes from helicopter through transition and airplane mode up to the tunnel capability of 170 knots. Results from these tests are presented.

Weiberg, J. A.↗

NASA NTRS1979

Design and development of a motion compensator for the RSRA main rotor control

The RSRA, an experimental helicopter, is equipped with an active isolation system that allows the transmission to move relative to the fuselage. The purpose of the motion compensator is to prevent these motions from introducing unwanted signals to the main rotor control. A motion compensator concept was developed that has six-degree-of-freedom capability. The mechanism was implemented on RSRA and its performance verified by ground and flight tests.

Jeffrey, P.↗

NASA NTRS1984

Measured and calculated inplane stability characteristics for an advanced bearingless main rotor

A program of experimental and analytical research has been performed to demonstrate the effects of rotor and fuselage design parameters on rotor in-plane stability, including aeromechanical stability. The experimental data were obtained from hover and wind-tunnel tests of a scaled advanced bearingless main rotor model. Both isolated-rotor and free-hub conditions were tested. Test parameters included blade built-in cone and sweep angles; rotor inplane structural stiffness and damping; pitch link stiffness and location; and fuselage natural frequency, damping, and inertia. The results show that rotor blade structural damping is one of the most influential design parameters in obtaining acceptable aeromechanical stability margins. Other parameters, such as blade cone angle, pitch link location (rotor delta 3) and anisotropic hub damper configurations, may be used to improve stability margins, but their individual effects are subtle.

Weller, W. H.↗

NASA NTRS2002

Acoustic Aspects of Active-Twist Rotor Control

The use of an Active Twist Rotor system to provide both vibration reduction and performance enhancement has been explored in recent analytical and experimental studies. Effects of active-twist control on rotor noise, however, had not been determined. During a recent wind tunnel test of an active-twist rotor system, a set of acoustic measurements were obtained to assess the effects of active-twist control on noise produced by the rotor, especially blade-vortex interaction (BVI) noise. It was found that for rotor operating conditions where BVI noise is dominant, active-twist control provided a reduction in BVI noise level. This BVI noise reduction was almost, but not quite, as large as that obtained in a similar test using HHC. However, vibration levels were usually adversely affected at operating conditions favoring minimum BVI noise. Conversely, operating conditions favoring minimum vibration levels affected BVI noise levels, but not always adversely.

Booth, Earl R., Jr.↗

NASA NTRS2007

Experimental Performance Evaluation of a High Speed Permanent Magnet Synchronous Motor and Drive for a Flywheel Application at Different Frequencies

This paper presents the results of an experimental performance characterization study of a high speed, permanent magnet motor/generator (M/G) and drive applied to a flywheel module. Unlike the conventional electric machine the flywheel M/G is not a separated unit; its stator and rotor are integrated into a flywheel assembly. The M/G rotor is mounted on a flywheel rotor, which is magnetically levitated and sealed within a vacuum chamber during the operation. Thus, it is not possible to test the M/G using direct load measurements with a dynamometer and torque transducer. Accordingly, a new in-situ testing method had to be developed. The paper describes a new flywheel M/G and drive performance evaluation technique, which allows the estimation of the losses, efficiency and power quality of the flywheel high speed permanent magnet M/G, while working in vacuum, over wide frequency and torque ranges. This method does not require any hardware modification nor any special addition to the test rig. This new measurement technique is useful for high-speed applications, when applying an external load is technically difficult.

Nagorny, Aleksandr S.↗

NASA NTRS2016

Compressible 2D Flow Field Interaction of Two Contra-Rotating Blades

The blades of coaxial, contra-rotating rotor systems cross each other in close proximity and at high relative speeds. This crossing event is a potential source of noise and severe blade loads. Effects of compressibility can aggravate the interaction and significantly alter the pressure field signature and phase relationships. A 2-D analysis of this phenomenon is performed by simulating two airfoils passing each other at specified speeds and vertical separation distances. Several test cases spanning a relevant range of Reynolds numbers, angles of attack, and relative Mach number are considered. The Mach number is varied to simulate the radial variation of velocity from the root to tip of a rotor blade to capture the pressure signature, lift, and drag of the airfoils. The velocity and pressure distributions on the airfoils, and in the space between the airfoils are computed before, at, and after airfoil crossing. The variations of lift and drag coefficients through the interaction are captured. The upper airfoil experiences an increase in lift followed by a very sharp drop in lift during the interaction. When relative Mach numbers are transonic, the region of interaction is greatly extended, with shock interactions occurring. The results show the complex nature of the aerodynamic and fluid dynamic impulses generated by blade-blade interactions, with implications to aeroelastic loads and aeroacoustic sources.

Barbely, Natasha L.↗

NASA NTRS2002

Rocket Engine Turbine Blade Surface Pressure Distributions Experiment and Computations

Understanding the unsteady aspects of turbine rotor flow fields is critical to successful future turbine designs. A technology program was conducted at NASA's Marshall Space Flight Center to increase the understanding of unsteady environments for rocket engine turbines. The experimental program involved instrumenting turbine rotor blades with miniature surface mounted high frequency response pressure transducers. The turbine model was then tested to measure the unsteady pressures on the rotor blades. The data obtained from the experimental program is unique in two respects. First, much more unsteady data was obtained (several minutes per set point) than has been possible in the past. Also, an extensive steady performance database existed for the turbine model. This allowed an evaluation of the effect of the on-blade instrumentation on the turbine's performance. A three-dimensional unsteady Navier-Stokes analysis was also used to blindly predict the unsteady flow field in the turbine at the design operating conditions and at +15 degrees relative incidence to the first-stage rotor. The predicted time-averaged and unsteady pressure distributions show good agreement with the experimental data. This unique data set, the lessons learned for acquiring this type of data, and the improvements made to the data analysis and prediction tools are contributing significantly to current Space Launch Initiative turbine airflow test and blade surface pressure prediction efforts.

Hudson, Susan T.↗

NASA NTRS1999

Multi-Body Analysis of the 1/5 Scale Wind Tunnel Model of the V-22 Tiltrotor

The paper presents a multi-body analysis of the 1/5 scale wind tunnel model of the V-22 tiltrotor, the Wing and Rotor Aeroelastic Testing System (WRATS), currently tested at NASA Langley Research Center. An original multi-body formulation has been developed at the Dipartimento di Ingegneria Aerospaziale of the Politecnico di Milano, Italy. It is based on the direct writing of the equilibrium equations of independent rigid bodies, connected by kinematic constraints that result in the addition of algebraic constraint equations, and by dynamic constraints, that directly contribute to the equilibrium equations. The formulation has been extended to the simultaneous solution of interdisciplinary problems by modeling electric and hydraulic networks, for aeroservoelastic problems. The code has been tailored to the modeling of rotorcrafts while preserving a complete generality. A family of aerodynamic elements has been introduced to model high aspect aerodynamic surfaces, based on the strip theory, with quasi-steady aerodynamic coefficients, compressibility, post-stall interpolation of experimental data, dynamic stall modeling, and radial flow drag. Different models for the induced velocity of the rotor can be used, from uniform velocity to dynamic in flow. A complete dynamic and aeroelastic analysis of the model of the V-22 tiltrotor has been performed, to assess the validity of the formulation and to exploit the unique features of multi-body analysis with respect to conventional comprehensive rotorcraft codes; These are the ability to model the exact kinematics of mechanical systems, and the possibility to simulate unusual maneuvers and unusual flight conditions, that are particular to the tiltrotor, e.g. the conversion maneuver. A complete modal validation of the analytical model has been performed, to assess the ability to reproduce the correct dynamics of the system with a relatively coarse beam model of the semispan wing, pylon and rotor. Particular care has been used to model the kinematics of the gimbal joint, that characterizes the rotor hub, and of the control system, consisting in the entire swashplate mechanism. The kinematics of the fixed and the rotating plates have been modeled, with variable length control links used to input the controls, the rotating flexible links, the pitch horns and the pitch bearings. The investigations took advantage of concurring wind tunnel test runs, that were performed in August 1998, and allowed the acquisition of data specific to the multi-body analysis.

Ghiringhelli, G. L.↗

DOE OSTI2023

Additive Manufacturing Case Study Test Report

Sandia National Labs collaborated with Oak Ridge National Laboratory on a case study examining additive manufacturing opportunities for Geothermal applications. The study focused on designing components with improved performance characteristics that cannot be fabricated conventionally. A rotor for a downhole motor was chosen based on the potential for improving its rotational dynamics. Topology optimization was used as a design method to reduce the rotational inertia of the part while preserving sufficient rotational stiffness to transmit the torque required for the drilling application. The optimization resulted in a nearly 50% reduction in polar moment of inertia while maintaining other desired performance characteristics. The design developed using the topology optimization approach was fabricated using additive manufacturing and cannot be fabricated conventionally.

15 GEOTHERMAL ENERGY↗