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Studies of the flow field behind a large scale 47.5 degree sweptback wing having circular-arc airfoil sections and equipped with drooped-nose and plain flaps

Description: Report presenting an investigation of the effect of separation vortex flow on the downwash, sidewash, and wake characteristics behind a 47.5 degree sweptback wing with symmetrical circular-arc airfoil sections. Three configurations were investigated: the basic wing, the wing with full-span drooped-nose flaps deflected 40 degrees, and the wing with semispan plain flaps and full-span drooped-nose flaps deflected 40 degrees. Results regarding the air-stream surveys, distribution of vorticity, average values of downwash and dynamic-pressure ratio, and correlation with theory are provided.
Date: March 10, 1952
Creator: Lange, Roy H. & Fink, Marvin P.
Partner: UNT Libraries Government Documents Department

Metastable states and intermittent switching of small populations of confined point vortices

Description: We have found that small populations of point vortices confined in a box exhibit a variety of new and interesting metastable collective motions, ranging from rigid body rotation to complete chaos. These motions are induced by simulated heating and cooling of the vortices; they do not appear in adiabatic systems. By judicious choice of vortex circulations, heating and cooling rates, and box size, we have produced systems that switch intermittently between several metastable states, that oscillate quasi-periodically, and that show a variety of interesting collective behaviors that in some cases are suggestive of biological organisms.
Date: July 1, 1995
Creator: Schmieder, R.W.
Partner: UNT Libraries Government Documents Department

Elliptical vortices in shear: Hamiltonian moment formulation and Melnikov analysis

Description: The equations of motion for interacting, elliptical vortices in a background shear flow are derived using a Hamiltonian moment formulation. The equations reduce to the 6th order system of Melander et al. [J. Fluid Mech. 167, 95 (1986)] when a pair of vortices is considered and shear is neglected. The equations for a pair of identical vortices axe analyzed with a number of methods, with particular emphasis on the basic interactions and on the implications for vortex merger. The splitting distance between the stable and unstable manifolds connecting the hyperbolic fixed points of the intercentroidal motion-the separatrix splitting-is estimated with a Melnikov analysis. This analysis differs from the standard time-periodic Melnikov analysis on two counts: (a) the ``periodic`` perturbation arises from a second degree of freedom in the system which is not wholly independent of the first degree of freedom, the intercentroidal motion; (b) this perturbation has a faster time scale than the intercentroidal motion. The resulting Melnikov integral appears to be exponentially small in the perturbation as the latter goes to zero. Numerical simulations, notably Poincare sections, provide a global view of the dynamics and indicate that there are two modes of merger. The effect of the shear on chaotic motion and on chaotic scattering is also discussed.
Date: July 1, 1995
Creator: Ngan, K.; Meacham, S. & Morrison, P.J.
Partner: UNT Libraries Government Documents Department

Mixing and chemical reaction in an idealized swirl chamber

Description: A vorticity-based, low-Mach-number model for simulating combustion in closed chambers is constructed. Numerical scheme is based on a mixed finite-difference pseudo-spectral discretization of the governing equations. Discrete evolution equations are integrated in time using a predictor-corrector scheme, while discrete elliptic systems are inverted with the help of fast-Poisson solver. Scheme is applied to analyze mixing and combustion in an idealized swirl cavity, which consists of the annular space between a spinning inner cylinder and a stationary reaction. To this end, we assume that the oxidizer and fuel are initially separated by a thin mixed region, and carefully control mixing levels by varying the duration of the swirl-driven mixing period. The mixture is then ignited along the boundary of the inner cylinder. When pre-mixing is complete, an axisymmetric flame front is established, and the reactants are consumed as the front propagates radially outwards. When the charge is partially mixed, combustion in the early stages predominantly occurs within a non-uniform premixed front. As this non-uniform front approaches the outer cylinder, a transition to a distributed combustion regime occurs. Following the transition, the remaining fuel burns at a slow rate within non-premixed flames which wrap around the inner cylinder. Results show that the mixing time has substantial effects on the pressure rise within the cavity and on the evolution of the burnt fraction, and that these effects become more pronounced as the Damkoehler number increases.
Date: January 1996
Creator: Knio, O. M.; Worlikar, A. S. & Najm, H. N.
Partner: UNT Libraries Government Documents Department

Modeling complex phenomena: Multiple length and time scales in extended dynamical systems

Description: This is the final report of a three-year, Laboratory Directed Research and Development (LDRD) project at Los Alamos National Laboratory (LANL). Using nonlinear techniques and large-scale simulations, we have systematically studied meso-scale pattern formation and dynamics in nonlinear, nonequilibrium systems exhibiting topological excitations (dislocations, vortices, vortex lines, domain walls); dislocation generation from crack fronts in ductile materials; the smoothing of rough surfaces in solid-on-solid models; ordering and melting of moving flux lattices in three-dimensional Josephson junction arrays with external magnetic field, current, and disorder; filamentary and plastic vortex flow in disordered thin films superconductors; magnetic vortices in Heisenberg spin layers; and hierarchical twinning and tweed texture in elastic models.
Date: December 31, 1998
Creator: Lomdahl, P.; Bishop, A. & Jensen, N.G.
Partner: UNT Libraries Government Documents Department

A Hybrid Vortex Method for Two-Dimensional Flow Over Tube Bundles

Description: A hybrid vortex method is presented for computing flows about objects that accurately resolves the boundary layer details while keeping the number of free vortices at a reasonable level. The method uses a wall layer model close to the body surface and discrete vortex blobs in the free wake. Details of the wall layer implementation are presented, and results of sample calculations are compared with known analytical solutions and with calculations from other vortex codes. These results show that the computed boundary layer details are accurate to approximately 0.3 percent of analytical solutions while using three orders of magnitude fewer vortices than other vortex simulations.
Date: November 13, 1998
Creator: Strickland, J.H. & Wolfe, W.P.
Partner: UNT Libraries Government Documents Department

Dynamic signatures of driven vortex motion.

Description: We probe the dynamic nature of driven vortex motion in superconductors with a new type of transport experiment. An inhomogeneous Lorentz driving force is applied to the sample, inducing vortex velocity gradients that distinguish the hydrodynamic motion of the vortex liquid from the elastic and-plastic motion of the vortex solid. We observe elastic depinning of the vortex lattice at the critical current, and shear induced plastic slip of the lattice at high Lorentz force gradients.
Date: September 16, 1999
Creator: Crabtree, G. W.; Kwok, W. K.; Lopez, D.; Olsson, R. J.; Paulius, L. M.; Petrean, A. M. et al.
Partner: UNT Libraries Government Documents Department

Investigation of heat transfer and combustion in the advanced fluidized bed combustor (FBC)

Description: This technical report summarizes the research work performed and progress achieved during the period of October 1, 1994 to December 31, 1994. The measurement of gas flow continued with the assumption of axisymmetric flow in the laboratory-scale FBC. The gas axial velocity distributions at two cross-section in the test chamber were presented. The circulating flow is relatively strong (swirl number of 3.0) near the freeboard wall for the two cross-sections because the flow has high reversal air velocity. The recirculation flow had weak air velocity when the swirl number of 0.60. For the non-swirling flow, the axial velocity was low near the freeboard wall. However, no circulating flow was observed at the two cross-sections. The measurement of the gas axial velocity will be continued to observe the effect of the secondary air injection angles.
Date: January 1, 1995
Creator: Lee, S.W.
Partner: UNT Libraries Government Documents Department


Description: An experimental investigation into the gas dynamics of a jet-driven vortex tube for application of a cavity nuclear reactor to rocket propulsion has shown that viscous retardation of the vortex motion is severe, because of a high level of turbulence near the periphery. Based on the experience gained in this study, it is estimated that the achievement of vortex strengths sufficient for practical application will require the use of small diameter tubes with appreciable expenditure of power for recirculation of the gas. The effect of the high degree of turbulence on the separation process near the periphery remains to be determined. The independent variables which were found to influence the vortex strength significantly for a given gas and temperature condition are the tube diameter, the mass flow rate per unit tube length, the injection velocity, and the wall pressure. Estimates of the degree of turbulence in vortex flow have been made from data on the variation in tangential velocity with radius. Virtual (total) viscosities near the periphery ranged from 30 to 700 times the molecular viscosity for tangential Reynolds numbers of from 4 x 10/sup 4/ to 2 x l0/sup 6/. Measurements of the position of the mole- fraction peak for separation of helium and a heavy vapor agreed with the theory for laminar flow. This suggests that near the center of the vortex tube where the peak developed the radial density gradient was sufficiently strong to suppress turbulence. It is concluded that the vortex reactor concept appears promising for application to nuclear rocket propulsion provided a satisfactory method can be devised for recirculation of the large excess mass flow required to maintain the vortex strength, and if turbulence does not appreciably limit the separation process. A separation experiment at elevated temperature appears to be the next logical step in ...
Date: June 13, 1960
Creator: Keyes, J.J. Jr. & Dial, R.E.
Partner: UNT Libraries Government Documents Department

Simulation of spray dispersion in a simplified heavy vehicle wake

Description: Simulations of spray dispersion in a simplified tractor-trailer wake have been completed with the goal of obtaining a better understanding of how to mitigate this safety hazard. The Generic Conventional Model (GCM) for the tractor-trailer was used. The impact of aerodynamic drag reduction devices, specifically trailer-mounted base flaps, on the transport of spray in the vehicle wake was considered using the GCM. This analysis demonstrated that base flaps including a bottom plate may actually worsen motorist visibility because of the interaction of fine spray with large vortex flows in the wake. This work suggests that to use computational fluid dynamics (CFD) to design and evaluate spray mitigation strategies the jet or sheet breakup processes can be modeled using an array of injectors of small (< 0.1 mm) water droplets; however the choice of size distribution, injection locations, directions and velocities is largely unknown and requires further study. Possible containment strategies would include using flow structures to 'focus' particles into regions away from passing cars or surface treatments to capture small drops.
Date: January 13, 2006
Creator: Paschkewitz, J S
Partner: UNT Libraries Government Documents Department

Vortical structures in pool fires: Observation, speculation, and simulation

Description: While all fires are complex and involve many phenomena, this report is limited to large, turbulent liquid-hydrocarbon pool fires. Large, liquid-hydrocarbon pool fires present a risk in petrochemical storage and processing facilities and transportation systems that contain large amounts of liquid hydrocarbons. This report describes observations, speculations, and numerical simulations of vortical structures in pool fires. Vortical structures are observed in fires with length scales ranging from those that bend millimeter-thick flame zones to those that entrain air many meters from the edge of the fire to its centerline. The authors propose that baroclinic vorticity generation is primarily responsible for production of rotational motion at small scale and that amalgamation is responsible for the production of large-scale rotational structures from the myriad of small-scale structures. Numerical simulations show that vortical structures having time-mean definitions can be resolved with a Reynolds-Average Navier-Stokes (RANS) approach. However, for vortical structures without time-mean definition, RANS is inappropriate, and another technique, such as Large Eddy Simulation (LES), should be employed. 39 refs., 52 figs., 3 tabs.
Date: November 1, 1996
Creator: Tieszen, S. R.; Nicolette, V. F.; Gritzo, L. A.; Moya, J. L.; Holen, J. K. & Murray, D.
Partner: UNT Libraries Government Documents Department

Investigation of heat transfer and combustion in the advanced fluidized bed combustor (FBC). Technical progress report

Description: Numerical simulation on the flow patterns/the velocity profiles was conducted and predicted. The test conditions and input boundary conditions are summarized. The flow patterns of the side view/top view are predicted along with stream lines. When the flow reached to the secondary air input of the lower air injection nozzles, the flow pattern was changed from a laminar flow to a turbulent flow. The velocity profiles at various locations of the combustor chamber was predicted. The velocity at the center of the combustor is greater than that of the wall region. The velocity of the top section is also greater than that of the lower section. The swirling velocity is reduced in both directions of the wall and the center of the combustor chamber. The velocity increased from the wall region to the center region at the top section of the secondary air injectors. Numerical modeling/simulation will be continued to determine the species profiles, temperature profiles, mass fraction profiles, and heat flux and heat transfer coefficient profiles. In addition, experimental test on the hot combustor model will be conducted and analyzed to compare with the numerical simulation results.
Date: January 1, 1998
Creator: Lee, S.W.
Partner: UNT Libraries Government Documents Department

Development of a low swirl injector concept for gas turbines

Description: This paper presents a demonstration of a novel lean premixed low-swirl injector (LSI) concept for ultra-low NOx gas turbines. Low-swirl flame stabilization method is a recent discovery that is being applied to atmospheric heating equipment. Low-swirl burners are simple and support ultra-lean premixed flames that are less susceptible to combustion instabilities than conventional high-swirl designs. As a first step towards transferring this method to turbines, an injector modeled after the design of atmospheric low-swirl burner has been tested up to T=646 F and 10 atm and shows good promise for future development.
Date: September 1, 2000
Creator: Cheng, R.K.; Fable, S.A.; Schmidt, D; Arellano, L. & Smith, K.O.
Partner: UNT Libraries Government Documents Department

Optimization of a premixed low-swirl burner for industrial applications

Description: This study was motivated by recent tests results showing that a 5cm i.d. low-swirl burner (LSB) stabilizes ultra-lean premixed turbulent flames up to 600kW. A parametric study has been performed to determine the optimum ultra-lean LSB configuration, i.e. one that will achieve low NOx and flame stability, for thermal input between 15kW to 150kW. Using Laser Doppler Velocimetry (LDV), non-reacting centerline velocity and rms fluctuation profiles were measured, and were found to show self-similar behavior. This self-similarity may explain why the flame remains stationary relative to the burner exit despite a change in bulk flow velocity from 5 to 90m/s. The recess distance of the swirler affects the shape of the mean and rms velocity profiles. Lean blow-off limits were also determined for various recess distances, and an optimum exit length was found that provides stable operation for ultra-lean flames.
Date: September 1, 2000
Creator: Fable, S.E. & Cheng, R.K.
Partner: UNT Libraries Government Documents Department

Alleviation of fuselage form drag using vortex flows: Final report

Description: The concept of using vortex generators to reduce the fuselage form drag of transport aircraft combines the outflow from the plane of symmetry which is induced by the rotational component of the vortex flow with the energization of the boundary layer to reduce the momentum thickness and to delay or eliminate flow separation. This idea was first advanced by the author in 1981. Under a DOE grant, the concept was validated in wind tunnel tests of approximately 1:17 scale models of fuselages of Boeing 747 and Lockheed C-5 aircraft. The search for the minimum drag involved three vortex generator configurations with three sizes of each in six locations clustered in the aft regions of the fuselages at the beginning of the tail upsweep. The local Reynolds number, which is referred to the length of boundary layer run from the nose, was approximately 10{sup 7} so that a fully developed turbulent boundary layer was present. Vortex generator planforms ranged from swept tapered, through swept straight, to swept reverse tapered wings whose semi-spans ranged from 50% to 125% of the local boundary layer thickness. Pitch angles of the vortex generators were varied by inboard actuators under the control of an external proportional digital radio controller. It was found that certain combinations of vortex generator parameters increased drag. However, with certain configurations, locations, and pitch angles of vortex generators, the highest drag reductions were 3% for the 747 and about 6% for the C-5, thus confirming the arguments that effectiveness increases with the rate of upsweep of the tail. Greatest gains in performance are therefore expected on aft loading military transports. 10 refs., 11 figs., 1 tab.
Date: September 15, 1987
Creator: Wortman, A.
Partner: UNT Libraries Government Documents Department

Confined superadiabatic premixed flame-flow interaction

Description: Laminar premixed unity-Lewis number flames are studied numerically, to examine flow-flame interaction in a two-dimensional closed domain. Two opposed planar flame fronts are perturbed sinusoidally and allowed to develop by consuming premixed reactants. Combustion heat release leads to global pressure and temperature rise in the domain, due to confinement. A superadiabatic condition, with products temperature rising with distance behind the flame front, is observed due to stagnation pressure rise. Variations in tangential strain rate behind the perturbed flame fronts, due to flame curvature and heat release, result in a modified local superadiabatic temperature gradient in the products. These variations in temperature gradients are shown to determine the net local confinement-heating rate in the products, leading to corresponding deviations in products temperature, and the local reaction rate along the flame front. These observations, which are not consistent with one-dimensional superadiabatic stagnation flame behavior, are a direct result of the unrestrained unsteady nature of two-dimensional flame-flow interaction.
Date: December 1995
Creator: Najm, H. N.
Partner: UNT Libraries Government Documents Department

A numerical and experimental investigation of premixed methane-air flame transient response

Description: The authors report the results of a numerical and experimental investigation of the response of premixed methane-air flames to transient strain-rate disturbances induced by a two-dimensional counter-rotating vortex-pair. The numerical and experimental time histories of flow and flame evolution are matched over a 10 ms interaction time. Measurements and computations of CH and OH peak data evolution are reported, and found to indicate mis-prediction of the flame time scales in the numerical model. Qualitative transient features of OH at rich conditions are not predicted in the computations. On the other hand, evolution of computed and measured normalized HCO fractions are in agreement. The computed CH{sub 3}O response exhibits a strong transient driven by changes to internal flame structure, namely temperature profile steepening, induced by the flow field. Steady state experimental PLIF CH{sub 3}O data is reported, but experimental transient CH{sub 3}O data is not available. The present analysis indicates that the flame responds at time scales that are quite distinct from ``propagation'' time scale derived from flame thickness and burning speed. Evidently, these propagation time scales are not adequate for characterizing the transient flame response.
Date: January 6, 2000
Creator: Najm, Habib N.; Paul, Phillip H.; Knio, Omar M. & McIlroy, Andrew
Partner: UNT Libraries Government Documents Department

Particulate behavior in a controlled-profile pulverized coal-fired reactor: A study of coupled turbulent particle dispersion and thermal radiation transport. Quarterly technical progress report, June 15, 1995--September 14, 1995

Description: During the sixteenth quarter progress has been made in the area of turbulence modeling and in the data reduction of heat flux measurements. A multiple-time-scale turbulence model was developed for axisymmetric, swirling flows.
Date: November 1, 1995
Creator: Queiroz, M. & Webb, B.W.
Partner: UNT Libraries Government Documents Department

Combustion of pulverized coal in vortex structures. Quarterly progress report No. 7, April 1, 1995--June 30, 1995

Description: This seventh quarterly report describes the activities and accomplishments of the research team at the University of Oklahoma, Norman, Oklahoma, related to the project entitled {open_quotes}Combustion of Pulverized Coal in Vortex Structures{close_quotes} during the period April 1, 1995 to June 30, 1995. The work performed in this quarter consisted of the following four tasks: (i) conducting experiments with particulate laden shear layers to measure mean velocity and turbulence intensity field (ii) preparing an abstract for the 1995 UCR contractor`s meeting, and a paper for the Energy Conference to be held in Houston in 1996, (iii) participating and presenting a paper UCR meeting in Nashville, Tennessee, (iv) design and installation of devices to traverse the test section while keeping the optics undisturbed, and (v) and design and testing of a natural gas burner system to heat either of the streams to conduct pyrolysis and combustion experiments. In the next quarter, we plan to continue this work with heated shear layers in which particles undergo pyrolysis and combustion. Flow visualization and mean velocity field measurement instrumentation will continue as the major experimental techniques.
Date: July 1, 1995
Creator: Gollahalli, S.R.
Partner: UNT Libraries Government Documents Department

Simulation Modeling of an Enhanced Low-Emission Swirl-Cascade Burner

Description: The research team was formed. The advanced CFDRC-CHEMKIN software package was installed on a SUN-SPARC dual processor workstation. The literature pertinent to the project was collected. The physical model was set and all parameters and variables were identified. Based on the physical model, the geometric modeling and grid generation processes were performed using the CFD-GEOM (Interactive Geometric Modeling and Grid Generation software). A total number of 11160 cells (248 x 45) were generated to numerically model the baseline, cascaded, swirling, and swirling-cascaded flames. With the cascade being added to the jet, the geometric complexity of the problem increased; which required multi-domain structured grid systems to be connected and matched on the boundaries.
Date: April 1, 2003
Creator: Qubbaj, Ala
Partner: UNT Libraries Government Documents Department

Heat Transfer Enhancement in Separated and Vortex Flows

Description: This document summarizes the research performance done at the Heat Transfer Laboratory of the University of Minnesota on heat transfer and energy separation in separated and vortex flow supported by DOE in the period September 1, 1998--August 31, 2003. Unsteady and complicated flow structures in separated or vortex flows are the main reason for a poor understanding of heat transfer under such conditions. The research from the University of Minnesota focused on the following important aspects of understanding such flows: (1) Heat/mass transfer from a circular cylinder; (2) study of energy separation and heat transfer in free jet flows and shear layers; and (3) study of energy separation on the surface and in the wake of a cylinder in crossflow. The current study used three different experimental setups to accomplish these goals. A wind tunnel and a liquid tunnel using water and mixtures of ethylene glycol and water, is used for the study of prandtl number effect with uniform heat flux from the circular cylinder. A high velocity air jet is used to study energy separation in free jets. A high speed wind tunnel, same as used for the first part, is utilized for energy separation effects on the surface and in the wake of the circular cylinder. The final outcome of this study is a substantial advancement in this research area.
Date: May 27, 2004
Creator: Goldstein, Richard J.
Partner: UNT Libraries Government Documents Department

Numerical Simulation of Natural Gas-Swirl Burner

Description: A numerical simulation of a turbulent natural gas jet diffusion flame at a Reynolds number of 9000 in a swirling air stream is presented. The numerical computations were carried out using the commercially available software package CFDRC. The instantaneous chemistry model was used as the reaction model. The thermal, composition, flow (velocity), as well as stream function fields for both the baseline and air-swirling flames were numerically simulated in the near-burner region, where most of the mixing and reactions occur. The results were useful to interpret the effects of swirl in enhancing the mixing rates in the combustion zone as well as in stabilizing the flame. The results showed the generation of two recirculating regimes induced by the swirling air stream, which account for such effects. The present investigation will be used as a benchmark study of swirl flow combustion analysis as a step in developing an enhanced swirl-cascade burner technology.
Date: March 1, 2005
Creator: Qubbaj, Ala
Partner: UNT Libraries Government Documents Department

Simulation Modeling of an Enhanced Low-Emission Swirl-Cascade Burner

Description: The numerical computations were conducted using the CFD-CHEMKIN computational program. A cell-centered control volume approach was used, in which the discretized equations or the finite difference equations (FDE) were formulated by evaluating and integrating fluxes across the faces of control volumes in order to satisfy the continuity, momentum, energy and mixture fractions conservation equations. The first order upwind scheme and the well-known SIMPLEC algorithm were used. The standard k-{var_epsilon} model was used to close the set of equations. The thermal and composition fields in the baseline, cascade, swirl, and swirl-cascade burners were simulated. The temperature and CO{sub 2} concentration fields were just computed and the observations are reported. The analysis of these results is currently underway.
Date: October 1, 2003
Creator: Qubbaj, Ala
Partner: UNT Libraries Government Documents Department

Comparative study of the vorticity field in turbulent flows: Theory, experiments and computations. Final report

Description: We have carried out a comprehensive study of unexcited and excited elliptic jets, addressing the effects of initial conditions, aspect ratio, excitation frequency, and excitation amplitude. We have studied the dynamics of the preferred mode structure and interactions of coherent structure in the near field of elliptic jets. The dynamics of elliptic jets are quite different from the extensively studied plane and circular jets -- owing mainly to the fact that the azimuthal curvature variation of a vortical structure causes a nonuniform self-induction and hence complex three-dimensional deformation. Such deformation, combined with properly selected excitation, can substantially alter entrainment and other turbulence phenomenon, thus suggesting a preference for the elliptic shape in many jet applications. In the following, we mention a few key results.
Date: December 31, 1991
Creator: Hussain, F.
Partner: UNT Libraries Government Documents Department