Chad Winkler - Academia.edu (original) (raw)
Papers by Chad Winkler
BCFD Analysis for the 1st AIAA Propulsion Workshop: S-Duct Results
49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, 2013
Forces on Particles in a Turbulent Square Duct Flow
The forces on dense solid particles in a turbulent square duct flow are examined using large eddy... more The forces on dense solid particles in a turbulent square duct flow are examined using large eddy simulations. Particle volume fractions are low such that the two-way coupling effect and particle-particle collisions may be neglected. A dynamic subgrid kinetic energy model is used to account for the unresolved scales. Due to the presence of mean secondary flows in a square duct, the relative importance of forces exerted on particles by the fluid may be different than what is observed in geometries with two homogeneous directions, such as channels and pipes. In particular, we examine the lift force due to the secondary flows, which acts in the streamwise direction, and is typically neglected in channel and pipe flow. The effect of including the lift force due to secondary flows on deposition rates is examined and compared to experimental data in pipe flow. We examine a range of particle response times as part of this study.
Particle Dispersion by Dean Vortices
Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2004
A computational study has been performed to study the effect of Dean vortices on heavy, small par... more A computational study has been performed to study the effect of Dean vortices on heavy, small particles in a laminar curved square duct flow. The simulations assume low volume fractions of particles, hence the one-way coupling approach is valid. Also, interparticle collisions are not considered. Particle response time is varied along with the Dean number to show the effects of preferential concentration of particles by the Dean vortices. Particle concentration profiles are reported and correlated to fluid statistics such as vorticity, and the right-hand side of the particle continuity equation is correlated to the preferential concentration effect for this flow.
Variable area flow duct employing secondary flows, and method therefor
Method and Apparatus for Variable Exhaust Nozzle Exit Area
Particle Dispersion and Deposition in a Curved Duct
Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C, 2009
ABSTRACT Particle transport in ducts of square cross-section with constant streamwise curvature i... more ABSTRACT Particle transport in ducts of square cross-section with constant streamwise curvature is studied using numerical simulations. The flow is laminar, with Reynolds numbers of Reτ = 40 and 67, based on the friction velocity and duct width. The corresponding Dean numbers for these cases are 82.45 and 184.5, respectively, where De = Rea/R, a is the duct width and R is the radius of curvature. A Lagrangian particle tracking method is used to account for the particle trajectories, with the particle volume fraction assumed to be low such that inter-particle collisions and two-way coupling effects are negligible. Four particle sizes are studied, τp + = 0.01, 0.05, 0.1, and 1. Particle dispersion patterns are shown for each Dean number, and the steady-state particle locations are found to be reflective of the Dean vortex structure. Particle deposition on the walls is shown to be dependent upon both the Dean number and particle response time, with the four-cell Dean vortex pattern able to prevent particle deposition along the center of the outer wall.
Evaluation of subgrid scale kinetic energy models in large eddy simulations of turbulent channel flow
International Journal of Numerical Methods for Heat & Fluid Flow, 2006
ABSTRACT Purpose ? To evaluate the performance of different subgrid kinetic energy models across ... more ABSTRACT Purpose ? To evaluate the performance of different subgrid kinetic energy models across a range of Reynolds numbers while keeping the grid constant. Design/methodology/approach ? A dynamic subgrid kinetic energy model, a static coefficient kinetic energy model, and a ?no-model? method are compared with direct numerical simulation (DNS) data at two friction Reynolds numbers of 180 and 590 for turbulent channel flow. Findings ? Results indicate that, at lower Reynolds numbers, the dynamic model more closely matches DNS data. As the amount of energy in the unresolved scales increases, the performance of both kinetic energy models is seen to decrease. Originality/value ? This paper provides guidance to engineers who routinely use a single grid to study a wide range of flow conditions (i.e. Reynolds numbers), and what level of accuracy can be expected by using kinetic energy models for large eddy simulations.
International Journal of Multiphase Flow, 2004
The preferential concentration of dense particles in a downward, fully developed turbulent square... more The preferential concentration of dense particles in a downward, fully developed turbulent square duct flow at Re s ¼ 360, based on mean friction velocity and duct width, is studied using large eddy simulations. Due to the low volume fractions involved (maximum volume fraction <10 À5 ), one-way coupled simulations are performed, i.e., two-way coupling and particle-particle collisions are not considered. The continuous and the dispersed phases are treated using Eulerian and Lagrangian approaches, respectively. A finite volume based second-order accurate fractional step scheme is used to integrate the unsteady, threedimensional Navier-Stokes equations. The subgrid stresses are modeled with a dynamic subgrid kinetic energy model, as reported previously. The particle equation of motion includes drag, lift and gravity forces and is integrated using the fourth-order accurate Runge-Kutta method. Four cross-sectional locations representative of the mean secondary flow patterns and six particle response times were chosen to study the effect of location and particle inertia on preferential concentration.
A Reduced Dissipation Approach for Unsteady Flows on Unstructured Grids
50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2012
Refinement of a Two-Equation Hybrid RANS/LES Model in BCFD
21st AIAA Computational Fluid Dynamics Conference, 2013
A Simple Alternative to Unsteady Stress-Flux RANS/LES Models
21st AIAA Computational Fluid Dynamics Conference, 2013
Performance of an Airfoil with a Power-saving, Tab-assisted Flap System
29th AIAA Applied Aerodynamics Conference, 2011
The effect of grid topology and resolution is studied for decaying, homogenous isotropic turbulen... more The effect of grid topology and resolution is studied for decaying, homogenous isotropic turbulence using unstruc-tured grids. The grid topology is examined via an ap-proach which includes grids of structured-like quality (or-dered hexahedra) and also grids which consist entirely of random tetrahedra. The grid resolution is varied to include three levels for each topology. Decaying turbulence is cho-sen for its well-documented behavior and ease for examin-ing statistical quantities. It is expected that not all turbu-lence models will behave the same on all grids. To limit such variability, Delayed Detached Eddy Simulations are considered exclusively. Metrics of merit include the en-ergy spectra measured at two different times, the decay of the resolved turbulent kinetic energy, time history of the skewness and kurtosis of the velocity gradients, and the evolution of the transverse Taylor microscale. Data are compared to available experiments. The goal of this work is to provide guid...
In the current dissertation work, the preferential concentration and deposition of heavy solid pa... more In the current dissertation work, the preferential concentration and deposition of heavy solid particles in a downward, fully developed turbulent square duct flow are studied using large eddy simulations. A second-order accurate, finite-volume based fractional step scheme, based on an unstructured Cartesian mesh, is used to integrate the unsteady, incompressible, three-dimensional Navier-Stokes equations. An algebraic multigrid solver is used to solve the Poisson equation resulting from the fractional step method. The subgrid stresses are modeled with a dynamic subgrid kinetic energy model. The particle equation of motion includes drag, lift and gravity forces and is integrated using the fourth-order accurate Runge-Kutta method. The Reynolds number for the square duct is 360, based on average friction velocity and duct width. The grid used is 80´80´128 in the two wall-normal and streamwise directions, respectively. The preferential concentration of particles is studied assuming that...
Analysis of the Common Research Model Using Structured and Unstructured Meshes
Journal of Aircraft, 2014
Structured and Unstructured Solvers for the 3rd CFD Drag Prediction Workshop (Invited)
45th AIAA Aerospace Sciences Meeting and Exhibit, 2007
RANS Technology for Transonic Drag Prediction; A Boeing Perspective of the 4th Drag Prediction Workshop
28th AIAA Applied Aerodynamics Conference, 2010
Reynolds-Averaged Navier–Stokes Technology for Transonic Drag Prediction: A Boeing Perspective
Journal of Aircraft, 2014
Novel Low Reynolds Number Mixers for Microfluidic Applications
Volume 2: Symposia, Parts A, B, and C, 2003
ABSTRACT We present two new designs of compact mixers that can provide good mixing at low Reynold... more ABSTRACT We present two new designs of compact mixers that can provide good mixing at low Reynolds numbers encountered in many microfluidic devices. The new designs benefit from curvature induced cross-stream vortices to enhance mixing of two co-flowing streams of fluids arranged side by side. One of the designs is a spiral of rectangular cross-section, while the other is a series of concentric circular channels arranged as a labyrinth. Both utilize the formation of sustained secondary flows to enhance mixing between two streams. Currently, the devices are fabricated in aluminum using standard machining techniques. However, they can be reduced further in size using standard microfabrication techniques. Mixing experiments were conducted in these channels at a Reynolds number of 6.8 using two sucrose solutions, one of which was laced with Rhodamine 6G dye. Compared to a experiment in an equivalent straight channel, a significant enhancement in the mixing of the two streams, as indicated by the intensity of the second fluid’s color, was observed. The present designs provide a compact and easy-to-fabricate alternative to various other concepts proposed in literature.
Grid Sensitivity of the Rudimentary Landing Gear Using Unstructured Finite Volume Methods
18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012
BCFD Analysis for the 1st AIAA Propulsion Workshop: S-Duct Results
49th AIAA/ASME/SAE/ASEE Joint Propulsion Conference, 2013
Forces on Particles in a Turbulent Square Duct Flow
The forces on dense solid particles in a turbulent square duct flow are examined using large eddy... more The forces on dense solid particles in a turbulent square duct flow are examined using large eddy simulations. Particle volume fractions are low such that the two-way coupling effect and particle-particle collisions may be neglected. A dynamic subgrid kinetic energy model is used to account for the unresolved scales. Due to the presence of mean secondary flows in a square duct, the relative importance of forces exerted on particles by the fluid may be different than what is observed in geometries with two homogeneous directions, such as channels and pipes. In particular, we examine the lift force due to the secondary flows, which acts in the streamwise direction, and is typically neglected in channel and pipe flow. The effect of including the lift force due to secondary flows on deposition rates is examined and compared to experimental data in pipe flow. We examine a range of particle response times as part of this study.
Particle Dispersion by Dean Vortices
Aps Division of Fluid Dynamics Meeting Abstracts, Nov 1, 2004
A computational study has been performed to study the effect of Dean vortices on heavy, small par... more A computational study has been performed to study the effect of Dean vortices on heavy, small particles in a laminar curved square duct flow. The simulations assume low volume fractions of particles, hence the one-way coupling approach is valid. Also, interparticle collisions are not considered. Particle response time is varied along with the Dean number to show the effects of preferential concentration of particles by the Dean vortices. Particle concentration profiles are reported and correlated to fluid statistics such as vorticity, and the right-hand side of the particle continuity equation is correlated to the preferential concentration effect for this flow.
Variable area flow duct employing secondary flows, and method therefor
Method and Apparatus for Variable Exhaust Nozzle Exit Area
Particle Dispersion and Deposition in a Curved Duct
Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C, 2009
ABSTRACT Particle transport in ducts of square cross-section with constant streamwise curvature i... more ABSTRACT Particle transport in ducts of square cross-section with constant streamwise curvature is studied using numerical simulations. The flow is laminar, with Reynolds numbers of Reτ = 40 and 67, based on the friction velocity and duct width. The corresponding Dean numbers for these cases are 82.45 and 184.5, respectively, where De = Rea/R, a is the duct width and R is the radius of curvature. A Lagrangian particle tracking method is used to account for the particle trajectories, with the particle volume fraction assumed to be low such that inter-particle collisions and two-way coupling effects are negligible. Four particle sizes are studied, τp + = 0.01, 0.05, 0.1, and 1. Particle dispersion patterns are shown for each Dean number, and the steady-state particle locations are found to be reflective of the Dean vortex structure. Particle deposition on the walls is shown to be dependent upon both the Dean number and particle response time, with the four-cell Dean vortex pattern able to prevent particle deposition along the center of the outer wall.
Evaluation of subgrid scale kinetic energy models in large eddy simulations of turbulent channel flow
International Journal of Numerical Methods for Heat & Fluid Flow, 2006
ABSTRACT Purpose ? To evaluate the performance of different subgrid kinetic energy models across ... more ABSTRACT Purpose ? To evaluate the performance of different subgrid kinetic energy models across a range of Reynolds numbers while keeping the grid constant. Design/methodology/approach ? A dynamic subgrid kinetic energy model, a static coefficient kinetic energy model, and a ?no-model? method are compared with direct numerical simulation (DNS) data at two friction Reynolds numbers of 180 and 590 for turbulent channel flow. Findings ? Results indicate that, at lower Reynolds numbers, the dynamic model more closely matches DNS data. As the amount of energy in the unresolved scales increases, the performance of both kinetic energy models is seen to decrease. Originality/value ? This paper provides guidance to engineers who routinely use a single grid to study a wide range of flow conditions (i.e. Reynolds numbers), and what level of accuracy can be expected by using kinetic energy models for large eddy simulations.
International Journal of Multiphase Flow, 2004
The preferential concentration of dense particles in a downward, fully developed turbulent square... more The preferential concentration of dense particles in a downward, fully developed turbulent square duct flow at Re s ¼ 360, based on mean friction velocity and duct width, is studied using large eddy simulations. Due to the low volume fractions involved (maximum volume fraction <10 À5 ), one-way coupled simulations are performed, i.e., two-way coupling and particle-particle collisions are not considered. The continuous and the dispersed phases are treated using Eulerian and Lagrangian approaches, respectively. A finite volume based second-order accurate fractional step scheme is used to integrate the unsteady, threedimensional Navier-Stokes equations. The subgrid stresses are modeled with a dynamic subgrid kinetic energy model, as reported previously. The particle equation of motion includes drag, lift and gravity forces and is integrated using the fourth-order accurate Runge-Kutta method. Four cross-sectional locations representative of the mean secondary flow patterns and six particle response times were chosen to study the effect of location and particle inertia on preferential concentration.
A Reduced Dissipation Approach for Unsteady Flows on Unstructured Grids
50th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2012
Refinement of a Two-Equation Hybrid RANS/LES Model in BCFD
21st AIAA Computational Fluid Dynamics Conference, 2013
A Simple Alternative to Unsteady Stress-Flux RANS/LES Models
21st AIAA Computational Fluid Dynamics Conference, 2013
Performance of an Airfoil with a Power-saving, Tab-assisted Flap System
29th AIAA Applied Aerodynamics Conference, 2011
The effect of grid topology and resolution is studied for decaying, homogenous isotropic turbulen... more The effect of grid topology and resolution is studied for decaying, homogenous isotropic turbulence using unstruc-tured grids. The grid topology is examined via an ap-proach which includes grids of structured-like quality (or-dered hexahedra) and also grids which consist entirely of random tetrahedra. The grid resolution is varied to include three levels for each topology. Decaying turbulence is cho-sen for its well-documented behavior and ease for examin-ing statistical quantities. It is expected that not all turbu-lence models will behave the same on all grids. To limit such variability, Delayed Detached Eddy Simulations are considered exclusively. Metrics of merit include the en-ergy spectra measured at two different times, the decay of the resolved turbulent kinetic energy, time history of the skewness and kurtosis of the velocity gradients, and the evolution of the transverse Taylor microscale. Data are compared to available experiments. The goal of this work is to provide guid...
In the current dissertation work, the preferential concentration and deposition of heavy solid pa... more In the current dissertation work, the preferential concentration and deposition of heavy solid particles in a downward, fully developed turbulent square duct flow are studied using large eddy simulations. A second-order accurate, finite-volume based fractional step scheme, based on an unstructured Cartesian mesh, is used to integrate the unsteady, incompressible, three-dimensional Navier-Stokes equations. An algebraic multigrid solver is used to solve the Poisson equation resulting from the fractional step method. The subgrid stresses are modeled with a dynamic subgrid kinetic energy model. The particle equation of motion includes drag, lift and gravity forces and is integrated using the fourth-order accurate Runge-Kutta method. The Reynolds number for the square duct is 360, based on average friction velocity and duct width. The grid used is 80´80´128 in the two wall-normal and streamwise directions, respectively. The preferential concentration of particles is studied assuming that...
Analysis of the Common Research Model Using Structured and Unstructured Meshes
Journal of Aircraft, 2014
Structured and Unstructured Solvers for the 3rd CFD Drag Prediction Workshop (Invited)
45th AIAA Aerospace Sciences Meeting and Exhibit, 2007
RANS Technology for Transonic Drag Prediction; A Boeing Perspective of the 4th Drag Prediction Workshop
28th AIAA Applied Aerodynamics Conference, 2010
Reynolds-Averaged Navier–Stokes Technology for Transonic Drag Prediction: A Boeing Perspective
Journal of Aircraft, 2014
Novel Low Reynolds Number Mixers for Microfluidic Applications
Volume 2: Symposia, Parts A, B, and C, 2003
ABSTRACT We present two new designs of compact mixers that can provide good mixing at low Reynold... more ABSTRACT We present two new designs of compact mixers that can provide good mixing at low Reynolds numbers encountered in many microfluidic devices. The new designs benefit from curvature induced cross-stream vortices to enhance mixing of two co-flowing streams of fluids arranged side by side. One of the designs is a spiral of rectangular cross-section, while the other is a series of concentric circular channels arranged as a labyrinth. Both utilize the formation of sustained secondary flows to enhance mixing between two streams. Currently, the devices are fabricated in aluminum using standard machining techniques. However, they can be reduced further in size using standard microfabrication techniques. Mixing experiments were conducted in these channels at a Reynolds number of 6.8 using two sucrose solutions, one of which was laced with Rhodamine 6G dye. Compared to a experiment in an equivalent straight channel, a significant enhancement in the mixing of the two streams, as indicated by the intensity of the second fluid’s color, was observed. The present designs provide a compact and easy-to-fabricate alternative to various other concepts proposed in literature.
Grid Sensitivity of the Rudimentary Landing Gear Using Unstructured Finite Volume Methods
18th AIAA/CEAS Aeroacoustics Conference (33rd AIAA Aeroacoustics Conference), 2012