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At least 1,459 records · Page 81

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NASA NTRSDate not supplied

On the Equivalence of Gas and Liquid Leak Flow Rates for Application to Propulsion and Propellant Transfer Systems

The equivalence of leak rates for gas flow and liquid flow through an arbitrary small leak size in pressurized systems has been investigated theoretically and experimentally. Measurements were taken for gaseous helium (GHe) rates and water flow issuing from the same leak configuration. The predictions for the correlation of GHe leak rates to water leak rates have been satisfactorily compared with present test data and those of other investigators over a wide range leak flow rates (many orders of magnitude) corresponding to a wide range of leak sizes (0.1 m to 0.1 mm). The results show that at extremely small leak sizes (sub-micron range), the effects of Knudsen number in the free molecular regime (rarefied gases) become important. By a proper scaling procedure, the measured flow rate for water could be applied to equivalent propellant leaks in flight operations. In the present tests the micro-channel range of the leak size is satisfactorily simulated by repeatable precision set needle position valve. Test results show that in general the theoretical model predicts the data reasonably well for GHe flow rates in the range of 0.001 to 1 sccs. Outside this range of GHe flow rates some adjustments (improvements) to the analytical model are required along with further testing.

Max Kandula↗

NASA NTRSDate not supplied

Conceptual Integration Studies of Localized Active Flow Control on the Wing of a Commercial Aircraft

A study of conceptual integration and performance of localized active flow control technology onto wings of short-to-medium-range project passenger airplanes is summarized. Using predicted aerodynamic performance improvement opportunities on a computational fluid dynamics reference aircraft, this paper presents the estimated performance opportunities for conceptual implementation of studied wing localized active flow control technology for low-speed (takeoff and landing) application on a Project Research Aircraft configuration. Using conceptual active flow control systems and structural integration weight penalties for studied concepts, potential relevant net performance benefits can be obtained with reliable active flow control in takeoff and landing. The conceptual integration study identifies potential localized wing active flow control application opportunities for high-lift conditions using energy sources available on modern aircraft. Material benefits are estimated for takeoff and landing configurations for selected localized wing active flow control applications. The study concluded that substantial low-speed Maximum Lift and Lift/Drag related performance improvements may be possible with localized wing high-lift active flow control systems powered by auxiliary power unit, engine bleed, or electrical compressors - with due consideration of integration and weight impacts as well as availability requirements of such systems.

drag reduction↗

NASA NTRSDate not supplied

Acoustic Mode Decomposition in Rectangular Ducts with Sheared Flow

The performance of new acoustic liner concepts are, in general, characterized and assessed in grazing flow rigs early in the development cycle. These test rigs expose an acoustic liner sample, installed on the side wall of the duct, to a grazing flow and incident acoustic field. The process to characterize these liners involves educing the impedance on the wall where the sample is installed and examining the acoustic power attenuation. Standard approaches to computing impedance or power attenuation generally consider only the effects of a 2D shear flow or uniform flow, on the acoustic field. In this study, the objective is to incorporate 3D shear flow effects in the analysis of acoustic mode attenuation in a rectangular duct flow rig. A modal analysis of microphone measurements obtained on the side walls of the duct upstream and downstream of the test section of the rig is developed. A Galerkin projection of the Pridmore-Brown equation is performed with Chebyshev basis functions in order to incorporate the effects of the Mach number profile on the computation of the axial wavenumber of each mode. Measurements of the Mach number profile are obtained in the test rig and used as input to compute the modes. Comparisons made between the sound field computed with traditional convective Helmholtz modes and the new procedure using Pridmore-Brown modes indicate that the computed acoustic field using Pridmore-Brown modes more accurately reconstructs the acoustic signal at each microphone in the array. The mode structure of the lowest-order mode is shown to be significantly impacted by shear flow refraction effects, and higher-order mode structures are also affected at higher frequencies and centerline Mach number. An assessment of the acoustic mode attenuation for two acoustic liner samples demonstrates that the computed mode amplitudes for both the traditional and new approach are in agreement for the lowest-order mode, but discrepancies arise when higher-order modes are the dominant component of the acoustic field.

Duct acoustics↗

NASA NTRSDate not supplied

Acoustic Mode Decomposition in Rectangular Ducts with Sheared Flow

The performance of new acoustic liner concepts are, in general, characterized and assessed in grazing flow rigs early in the development cycle. These test rigs expose an acoustic liner sample, installed on the side wall of the duct, to a grazing flow and incident acoustic field. The process to characterize these liners involves educing the impedance on the wall where the sample is installed and examining the acoustic power attenuation. Standard approaches to computing impedance or power attenuation generally consider only the effects of a 2D shear flow or uniform flow, on the acoustic field. In this study, the objective is to incorporate 3D shear flow effects in the analysis of acoustic mode attenuation in a rectangular duct flow rig. A modal analysis of microphone measurements obtained on the side walls of the duct upstream and downstream of the test section of the rig is developed. A Galerkin projection of the Pridmore-Brown equation is performed with Chebyshev basis functions in order to incorporate the effects of the Mach number profile on the computation of the axial wavenumber of each mode. Measurements of the Mach number profile are obtained in the test rig and used as input to compute the modes. Comparisons made between the sound field computed with traditional convective Helmholtz modes and the new procedure using Pridmore-Brown modes indicate that the computed acoustic field using Pridmore-Brown modes more accurately reconstruct the acoustic signals at each microphone in the array. The mode structure of the lowest order mode is shown to be significantly impacted by shear flow refraction effects, and higher order mode structures are also effected at higher frequencies and centerline Mach number. An assessment of the acoustic mode attenuation for two acoustic liner samples demonstrates that the computed mode amplitudes for both the traditional and new approach are in agreement for the lowest order mode, but discrepancies arise when higher order modes are the dominant component of the acoustic field.

Duct acoustics↗

NASA NTRSDate not supplied

Joule-Thomson Cryogenic Nitrogen Orifice Flows

The Joule-Thomson Effect involves the expansion of a fluid through a throttling device, often a simple orifice, resulting in a change in the fluid's temperature. It has been leveraged in the design and analysis of Thermodynamic Vent Systems and integrated into injector designs for cryogenic no-vent fill tank-to-tank transfer testing. There is a scarcity of comprehensive data available to model the phenomenon effectively using tools such as GFSSP for cryogenic nitrogen flows. This experiment aims to model the Joule-Thomson effect of liquid nitrogen through seven traditionally manufactured, sharp-edged orifices manufactured by O’Keefe and three additively manufactured (AM) orifices manufactured by Cumberland Additive. The traditional orifice sizes were 0.016, 0.02, 0.024, 0.032, 0.037, and 0.04 inch in diameter. The three additive orifices had diameters with target/nominal sizes equal to the 0.016, 0.024, and 0.04 inch O’Keefe orifices. However, the actual diameters of the AM orifices were found to be 0.014, 0.024, and 0.035 inches due to additive manufacturing restrictions. Water was flowed through the orifices to verify that their flow coefficients matched published values and to establish flow coefficients for the AM orifices. Liquid nitrogen was flowed through the orifices in a separate test apparatus. The liquid nitrogen started as a subcooled liquid upstream of the orifice and transitioned into a two-phase gas-liquid mixture after passing through each orifice. The upstream pressure was set to 29 psia, 34 psia, 39 psia, and/or 42 psia or 44 psia. The pressure, temperature, and flow rate were measured upstream and downstream of the orifice for three trials at each set point. The average volumetric flow rate and Joule-Thomson Coefficients were calculated from this data. The AM orifices and traditionally manufactured orifices displayed similar results. This data will refine the dataset GFSSP uses to model the J-T Effect more accurately.

Joule-Thomson↗

NASA NTRS1963

Application of Dorodnitsyn's Integral Method to Nonequilibrium Flows over Pointed Bodies

Dorodnitsyn's integral method is used to obtain an approximate solution to the supersonic nonequilibrium flow over pointed bodies with attached shock waves. The partial differential equations governing the flow are converted to an approximate set of ordinary equations, which are solved by numerical integration starting at the body tip. Detailed analytical and numerical results for the first approximation are presented, considering the vibrational relaxation of a diatomic gas over a wedge or cone. It is shown that the first approximation yields: (1) The exact flow-variable gradients at the wedge tip (2) Expressions for the flow-variable gradients at the cone tip which are in agreement with extrapolations of characteristics calculations (3) A good approximate algebraic solution for frozen or equilibrium conical flow (4) An approximate expression for the nonequilibrium-flow stream function which affords a means of obtaining variations across the shock layer of the temperature and vibrational energy. Numerical results for both the wedge and cone compare favorably with identical cases computed by the method of characteristics.

NONEQUILIBRIUM FLOW↗

NASA NTRS2013

Flow Control and Measurement in Electric Propulsion Systems: Towards an AIAA Reference Standard

Accurate control and measurement of propellant flow to a thruster is one of the most basic and fundamental requirements for operation of electric propulsion systems, whether they be in the laboratory or on flight spacecraft. Hence, it is important for the electric propulsion community to have a common understanding of typical methods for flow control and measurement. This paper addresses the topic of propellant flow primarily for the gaseous propellant systems which have dominated laboratory research and flight application over the last few decades, although other types of systems are also briefly discussed. While most flight systems have employed a type of pressure-fed flow restrictor for flow control, both thermal-based and pressure-based mass flow controllers are routinely used in laboratories. Fundamentals and theory of operation of these types of controllers are presented, along with sources of uncertainty associated with their use. Methods of calibration and recommendations for calibration processes are presented. Finally, details of uncertainty calculations are presented for some common calibration methods and for the linear fits to calibration data that are commonly used.

thrust measurement↗

NASA NTRSDate not supplied

Active Flow Control Enhanced Aileron of the High-Lift Common Research Model at Takeoff Condition

An experimental investigation was conducted in the NASA Langley 14- by 22-Foot Subsonic Tunnel on the NASA 10% scale High-Lift Common Research Model (CRM-HL) to improve the high-lift aerodynamic performance of the takeoff configuration. Active flow control (AFC) was applied at the aileron hinge line to control flow separation at high aileron deflection angles ( δ a ) to increase lift-to-drag ratio (R/J). Improvements in low speed R/J can increase vehicle payload and/or range resulting in a more efficient vehicle. Aileron deflection angles of 0°, 7.5°, 16°, and 25° were investigated. Flow control was applied to the two largest aileron deflections, which are considered the high-lift (HL) improved takeoff configurations. A companion paper will discuss baseline flow characteristics of the CRM-HL at the three takeoff conditions: reference, nominal, and HL-improved. In this paper, we focus on the aerodynamic improvement obtained when AFC was applied to δ a = 16° relative to the nominal configuration, δ a = 7.5°. Multiple flow control parameters, including actuator type, spacing, and intensity, were investigated to evaluate the efficiency of the actuation system. The different AFC configurations tested were assessed with tuft visualization, steady surface pressure data, and force and moment data. The results indicated that all actuation types and spacings examined led to an increase in lift across the range of angles of attack investigated. Flow separation was mitigated with the injection of momentum at the aileron hinge line. The configurations with the smallest spacing produced the highest improvement in L/D . Steady jet actuation showed higher efficiency but similar aerodynamic performance when compared to the sweeping jet actuators. This work was performed in support of the NASA Advanced Air Transport Technology (AATT) Project.

High-Lift Common Research Model↗

NASA NTRSDate not supplied

Active Flow Control Enhanced Aileron of the High-Lift Common Research Model at Takeoff Condition

An experimental investigation was conducted in the NASA Langley 14- by 22-Foot Subsonic Tunnel on the NASA 10% scale High-Lift Common Research Model (CRM-HL) to improve the high-lift aerodynamic performance of the takeoff configuration. Active flow control (AFC) was applied at the aileron hinge line to control flow separation at high aileron deflection angles to increase lift-to-drag ratio (L/D). Improvements in low speed L/D can increase vehicle payload and/or range resulting in a more efficient vehicle. Aileron deflection angles of 0°, 7.5°, 16°, and 25° were investigated. Flow control was applied to the two largest aileron deflections, which are considered the high-lift (HL) improved takeoff configurations. A companion paper will discuss baseline flow characteristics of the CRM-HL at the three takeoff conditions: reference, nominal, and HL-improved. In this paper, we focus on the aerodynamic improvement obtained when AFC was applied to an aileron deflected at 16° relative to the nominal configuration of 7.5° deflection. Multiple flow control parameters, including actuator type, spacing, and intensity, were investigated to evaluate the efficiency of the actuation system. The different AFC configurations tested were assessed with tuft visualization, steady surface pressure data, and force and moment data. The results indicated that all actuation types and spacings examined led to an increase in lift across the range of angles of attack investigated. Flow separation was mitigated with the injection of momentum at the aileron hinge line. The configurations with the smallest spacing produced the highest improvement in L/D. Steady jet actuation showed higher efficiency but similar aerodynamic performance when compared to the sweeping jet actuators. This work was performed in support of the NASA Advanced Air Transport Technology (AATT) Project.

CRM-HL↗

NASA NTRSDate not supplied

Preliminary Findings of the Experimental Development Unit Cold Flow Test for a Generation Zero Nuclear Propulsion Engine

Nuclear thermal propulsion (NTP) technology will greatly benefit human travel to Mars by significantly shortening transit times, improving crew safety, and providing more mission flexibility than traditional chemical rockets. As part of DRACO follow-on work to develop, build, and fly a generation zero NTP engine, a full scale flight-like experimental design unit (EDU) reactor was constructed to collect sufficient on-ground performance data to characterize flow induced vibrations (FIV) of critical reactor structures/components, inform development of the engine and reactor control algorithm, and collect pressure drop and flow distribution data across the reactor. The fluid conditions for the test program were designed to achieve system responses equivalent to that of an operational engine through all phases of engine operation including reactor startup, mainstage operation, reactor shutdown, and reactor cooldown. Over 100 tests were executed, flowing either GN2 or GHe through the EDU at varying flow rates and pressures. This experiment provided early validation of flow behavior and vibration risks before nuclear testing, boosted critical subsystem TRLs, informed design iterations, and reduced future test costs. The steady-state flow parameters for the experiment were modeled in Ansys Thermal Desktop, allowing rapid tuning and experiment-informed updates to a flight-like test matrix. The EDU dynamic environment was characterized with accelerometers, strain gauges, and high-frequency pressure transducers all sampled at 20 kHz. While many narrow-band oscillations were identified, no significant FIV occurred; the reactor structural responses tend to be enveloped by typical launch vehicle ascent vibration environments (defined up to 2 kHz), although significant energy is also present at higher frequencies.

Flow Induced Vibration↗

NASA NTRS1955

General theory of conical flows and its application to supersonic aerodynamics

Points treated in this report are: homogeneous flows, the general study of conical flows with infinitesimal cone angles, the numerical or analogous methods for the study of flows flattened in one direction, and a certain number of results. A thorough consideration of the applications on conical flows and demonstration of how one may solve within the scope of linear theory, by combinations of conical flows, the general problems of the supersonic wing, taking into account dihedral and sweepback, and also fuselage and control surface effects.

THEORIES - FLOW - LINEAR↗

NASA NTRS2015

Flight Tests of a Supersonic Natural Laminar Flow Airfoil

A flight-test campaign of a supersonic natural laminar flow airfoil has been recently completed. The test surface was an 80-inch (203 cm) chord and 40-inch (102 cm) span article mounted on the centerline store location of an F-15B airplane (McDonnell Douglas Corporation, now The Boeing Company, Chicago, Illinois). The test article was designed with a leading edge sweep of effectively 0 deg to minimize boundary layer crossflow. The test article surface was coated with an insulating material to avoid significant heat transfer to and from the test article structure to maintain a quasi-adiabatic wall. An aircraft-mounted infrared camera system was used to determine boundary layer transition and the extent of laminar flow. The tests were flown up to Mach 2.0 and chord Reynolds numbers in excess of 30 million. The objectives of the tests were to determine the extent of laminar flow at high Reynolds numbers and to determine the sensitivity of the flow to disturbances. Both discrete (trip dots) and 2-D disturbances (forward-facing steps) were tested. A series of oblique shocks, of yet unknown origin, appeared on the surface, which generated sufficient crossflow to affect transition. Despite the unwanted crossflow, the airfoil performed well. The results indicate the sensitivity of the flow to the disturbances, which can translate into manufacturing tolerances, were similar to that of subsonic natural laminar flow wings.

supersonic boundary layer↗

NASA NTRS2019

Optical Flow for Intermediate Frame Interpolation of Multispectral Geostationary Satellite Data

Applications in areas such as weather tracking and modeling, ecosystem monitoring, wildfire detection, and land-cover change are heavily dependent on spatial and temporal resolutions of satellite observations. However, there are typically trade-offs between spatial and temporal resolutions in dataset selection. For instance, geostationary weather tracking satellites are designed to take snapshots many times throughout the day but sensor hardware limits data collection. In this work we tackle this limitation, developing a method for temporal upsampling of multi-spectral satellite imagery using optical flow video interpolation deep convolutional neural networks. The presented model, extends Super SloMo (SSM) from single optical flow estimates to multichannel where flows are computed per band. We apply this technique on 8 multi-spectral bands of NOAA/NASA's GOES-16 mesoscale dataset to temporally enhance full disk hemispheric snapshots from 15 minutes to 1 minute. Through extensive experimentation, we show SSM vastly outperforms the linear interpolation baseline and that multichannel optical flows improves performance on GOES-16. A visual analysis of optical flow vectors clearly identifies hurricanes and large-scale atmospheric dynamics. Furthermore, we discuss challenges and open questions related to optical flow and temporal interpolation of multispectral geostationary satellite imagery.

Optical Flow↗

NASA NTRS2021

Assessment and Improvement of RANS-based Transition Models based on Experimental Data of the Common Research Model with Natural Laminar Flow

Transition models based on auxiliary transport equations augmenting the Reynolds-averaged Navier-Stokes (RANS) framework often rely upon the correlations that were derived from a limited number of low-speed experiments and do not account for all of the transition mechanisms and/or their variation with the significant flow parameters. Available data from a recent experiment in the National Transonic Facility at the NASA Langley Research Center are used to assess the current transition modeling capability in NASA's OVERFLOW 2.2o code for a swept wing configuration at transonic cruise conditions. Specifically, the OVERFLOW solutions are used together with detailed stability analysis of the boundary layer flow over the new Common Research Model with Natural Laminar Flow (CRM-NLF) to evaluate the accuracy and the robustness of the transport-equation-based transition models, with the goal of proposing improvements that would help to strengthen the physical basis of these models for the important class of flows involving the combined effects of crossflow and flow compressibility. Results highlight the significant underprediction of the laminar flow extent within the inboard region of the wing, wherein the onset of transition may be attributed to a gradual amplification of Tollmien-Schlichting instabilities.

Boundary layer transition↗

NASA NTRSDate not supplied

A New Flow-Through Wind Tunnel Balance for Retropropulsion Testing

Supersonic retropropulsion is believed to be an enabling technology for large-scale human Mars lander vehicle concepts. Ground testing of such vehicles requires the development of new flow-through wind tunnel balances because no suitable balances exist. A new flow-through balance is designed that employs membranes in place of bellows, which have historically been used, and that passes the flow through load bearing parts of the balance. Flow through the balance is optimized via the addition of flow guides, which are manufactured as separate parts, and attached to the balance. Calibration of this new flow-through balance demonstrates that it can suitably characterize the load and pressure ranges it was designed for, which provides aero researchers a new tool to directly measure supersonic retropropulsion performance of powered descent vehicles.

Flow through balance↗

NASA NTRSDate not supplied

A New Flow-Through Balance for Retropropulsion Testing

Flow through balance↗

NASA NTRSDate not supplied

Enabling Metric-Based Mesh Adaptation for Advanced Compressible Flow Simulations Using US3D

This work presents a metric-based mesh adaptation capability added to the flow solver US3D that is used to improve the accuracy of atmospheric entry simulations. Flow past an entry vehicle in free-flight is usually unsteady and characterized by anisotropic flow features like a strong bow shock and small-scale isotropic flow features like turbulent eddies in the wake. The results presented in this paper demonstrate that we are currently able to iteratively apply metric-based mesh adaptation to improve the solution accuracy by simultaneously targeting isotropic and anisotropic flow features. A simplified workflow of running CFD simulations for entry vehicles is presented where we start off with a coarse initial mesh to compute a first approximation of the flow. This coarse mesh is then iteratively refined using the newly developed metric to improve the resolution of the CFD computation. Furthermore, we demonstrate that we are able to adapt large mesh sizes in a timely fashion which allows us to start thinking about applying this adaptive framework to unsteady atmospheric entry CFD simulations.

Mesh adaptation↗

NASA NTRSDate not supplied

On Characterization of Laminar to Turbulent Transitional Flow in the Truncated IHF Semi-Elliptical Nozzle

This paper reports computational analysis and experimental data to characterize the laminar to turbulent flow transition in a high-enthalpy panel test facility at NASA Ames Research Center. The recently developed facility configuration uses a truncated version of an existing semi-elliptical nozzle in the 60-MW Interaction Heating Facility, and it provides testing capability for panel test articles as large as 43.2 cm x 43.2 cm (17 in x 17 in). A water-cooled calibration plate, which is attached to the semi-elliptical nozzle bottom surface and instrumented with twenty Gardon-gage heat flux calorimeters and twelve pressure gages, is used to characterize the convective heating environment over the panel test articles. The present analysis comprises computational fluid dynamics simulations of the nonequilibrium flowfield in the facility nozzle and test box, and the flowfields over panel test articles, and comparisons with the measured test data. Both laminar and turbulent simulations are performed. Constant current studies are conducted: the measured data are grouped at the same arc current levels with varying mass flow rates, and they are compared with corresponding computations. For all currents considered, these studies indicate that the semi-elliptical nozzle flow is transitional at relatively higher mass flow rates within the facility operating envelope. An approximate facility map for the transitional flow characterization is developed, showing laminar and transitional to turbulent flow regions.

Arc-jets↗