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At least 145 records · Page 8

All sources NASA NTRS DOE OSTI

NASA NTRS1999

Aerodynamic Analysis of Multistage Turbomachinery Flows in Support of Aerodynamic Design

This paper summarizes the state of 3D CFD based models of the time average flow field within axial flow multistage turbomachines. Emphasis is placed on models which are compatible with the industrial design environment and those models which offer the potential of providing credible results at both design and off-design operating conditions. The need to develop models which are free of aerodynamic input from semi-empirical design systems is stressed. The accuracy of such models is shown to be dependent upon their ability to account for the unsteady flow environment in multistage turbomachinery. The relevant flow physics associated with some of the unsteady flow processes present in axial flow multistage machinery are presented along with procedures which can be used to account for them in 3D CFD simulations. Sample results are presented for both axial flow compressors and axial flow turbines which help to illustrate the enhanced predictive capabilities afforded by including these procedures in 3D CFD simulations. Finally, suggestions are given for future work on the development of time average flow models.

Adamczyk, John J.↗

NASA NTRS2006

Observations of Shock Diffusion and Interactions in Supersonic Freestreams with Counterflowing Jets

One of the technical challenges in long-duration space exploration and interplanetary missions is controlled entry and re-entry into planetary and Earth atmospheres, which requires the dissipation of considerable kinetic energy as the spacecraft decelerates and penetrates the atmosphere. Efficient heat load management of stagnation points and acreage heating remains a technological challenge and poses significant risk, particularly for human missions. An innovative approach using active flow control concept is proposed to significantly modify the external flow field about the spacecraft in planetary atmospheric entry and re-entry in order to mitigate the harsh aerothermal environments, and significantly weaken and disperse the shock-wave system to reduce aerothermal loads and wave drag, as well as improving aerodynamic performance. To explore the potential benefits of this approach, we conducted fundamental experiments in a trisonic blow down wind tunnel to investigate the effects of counterflowing sonic and supersonic jets against supersonic freestreams to gain a better understanding of the flow physics of the interactions of the opposing flows and the resulting shock structure.

Daso, Endwell O.↗

NASA NTRS2008

Ares I-X Flight Test Vehicle Similitude to the Ares I Crew Launch Vehicle

The Ares I-X Flight Test Vehicle is the first in a series of flight test vehicles that will take the Ares I Crew Launch Vehicle design from development to operational capability. The test flight is scheduled for April 2009, relatively early in the Ares I design process so that data obtained from the flight can impact the design of Ares I before its Critical Design Review. Because of the short time frame (relative to new launch vehicle development) before the Ares I-X flight, decisions about the flight test vehicle design had to be made in order to complete analysis and testing in time to manufacture the Ares I-X vehicle hardware elements. This paper describes the similarities and differences between the Ares I-X Flight Test Vehicle and the Ares I Crew Launch Vehicle. Areas of comparison include the outer mold line geometry, aerosciences, trajectory, structural modes, flight control architecture, separation sequence, and relevant element differences. Most of the outer mold line differences present between Ares I and Ares I-X are minor and will not have a significant effect on overall vehicle performance. The most significant impacts are related to the geometric differences in Orion Crew Exploration Vehicle at the forward end of the stack. These physical differences will cause differences in the flow physics in these areas. Even with these differences, the Ares I-X flight test is poised to meet all five primary objectives and six secondary objectives. Knowledge of what the Ares I-X flight test will provide in similitude to Ares I as well as what the test will not provide is important in the continued execution of the Ares I-X mission leading to its flight and the continued design and development of Ares I.

Huebner, Lawrence D.↗

NASA NTRS2009

Ares I-X Flight Test Vehicle Similitude to the Ares I Crew Launch Vehicle

The Ares I-X Flight Test Vehicle is the first in a series of flight test vehicles that will take the Ares I Crew Launch Vehicle design from development to operational capability. Ares I-X is scheduled for a 2009 flight date, early enough in the Ares I design and development process so that data obtained from the flight can impact the design of Ares I before its Critical Design Review. Decisions on Ares I-X scope, flight test objectives, and FTV fidelity were made prior to the Ares I systems requirements being baselined. This was necessary in order to achieve a development flight test to impact the Ares I design. Differences between the Ares I-X and the Ares I configurations are artifacts of formulating this experimental project at an early stage and the natural maturation of the Ares I design process. This paper describes the similarities and differences between the Ares I-X Flight Test Vehicle and the Ares I Crew Launch Vehicle. Areas of comparison include the outer mold line geometry, aerosciences, trajectory, structural modes, flight control architecture, separation sequence, and relevant element differences. Most of the outer mold line differences present between Ares I and Ares I-X are minor and will not have a significant effect on overall vehicle performance. The most significant impacts are related to the geometric differences in Orion Crew Exploration Vehicle at the forward end of the stack. These physical differences will cause differences in the flow physics in these areas. Even with these differences, the Ares I-X flight test is poised to meet all five primary objectives and six secondary objectives. Knowledge of what the Ares I-X flight test will provide in similitude to Ares I - as well as what the test will not provide - is important in the continued execution of the Ares I-X mission leading to its flight and the continued design and development of Ares I.

Huebner, Lawrence D.↗

NASA NTRS2011

Inlet Flow Control and Prediction Technologies for Embedded Propulsion Systems

Fail-safe, hybrid, flow control (HFC) is a promising technology for meeting high-speed cruise efficiency, low-noise signature, and reduced fuel-burn goals for future, Hybrid-Wing-Body (HWB) aircraft with embedded engines. This report details the development of HFC technology that enables improved inlet performance in HWB vehicles with highly integrated inlets and embedded engines without adversely affecting vehicle performance. In addition, new test techniques for evaluating Boundary-Layer-Ingesting (BLI)-inlet flow-control technologies developed and demonstrated through this program are documented, including the ability to generate a BLI-like inlet-entrance flow in a direct-connect, wind-tunnel facility, as well as, the use of D-optimal, statistically designed experiments to optimize test efficiency and enable interpretation of results. Validated improvements in numerical analysis tools and methods accomplished through this program are also documented, including Reynolds-Averaged Navier-Stokes CFD simulations of steady-state flow physics for baseline, BLI-inlet diffuser flow, as well as, that created by flow-control devices. Finally, numerical methods were employed in a ground-breaking attempt to directly simulate dynamic distortion. The advances in inlet technologies and prediction tools will help to meet and exceed "N+2" project goals for future HWB aircraft.

McMillan, Michelle L.↗

NASA NTRS2014

Jet-Surface Interaction Test: Flow Measurements Results

Modern aircraft design often puts the engine exhaust in close proximity to the airframe surfaces. Aircraft noise prediction tools must continue to develop in order to meet the challenges these aircraft present. The Jet-Surface Interaction Tests have been conducted to provide a comprehensive quality set of experimental data suitable for development and validation of these exhaust noise prediction methods. Flow measurements have been acquired using streamwise and cross-stream particle image velocimetry (PIV) and fluctuating surface pressure data acquired using flush mounted pressure transducers near the surface trailing edge. These data combined with previously reported far-field and phased array noise measurements represent the first step toward the experimental data base. These flow data are particularly applicable to development of noise prediction methods which rely on computational fluid dynamics to uncover the flow physics. A representative sample of the large flow data set acquired is presented here to show how a surface near a jet affects the turbulent kinetic energy in the plume, the spatial relationship between the jet plume and surface needed to generate surface trailing-edge noise, and differences between heated and unheated jet flows with respect to surfaces.

Flow↗

NASA NTRSDate not supplied

Flow Boiling and Condensation Experiment: Flow Boiling in a Rectangular Channel with Subcooled Inlet Conditions in Microgravity

Two-phase thermal management subsystems that take advantage of both the sensible and latent heat of a working fluid can potentially yield significant enhancements in overall performance by adopting heat transfer processes that are based on phase transition like boiling and condensation. Performance of terrestrial two-phase flow systems may be predictable because the hydrodynamic and body forces are understood, however, in microgravity, which is predominant during planetary space travel, forces that are masked by the strong body force on Earth (gravitational or buoyancy force) reappear with different magnitude and influence. The need arose for a facility that provides for two-phase flow with phase transition testing in microgravity. The Flow Boiling and Condensation Experiment (FBCE) is a facility that was launched to the International Space Station in August of 2021 and is in operation since February of 2022. This facility enables investigators to perform two-phase flow and phase transition research in flow boiling and condensation. Along with the test module that is experiment specific, the FBCE system consists of the fluid, avionics, and software subsystems. Currently two test modules, namely, the Flow Boiling Module (FBM) and the Condensation Module for Heat Transfer (CM-HT) are available. A third module, the Transfer Line test Module (TL) is being developed. The fluid subsystem conditions and delivers the fluid at the desired thermodynamic state to the test module. It consists of two fluid modules and a heater module that are connected by flex hoses for fluid circulation and by data and electrical cables for control and data acquisition. Two avionics modules acquire pressure and temperature data from various sensors in the flow loop. For FBM, a high-speed camera is available to acquire images of the boiling process. Experiments are operated autonomously by software and are based on an Experiment Parameters Master Table (EPMT) that is uploaded to ISS and is executed by the FBCE flight software. This presentation briefly introduces the objectives of FBCE and provides a system description of the experiment onboard of the ISS/Fluid Integrated Rack (FIR). Results of the test campaign carried out using the FBM are presented. Specifically, microgravity flow boiling of n-perfluorohexane (test fluid) is discussed with subcooled inlet conditions in a single-side-heated rectangular channel of dimensions 114.6-mm heated length, 2.5-mm heated width, and 5.0-mm height. Key operating parameters investigated are mass velocity (199.90 – 3200.13 kg/m2s), inlet subcooling (0.10 – 45.76°C), and inlet pressure (113.30 – 164.29 kPa). Image sequences acquired via high-speed-video are shown to elucidate the interfacial flow physics. The effects of various parameters on flow boiling heat transfer in microgravity, from the onset of boiling to the critical heat flux are discussed. Heat transfer results are presented in terms of flow boiling curves, streamwise profiles of wall temperature and heat transfer coefficient, and parametric trends of local and averaged heat transfer coefficient, and the critical heat flux.

Two-phase flow and phase transition↗

DOE OSTI2019

Chapter 2: Blade-Resolved Modeling with Fluid-Structure Interaction

Blade -resolved simulations are a high-fidelity modeling tool that helps understand the fundamental flow physics that create loads on wind turbines. Along with fluid - structure interaction (FSI), they provide a foundation to improve the state-of-the-art aerodynamic models of modern wind turbines with large flexible blades and thus the design of the next generation of wind turbines. One of the most important parts of wind-turbine simulation is modeling the conversion of kinetic energy in the wind into mechanical energy using principles of aerodynamics. The hierarchies of aerodynamic models for wind turbines in increasing the order of complexity, cost, and fidelity are blade element momentum (BEM) theory (BEMT), vortex methods, actuator disc/line methods, and blade -resolved modeling.

17 WIND ENERGY↗

NASA NTRS2017

FLEET Velocimetry Measurements on a Transonic Airfoil

Femtosecond laser electronic excitation tagging (FLEET) velocimetry was used to study the flowfield around a symmetric, transonic airfoil in the NASA Langley 0.3-m TCT facility. A nominal Mach number of 0.85 was investigated with a total pressure of 125 kPa and total temperature of 280 K. Two-components of velocity were measured along vertical profiles at different locations above, below, and aft of the airfoil at angles of attack of 0 deg, 3.5 deg, and 7deg. Measurements were assessed for their accuracy, precision, dynamic range, spatial resolution, and overall measurement uncertainty in the context of the applied flowfield. Measurement precisions as low as 1 m/s were observed, while overall uncertainties ranged from 4 to 5 percent. Velocity profiles within the wake showed sufficient accuracy, precision, and sensitivity to resolve both the mean and fluctuating velocities and general flow physics such as shear layer growth. Evidence of flow separation is found at high angles of attack.

Burns, Ross A.↗

DOE OSTI2023

Mixing in Low Reynolds Number Reacting Impinging Jets in Crossflow

Previous efforts to model uranyl fluoride formation in an impinging jet gas reactor underpredicted spatial mixing and overpredicted chemical conversion into particulates. The previous fluid dynamics model was based on the solution of the Reynolds Averaged Navier Stokes equations. After simulating fluid dynamics, aerosol dynamics were superimposed onto CFD-simulated gas reactant species concentrations. The current work explores the influence of complex unsteady flow features on the overall flow physics and chemistry for a low Reynolds number, opposed flow, impinging jet gas reactor where there is a low Reynolds number cross flow. The objective of this study was to assess the impact of model formulation on scalar mixing and transport. Here, transient flow simulations were performed using Scale Resolving Simulations. Large-Eddy Simulations with the dynamic Smagorinsky turbulence model were performed along with simulations which directly resolved the flow. Average and root-mean-square (RMS) velocities and species concentrations were computed along with modeled and resolved turbulence kinetic energy (TKE), modeled turbulence dissipation, and modeled turbulent viscosity. Lagrangian flow tracers were also used to quantify species concentrations along path lines emanating from the jet tips. Transient simulation data were compared to results from RANS simulations using the k-ω shear stress transport (SST) model and Reynolds Stress Model (RSM). Transient simulations showed spatial mixing patterns which were more consistent with experimental data and helped elucidate the process of particle formation observed in experiments.

42 ENGINEERING↗

NASA NTRS1998

The Three Dimensional Flow Field at the Exit of an Axial-Flow Turbine Rotor

A systematic and comprehensive investigation was performed to provide detailed data on the three dimensional viscous flow phenomena downstream of a modem turbine rotor and to understand the flow physics such as origin, nature, development of wakes, secondary flow, and leakage flow. The experiment was carried out in the Axial Flow Turbine Research Facility (AFTRF) at Penn State, with velocity measurements taken with a 3-D LDV System. Two radial traverses at 1% and 10% of chord downstream of the rotor have been performed to identify the three-dimensional flow features at the exit of the rotor blade row. Sufficient spatial resolution was maintained to resolve blade wake, secondary flow, and tip leakage flow. The wake deficit is found to be substantial, especially at 1% of chord downstream of the rotor. At this location, negative axial velocity occurs near the tip, suggesting flow separation in the tip clearance region. Turbulence intensities peak in the wake region, and cross- correlations are mainly associated with the velocity gradient of the wake deficit. The radial velocities, both in the wake and in the endwall region, are found to be substantial. Two counter-rotating secondary flows are identified in the blade passage, with one occupying the half span close to the casino and the other occupying the half span close to the hub. The tip leakage flow is well restricted to 10% immersion from the blade tip. There are strong vorticity distributions associated with these secondary flows and tip leakage flow. The passage averaged data are in good agreement with design values.

Lakshminarayana, B.↗

NASA NTRS2003

Computational and Experimental Flow Field Analyses of Separate Flow Chevron Nozzles and Pylon Interaction

A computational and experimental flow field analyses of separate flow chevron nozzles is presented. The goal of this study is to identify important flow physics and modeling issues required to provide highly accurate flow field data which will later serve as input to the Jet3D acoustic prediction code. Four configurations are considered: a baseline round nozzle with and without a pylon, and a chevron core nozzle with and without a pylon. The flow is simulated by solving the asymptotically steady, compressible, Reynolds-averaged Navier-Stokes equations using an implicit, up-wind, flux-difference splitting finite volume scheme and standard two-equation kappa-epsilon turbulence model with a linear stress representation and the addition of a eddy viscosity dependence on total temperature gradient normalized by local turbulence length scale. The current CFD results are seen to be in excellent agreement with Jet Noise Lab data and show great improvement over previous computations which did not compensate for enhanced mixing due to high temperature gradients.

Massey, Steven J.↗

NASA NTRSDate not supplied

An Overview of the Proprotor Performance Test in the 14- by 22-Foot Subsonic Tunnel

This work experimentally investigates the aerodynamic behavior of proprotors across a wide range of angles of attack. These flight conditions are intended to be representative of Urban Air Mobility (UAM) vehicle platforms that utilize articulating propulsors to transition from a vertical takeoff and landing (VTOL) phase typical of a conventional rotorcraft, to an axial mode of forward flight typical of a fixed-wing aircraft. These data are used to identify the potential limits of lower fidelity aerodynamic modeling tools, as well as to inform future acoustic phases of testing. Tests were conducted on two proprotor designs in the NASA Langley 14- by 22-Foot Subsonic Tunnel using an articulating propeller test stand. Hover results identified unique flow physics on one of the proprotors, including severe outboard flow separation and perpendicular blade vortex interactions on the outboard portions of the blades. Transition and forward flight conditions yielded very informative trends in terms of both on- and off-axis forces and moments against which low-fidelity prediction models were compared.

aerodynamics↗

NASA NTRSDate not supplied

An Overview of the Proprotor Performance Test in the 14- by 22-Foot Subsonic Tunnel

Nikolas Zawodny↗

NASA NTRS1997

Microgravity Fluid Separation Physics: Experimental and Analytical Results

Effective, low power, two-phase separation systems are vital for the cost-effective study and utilization of two-phase flow systems and flow physics of two-phase flows. The study of microgravity flows have the potential to reveal significant insight into the controlling mechanisms for the behavior of flows in both normal and reduced gravity environments. The microgravity environment results in a reduction in gravity induced buoyancy forces acting on the discrete phases. Thus, surface tension, viscous, and inertial forces exert an increased influence on the behavior of the flow as demonstrated by the axisymmetric flow patterns. Several space technology and operations groups have studied the flow behavior in reduced gravity since gas-liquid flows are encountered in several systems such as cabin humidity control, wastewater treatment, thermal management, and Rankine power systems.

Shoemaker, J. Michael↗

NASA NTRS1983

Topology of vortices in conical flow

The possibility of the existence of a viscous vortex in a conical flow is discussed. Existence of a viscous vortex is shown to be consistent with a flow-field model where only the velocity components and the total enthalpy behave conically. Existence of a viscous vortex is not consistent with the fully conical, flow-field model; however, far from the nose tip, the physical flow quantities tend to behave asymptotically as a full conical flow. Such a viscous vortex, when it exists, must spiral inwards to the focal point. It can be used as a reasonable model to start numerical solutions of various kinds.

Almosnino, D.↗

NASA NTRS1990

Unsteady airloads due to separated flow on airfoils and wings

Experimental and computational studies of airloads due to separated flows over airfoils and wings conducted at the NASA Langley Research Center are surveyed. Results are presented for cases involving local flow separation such as shock-induced separation, for the initiation of leading-edge vortex flows, and for cases involving unsteady airloads due to flows separating over remote aircraft components. Good correlation is obtained between experiment and computation for cases of locally separating flow and steady computations of vortex flow over delta wings and complex forebody geometries are shown. Physical flow modeling issues and computational requirements for the case of vertical tail buffeting are developed.

Edwards, John W.↗

NASA NTRS1990

Unsteady airloads due to separated flow on airfoils and wings

Edwards, John W.↗