Counter-rotating Vortex Structures Research Articles

Investigation into the laminar separation control of airfoils at low Reynolds numbers by dimple vortex generators

Unmanned Air Vehicles (UAV) usually encounter flows at low Reynolds numbers, especially for the small and high-altitude ones. For an airfoil in a low-Reynolds-number flow, laminar separation can significantly downgrade the lift and increase the drag, causing a large reduction in the lift-drag ratio. The present study investigates a passive laminar separation control approach by the dimple vortex generator, while considering the effect of Reynolds numbers on aerodynamic performances. By using the strategically designed dimples, this passive approach is expected to improve airfoil performances at low Reynolds numbers and cause small penalties at high Reynolds numbers. For the applications in UAV, the natural-laminar-flow airfoil NLF(1)-0416 is used as the baseline case, and a moderate angle of attack of 5° is studied. For both the baseline and the dimpled airfoils, large eddy simulations are conducted at the Reynolds numbers of 68,500, 137,000, and 205,400. The lift and drag forces of the airfoils are measured during the wind tunnel experiments within the Reynolds number range of 39,000–230,000. The numerical results provide the in-depth investigation of the flow transition processes and the separation-reattachment flows at different Reynolds numbers, demonstrating their coupling mechanisms and the consequences for the aerodynamic performances. The utilization of dimple vortex generators can significantly reduce the separation region and tremendously improve the low-Reynolds-number performances of the airfoil. For the dimpled airfoil, the experimental results show that the total drag can be reduced by up to 43%, and the lift-drag ratio can be greatly improved by up to 337%, which are the encouraging results achieved by the passive control approach using dimples. For the numerical results, the vortex visualization shows that the Kelvin–Helmholtz instability over the dimples results in the three-dimensional vortex shedding and the transition to turbulence. The streamwise counter-rotating vortex structures induced by the dimples also contribute to the earlier reattachment of the near-wall flow.

Dynamic mode decomposition to classify cavitating flow regimes induced by thermodynamic effects

The effect of temperature on the intensity and the dynamics of cavitation is investigated. Experiments of cavitating flows are conducted at various cavitation numbers and temperatures, leading to different cavity intensities and dynamic behaviors. The thermodynamic effects significantly influence the cavitation extent at elevated temperatures (over 58 °C) in water. Three regimes of instability, i.e. the sheet cavitation, the periodic single-cloud cavitation, and the aperiodic multi-clouds cavitation are distinguished based on their temporal-spatial evolutions. Application of DMD and POD decompositions on the velocity fields and gray level snapshots to determine the coherent structures and the various mechanics causing different shedding behaviors are discussed. The coherent structures obtained in cloud cavitation consist of the re-entrant jet and counter-rotating vortex structures, which are more aggressive dynamic behavior and are absent in the sheet cavitation. To inhibit the effects of hydrodynamic cavitation, it is recommended that a temperature range (55 °C–60 °C) of water be avoided in practical applications. Since working under this temperature range has larger potentials of transforming the steady sheet cavitation to unsteady cloud cavitation with the larger cavitation extent and the vigorous vapor cloud shedding.

Evolution of wake structures behind oscillating hydrofoils with combined heaving and pitching motion

The wake of an oscillating teardrop hydrofoil with combined heaving and pitching motion was studied numerically at Reynolds number of 8000 and Strouhal numbers of $St=0.21{-}0.94$ . The lower Strouhal number exhibited high efficiency propulsion with small thrust generation. However, larger thrust generation at high $St$ required more power, which lowered the propulsive efficiency. Quantitative assessment of vortex evolution, along with qualitative investigation of the formation and interaction of primary structures, revealed the association with elliptic instability characteristics for both co-rotating and counter-rotating vortex structures in both wakes. With respect to advection of the leading-edge vortex, the pressure distribution further depicted evidence of spanwise instability with distinct temporal evolution along the suction and pressure surfaces of the oscillating foil. Three-dimensional assessment of wake structures located downstream of the trailing edge depicted the existence of dislocations associated with primary vortex ‘rollers’. At low $St$ , these were limited to fine spanwise corrugations (valleys and bulges) on weaker leading edge rollers, which enlarged as the rollers advected downstream. In contrast, at high $St$ , the wake exhibited conjoint hairpin-horseshoe vortex structures that led to stronger deformations on the coupled vortex rollers. The statistical characteristics of secondary structures resembled the long wavelength mode and mode A identified previously for purely pitching and heaving foils, respectively. They also mimicked mode B for stationary cylinders. Novel wake models are introduced based on a complete vivid three-dimensional depiction of coherent wake structures.

Enhancement in Film Cooling Effectiveness Using Delta Winglet Pair

Abstract A simulation study has been carried out to investigate the influence of delta winglet pair (DWP) for improving the film cooling effectiveness of a gas turbine blade. Incompressible continuity, momentum, energy, and two equations k − ω SST model have been used for investigating the nature of flow field, temperature field, and turbulent statistics. The Reynolds number based on the jet velocity and the diameter of the film cooling hole is set at a constant value equal to 4232. The jet to the crossflow blowing ratio has been varied as 0.5, 1.0, and 1.5. The corresponding Reynolds numbers based on the crossflow inlet velocity and film hole diameter are equal to 6462, 4229, and 3231, respectively. It is observed that common-flow-down (CFD) DWP configuration augments the film cooling effectiveness due to generation of secondary longitudinal vortices, which annihilates the counter-rotating vortex structures present in the baseline flow. The generation of hairpin vortices and the growth of shear layer vortices are modified due to the implementation of DWP. The overall turbulence intensity and vorticity get reduced due to the presence of DWP. A maximum of 97.46% and a minimum of 61.50% enhancement in film cooling effectiveness have been observed at blowing ratio of M = 1.5 and M = 0.5, respectively. The wake region of the film cooling jet is modified due to DWP leading to formation of stagnation region and lower mixing resulting in higher film cooling effectiveness. The strength of horseshoe vortices is reduced due to the presence of DWP, resulting in lower mixing between the jet with the cross flows and stable film formation. Lower thermal boundary layer thickness is observed in DWP configuration compared to that of the baseline case confirming lower mixing due to the implementation of DWP. Overall, the present study explains the effectiveness of DWP configuration for enhancement of film cooling effectiveness of a DWP.

Measurement of three-dimensional flow structure and transient heat transfer on curved surface impinged by round jet

In this study, the transient heat transfer characteristics of a circular cylinder surface cooled by an impinging air jet were measured through thermographic phosphor thermometry. Time-resolved surface temperature fields were visualized under constant heat flux conditions. After the jet impingement on the circular cylinder, the curved three-dimensional (3D) wall jet developed toward both spanwise and streamwise directions, followed by most of the fluid moving along the curved surface due to the Coanda effect. Therefore, the high heat transfer region was elongated toward the streamwise direction. The impinging angle was established to be a dominant factor in heat transfer characteristics. The heat transfer was improved with an increase in the impinging angle, as the cooling area expanded toward the streamwise direction. To discuss the transient heat transfer characteristics, time-resolved two-dimensional Nusselt number distributions were obtained according to the varied impinging angles and Reynolds numbers. The secondary peak of heat transfer was not clearly observed due to the stabilizing effect of curvature on the wall jet. To understand the heat transfer phenomenon, the 3D flow structures of the jet on the curved surface were obtained using time-resolved volumetric particle tracking velocimetry (PTV). The velocity vectors and streamwise vortices were visualized according to the impinging angle and analyzed in three-dimensions. The 3D curved wall jet possessed a big counter-rotating streamwise vortex structure in the upper region of the attached wall jet on the cylinder wall. With an increase in the impingement angle, the streamwise vortex developed longer at the same Reynolds number. The 3D flow structure and heat transfer distribution were found to demonstrate similar tendencies.

Coherent dynamics in the rotor tip shear layer of utility-scale wind turbines

Recent field experiments conducted in the near wake (up to 0.5 rotor diameters downwind of the rotor) of a Clipper Liberty C96 2.5 MW wind turbine using snow-based super-large-scale particle image velocimetry (SLPIV) (Hong et al., Nat. Commun., vol. 5, 2014, 4216) were successful in visualizing tip vortex cores as areas devoid of snowflakes. The so-visualized snow voids, however, suggested tip vortex cores of complex shape consisting of circular cores with distinct elongated comet-like tails. We employ large-eddy simulation (LES) to elucidate the structure and dynamics of the complex tip vortices identified experimentally. We show that the LES, with inflow conditions representing as closely as possible the state of the flow approaching the turbine when the SLPIV experiments were carried out, reproduce vortex cores in good qualitative agreement with the SLPIV results, essentially capturing all vortex core patterns observed in the field in the tip shear layer. The computed results show that the visualized vortex patterns are formed by the tip vortices and a second set of counter-rotating spiral vortices intertwined with the tip vortices. To probe the dependence of these newly uncovered coherent flow structures on turbine design, size and approach flow conditions, we carry out LES for three additional turbines: (i) the Scaled Wind Farm Technology (SWiFT) turbine developed by Sandia National Laboratories in Lubbock, TX, USA; (ii) the wind turbine developed for the European collaborative MEXICO (Model Experiments in Controlled Conditions) project; and (iii) the model turbine presented in the paper by Lignarolo et al. (J. Fluid Mech., vol. 781, 2015, pp. 467–493), and the Clipper turbine under varying inflow turbulence conditions. We show that similar counter-rotating vortex structures as those observed for the Clipper turbine are also observed for the SWiFT, MEXICO and model wind turbines. However, the strength of the counter-rotating vortices relative to that of the tip vortices from the model turbine is significantly weaker. We also show that incoming flows with low level turbulence attenuate the elongation of the tip and counter-rotating vortices. Sufficiently high turbulence levels in the incoming flow, on the other hand, tend to break up the coherence of spiral vortices in the near wake. To elucidate the physical mechanism that gives rise to such rich coherent dynamics we examine the stability of the turbine tip shear layer using the theory proposed by Leibovich & Stewartson (J. Fluid Mech., vol. 126, 1983, pp. 335–356). We show that for all simulated cases the theory consistently indicates the flow to be unstable exactly in the region where counter-rotating spirals emerge. We thus postulate that centrifugal instability of the rotating turbine tip shear layer is a possible mechanism for explaining the phenomena we have uncovered herein.

A pancake droplet translating in a Hele-Shaw cell: lubrication film and flow field

We adopt a boundary integral method to study the dynamics of a translating droplet confined in a Hele-Shaw cell in the Stokes regime. The droplet is driven by the motion of the ambient fluid with the same viscosity. We characterize the three-dimensional (3D) nature of the droplet interface and of the flow field. The interface develops an arc-shaped ridge near the rear-half rim with a protrusion in the rear and a laterally symmetric pair of higher peaks; this pair of protrusions has been identified by recent experiments (Huerre et al., Phys. Rev. Lett., vol. 115 (6), 2015, 064501) and predicted asymptotically (Burgess & Foster, Phys. Fluids A, vol. 2 (7), 1990, pp. 1105–1117). The mean film thickness is well predicted by the extended Bretherton model (Klaseboer et al., Phys. Fluids, vol. 26 (3), 2014, 032107) with fitting parameters. The flow in the streamwise wall-normal middle plane is featured with recirculating zones, which are partitioned by stagnation points closely resembling those of a two-dimensional droplet in a channel. Recirculation is absent in the wall-parallel, unconfined planes, in sharp contrast to the interior flow inside a moving droplet in free space. The preferred orientation of the recirculation results from the anisotropic confinement of the Hele-Shaw cell. On these planes, we identify a dipolar disturbance flow field induced by the travelling droplet and its $1/r^{2}$ spatial decay is confirmed numerically. We pinpoint counter-rotating streamwise vortex structures near the lateral interface of the droplet, further highlighting the complex 3D flow pattern.

Enhanced Mixing in Supersonic Flow Using a Pulse Detonator

Mixing enhancement in a crossflow using the transient high-pressure, high-temperature, and high-velocity pulse from a detonation was investigated experimentally. High-frame-rate shadowgraphy and planar laser-induced fluorescence of the nitric oxide molecule showed the structure and time-dependent interaction of the detonation plume with the supersonic flow. The high-momentum flux from the detonation provided significant penetration, with blowdown times of 4–8 ms achieved. Planar laser-induced fluorescence of nitric oxide captured the spanwise structure of the plume and the large counter-rotating vortex structure for enhanced mixing. The upstream jet was shown to be drawn into the pulse detonator’s plume, providing distribution to the core supersonic flow. Significant coupling between a continuous upstream jet and the pulse detonator plume was found and indicated that there was an optimal staging distance for enhanced mixing.

Vortex-Generator Models for Zero- and Adverse-Pressure-Gradient Flows

A computational fluid-dynamics investigation, including passive vortex generators (VGs) that generate streamwise counter-rotating vortex structures, usually requires a grid with fully resolved VG g ...

Parametric experimental and numerical study on mixing characteristics in a supersonic combustor with gaseous fuel injection upstream of cavity flameholders

Non-reacting experiments and numerical simulations were performed to investigate the mixing characteristics of gaseous fuel injection upstream of a flameholding cavity in supersonic vitiated air flow. The investigation considered the effects of various flow or geometry parameters, including injection stagnation pressure, cavity length to depth ratio, and distance between the injection orifice and the cavity front wall. The nanoparticle-based laser scattering technique was used. Mix the injection nitrogen gas with nanoparticles; the fuel distribution and instantaneous displacement demonstrated by the nanoparticles were imaged with laser sheet scattering measurement. The flowfields with various mixing schemes were calculated by large eddy simulation. Experimental and numerical results showed that most of the fuel flows away upon the open cavity and only a small portion of the fuel is convected into the cavity shear layer. Fuel distribution and convection around cavity flameholders are determined by the interaction of the lifting counter-rotating vortex structures induced by the jet with the cavity shear layer. With the reduction of cavity length to depth ratio, the increase in distance between the cavity front wall and the injection exit or the increase in injection pressure, the coupling interaction between the injection, and the cavity shear layer would be changed, and the intensity of fuel mass transport from the jet to cavity would decrease.

Control of Separation Using Spanwise Periodic Porosity

Effects of spanwise-periodic disturbances generated by steady active ventilation on the surface of a cylinder are investigated. The wake flow is studied experimentally using flow visualization and hot-wire measurements and numerically using FLUENT TM . Periodic porosity induces the formation of a series of steady counter-rotating vortex structures behind the porous patches, with or without suction being applied. A considerable closing of the wake occurs when porosity is placed on both the top and bottom surfaces, leading to a reduction in drag. The formation of spanwise vortices is suppressed, resulting in a reduction of the velocity fluctuation level and the elimination of oscillation in lift. The formation and spatial evolution of streamwise vortices is discussed.

Mixing Characteristics in a Supersonic Combustor with Gaseous Fuel Injection Upstream of a Cavity Flameholder

Non-reacting experiments and numerical simulations have been performed to investigate the mixing characteristics in a supersonic combustor with gaseous fuel injection upstream of a flameholding cavity in a supersonic vitiated air flow with stream Mach number 1.7. Using helium as simulated fuel, the acetone vapor is adulterated into the fuel jet. The fuel distribution in spanwise and streamwise direction is imaged by the planar laser-induced fluorescence (PLIF) measurement. According to the similarity of experimental observations with different cavities, the typical L/D = 7 cavity with aft wall angle 45° is chosen and the flowfield with the injection is calculated by Large Eddy Simulation. Experimental and numerical results have shown that most of the fuel flow away upon the open cavity with the lifting counter-rotating vortex structures induced by the transverse jet. Only a small portion of the fuel is convected into the cavity shear layer by the vortex interaction of the jet with cavity shear layer, and then transported into the cavity due to the cavity shear layer motion and the interaction of the shear layer with the cavity trailing edge.

An Application of Overset Grids To Payload/Fairing Three-Dimensional Internal Flow CFD Analysis

The application of overset grids to the computational fluid dynamics analysis of three-dimensional internal flow in the payload/fairing of an expendable launch vehicle is described. In conjunction with the overset grid system, the flowfield in the payload/fairing configuration is obtained with the aid of OVERFLOW Navier-Stokes code. The solution exhibits a highly three-dimensional complex flowfield with swirl, separation, and vortices. Some of the computed flow features are compared with the measured Laser-Doppler Velocimetry (LDV) data on a 1/5th scale model of the payload/fairing configuration. The counter-rotating vortex structures and the location of the saddle point predicted by the CFD analysis are in general agreement with the LDV data. Comparisons of the computed (CFD) velocity profiles on horizontal and vertical lines in the LDV measurement plane in the faring nose region show reasonable agreement with the LDV data.

Numerical simulation of wind-aided flame propagation over horizontal surface of liquid fuel in a model tunnel

A numerical study is performed to give a quantitative description of the fire development in a horizontal model tunnel with a wind velocity, U 0, ranging from 0.5 to 2.5 m/s. Controlling mechanisms of three-dimensional (3D) flow, combustion, soot production and radiation are coupled with a large eddy simulation (LES). The computed, time-averaged flame shape (length/height) and heat flux are compared with experimental data from a simplified model tunnel, and a good agreement is attained. Then, a numerical study on flame propagation over a liquid fuel (heptane) surface in a 3D model tunnel is performed. Predictions of the radiation flux, turbulence intensity and air entrainment velocity show an inverse dependence with wind velocity. For the wind velocity lower than 1.5 m/s, the extent of the flame is up to 9 times pyrolysis length due to lack of oxygen. As the wind velocity increases to 2 m/s, the flame length is reduced to approximately 4 times the pyrolysis length because of the sufficient oxygen supply in the reacting zone and development of the counter-rotating vortex structure on the cross-section of the tunnel. The safety limit for which the heat flux is lower than 5 kW/m 2 downstream the fire is about 5 times the pyrolysis zone in length, practically insensitive to the wind velocity.

Self-Preserving Mixing Properties of Steady Round Nonbuoyant Turbulent Jets in Uniform Crossflows

The self-preserving mixing properties of steady round nonbuoyant turbulent jets in uniform crossflows were investigated experimentally. The experiments involved steady round nonbuoyant fresh water jet sources injected into uniform and steady fresh water crossflows within the windowed test section of a water channel facility. Mean and fluctuating concentrations of source fluid were measured over cross sections of the flow using planar-laser-induced-fluorescence (PLIF). The self-preserving penetration properties of the flow were correlated successfully similar to Diez et al. [ASME J. Heat Transfer, 125, pp. 1046–1057 (2003)] whereas the self-preserving structure properties of the flow were correlated successfully based on scaling analysis due to Fischer et al. [Academic Press, New York, pp. 315–389 (1979)]; both approaches involve assumptions of no-slip convection in the cross stream direction (parallel to the crossflow) and a self-preserving nonbuoyant line puff having a conserved momentum force per unit length that moves in the streamwise direction (parallel to the initial source flow). The self-preserving flow structure consisted of two counter-rotating vortices, with their axes nearly aligned with the crossflow (horizontal) direction, that move away from the source in the streamwise direction due to the action of source momentum. Present measurements extended up to 260 and 440 source diameters from the source in the streamwise and cross stream directions, respectively, and yielded the following results: jet motion in the cross stream direction satisfied the no-slip convection approximation; geometrical features, such as the penetration of flow boundaries and the trajectories of the axes of the counter-rotating vortices, reached self-preserving behavior at streamwise distances greater than 40–50 source diameters from the source; and parameters associated with the structure of the flow, e.g., contours and profiles of mean and fluctuating concentrations of source fluid, reached self-preserving behavior at streamwise (vertical) distances from the source greater than 80 source diameters from the source. The counter-rotating vortex structure of the self-preserving flow was responsible for substantial increases in the rate of mixing of the source fluid with the ambient fluid compared to corresponding axisymmetric flows in still environments, e.g., transverse dimensions in the presence of the self-preserving counter-rotating vortex structure were 2–3 times larger than transverse dimensions in self-preserving axisymmetric flows at comparable conditions.

Evolution of the Counter-Rotating Vortex Structure in a Crossflow Jet.

The structure of counter-rotating vortex pair of round jet issuing normally into a crossflow was studied using a flow visualization technique and PIV measurements. Experiments were performed at a jet-to-crossflow velocity ratio of 3.3, and the Reynolds number of 1, 050, based on the crossflow velocity and jet diameter. Instantaneous velocity field was acquired using two frame cross correlation PIV technique. The angle of laser sheet beam was set to be perpendicular to the ensemble averaged trajectory of the crossflow jet. The mean velocity field was obtained by ensemble averaging over 300 realizations of instantaneous velocity fields for each plane. It was found that the counter-rotating vortex pair was initiated from the hanging vortices appearing at both sides of the jet colunm. The detailed characteristics of the velocity fields were discussed with the evolution of the counter-rotating vortex pair.

A Detailed Analysis of Film Cooling Physics: Part II—Compound-Angle Injection With Cylindrical Holes

Detailed analyses of computational simulations with comparisons to experimental data were performed to identify and explain the dominant flow mechanisms responsible for film cooling performance with compound angle injection, Φ, of 45, 60, and 90 deg. A novel vorticity and momentum based approach was implemented to document how the symmetric, counterrotating vortex structure typically found in the crossflow region in streamwise injection cases, becomes asymmetric with increasing Φ. This asymmetry eventually leads to a large, single vortex system at Φ=90 deg and fundamentally alters the interaction of the coolant jet and hot crossflow. The vortex structure dominates the film cooling performance in compound angle injection cases by enhancing the mixing of the coolant and crossflow in the near wall region, and also by enhancing the lateral spreading of the coolant. The simulations consist of fully elliptic and fully coupled solutions for field results in the supply plenum, film hole, and crossflow regions and includes surface results for adiabatic effectiveness η and heat transfer coefficient h. Realistic geometries with length-to-diameter ratio of 4.0 and pitch-to-diameter ratio of 3.0 allowed for accurate capturing of the strong three-way coupling of flow in this multiregion flowfield. The cooling configurations implemented in this study exactly matched experimental work used for validation purposes and were represented by high-quality computational grid meshes using a multiblock, unstructured grid topology. Blowing ratios of 1.25 and 1.88, and density ratio of 1.6 were used to simulate realistic operating conditions and to match the experiments used for validation. Predicted results for η and h show good agreement with experimental data. [S0889-504X(00)01301-5]

A numerical simulation on the effect of hole geometry for film cooling flow

In this study, the effect of hole geometry of the cooling system on the flow and temperature field was numerically calculated. The finite volume method was employed to discretize the governing equation based on the non-orthogonal coordinate with non-staggered variable arrangement. The standard k-.epsilon. turbulence model was used and also the predicted results were compared with the experimental data to validate numerical modeling. The predicted results showed good agreement in all cases. To analyze the effect of the discharge coefficient for slots of different length to width, the inlet chamfering and radiusing holes were considered. The discharge coefficient was increased with increment of the chamfering ratio, radiusing ratio and slot length to width and also the effect of radiusing showed better result than chamfering in all cases. In order to analyze the difference between the predicted results with plenum region and without plenum region, the velocity profiles of jet exit region for a various flow conditions were calculated. The normal velocity components of jet exit showed big difference for the low slot length to width and high blowing rate cases. To analyze the flow phenomena injected from a row of inclined holes in a real turbine blade, three dimensional flow and temperature distribution of the region including plenum, hole and cross stream with flow conditions were numerically calculated. The results have shown three-dimensional flow characteristics, such as the development of counter rotating vortices, jetting effect and low momentum region within the hole in addition to counter rotating vortex structure in the cross stream.

Discrete-Jet Film Cooling: A Comparison of Computational Results With Experiments

Large-scale computational analyses have been conducted and results compared with experiments to understand coolant jet and crossflow interaction in discrete-jet film cooling. Detailed three-dimensional elliptic Navier–Stokes solutions, with high-order turbuence modeling, are presented for film cooling using a new model enabling simultaneous solution of fully coupled flow in plenum, film-hole, and cross-stream regions. Computations are carried out for the following range of film cooling parameters typically found in gas turbine airfoil applications: single row of jets with a film-hole length-to-diameter ratio of 1.75 and 3.5; blowing ratio from 0.5 up to 2; coolant-to-crossflow density ratio of 2; streamwise injection angle of 35 deg; and pitch-to-diameter ratio of 3. Comparison of computational solutions with experimental data give good agreement. Moreover, the current results complement experiments and support previous interpretations of measured data and flow visualization. The results also explain important aspects of film cooling, such as the development of complex flow within the film-hole in addition to the well-known counterrotating vortex structure in the cross-stream.

A numerical/experimental study of the dynamic structure of a buoyant jet diffusion flame

An overview of a joint numerical/experimental investigation of the dynamic structure of a low-speed buoyant jet diffusion flame is presented. The dynamic interactions between the flame surface and the surrounding fluid mechanical structures are studied by means of a direct numerical simulation closely coordinated with experiments. The numerical simulation employs the full compressible axisymmetric Navier-Stokes equations coupled with a flame sheet model. Counterrotating vortex structures both internal and external to the flame surface are seen to move upward along with flame sheet bulges. These buoyancy-driven dynamic features compare well with those observed experimentally by means of phase-locked flow visualizations over entire flame-flickering cycles. The flicker frequencies measured both computationally and experimentally also compare well. Other aspects of this investigation which are discussed include sudden jumps in flicker frequency with increasing coflow velocity and the utilization of background pressure changes to simulate gravitational force variations experimentally.