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NASA NTRS2006

Direct Numerical Simulation of Transitional Multicomponent-Species Gaseous and Multicomponent-Liquid Drop-Laden Mixing

A model of multicomponent-liquid (MC-liquid) drop evaporation in a three-dimensional mixing layer is here exercised at larger Reynolds numbers than in a previous study, and transitional states are obtained. The gas phase is followed in an Eulerian frame and the multitude of drops is described in a Lagrangian frame. Complete coupling between phases is included with source terms in the gas conservation equations accounting for the drop/flow interaction in terms of drop drag, drop heating and species evaporation. The liquid composition, initially specified as a single-Gamma (SG) probability distribution function (PDF) depending on the molar mass is allowed to evolve into a linear combination of two SGPDFs, called the double-Gamma PDF (DGPDF). The compositions of liquid and vapor emanating from the drops are calculated through four moments of the DGPDFs, which are drop-specific and location-specific, respectively. The mixing layer is initially excited to promote the double pairing of its four initial spanwise vortices into an ultimate vortex in which small scales proliferate. Simulations are performed for four liquids of different compositions and the effect of the initial mass loading and initial free-stream gas temperature are explored. For reference, Simulations are also performed for gaseous multicomponent mixing layers for which the effect of Reynolds number is investigated. The results encompass examination of the global layer characteristics, flow visualizations and homogeneous-plane statistics at transition. Comparisons are performed with previous pre-transitional MC-liquid simulations and with transitional single-component (SC) liquid studies. It is found that MCC flows at transition, the classical energy cascade is of similar strength, but that the smallest scales contain orders of magnitude less energy than SC flows, which is confirmed by the larger viscous dissipation in the former case. Contrasting to pre-transitional MC flows, the vorticity and drop organization depend on the initial gas temperature, this being due to the drop/turbulence coupling. The vapor-composition mean molar mass and standard deviation distributions strongly correlate with the initial liquid-composition PDF; such a correlation only exists for the magnitude of the mean but not for that of the standard deviation. Unlike in pre-transitional situations, regions of large composition standard deviation no longer necessarily coincide with regions of large mean molar mass. The kinetic energy, rotational and composition characteristics, and dissipation are liquid specific and the variation among liquids is amplified with increasing free-stream gas temperature. Eulerian and Lagrangian statistics of gas-phase quantities show that the different. Observation framework may affect the perception of the flow characteristics. The gas composition, of which the first four moments are calculated, is shown to be close to, but distinct from a SGPDF. The PDF of the scalar dissipation rate is calculated for drop-laden layers and is shown to depart more significantly from the typically assumed Gaussian in gaseous flows than experimentally measured gaseous scalar dissipation rates, this being attributed to the increased heterogeneity due to drop/flow interactions.

tubulent multicompenent-species↗

NASA NTRS2012

Investigation of Turbulent Tip Leakage Vortex in an Axial Water Jet Pump with Large Eddy Simulation

Detailed steady and unsteady numerical studies were performed to investigate tip clearance flow in an axial water jet pump. The primary objective is to understand physics of unsteady tip clearance flow, unsteady tip leakage vortex, and cavitation inception in an axial water jet pump. Steady pressure field and resulting steady tip leakage vortex from a steady flow analysis do not seem to explain measured cavitation inception correctly. The measured flow field near the tip is unsteady and measured cavitation inception is highly transient. Flow visualization with cavitation bubbles shows that the leakage vortex is oscillating significantly and many intermittent vortex ropes are present between the suction side of the blade and the tip leakage core vortex. Although the flow field is highly transient, the overall flow structure is stable and a characteristic frequency seems to exist. To capture relevant flow physics as much as possible, a Reynolds-averaged Navier-Stokes (RANS) calculation and a Large Eddy Simulation (LES) were applied for the current investigation. The present study reveals that several vortices from the tip leakage vortex system cross the tip gap of the adjacent blade periodically. Sudden changes in local pressure field inside tip gap due to these vortices create vortex ropes. The instantaneous pressure filed inside the tip gap is drastically different from that of the steady flow simulation. Unsteady flow simulation which can calculate unsteady vortex motion is necessary to calculate cavitation inception accurately even at design flow condition in such a water jet pump.

Hah, Chunill↗

NASA NTRSDate not supplied

A Comparison of NO Laser-Induced Fluorescence Models at Conditions Relevant to Supersonic and Hypersonic Flows

Planar laser-induced fluorescence (PLIF) of the nitric oxide (NO) molecule has been widely used in wind tunnel facilities for flow visualization, velocity, and temperature measurements. The experimental PLIF measurements are often compared with synthetic PLIF images using computationally derived temperatures, pressures, velocities, and species mole fractions. This approach is commonly referred to as computational flow imaging (CFI). In the present work, we compare signal intensity from PLIF models with experimental PLIF measurements obtained within a low pressure gas cell system at pressures and NO mole fractions relevant to supersonic and hypersonic flowfields. Experimental measurements were compared to several different laser induced-fluorescence models reported in the literature including LIFBASE, LINUS, and a NASA two-level model. The experimental measurements agreed well with all of the models at lower pressures and lower NO mole fractions; the fluorescence there is linear with both of these parameters. However, at higher pressures and mole fractions, the signal becomes nonlinear with respect to these parameters as self-quenching limits the signal and absorption further limits the signal. In fact, for the experimental path length of the experiment, the combination of high pressure and high NO mole fraction causes the experimental results to deviate significantly from the predicted results that neglect absorption of the incident laser sheet. The LINUS model, which allows absorption to be calculated, provided results that agreed better with the experimental measurements. Since supersonic and hypersonic flowfields may contain a region of the flow with high pressures and measurements in large-scale facilities often include a long path length, neglecting absorption may have a significantly negative effect on the CFI comparison to experimental PLIF images. As a result, PLIF models that account for absorption should be included in computational flow imaging approaches for laser induced fluorescence.

laser-induced fluorescence↗

NASA NTRS1985

Space Shuttle ice prevention studies

Turbojet engine exhausts are being considered for the prevention of ice formation on the Space Shuttle External Tank (ET) when cryogenic propellants are loaded. The ice could dislodge and damage the Thermal Protection System tiles of the Shuttle Orbiter. An oil flow visualization technique was developed to quickly and inexpensively study the flowfields created by jet exhausts. The procedure can also determine the influence of geometry, jet exhausts, and wind conditions on the size and location of flow regions. A black tempra and kerosene mixture was applied to an ET model; the wind tunnel and jet flow were started; and when they stopped the flow patterns were photographed to determine which parameters had the greatest influence on the flowfields.

Porteiro, J. L. F.↗

NASA NTRS1988

Aircraft vortices - Juncture, wing, and wake

Many real aircraft flows contain regions of three-dimensional separation with vortices. This paper presents selected results for three representative flows: juncture vortex, lifting-wing vortex, and wake vortex. Due to the difficulty of studying vortices, flow visualization was used as a primary research tool. Vortices are found to depend in subtle ways on details of the configuration, Reynolds number, or the environment. Examples showing the effect of filleting on the juncture flow, Reynolds number on the wing flow, and density gradients on the wake flow are presented.

Greene, George C.↗

NASA NTRS1992

Experimental results for a hypersonic nozzle/afterbody flow field

The flow field created by the interaction of a single-expansion-ramp-nozzle (SERN) flow with a hypersonic external stream has been experimentally characterized using a generic nozzle/afterbody model in the 3.5-foot hypersonic wind tunnel of the NASA Ames Research Center. The presented results include oil-flow and shadowgraph flow visualization photographs, afterbody surface-pressure distributions, boundary layer rake measurements, and Preston-tube skin-friction measurements. The design, construction, and operation of the model was found to be successful. Surface oil-flow patterns show that the jet-plume flow attaches to the afterbody surface at jet pressure ratios between 154 and 234. The oil flow also shows the pattern of lines where the jet flow separates from the ramp, apparently as a result of interaction of the jet-plume internal shock wave with the ramp boundary layer.

Spaid, Frank W.↗

NASA NTRS1992

A summary of the forebody high-angle-of-attack aerodynamics research on the F-18 and the X-29A aircraft

High-angle-of-attack aerodynamic studies have been conducted on both the F18 High Alpha Research Vehicle (HARV) and the X-29A aircraft. Data obtained include on- and off-surface flow visualization and static pressure measurements on the forebody. Comparisons of similar results are made between the two aircraft where possible. The forebody shapes of the two aircraft are different and the X-29A forebody flow is affected by the addition of nose strakes and a flight test noseboom. The forebody flow field of the F-18 HARV is fairly symmetric at zero sideslip and has distinct, well-defined vortices. The X-29A forebody vortices are more diffuse and are sometimes asymmetric at zero sideslip. These asymmetries correlate with observed zero-sideslip aircraft yawing moments.

Bjarke, Lisa J.↗

NASA NTRS1992

A summary of the forebody high-angle-of-attack aerodynamics research on the F-18 and the X-29A aircraft

Bjarke, Lisa J.↗

NASA NTRS1982

3-D supersonic combustion experiments with hydrogen in V-trough

Both supersonic blowdown and free jet wind tunnels were used in oil flow visualization and hydrogen gas burning tests of 60- and 90-deg V-shaped trough combustion characteristics. Oil dots showed that mass outflow from the reattachment region at the bottom of the V-trough dominated flow behavior, and occupied the trough's entire length and 10% of its cross-section. Intermingled vortex pairs were also found to superimpose themselves upon the outflow, and hydrogen burning within troughs reduced missile base drag by 25%. The troughs were aligned so that their long dimensions were parallel to the airflow, and the two top edges of the V section were mounted flush with respect to the upstream flat surfaces. Step heights tested ranged from 3.4 mm to 6.25 cm.

Friedberg, R. A.↗

NASA NTRS1987

An investigation of the flow characteristics in the blade endwall corner region

Studies were undertaken to determine the structure of the flow in the blade end wall corner region simulated by attaching two uncambered airfoils on either side of a flat plate with a semicircular leading edge. Detailed measurements of the corner flow were obtained with conventional pressure probes, hot wire anemometry, and flow visualization. The mean velocity profiles and six components of the Reynolds stress tensor were obtained with an inclined single sensor hot wire probe whereas power spectra were obtained with a single sensor oriented normal to the flow. Three streamwise vortices were identified based on the surface streamlines, distortion of total pressure profiles, and variation of mean velocity components in the corner. A horseshoe vortex formed near the leading edge of the airfoil. Within a short distance downstream, a corner vortex was detected between the horseshoe vortex and the surfaces forming the corner. A third vortex was formed at the rear portion of the corner between the corner vortex and the surface of the flat plate. Turbulent shear stress and production of turbulence are negligibly small. A region of negative turbulent shear stress was also observed near the region of low turbulence intensity from the vicinity of the flat plate.

Hazarika, Birinchi K.↗

NASA NTRS1993

Analytical modeling and sensor monitoring for optimal processing of advanced textile structural composites by resin transfer molding

A two-dimensional model of the resin transfer molding (RTM) process was developed which can be used to simulate the infiltration of resin into an anisotropic fibrous preform. Frequency dependent electromagnetic sensing (FDEMS) has been developed for in situ monitoring of the RTM process. Flow visualization tests were performed to obtain data which can be used to verify the sensor measurements and the model predictions. Results of the tests showed that FDEMS can accurately detect the position of the resin flow-front during mold filling, and that the model predicted flow-front patterns agreed well with the measured flow-front patterns.

Loos, Alfred C.↗

NASA NTRS1997

Improved Optical Techniques for Studying Sonic and Supersonic Injection into MACH-3 Flow. Video Supplement E-10853-V

This video supplements a report examining optical techniques for studying sonic and supersonic injection into MACH-3 flow The study used an injection-seeded, frequency doubled ND:YAG pulsed laser to illuminate a transverse section of the injectant plume. Rayleigh scattered light was passed through an iodine absorption cell to suppress stray laser light and was imaged onto a cooled CCD camera. The scattering was based on condensation of water vapor in the injectant flow. High speed shadowgraph flow visualization images were obtained with several video camera systems. Roof and floor static pressure data are presented several ways for the three configurations of injection designs with and without helium and/or air injection into Mach 3 flow.

Buggele, A. E.↗

NASA NTRS1978

Water-tunnel experiments on an oscillating airfoil at RE equals 21,000

Flow visualization experiments were performed in a water tunnel on a modified NACA 0012 airfoil undergoing large amplitude harmonic oscillations in pitch. Hydrogen bubbles were used to: (1) create a conveniently striated and well preserved set of inviscid flow markers; and (2) to expose the succession of events occurring within the viscous domain during the onset of dynamic stall. Unsteady effects were shown to have an important influence on the progression of flow reversal along the airfoil surface prior to stall. A region of reversed flow underlying a free shear layer was found to momentarily exist over the entire upper surface without any appreciable disturbance of the viscous-inviscid boundary. A flow protuberance was observed to develop near the leading edge, while minor vortices evolve from an expanding instability of the free shear layer over the rear portion of the airfoil. The complete breakdown of this shear layer culminates in the successive formation of two dominant vortices.

Mcalister, K. W.↗

NASA NTRS1986

An experimental investigation of vortex breakdown on a delta wing

An experimental investigation of vortex breakdown on delta wings at high angles is presented. Thin delta wings having sweep angles of 70, 75, 80 and 85 degrees are being studied. Smoke flow visualization and the laser light sheet technique are being used to obtain cross-sectional views of the leading edge vortices as they break down. At low tunnel speeds (as low as 3 m/s) details of the flow, which are usually imperceptible or blurred at higher speeds, can be clearly seen. A combination of lateral and longitudinal cross-sectional views provides information on the three dimensional nature of the vortex structure before, during and after breakdown. Whereas details of the flow are identified in still photographs, the dynamic characteristics of the breakdown process were recorded using high speed movies. Velocity measurements were obtained using a laser Doppler anemometer with the 70 degree delta wing at 30 degrees angle of attack. The measurements show that when breakdown occurs the core flow transforms from a jet-like flow to a wake-like flow.

Payne, F. M.↗

NASA NTRS1990

Computational flow simulation of liquid oxygen in a SSME preburner injector element LOX post

Liquid oxygen (LOX) is simulated as an incompressible flow through a Space Shuttle main engine fuel preburner injector element LOX post for the full range of operating conditions. Axial profiles of axial velocity and static pressure are presented. For each operating condition analyzed, the minimum pressure downstream of the orifice is compared to the vapor pressure to determine if cavitation could occur. Flow visualization is provided by velocity vectors and stream function contours. The results indicate that the minimum pressure is too high for cavitation to occur. To establish confidence in the CFD analysis, the simulation is repeated with water flow through a superscaled LOX post and compared with experimental results. The agreement between calculated and experimental results is very good.

Rocker, Marvin↗

NASA NTRS1988

Observation of airplane flow fields by natural condensation effects

In-flight condensation patterns can illustrate a variety of airplane flow fields, such as attached and separated flows, vortex flows, and expansion and shock waves. These patterns are a unique source of flow visualization that has not been utilized previously. Condensation patterns at full-scale Reynolds number can provide useful information for researchers experimenting in subscale tunnels. It is also shown that computed values of relative humidity in the local flow field provide an inexpensive way to analyze the qualitative features of the condensation pattern, although a more complete theoretical modeling is necessary to obtain details of the condensation process. Furthermore, the analysis revealed that relative humidity is more sensitive to changes in local static temperature than to changes in pressure.

Campbell, James F.↗

NASA NTRS1988

Vortex breakdown in channel flow transition

The time-dependent three-dimensional incompressible Navier-Stokes equations are used to study the mechanisms and developing structures comprising the later stages of the transition to turbulence in plane channel flow. Computer animated flow visualizatons are employed using three-dimensional vortex lines and other graphical representations. The flow visualizations clearly show the development of organized structures such as vortex loops, horse-show vortices, and vortex rings. It is noted that the development of these structures is similar to the bursting process found in turbulent channel flow.

Biringen, S.↗

NASA NTRS1988

Wind-tunnel investigation of the forebody aerodynamics of a vortex-lift fighter configuration at high angles of attack

Results of a recent low-speed wind-tunnel investigation conducted to define the forebody flow on a 16-percent scale model of the NASA High Angle-of-Attack Research Vehicle, an F-18 configuration, are presented with analysis. Measurements include force and moment data, oil-flow visualizations, and surface pressure data taken at angles of attack near and above maximum lift (36 to 52 deg) at a Reynolds number of one million (based on mean aerodynamic chord). The results presented identify the key flow-field features on the forebody including the wing-body strake.

Banks, Daniel W.↗