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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

The development of a turbulent junction vortex system

The growth and development of a horseshoe vortex system in an incompressible, three-dimensional turbulent junction flow were investigated experimentally. A streamlined cylinder mounted with its axis normal to a flat surface was used to generate the junction vortex flow. The flow environment was characterized by a body Reynolds number of 183,000, based on the leading edge diameter of the streamlined cylinder. The study included surface flow visualizations, surface pressure measurements, and mean flow measurements of total pressure, static pressure, and velocity distributions in three planes around the base of the streamlined cylinder, and in two planes in the wake flow. Some characterizations of vortex properties based on the measured mean cross-flow velocity components are presented. The results show the presence of a single large, dominant vortex, with strong evidence of a very small corner vortex in the junction between the cylinder and the flat surface. The center of the dominant vortex drifts away from both the body and the flat surface as the flow develops along and downstream of the body. The growth and development of the core of the large, dominant vortex are documented.

Pierce, F. J.↗
NASA NTRS1993

Fluidic scale model multi-plane thrust vector control test results

An experimental investigation has been conducted at the NASA Langley 16-Foot Transonic Tunnel Static Test Facility to determine the concept feasibility of using fluidics to achieve multiplane thrust vector control in a 2D convergent-divergent (2D-CD) fixed aperture nozzle. Pitch thrust vector control is achieved by injection of flow through a slot in the divergent flap into the primary nozzle flow stream. Yaw vector control results from secondary air delivered tangentially to vertical Coanda flaps. These flaps are offset laterally and aligned parallel to the primary nozzle side walls. All tests were conducted at static (no external flow) conditions. Flow visualization was conducted using a paint flow technique and Focus Schlieren. Significant levels of pitch deflection angles (19 deg) were achieved at low pressure ratios and practical levels (14 deg) resulted at typical intermediate power settings. The ability of the Coanda surface blowing concept to produce yaw deflection was limited to NPR not greater than 4.

Chiarelli, Charles↗
NASA NTRS1993

An experimental investigation of a Mach 3.0 high-speed civil transport at supersonic speeds

An experimental study was conducted to determine the aerodynamic characteristics of a proposed high speed civil transport. This configuration was designed to cruise at Mach 3.0 and sized to carry 250 passengers for 6500 n.mi. The configuration consists of a highly blended wing body and features a blunt parabolic nose planform, a highly swept inboard wing panel, a moderately swept outboard wing panel, and a curved wingtip. Wind tunnel tests were conducted in the Langley Unitary Plan Wind Tunnel on a 0.0098-scale model. Force, moment, and pressure data were obtained for Mach numbers ranging from 1.6 to 3.6 and at angles of attack ranging from -4 to 10 deg. Extensive flow visualization studies (vapor screen and oil flow) were obtained in the experimental program. Both linear and advanced computational fluid dynamics (CFD) theoretical comparisons are shown to assess the ability to predict forces, moments, and pressures on configurations of this type. In addition, an extrapolation of the wind tunnel data, based on empirical principles, to full-scale conditions is compared with the theoretical aerodynamic predictions.

Hernandez, Gloria↗
NASA NTRS1995

Navier-Stokes analysis of a delta wing in static and dynamic roll

The three-dimensional, Reynolds-averaged, Navier-Stokes equations are used to numerically simulate non-steady high-incidence vortical flow about a 65 degree sweep delta wing under static roll and forced periodic roll motions. These computations have been previously reported in the literature, where emphasis was placed on validating the computational results with nonsteady experimental surface pressures, forces and moments. The emphasis of this research is to revisit these earlier computations and use nonsteady numerical flow visualization to analyze the nonlinear surface flow and vortex breakdown dynamics. Most notable are the periodic formation of surface-flow separation lines, and the periodic formation of vortex breakdown near the delta wing trailing edge.

Chaderjian, N.↗
NASA NTRSDate not supplied

A Separation Control CFD Validation Test Case: Baseline and Steady Suction - Part 1

Low speed flow separation over a wall-mounted hump, and its control using steady suction, were studied experimentally in order to generate a data set for a workshop aimed at validating CFD turbulence models. The baseline and controlled data sets comprised static and dynamic surface pressure measurements, flow field measurements using Particle Image Velocimetry (PIV) and wall shear stress obtained via oil-film interferometry. In addition to the specific test cases studied, surface pressures for a wide variety of conditions were reported for different Reynolds numbers and suction rates. Stereoscopic PIV and oil-film flow visualization indicated that the baseline separated flow field was mainly two- dimensional. With the application of control, some three-dimensionality was evident in the spanwise variation of pressure recovery, reattachment location and spanwise pressure fluctuations. Part 2 of this paper, under preparation for the AIAA Meeting in Reno 2005, considers separation control by means of zero-efflux oscillatory blowing.

David Greenblatt↗
NASA NTRS2004

A Separation Control CFD Validation Test Case: Baseline and Steady Suction - Part 1

Low speed flow separation over a wall-mounted hump, and its control using steady suction, were studied experimentally in order to generate a data set for a workshop aimed at validating CFD turbulence models. The baseline and controlled data sets comprised static and dynamic surface pressure measurements, flow field measurements using Particle Image Velocimetry (PIV) and wall shear stress obtained via oil-film interferometry. In addition to the specific test cases studied, surface pressures for a wide variety of conditions were reported for different Reynolds numbers and suction rates. Stereoscopic PIV and oil-film flow visualization indicated that the baseline separated flow field was mainly two-dimensional. With the application of control, some three-dimensionality was evident in the spanwise variation of pressure recovery, reattachment location and spanwise pressure fluctuations. Part 2 of this paper, under preparation for the AIAA Meeting in Reno 2005, considers separation control by means of zero-efflux oscillatory blowing.

Greenblatt, David↗
NASA NTRS2015

An Experimental Investigation of the Flow Physics Associated With End Wall Losses and Large Rotor Tip Clearances as Found in the Rear Stages of a High Pressure Compressor

The focus of this work was to characterize the fundamental flow physics and the overall performance effects due to increased rotor tip clearance heights in axial compressors. Data have been collected in the three-stage axial research compressor at Purdue University with a specific focus on analyzing the multistage effects resulting from the tip leakage flow. Three separate rotor tip clearance heights were studied with nominal tip clearance heights of 1.5%, 3.0%, and 4.0% based on a constant annulus height. Overall compressor performance was investigated at four corrected speedlines (100%, 90%, 80%, and 68%) for each of the three tip clearance configurations using total pressure and total temperature rakes distributed throughout the compressor. The results have confirmed results from previous authors showing a decrease of total pressure rise, isentropic efficiency, and stall margin which is approximately linear with increasing tip clearance height. The stall inception mechanisms have also been evaluated at the same corrected speeds for each of the tip clearance configurations. Detailed flow field measurements have been collected at two loading conditions, nominal loading (NL) and high loading (HL), on the 100% corrected speedline for the smallest and largest tip clearance heights (1.5% and 4.0%). Steady detailed radial traverses of total pressure at the exit of each stator row have been supported by flow visualization techniques to identify regions of flow recirculation and separation. Furthermore, detailed radial traverses of time-resolved total pressures at the exit of each rotor row have been measured with a fast-response pressure probe. These data have helped to quantify the size of the leakage flow at the exit of each rotor. Thermal anemometry has also been implemented to evaluate the time-resolved three-dimensional components of velocity throughout the compressor and calculate blockage due to the rotor tip leakage flow throughout the compressor. These measurements have also been used to calculate streamwise vorticity. Time-resolved static pressure measurements have been collected over the rotor tips for all rotors with each of the three tip clearance configurations for up to five loading conditions along the 100% corrected speedline using fast-response piezoresistive pressure sensors. These time-resolved static pressure measurements, as well as the time-resolved total pressures and velocities have helped to reveal a profound influence of the upstream stator vane on the size and shape of the rotor tip leakage flow. Finally, a novel particle image velocimetry (PIV) technique has been developed as a proof-of- concept. In contrast to PIV methods that have been typically been utilized for turbomachinery applications in the past, the method used for this study introduced the laser light through the same access window that was also used to image the flow. This new method addresses potential concerns related to the intrusive laser-introducing techniques that have typically been utilized by other authors in the past. Ultimately, the data collected for this project represent a unique data set which contributes to build a better understanding of the tip leakage flow field and its associated loss mechanisms. These data will facilitate future engine design goals leading to small blade heights in the rear stages of high pressure compressors and aid in the development of new blade designs which are desensitized to the performance penalties attributed to rotor tip leakage flows.

turbomachinery↗
NASA NTRS2017

Toward Understanding Tip Leakage Flows in Small Compressor Cores Including Stator Leakage Flow

The focus of this work was to provide additional data to supplement the work reported in NASA/CR-2015-218868 (Berdanier and Key, 2015b). The aim of that project was to characterize the fundamental flow physics and the overall performance effects due to increased rotor tip clearance heights in axial compressors. Data have been collected in the three-stage axial research compressor at Purdue University with a specific focus on analyzing the multistage effects resulting from the tip leakage flow. Three separate rotor tip clearances were studied with nominal tip clearance gaps of 1.5 percent, 3.0 percent, and 4.0 percent based on a constant annulus height. Overall compressor performance was previously investigated at four corrected speedlines (100 percent, 90 percent, 80 percent, and 68 percent) for each of the three tip clearance configurations. This study extends the previously published results to include detailed steady and time-resolved pressure data at two loading conditions, nominal loading (NL) and high loading (HL), on the 100 percent corrected speedline for the intermediate clearance level (3.0 percent). Steady detailed radial traverses of total pressure at the exit of each stator row are supported by flow visualization techniques to identify regions of flow recirculation and separation. Furthermore, detailed radial traverses of time-resolved total pressures at the exit of each rotor row have been measured with a fast-response pressure probe. These data were combined with existing three-component velocity measurements to identify a novel technique for calculating blockage in a multistage compressor. Time-resolved static pressure measurements have been collected over the rotor tips for all rotors with each of the three tip clearance configurations for up to five loading conditions along the 100 percent corrected speedline using fast-response piezoresistive pressure sensors. These time-resolved static pressure measurements reveal new knowledge about the trajectory of the tip leakage flow through the rotor passage. Further, these data extend previous measurements identifying a modulation of the tip leakage flow due to upstream stator wake propagation. Finally, a novel instrumentation technique has been implemented to measure pressures in the shrouded stator cavities. These data provide boundary conditions relating to the flow across the shrouded stator knife seal teeth. Moreover, the utilization of fast-response pressure sensors provides a new look at the time-resolved pressure field, leading to instantaneous differential pressures across the seal teeth. Ultimately, the data collected for this project represent a unique data set which contributes to build a better understanding of the tip leakage flow field and its associated loss mechanisms. These data will facilitate future engine design goals leading to small blade heights in the rear stages of high pressure compressors and aid in the development of new blade designs which are desensitized to the performance penalties attributed to rotor tip leakage flows.

Berdanier, Reid A.↗
NASA NTRS2015

An Experimental Investigation of the Flow Physics Associated With End Wall Losses and Large Rotor Tip Clearances as Found in the Rear Stages of a High Pressure Compressor

The focus of this work was to characterize the fundamental flow physics and the overall performance effects due to increased rotor tip clearance heights in axial compressors. Data have been collected in the three-stage axial research compressor at Purdue University with a specific focus on analyzing the multistage effects resulting from the tip leakage flow. Three separate rotor tip clearance heights were studied with nominal tip clearance heights of 1.5%, 3.0%, and 4.0% based on a constant annulus height. Overall compressor performance was investigated at four corrected speedlines (100%, 90%, 80%, and 68%) for each of the three tip clearance configurations using total pressure and total temperature rakes distributed throughout the compressor. The results have confirmed results from previous authors showing a decrease of total pressure rise, isentropic efficiency, and stall margin which is approximately linear with increasing tip clearance height. The stall inception mechanisms have also been evaluated at the same corrected speeds for each of the tip clearance configurations. Detailed flow field measurements have been collected at two loading conditions, nominal loading (NL) and high loading (HL), on the 100% corrected speedline for the smallest and largest tip clearance heights (1.5% and 4.0%). Steady detailed radial traverses of total pressure at the exit of each stator row have been supported by flow visualization techniques to identify regions of flow recirculation and separation. Furthermore, detailed radial traverses of time-resolved total pressures at the exit of each rotor row have been measured with a fast-response pressure probe. These data have helped to quantify the size of the leakage flow at the exit of each rotor. Thermal anemometry has also been implemented to evaluate the time-resolved three-dimensional components of velocity throughout the compressor and calculate blockage due to the rotor tip leakage flow throughout the compressor. These measurements have also been used to calculate streamwise vorticity. Time-resolved static pressure measurements have been collected over the rotor tips for all rotors with each of the three tip clearance configurations for up to five loading conditions along the 100% corrected speedline using fast-response piezoresistive pressure sensors. These time-resolved static pressure measurements, as well as the time-resolved total pressures and velocities have helped to reveal a profound influence of the upstream stator vane on the size and shape of the rotor tip leakage flow. Finally, a novel particle image velocimetry (PIV) technique has been developed as a proof-of- concept. In contrast to PIV methods that have been typically been utilized for turbomachinery applications in the past, the method used for this study introduced the laser light through the same access window that was also used to image the flow. This new method addresses potential concerns related to the intrusive laser-introducing techniques that have typically been utilized by other authors in the past. Ultimately, the data collected for this project represent a unique data set which contributes to build a better understanding of the tip leakage flow field and its associated loss mechanisms. These data will facilitate future engine design goals leading to small blade heights in the rear stages of high pressure compressors and aid in the development of new blade designs which are desensitized to the performance penalties attributed to rotor tip leakage flows.

Berdanier, Reid A.↗
NASA NTRS2004

A Resonant Pulse Detonation Actuator for High-Speed Boundary Layer Separation Control

A variety of different types of actuators have been previously investigated as flow control devices. Potential applications include the control of boundary layer separation in external flows, as well as jet engine inlet and diffuser flow control. The operating principles for such devices are typically based on either mechanical deflection of control surfaces (which include MEMS flap devices), mass injection (which includes combustion driven jet actuators), or through the use of synthetic jets (diaphragm devices which produce a pulsating jet with no net mass flow). This paper introduces some of the initial flow visualization work related to the development of a relatively new type of combustion-driven jet actuator that has been proposed based on a pulse detonation principle. The device is designed to utilize localized detonation of a premixed fuel (Hydrogen)-air mixture to periodically inject a jet of gas transversely into the primary flow. Initial testing with airflow successfully demonstrated resonant conditions within the range of acoustic frequencies expected for the design. Schlieren visualization of the pulsating air jet structure revealed axially symmetric vortex flow, along with the formation of shocks. Flow visualization of the first successful sustained oscillation condition is also demonstrated for one configuration of the current test section. Future testing will explore in more detail the onset of resonant combustion and the approach to conditions of sustained resonant detonation.

Beck, B. T.↗
NASA NTRSDate not supplied

Experimental Identification of Bistable Flow States on the Space Launch System at Liftoff Conditions

Time-averaged global force and moment measurements in wind tunnel tests can obscure complex flow dynamics, including bistability phenomena. This paper presents a detailed analysis into the potential cause of previously unobserved discrepancies among repeat runs during the 202114- by 22-Foot Subsonic Tunnel test of the Space Launch System. During the test, it was observed that liftoff configuration repeatability was not as strong as expected when compared to previous tests. These discrepancies occurred between wind angle azimuths of approximately 150◦ and 210◦, as well as between 330◦ and 30◦. After ruling out common confounding factors such as instrumentation hysteresis and temperature, it was hypothesized that the lack of repeatability was caused by the Coandă effect producing a bistable flow state at different locations between the cylindrical rocket centerbody and solid rocket boosters during the acquisition of data. Evidence to support this hypothesis is provided in this paper in the form of time-averaged force and moment coefficient data, time-dependent force and moment coefficient data, and still images from smoke flow and tuft flow visualization runs.

SLS↗
NASA NTRS1994

Patterns in the sky: Natural visualization of aircraft flow fields

The objective of the current publication is to present the collection of flight photographs to illustrate the types of flow patterns that were visualized and to present qualitative correlations with computational and wind tunnel results. Initially in section 2, the condensation process is discussed, including a review of relative humidity, vapor pressure, and factors which determine the presence of visible condensate. Next, outputs from computer code calculations are postprocessed by using water-vapor relationships to determine if computed values of relative humidity in the local flow field correlate with the qualitative features of the in-flight condensation patterns. The photographs are then presented in section 3 by flow type and subsequently in section 4 by aircraft type to demonstrate the variety of condensed flow fields that was visualized for a wide range of aircraft and flight maneuvers.

Campbell, James F.↗
NASA NTRS1985

Some unique experiments on receptivity

The objective of this study is to determine whether or not a solid trailing edge is required to produce efficient coupling between sound and instability waves in a shear layer. Instability waves in the shear layer of a subsonic jet, excited externally by a point sound source, were first visualized by using a phase-locked flow visualization technique. Various means were adopted to shield the sound reaching the nozzle lip. It was found that the low frequency sound couples more efficiently at distances downstream of the nozzle exit. To substantiate the findings further, a supersonic screeching jet was tested such that it passed through a small opening in a baffle placed parellel to the exit plane. The measured feedback or screech frequencies, and also the excited flow disturbances, were found to change drastically on traversing the baffle axially. Similar conclusions were reached when a second baffle was placed downstream of the first baffle, and the effects of moving the first baffle on the feedback frequency of sound generated by flow impingement on the second baffle were examined. It is argued that sound waves passing through the mixing layer of a jet can excite flow instability without the benefit of assistance and coupling at the trailing edge.

Ahuja, K. K.↗
DOE OSTI2024

Optical Flow Diagnostics of Counter Fluidization of Gravity-Driven Moving Packed Bed for a CSP Receiver Section Featuring Staggered Array of Cylindrical Pins

Particle fluidized beds have the potential to improve the efficiency of heat transfer in concentrated solar receiver furnace for use in next generation concentrated solar power (CSP) plants. This study presents an experimental investigation on the flow characterization of vertically downward moving packed bed with counter fluidization through an array of jets. To control the bubble size and its distribution in the bubbling fluidized bed, an array of cylindrical pin fins was arranged uniformly across the test article. The flow visualization was performed on the surface of transparent glass coated with electrically conductive materials for electrostatic dissipation purposes. The image acquisition was carried out via high-speed camera at a frequency of ~ 1kHz. The acquired images were analyzed in pairs with the help of a modern optical flow algorithm capable of calculating the movement of dense particle flow in the fluidized bed by tracking the light intensity of each predefined window of the frames. A comparison of fluidized beds with plane and pin-finned channels revealed distinct bubble behavior. Pin-finned channels were found to produce a larger number of small-sized bubbles, while plane channels generated fewer but larger bubbles at any given instant. The presence of pin fins was observed to reduce bubble size by preventing bubble merging and splitting larger bubbles when they encountered a pin.

concentrating solar power↗
NASA NTRS1974

Investigation of the Kline-Fogleman airfoil section for rotor blade applications

Wind tunnel tests of a wedgeshaped airfoil with sharp leading edge and a spanwise step were conducted. The airfoil was tested with variations of the following parameters: (1) Reynolds number, (2) step location, (3) step shape, (4) apex angle, and (5) with the step on either the upper or lower surface. The results are compared with a flat plate and with wedge airfoils without a step having the same aspect ratio. Water table tests were conducted for flow visualization and it was determined that the flow separates from the upper surface at low angles of attack. The wind tunnel tests show that the lift/drag ratio of the airfoil is lower than for a flat plate and the pressure data show that the airfoil derives its lift in the same manner as a flat plate.

Lumsdaine, E.↗
NASA NTRS1981

The boundary layer on compressor cascade blades

The flow field about an airfoil in cascade at a Reynolds number of 5 x 10 to the 5th power is described. Hot wire and laser anemometry are combined with flow visualization techniques in order to obtain detailed flow data (e.g., boundary layer profiles, points of separation, and the transition zone) on a cascade of relatively highly loaded blades. Benchmark data is provided for the evaluation of current and future predictive models, in this way aiding in the compressor design process.

Deutsch, S.↗
NASA NTRS1982

An experimental study of mushroom shaped stall cells

Surface patterns characterized by a pair of counter-rotating swirls have been observed in connection with the conduction of surface flow visualization experiments involving test geometries with separated flows. An example of this phenomenon occurring on a finite wing with trailing edge stall has been referred to by Winkelmann and Barlow (1980) as 'mushroom shaped'. A description is presented of a collection of experimental results which show or suggest the occurrence of mushroom shaped stall cells on a variety of test geometries. Investigations conducted with finite wings, airfoil models, and flat plates are considered, and attention is given to studies involving the use of bluff models, investigations of shock induced boundary layer separation, and mushroom shaped patterns observed in a number of miscellaneous cases. It is concluded that the mushroom shaped stall cell appears commonly in separated flow regions.

Winkelmann, A. E.↗