Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “shear flow”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Time dependent inflow-outflow boundary conditions for 2D acoustic systems

An analysis of the number and form of the required inflow-outflow boundary conditions for the full two-dimensional time-dependent nonlinear acoustic system in subsonic mean flow is performed. The explicit predictor-corrector method of MacCormack (1969) is used. The methodology is tested on both uniform and sheared mean flows with plane and nonplanar sources. Results show that the acoustic system requires three physical boundary conditions on the inflow and one on the outflow boundary. The most natural choice for the inflow boundary conditions is judged to be a specification of the vorticity, the normal acoustic impedance, and a pressure gradient-density gradient relationship normal to the boundary. Specification of the acoustic pressure at the outflow boundary along with these inflow boundary conditions is found to give consistent reliable results. A set of boundary conditions developed earlier, which were intended to be nonreflecting is tested using the current method and is shown to yield unstable results for nonplanar acoustic waves.

Watson, Willie R.↗
DOE OSTI2021

Grid resolution requirement for resolving rare and high intensity wall-shear stress events in direct numerical simulations

Turbulent signals are intermittent with large instantaneous fluctuations. Such large fluctuations lead to small Kolmogorov scales that are hard to resolve in numerical simulations [P. K. Yeung, K. R. Sreenivasan, and S. B. Pope, Effects of finite spatial and temporal resolution in direct numerical simulations of incompressible isotropic turbulence, Phys. Rev. Fluids 3, 064603 (2018)]. Here, the present paper follows the above basic logic, but instead of dissipation events in isotropic turbulence, we study wall-shear stress events in plane channel flow. Wall-shear stress fluctuations are increasingly more intermittent as the Reynolds number increases. Hence, one has to employ higher grid resolutions as the Reynolds number increases in order to resolve a given percentage of wall-shear stress events. The objective of this paper is to quantify effects of the grid resolutions on the rare and high intensity wall-shear stress events. We find that the standard grid resolution resolves about 99% of the wall-shear stress events at Re τ = 180. A slightly higher grid resolution has to be employed in order to resolve 99% of the wall-shear stress events at higher Reynolds numbers, and if the standard grid resolution is used for, e.g., a Re τ = 10000 channel flow, one resolves about 90%–95% wall-shear stress events.

42 ENGINEERING↗
NASA NTRS1999

Turbulent Diffusivities for Momentum, Heat, Salt and Passive Scalars

A program began ten years ago to build a turbulence model to describe high Reynolds numbers flows. Specifically, the aim was to devise a model that would satisfy two basic conditions: reproduce available turbulence data (laboratory, numerical simulations, etc.) concerning shear driven flows, buoyancy driven flows, 2D turbulence, freely decaying turbulence etc., and yet be manageable so as to be used, for example, in GCM'S. The model was presented in a series of papers that have appeared in Physics of Fluids since 1996. A total of about 80 turbulence statistics were reproduced. The model has no adjustable parameters. The next step was to apply the model to construct the vertical diffusities K for moment K(sub m), temperature K(sub h), salt K(sub s), and passive scalars K(sub c). First, we took K(sub c) = K(sub h) and tested the model using the GFDL ocean model. The results for the profiles of T and S vs. depth are indistinguishable from those derided using the latest model, the KPP model by the NCAR group. Presently, we are running the same GFDL code relaxing the assumptive K(sub c) = K(sub h). Indeed, the turbulence model yelds a salt diffusivity that depends on R(sub i) and R(sub rho) = ((beta)(delta)S/(alpha)(delta)T/(delta)z) in such a way that K(sub s) may be quite different from K(sub h). Salt fingers and double diffusivity laboratory data are reproduced. Results from the ocean model will be available shortly. Finally, we are trying to derive the horizontal diffusivities with the goal of providing a physically acceptable representation of mesoscale eddies. The recently suggested GMW parameterization has improved several O-GCM results and the goal here is to try to derive/justify it from a turbulence model and/or propose improvements/modifications. Theoretical work is in progress.

Canuto, V. M.↗
NASA NTRS1999

Turbulent Diffusivities for Momentum, Heat, Salt and Passive Scalars

A program began ten years ago to build a turbulence model to describe high Reynolds numbers flows. Specifically, the aim was to devise a model that would satisfy two basic conditions: reproduce available turbulence data (laboratory, numerical simulations, etc.) concerning shear driven flows, buoyancy driven flows, 2D turbulence, freely decaying turbulence etc., and yet be manageable so as to be used, for example, in General Circulation Models (GCM'S). The model was presented in a series of papers that have appeared in Physics of Fluids since 1996. A total of about 80 turbulence statistics were reproduced. The model has no adjustable parameters. The next step was to apply the model to construct the vertical diffusities K for moment K(sub m), temperature K(sub h), salt K(sub s). and passive scalars K(sub c). First, we took K(sub s) = K(sub h) and tested the model using the GFDL ocean model. The results for the profiles of T and S vs. depth are indistinguishable from those derived using the latest model, the KPP model by the NCAR group. Presently, we are running the same Geophysical Fluid Dynamics Laboratory (GFDL) code relaxing the assumptive K(sub s) = K(sub h). Indeed, the turbulence model yields a salt diffusivity that depends on Ri and R rho (= Beta delta S/delta z/alpha delta T/delta z) in such a way that K(sub s) may be quite different from K(sub h). Salt fingers and double diffusivity laboratory data are reproduced. Results from the ocean model will be available shortly. Finally, we are trying to derive the horizontal diffusivities with the goal of providing a physically acceptable representation of mesoscale eddies. The recently suggested GMW parameterization has improved several O-GCM results and the goal here is to try to derive/justify it from a turbulence model and/or propose improvements/modifications. Theoretical work is in progress.

Canuto, V. M.↗
NASA NTRS1999

Turbulent Diffusivities for Momentum, Heat, Salt and Passive Scalars

A program began ten years ago to build a turbulence model to describe high Reynolds numbers flows. Specifically, the aim was to devise a model that would satisfy two basic conditions: reproduce available turbulence data (laboratory, numerical simulations, etc.) concerning shear driven flows, buoyancy driven flows, 2D turbulence, freely decaying turbulence etc., and yet be manageable so as to be used, for example, in GCM'S. The model was presented in a series of papers that have appeared in Physics of FLuids since 1996. A total of about 80 turbulence statistics were reproduced. The model has no adjustable parameters. The next step was to apply the model to construct the vertical diffusivities K for moment K(sub m), temperature K(sub h), salt K(sub g) and passive scalars K(sub c). First, we took K(sub g) = K(sub h) and tested the model using the Geophysical Fluid Dynamics Laboratory (GFDL) ocean model. The results for the profiles of T and S vs. depth are indistinguishable from those derided using the latest model, the KPP model by the NCAR group. Presently, we are running the same GFDL code relaxing the assumptive K(sub g) = K(sub h). Indeed, the turbulence model yields a salt diffusivity that depends on Ri and R Rho (= Beta Sigma S/Sigma z/Alpha Sigma T/Sigma z) in such a way that K(sub g) may be quite different from K(sub h). Salt fingers and double diffusivity laboratory data are reproduced. Results from the ocean model will be available shortly. Finally, we are trying to derive the horizontal diffusivities with the goal of providing a physically acceptable representation of mesoscale eddies. The recently suggested GMW parameterization has improved several O-GCM results and the goal here is to try to derive/justify it from a turbulence model and/or propose improvements/modifications. Theoretical work is in progress.

Canuto, Vittorio↗
NASA NTRS1975

Numerical simulation of turbulence in the presence of shear

The numerical calculations are presented of the large eddy structure of turbulent flows, by use of the averaged Navier-Stokes equations, where averages are taken over spatial regions small compared to the size of the computational grid. The subgrid components of motion are modeled by a local eddy-viscosity model. A new finite-difference scheme is proposed to represent the nonlinear average advective term which has fourth-order accuracy. This scheme exhibits several advantages over existing schemes with regard to the following: (1) the scheme is compact as it extends only one point away in each direction from the point to which it is applied; (2) it gives better resolution for high wave-number waves in the solution of Poisson equation, and (3) it reduces programming complexity and computation time. Examples worked out in detail are the decay of isotropic turbulence, homogeneous turbulent shear flow, and homogeneous turbulent shear flow with system rotation.

Shaanan, S.↗
DOE OSTI2025

Let’s Stick Together: Interplay of Moisture, Particle Size, and Anatomical Fraction in the Flowability of Corn Stover Crumbles

Handling of agricultural waste biomass feedstocks (such as corn stover) is a persistent challenge in the production of biofuels and chemicals at integrated biorefineries. Inconsistent flowability and high feedstock variability creates equipment downtime and processing challenges. This work investigates the influence of anatomical fractionation and moisture content on the bulk solids handling behavior of corn stover crumbles. A combination of rotational shear testing, tribological measurements, and surface and sorption characterization techniques (inverse gas chromatography (IGC), dynamic vapor sorption (DVS), and electron microscopy) were used to evaluate the contributions of particle composition, size, and surface properties to flow behavior. Shear and frictional testing revealed that moisture content has the greatest effect on flowability, significantly increasing unconfined yield strength (ƒ c ) and reducing the flow function coefficient (F F C), regardless of anatomical fraction. While differences in surface energy were observed between fractions, particularly in polar contributions (γ AB ), these did not correspond to meaningful differences in flow behavior. Coarser 6 mm particles exhibited poorer flow performance than 4 mm crumbles, likely due to broader particle size distributions and increased particle interlocking. Taken together, these results suggest that anatomical fractionation provides minimal benefit from a bulk handling perspective. Moisture content and particle size heterogeneity dominate handling behavior, reinforcing the utility of unfractionated corn stover in processing environments. These insights can inform the design of more efficient and reliable feedstock processing systems for agricultural biomass in integrated biorefineries.

09 BIOMASS FUELS↗
NASA NTRS1996

Liquid Crystals Indicate Directions Of Surface Shear Stresses

Report consisting of main text of U.S. Patent 5,394,752 presents detailed information on one aspect of method of using changes in colors of liquid-crystal coatings to indicate instantaneous directions of flow-induced shear stresses (skin friction) on aerodynamic surfaces.

Reda, Daniel C.↗
NASA NTRS1976

New theory of the Great Red Spot from solitary waves in the Jovian atmosphere

It is shown that many characteristics of the Great Red Spot (GRS) and numerous other features that have been observed on Jupiter can be explained by solitary waves on a horizontally sheared zonal flow in a rotating, stratified atmosphere. Streamline patterns for waves corresponding to combined depression-elevation solitary waves (D-E solitrons) show a strong resemblence to the flow around the GRS. The morphology and flow pattern of the South Tropical Disturbance indicate that it was a D solitron. Numerous spot-like features situated in regions between cloud bands where horizontal shear forces might be expected have the morphology of E solitrons. Restrictions placed on the atmospheric parameters by the model are consistent with available models and observations.

Maxworthy, T.↗
NASA NTRS1995

Effects of highly intermittent magnetic fields and plasma flows on solar wind dynamics

Filamentary magnetic fields and intermittent mass flows with highly variant physical parameters as observed in coronal holes provide, from a theoretical point of view, natural conditions for strongly nonlinear dynamics. The presence of sheared mass flows along fine scale magnetic structures results in strong nonlinear instability, most important of which is the explosive instability. We specify the physical conditions for several different manifestations of the onset of explosive instability and its further evolution: (1) fully developed explosive instability - explosive release of the energy; (2) shock formation - stabilization of instability by small scale spatial inhomogeneities leads to formation of subsequent shocks having a number of peculiarities that is determined by the interplay of thermal and viscous losses (for example, in predominance of thermal losses the isothermal jump occurs); and (3) solitary waves - stabilization of explosive instability by nonlinear dispersion effect leads to formation of a 'gas' of solitons which are later either damped away with characteristic time and energy input or evolve to solitons with explosively growing amplitudes. Each scenario is completely determined by the physical parameters of the medium, thus producing a quite uneven distribution of energy in a coronal hole and, respectively, an uneven outward propagation of the energy flux.

Ryutova, M.↗
NASA NTRS1971

A turbulence description of couette flow

Statistical mechanics for wall shear turbulence in couette flow based on Brownian motion and comparison with stochastic theory based on Navier-Stokes equation

Chung, P. M.↗
NASA NTRS1991

A laser fluorescence anemometer system for the Langley 16- by 24-inch water tunnel

A laser fluorescence anemometer which comprises a three-component laser Doppler velocimeter system with a fourth channel to measure fluorescent dye concentration has been installed in the NASA Langley 16- by 24-in water tunnel. The system includes custom designed optics, data acquisition, and traverse control instruments and a custom software package. Feasibility studies demonstrated how water tunnels can be used in conjunction with advanced optical techniques to provide nonintrusive detailed flow field measurements of complex fluid flows with a minimum of expense. The measurements show that the laser fluorescence anemometer can provide new insight into the structure, entrainment, control and of mixing vortical and shear layer flows.

Owen, F. K.↗
NASA NTRS1972

Transmission of sound in ducts with thin shear layers - Convergence to the uniform flow case.

The problem of the transmission of sound in a duct with very thin shear layers at the walls is treated by an inner expansion method. The results show that the formulation of the problem of the transmission of sound in a duct with a shear layer at the wall converges, in the case of a vanishingly thin shear layer, to the formulation of the same problem when uniform flow is assumed and the wall boundary condition is that of continuity of particle displacement.

Eversman, W.↗
NASA NTRS1976

Observations of velocity shear driven plasma turbulence

Electrostatic and magnetic turbulence observations from HAWKEYE-1 during the low altitude portion of its elliptical orbit over the Southern Hemisphere are presented. The magnetic turbulence is confined near the auroral zone and is similar to that seen at higher altitudes by HEOS-2 in the polar cusp. The electrostatic turbulence is composed of a background component with a power spectral index of 1.89 + or - .26 and an intense component with a power spectral index of 2.80 + or - .34. The intense electrostatic turbulence and the magnetic turbulence correlate with velocity shears in the convective plasma flow. Since velocity shear instabilities are most unstable to wave vectors perpendicular to the magnetic field, the shear correlated turbulence is anticipated to be two dimensional in character and to have a power spectral index of 3 which agrees with that observed in the intense electrostatic turbulence.

Kintner, P. M., Jr.↗
NASA NTRS1990

Mantle flow tectonics - The influence of a ductile lower crust and implications for the formation of topographic uplands on Venus

The crust and mantle of Venus can be represented by a model of a layered structure stratified in both density and viscosity. This structure consists of a brittle-elastic upper crustal layer; a ductile weaker crustal layer; a strong upper mantle layer, about 10 percent denser than the crust; and a weaker substrate, representing the portion of the mantle in which convective flow occurs which is a primary source of large-scale topographic and tectonic features. This paper examines the interactions between these four layers and the mantle flow driven by thermal or compositional variations. Solutions are found for a flow driven by a buoyancy-force distribution within the mantle and by relief at the surface and crust-mantle boundary. It is shown that changes in crustal thickness are driven by vertical normal stresses due to mantle flow and by shear coupling of horizontal mantle flow into the crust.

Bindschadler, Duane L.↗
NASA NTRS1993

A comparative study of computational solutions to flow over a backward-facing step

A comparative study was conducted for computational fluid dynamic solutions to flow over a backward-facing step. This flow is a benchmark problem, with a simple geometry, but involves complicated flow physics such as free shear layers, reattaching flow, recirculation, and high turbulence intensities. Three Reynolds-averaged Navier-Stokes flow solvers with k-epsilon turbulence models were used, each using a different solution algorithm: finite difference, finite element, and hybrid finite element - finite difference. Comparisons were made with existing experimental data. Results showed that velocity profiles and reattachment lengths were predicted reasonably well by all three methods, while the skin friction coefficients were more difficult to predict accurately. It was noted that, in general, selecting an appropriate solver for each problem to be considered is important.

Mizukami, M.↗
NASA NTRS1982

Hypersonic Laminar Viscous Flow Past Spinning Cones at Angle of Attack

Computational results are presented for hypersonic viscous flow past spinning sharp and blunt cones of angle of attack, obtained with a parabolic Navier-Stokes marching code. The code takes into account the asymmetries in the flowfield resulting from spinning motion and computes the asymmetric shock shape, cross-flow and streamwise shear, heat transfer, cross-flow separation, and vortex structure. The Magnus force and moments are also computed. Comparisons are made with other theoretical analyses based on boundary-layer and boundary-region equations, and an anomaly is discovered in the displacement thickness contribution to the Magnus force when compared with boundary-layer results.

Agarwal, Ramesh↗
NASA NTRS1987

Steady state flow/field model of solar wind interaction with Venus - Global implications of local effects

Physical and chemical processes in the Venus ionosphere driven by the interaction of the solar wind with the atmosphere of Venus are described, and a model describing the interrelationships of these processes in a self-consistent manner is formulated. It is shown that the magnetic field configuration of the ionosphere is a steady state global structure which results from a combination of a large-scale 'open' current system connecting through the ionopause to the postshock solar wind and two small-scale 'closed' current systems entirely confined within the ionosphere and generated by ionospheric flows and shears. A previously detected ionospheric layer in O2(+) near 170 km altitude is shown to be a new type of ionospheric layer resulting from transition of solar-wind-driven vertical flow to velocities approaching Mach 1.

Cloutier, P. A.↗