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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS2016

Development of Hydroxyl Tagging Velocimetry for Low Velocity Flows

Hydroxyl tagging velocimetry (HTV) is a molecular tagging technique that relies on the photo-dissociation of water vapor into OH radicals and their subsequent tracking using laser induced fluorescence. Velocities are then obtained from time-of-flight calculations. At ambient temperature in air, the OH species lifetime is relatively short (<50 μs), making it suited for high speed flows. Lifetime and radicals formation increases with temperature, which allows HTV to also probe low-velocity, high-temperature flows or reacting flows such as flames. The present work aims at extending the domain of applicability of HTV, particularly towards low-speed (<10 m/s) and moderate (<500 K) temperature flows. Results are compared to particle image velocimetry (PIV) measurements recorded in identical conditions. Single shot and averaged velocity profiles are obtained in an air jet at room temperature. By modestly raising the temperature (100-200 degC) the OH production increases, resulting in an improvement of the signal-to-noise ratio (SNR). Use of nitrogen - a non-reactive gas with minimal collisional quenching - extends the OH species lifetime (to over 500 μs), which allows probing of slower flows or, alternately, increases the measurement precision at the expense of spatial resolution. Instantaneous velocity profiles are resolved in a 100degC nitrogen jet (maximum jet-center velocity of 6.5 m/s) with an uncertainty down to 0.10 m/s (1.5%) at 68% confidence level. MTV measurements are compared with particle image velocimetry and show agreement within 2%.

Andre, Matthieu A.↗
NASA NTRS1951

A general integral form of the boundary-layer equation for incompressible flow with an application to the calculation of the separation point of turbulent boundary layers

A general integral form of the boundary-layer equation, valid for either laminar or turbulent incompressible boundary-layer flow, is derived. By using the experimental finding that all velocity profiles of the turbulent boundary layer form essentially a single-parameter family, the general equation is changed to an equation for the space rate of change of the velocity-profile shape parameter. The lack of precise knowledge concerning the surface shear and the distribution of the shearing stress across turbulent boundary layers prevented the attainment of a reliable method for calculating the behavior of turbulent boundary layers.

Tetervin, Neal↗
NASA NTRS2007

Analysis Method for Non-Nominal First Acquisition

First this paper describes a method how the trajectory of the launcher can be modelled for the contingency analysis without having much information about the launch vehicle itself. From a dense sequence of state vectors a velocity profile is derived which is sufficiently accurate to enable the Flight Dynamics Team to integrate parts of the launcher trajectory on its own and to simulate contingency cases by modifying the velocity profile. Then the paper focuses on the thorough visibility analysis which has to follow the contingency case or burn performance simulations. In the ideal case it is possible to identify a ground station which is able to acquire the satellite independent from the burn performance. The correlations between the burn performance and the pointing at subsequent ground stations are derived with the aim of establishing simple guidelines which can be applied quickly and which significantly improve the chance of acquisition at subsequent ground stations. In the paper the method is applied to the Soyuz/Fregat launch with the MetOp satellite. Overall the paper shows that the launcher trajectory modelling with the simulation of contingency cases in connection with a ground station visibility analysis leads to a proper selection of ground stations and acquisition methods. In the MetOp case this ensured successful contact of all ground stations during the first hour after separation without having to rely on any early orbit determination result or state vector update.

Sieg, Detlef↗
NASA NTRS2003

Rough-Wall Channel Analysis Using Suboptimal Control Theory

The original aim of this work was to shed some light on the physics of turbulence over rough walls using large-eddy simulations and the suboptimal-control wall boundary conditions introduced by Nicoud et al. It was hoped that, if that algorithm was used to fit the mean velocity profile of the simulations to that of a rough-walled channel, instead of to a smooth one, the wall stresses introduced by the control algorithm would give some indication of what aspects of rough walls are most responsible for the modification of the flow in real turbulence. It was similarly expected that the structure of the resulting velocity fluctuations would share some of the characteristics of rough-walled flows, thus again suggesting what is intrinsic and what is accidental in the effect of geometric wall roughness. A secondary goal was to study the effect of 'unphysical' boundary conditions on the outside flow by observing how a relatively major change of the target velocity profile, and therefore presumably of the applied wall stresses, modifies properties such as the dominant length scales of the velocity fluctuations away from the wall. As will be seen below, this secondary goal grew more important during the course of the study, which was carried out during a short summer visit of the first two authors to the CTR. It became clear that there are open questions about the way in which the control algorithm models the boundary conditions, even for smooth walls, and that these questions make the physical interpretation of the results difficult. Considerable more work in that area seems to be needed before even relatively advanced large-eddy simulations, such as these, can be used to draw conclusions about the physics of wall-bounded turbulent flows. The numerical method is the same as in Nicoud et al. The modifications introduced in the original code are briefly described in section 2, but the original paper should be consulted for a full description of the algorithm. The results are presented in section 3 and summarized in section 4. The elementary properties of turbulence over rough walls which are used in the text have been taken from recent reviews such as Raupach et al. or Jimenez.

Flores, O.↗
NASA NTRS2003

Coordinated turn-and-reach movements. II. Planning in an external frame of reference

The preceding study demonstrated that normal subjects compensate for the additional interaction torques generated when a reaching movement is made during voluntary trunk rotation. The present paper assesses the influence of trunk rotation on finger trajectories and on interjoint coordination and determines whether simultaneous turn-and-reach movements are most simply described relative to a trunk-based or an external reference frame. Subjects reached to targets requiring different extents of arm joint and trunk rotation at a natural pace and quickly in normal lighting and in total darkness. We first examined whether the larger interaction torques generated during rapid turn-and-reach movements perturb finger trajectories and interjoint coordination and whether visual feedback plays a role in compensating for these torques. These issues were addressed using generalized Procrustes analysis (GPA), which attempts to overlap a group of configurations (e.g., joint trajectories) through translations and rotations in multi-dimensional space. We first used GPA to identify the mean intrinsic patterns of finger and joint trajectories (i.e., their average shape irrespective of location and orientation variability in the external and joint workspaces) from turn-and-reach movements performed in each experimental condition and then calculated their curvatures. We then quantified the discrepancy between each finger or joint trajectory and the intrinsic pattern both after GPA was applied individually to trajectories from a pair of experimental conditions and after GPA was applied to the same trajectories pooled together. For several subjects, joint trajectories but not finger trajectories were more curved in fast than slow movements. The curvature of both joint and finger trajectories of turn-and-reach movements was relatively unaffected by the vision conditions. Pooling across speed conditions significantly increased the discrepancy between joint but not finger trajectories for most subjects, indicating that subjects used different patterns of interjoint coordination in slow and fast movements while nevertheless preserving the shape of their finger trajectory. Higher movement speeds did not disrupt the arm joint rotations despite the larger interaction torques generated. Rather, subjects used the redundant degrees of freedom of the arm/trunk system to achieve similar finger trajectories with differing joint configurations. We examined finger movement patterns and velocity profiles to determine the frame of reference in which turn-and-reach movements could be most simply described. Finger trajectories of turn-and-reach movements had much larger curvatures and their velocity profiles were less smooth and less bell-like in trunk-based coordinates than in external coordinates. Taken together, these results support the conclusion that turn-and-reach movements are controlled in an external frame of reference.

NASA Discipline Neuroscience↗
NASA NTRS1972

Analysis and testing of high entrainment single nozzle jet pumps with variable mixing tubes

An analytical model was developed to predict the performance characteristics of axisymmetric single-nozzle jet pumps with variable area mixing tubes. The primary flow may be subsonic or supersonic. The computer program uses integral techniques to calculate the velocity profiles and the wall static pressures that result from the mixing of the supersonic primary jet and the subsonic secondary flow. An experimental program was conducted to measure mixing tube wall static pressure variations, velocity profiles, and temperature profiles in a variable area mixing tube with a supersonic primary jet. Static pressure variations were measured at four different secondary flow rates. These test results were used to evaluate the analytical model. The analytical results compared well to the experimental data. Therefore, the analysis is believed to be ready for use to relate jet pump performance characteristics to mixing tube design.

Hickman, K. E.↗
NASA NTRS1979

Theoretical fan velocity distortions due to inlets and nozzles

Nonuniform velocity profiles imposed on the propulsion system fan can cause fan blade stresses and thrust losses. A theoretical parametric study of the effects of inlets with 0 deg and 90 deg nozzle deflection on the velocity profile at a hypothetical fan is presented. The parameters investigated are fan-to-nozzle spacing and inlet centerline offset. The interaction between the inlet and nozzle is also investigated. The study is made using a two-dimensional analysis.

Hawk, J. D.↗
NASA NTRS1972

Turbulent boundary layer on a rotating helical blade.

Investigation of the boundary-layer characteristics on a helical blade of large chord length, enclosed in an annulus and rotating in a fluid otherwise at rest. The three-dimensional form of momentum integral equations is derived, and is used to predict the boundary-layer growth and limiting streamline angles on the blade surface. The measurements are in general agreement with the predictions. The wall shear stress correlation, which includes both Reynolds number and rotation parameters, valid for a rotating blade operating at zero pressure gradient, is derived. Radial and tangential velocity profiles, the tangential component of turbulence intensity, and blade static pressures are measured at several locations on the blade surface. The nature of flow near the blade tip is discussed. An expression for the radial velocity profile, valid in the outer region of the boundary layer, is derived theoretically.

Lakshminarayana, B.↗
NASA NTRS1997

Investigation of Mixing a Supersonic Stream with the Flow Downstream of a Wedge

The flow characteristics in the base region of a two-dimensional supersonic compression ramp are investigated. A stream-wise oriented air jet, M = 1.75, is injected through a thin horizontal slot into a supersonic air main flow, M = 2.3, at the end of a two-dimensional compression ramp. The velocity profile and basic characteristics of the flow in the base region immediately following the ramp are determined. Visualization of the flowfield for qualitative observations is accomplished via Dark Central Ground Interferometry (DCGI). Two-dimensional velocity profiles are obtained using Laser Doppler Velocimetry (LDV). The study is the initial phase of a four-year investigation of base flow mixing. The current study is to provide more details of the flowfield.

Sheeley, Joseph↗
NASA NTRS2019

Comparison of Boundary Layer Similarity Transformations for High Mach Number Flows

Reynolds averaged Navier-Stokes (RANS) simulations of the turbulent boundary layer flow on a flat plate are performed across a Mach number range of 0.3 up to 16 using the computational fluid dynamics (CFD) software, VULCAN-CFD. The simulation results are used to evaluate the ability of the Van Driest transformation and the transformation of Trettel and Larsson to collapse boundary layer velocity profiles under various flow conditions across the range of Mach numbers. The flat platewall boundary conditions and leading edge geometry are varied from adiabatic to isothermal and sharp to blunted to reveal the physics of how these effects impact the performance of the chosen flow transformations. Results indicate that the transformation of Trettel and Larsson produces a better collapse of velocity profile data than the Van Driest transformation regardless of Mach number, wall boundary condition, or leading edge geometry. In addition, the velocity gradients obtained from the transformation of Trettel and Larsson match the normalized untransformed velocity gradients much more closely than those obtained using the Van Driest transformation.

DiGregorio, Nicholas J.↗
NASA NTRS1991

Laser Doppler velocimetry for continuous flow solar-pumped iodine laser system

A laser Doppler velocimetry (LDV) system was employed to measure the flow velocity profile of iodide vapor inside laser tubes of 36 mm ID and 20 mm ID. The LDV, which was operated in the forward scatter mode used a low power (15 mW) He-Ne laser beam. Velocity ranges from 1 m/s was measured to within one percent accuracy. The flow velocity profile across the laser tube was measured and the intensity of turbulence was determined. The flow of iodide inside the laser tube demonstrated a mixture of both turbulence and laminar flow. The flowmeter used for the laser system previously was calibrated with the LDV and found to be in good agreement.

Tabibi, Bagher M.↗
NASA NTRS1993

The role of the margins in ice stream dynamics

At first glance, it would appear that the bed of the active ice stream plays a much more important role in the overall force balance than do the margins, especially because the ratio of the half-width to depth for a typical ice stream is large (15:1 to 50:1). On the other hand, recent observations indicate that at least part of the ice stream is underlain by a layer of very weak till (shear strength about 2 kPa), and this weak basal layer would then imply that some or all of the resistive drag is transferred to the margins. In order to address this question, a detailed velocity profile near Upstream B Camp, which extends from the center of the ice stream, across the chaotic shear margin, and onto the Unicorn, which is part of the slow-moving ice sheet was measured. Comparison of this observed velocity profile with finite-element models of flow shows several interesting features. First, the shear stress at the margin is on the order of 130 kPa, while the mean value along the bed is about 15 kPa. Integration of these stresses along the boundaries indicates that the margins provide 40 to 50 percent, and the bed, 60 to 40 percent of the total resistive drag needed to balance the gravitational driving stress in this region. (The range of values represents calculations for different values of surface slope.) Second, the mean basal stress predicted by the models shows that the entire bed cannot be blanketed by the weak till observed beneath upstream B - instead there must be a distribution of weak till and 'sticky spots' (e.g., 85 percent till and 15 percent sticky spots of resistive stress equal to 100 kPa). If more of the bed were composed of weak till, then the modeled velocity would not match that observed. Third, the ice must exhibit an increasing enhancement factor as the margins are approached (E equals 10 in the chaotic zone), in keeping with laboratory measurements on ice under prolonged shear strain. Also, there is either a narrow zone of somewhat stiffer ice (E equals 5) outward of the shear margin, or the bed is frozen there. And last, the high shear stress and strain rate found at the margin are likely to cause significant viscous heating (q) in the marginal ice. The increase in temperature is proportional to qX/u, where X is the width of the shear zone and u is the transverse velocity component bringing cold ice in from the ice sheet outside the shear zone. Near upstream B, this heating is likely to cause an increase in temperature of 4 to 10 K. Plans are to measure this temperature increase in a series of bore holes near the margin during the 1992-93 field season, as well as to provide a more detailed description of the velocity field there.

Echelmeyer, Keith↗
NASA NTRS1979

Theoretical fan velocity distortions due to inlets and nozzles

Nonuniform velocity profiles imposed on the propulsion system fan can cause fan blade stresses and thrust losses. This paper presents a theoretical parametric study of the effects of inlets with 0 deg and 90 deg nozzle deflection on the velocity profile at a hypothetical fan. The parameters investigated are fan-to-nozzle spacing and inlet centerline offset. The interaction between the inlet and nozzle is also investigated. The study is made using a two-dimensional analysis

Hawk, J. D.↗
NASA NTRS1984

Experimental studies of the separated flow over a NASA GA(W)-1 airfoil

The separated flow over the 17-percent-thick blunt-trailing-edge NASA GA(W)-1 airfoil is investigated experimentally at angles of attack 10.3-18.4 deg and velocities up to 92 m/sec in the 1.09 x 0.76 x 1.22-m working section of a closed-circuit wind tunnel, with typical Reynolds numbers of the order 4 x 10 to the 6th. The results are presented graphically and characterized. Separated-flow velocity profiles and skin-friction distributions are obtained, and the boundary-layer integral properties are shown to be in good agreement with the separation criteria of Sandborn and Kline (1961). The chordwise development of the mean velocity is reduced to a universal curve, and some similarity is found in the outer-region velocity profiles downstream of the separation.

Mehta, J. M.↗
NASA NTRS2013

Trip-Induced Transition Measurements in a Hypersonic Boundary Layer Using Molecular Tagging Velocimetry

Measurements of mean streamwise velocity, fluctuating streamwise velocity, and instantaneous streamwise velocity profiles in a hypersonic boundary layer were obtained over a 10-degree half-angle wedge model. A laser-induced fluorescence-based molecular tagging velocimetry technique was used to make the measurements. The nominal edge Mach number was 4.2. Velocity profiles were measured both in an untripped boundary layer and in the wake of a 4-mm diameter cylindrical tripping element centered 75.4 mm downstream of the sharp leading edge. Three different trip heights were investigated: k = 0.53 mm, k = 1.0 mm and k = 2.0 mm. The laminar boundary layer thickness at the position of the measurements was approximately 1 mm, though the exact thickness was dependent on Reynolds number and wall temperature. All of the measurements were made starting from a streamwise location approximately 18 mm downstream of the tripping element. This measurement region continued approximately 30 mm in the streamwise direction. Additionally, measurements were made at several spanwise locations. An analysis of flow features show how the magnitude, spatial location, and spatial growth of streamwise velocity instabilities are affected by parameters such as the ratio of trip height to boundary layer thickness and roughness Reynolds number. The fluctuating component of streamwise velocity measured along the centerline of the model increased from approximately 75 m/s with no trip to +/-225 m/s with a 0.53-mm trip, and to +/-240 m/s with a 1-mm trip, while holding the freestream Reynolds number constant. These measurements were performed in the 31-inch Mach 10 Air Tunnel at the NASA Langley Research Center.

Bathel, Brett F.↗
NASA NTRS1987

Control of turbulence through a row of Helmholtz resonators

The manipulation of turbulent boundary layers is useful in a variety of situations including drag reduction and separation delay. In this study a passive method of altering the turbulence in a boundary layer is investigated. Ten Helmholtz resonators were imbedded in a spanwise row under a turbulent boundary layer. At certain airspeeds the resonators were strongly excited by the turbulence. In turn, the resonator motions interact to modify the turbulence and mean velocity profiles in the boundary layer. Tests were conducted to measure the response of the resonators as a function of freestream speed. Additional tests, conducted at the conditions for maximum response, documented the affect on the mean and turbulent velocity profiles.

Panton, Ronald L.↗
NASA NTRS1992

Wall functions for the kappa-epsilon turbulence model in generalized nonorthogonal curvilinear coordinates

A k-epsilon turbulence model suitable for compressible flow, including the new wall function formulation, has been incorporated into an existing compressible Reynolds-averaged Navier-Stokes code, F3D. The low Reynolds number k-epsilon model of Chien (1982) was added for comparison with the present method. A number of features were added to the F3D code including improved far-field boundary conditions and viscous terms in the streamwise direction. A series of computations of increasing complexity was run to test the effectiveness of the new formulation. Flow over a flat plate was computed by using both orthogonal and nonorthogonal grids, and the friction coefficients and velocity profiles compared with a semi-empirical equation. Flow over a body of revolution at zero angle of attack was then computed to test the method's ability to handle flow over a curved surface. Friction coefficients and velocity profiles were compared to test data. All models gave good results on a relatively fine grid, but only the wall function formulation was effective with coarser grids. Finally, in order to demonstrate the method's ability to handle complex flow fields, separated flow over a prolate spheroid at angle of attack was computed, and results were compared to test data. The results were also compared to a k-epsilon model by Kim and Patel (1991), in which one equation model patched in at the wall was employed. Both models gave reasonable solutions, but improvement is required for accurate prediction of friction coefficients in the separated regions.

Sondak, D. L.↗
NASA NTRSDate not supplied

Hydroxyl Tagging Velocimetry Demonstration in an Augmented Spark Igniter

Hydroxyl tagging velocimetry (HTV) involves tagging a flow by “writing” a line of OH molecules using a laser beam to dissociate H2O molecules and capturing an image of the line after a short delay using laser-induced fluorescence. Velocity is obtained by a time-of-flight analysis of the data. In this effort, HTV was used for obtaining both instantaneous and average velocity profiles in the flow of an augmented spark igniter. Two modes of camera readout were investigated, called conventional full frame mode and dual image mode feature (DIF) mode. In DIF mode, two images are captured in quick succession and therefore the measurement is immune to vibration effects. Measurement uncertainty for the DIF case varied from 3% at the centerline to 10% at the edges of the profile in a 1000-m/s flow. For the full-frame case, measurement uncertainty varied from 3% at the centerline to 7% at the edges. This demonstration provides evidence that the HTV technique is well suited for obtaining velocity profiles in the challenging environment of either a rocket engine or rocket engine igniter.

Augmented Spark Igniter↗