Turbulent Vortex Flow Research Articles

Shale Gas Nanofluid in the Curved Carbon Nanotube: A Molecular Dynamics Simulation Study.

Curved nanochannels are prevalent in porous and tortuous materials, with shale matrices being a noteworthy example. The tortuosity of shale matrices significantly influences the behavior of shale gas, holding crucial implications for gas recovery engineering. In this study, we employ molecular dynamics simulation (MD) to investigate the impact of curvature and radius in tortuous nanochannel formed by a curved single-walled carbon nanotube (SWCNT) on the adsorption and transport properties of methane gas fluid. Our findings reveal that the inner half surface of the SWCNT, characterized by negative curvature, exhibits enhanced methane adsorption. Methane in straighter and narrower channels displays higher flow velocities, while wider channels exhibit higher flow flux. The nonzero flow velocity alters adsorption strength, causing the outer half to surpass the inner half. Tangent and vertical velocities of the flow are heterogeneously distributed in the channel, with the outer half having higher tangent velocities. Additionally, a vertical velocity pulse near the entrance induces turbulent vortex flow, slowing down the tangent flow velocity. This research contributes to a deeper understanding of shale gas properties in matrices with bent and curved channels, offering insights into nanofluids in carbon nanotubes and porous media featuring curved nanochannels.

Three-dimensional particle image velocimetry experimental study of transient motion characteristics of different scale vortices in gasoline engine

The paper adopted three-dimensional (3D) Particle Image Velocimetry (PIV) combined with high-speed measurement technology to study the transient motion characteristics of tumble flow induced by small and medium-sized vortices on an optical gasoline engine. Meanwhile, the Proper Orthogonal Decomposition (POD) method was introduced to analyze the evolution of transient vortices, revealing the three-dimensional motion principle of vortices with different spatial scales within the cylinder. The results showed that increasing the engine speed can cause boosted in-plane and out-of-plane velocity, especially for the in-plane velocity. However, the average velocity in the plane was higher than that out of the plane with the difference generally within an order of magnitude. The strong intake jet was the main reason for bringing turbulent kinetic energy in the cylinder. The average kinetic energy and turbulent kinetic energy in the cylinder are both significantly improved at high engine speed. From the results of this experiment, it was revealed that there exists isotropic turbulent pulsation characteristics. Overall, the corresponding flow characteristics of different decomposed modes were different. The first mode section had the lowest average velocity ratio, while the other two had the highest. Due to the dissipation of large vortices into small vortices or the shear action between flow layers, new vortices were generated, leading to the intermittent phenomenon of the motion path of the vortex cluster in the target plane. The average vortex size and velocity circularity corresponding to two varied engine speeds presented a downward trend. The average vortex size was smaller at high engine speed, while the vortex intensity was higher. In addition, increasing the engine speed would decrease the vortex scale but increase the vortex strength. This work provided new fundamental insights into analyzing the characteristics of micro-scaled vortices in turbulent flow, as well as the organization of intake in the gasoline engine.

Monge–Ampère geometry and vortices

We introduce a new approach to Monge–Ampère geometry based on techniques from higher symplectic geometry. Our work is motivated by the application of Monge–Ampère geometry to the Poisson equation for the pressure that arises for incompressible Navier–Stokes flows. Whilst this equation constitutes an elliptic problem for the pressure, it can also be viewed as a non-linear partial differential equation connecting the pressure, the vorticity, and the rate-of-strain. As such, it is a key diagnostic relation in the quest to understand the formation of vortices in turbulent flows. We study this equation via an associated (higher) Lagrangian submanifold in the cotangent bundle to the configuration space of the fluid. Using our definition of a (higher) Monge–Ampère structure, we study an associated metric on the cotangent bundle together with its pull-back to the (higher) Lagrangian submanifold. The signatures of these metrics are dictated by the relationship between vorticity and rate-of-strain, and their scalar curvatures can be interpreted in a physical context in terms of the accumulation of vorticity, strain, and their gradients. We show explicity, in the case of two-dimensional flows, how topological information can be derived from the Monge–Ampère geometry of the Lagrangian submanifold. We also demonstrate how certain solutions to the three-dimensional incompressible Navier–Stokes equations, such as Hill’s spherical vortex and an integrable case of Arnol’d–Beltrami–Childress flow, have symmetries that facilitate a formulation of these solutions from the perspective of (higher) symplectic reduction.

On Turbulent Helicity in the Surface Layer of the Atmosphere

Synchronous measurements of vorticity and velocity in the boundary layer of the atmosphere were carried out using the original 3-component acoustic circulator developed at the A.M. Obukhov Institute of Physical Physics in 2019–2020. The measurements were carried out in summer at the Tsimlyansk scientific station (in 2021, 2022) at altitudes of 1.75 and 30 m. For different realizations, turbulent helicity has negative values on average, which is possibly due to the presence of local (breeze) winds. The observed spectra of turbulent helicity exhibit a slope close to –5/3, which corresponds to the transfer of helicity along the spectrum towards small scales (direct cascade). Spectrum slopes of –4/3 are also observed, and in the low-frequency region – –1, associated with the convective component, wind shear, and submesoscale structures. The components of the turbulent vortex flow are calculated. The helicity values agree with the previously measured and theoretical estimates obtained for neutral conditions.

Compact analogs of the models of vortex flows generated by aircraft flight

The subject of this work is the development of compact analogs of vortex flows models, which are used in the modeling of vortex structures observed during the flight of an aircraft and the motion of a body in a fluid. In particular, two significant misunderstandings prevailing in this area of science are highlighted. The first misunderstanding is that the stationary motion of fluid parcels in a circle is treated as an inviscid vortex. Therefore, any vortex flow model that does not explicitly contain viscosity is considered to describe inviscid vortex motion. It has been proven that this is not so: the stationary viscous motion of fluid parcels in circular orbits corresponds to the self-balance of one force - the force of viscosity. This conclusion, in an explicit form, was made for the first time. This is very important because it changes our ideas about force balance, where two or more forces of different natures must necessarily be present. Overcoming this misunderstanding opens the way for creating compact analogs of existing models of vortex motions. Along the way, one more - the second general misunderstanding in the field of vortex dynamics was eliminated. Wherever we read it, we can see that the compactness of the vortex flow is associated with the compactness of the vorticity field. This is facilitated by the fact that the equations for vorticity and not for velocity are considered. As a result, except for one or two models of vortices, which correspond to the rotation of the entire space, up to infinity, this violates the fundamental law of physics - the law of conservation and transformation of energy. It is about the fact that, as a second misunderstanding, an error is assumed when calculating the kinetic energy of the vortex flows: the Jacobian in cylindrical (polar) coordinates is not considered. As a result, all the mentioned models of vortex flows, which correspond to the hyperbolic law as their asymptotics in the periphery, have infinite kinetic energy. Certainly, this does not correspond to the formation and evolution of compact vortex structures. Therefore, in this work, based on overcoming the aforementioned misunderstandings, many previously obtained models of compact vortex flows, as well as those obtained for the first time, are presented. In particular, this applies to the turbulent vortex flow during the formation of a vortex sheet, which is a compact analog of the Burgers-Rott vortex - both the classical one corresponding to laminar motion and the one consisting of a laminar flow in the core and a turbulent flow on the periphery of the vortex. Research methods are entirely theoretical. Well-known theorems of theoretical mechanics, mathematical theory of field, and calculus of variations, etc. are used. The obtained solutions are compared with the existing corresponding analogs of non-compact flows. Conclusions. Using the methods of calculus of variation, it was possible to show the possibility of the formation of quasi-solid-like rotational motion in a boundary layer of an incompressible fluid. The very presence of viscosity, or rather its taking into account (boundary layer), indicates a possible transition of the flow from plane-parallel motion to the just-mentioned rotational one due to the Kelvin-Helmholtz instability. In addition, two new models of the Burgers-Rott vortex flow were obtained in this study. The first model uses the general solution obtained by Burgers, but this model corresponds to a combined vortex: although the velocity field is continuous, the vorticity field has a discontinuity - at the point of maximum velocity. It is proved that such an approach is quite possible: the equation of motion is satisfied everywhere, i.e., at every point in space, and the tangential stresses are continuous functions. Since the periphery of the Burgers-Rott vortex is an unstable flow, another model is proposed - with a laminar core and a turbulent periphery. Certainly, the motion of fluid parcels in the peripheral region is described by a velocity distribution other than that of Burgers. Finally, the possible use of known models of compact vortex flows to simulate the von Karman vortex street is considered, with an indication of the advantages of these models.

First electrochemical Couette-Taylor reactor for studying the influence of transport phenomena on electrochemical kinetics

This study presents the first electrochemical Couette-Taylor reactor (eCTR). It was implemented with 20 large electrodes exposed to the same hydrodynamics from Taylor numbers (Ta) of 144 to 28,800. The limiting currents (IL) recorded with hexacyanoferrate (III/II) at different concentrations and at different Ta were used to calculate the Nernst diffusive layer thickness (δN, ranged from 14.6 to 423 µm). Two hydrodynamic regimes were identified: the wavy (Ta from 144 to 1,440) and the turbulent (Ta > 2,200) vortex flows which corresponded to the correlations δN∝Ta-0.44 and δN∝Ta-0.70, respectively. The second correlation confirmed the theoretical equation established by Gabe & Robinson for turbulent flow. In contrast, the wavy vortex flow cannot be approached by the laminar or turbulent hypothesis. Dimensionless correlations gave comparable results between the eCTR and rotating cylinder electrodes under turbulent vortex flow and confirmed the specific behavior of the Couette-Taylor wavy vortex flow.

Extract and Characterize Hairpin Vortices in Turbulent Flows.

Hairpin vortices are one of the most important vortical structures in turbulent flows. Extracting and characterizing hairpin vortices provides useful insight into many behaviors in turbulent flows. However, hairpin vortices have complex configurations and might be entangled with other vortices, making their extraction difficult. In this work, we introduce a framework to extract and separate hairpin vortices in shear driven turbulent flows for their study. Our method first extracts general vortical regions with a region-growing strategy based on certain vortex criteria (e.g., λ2) and then separates those vortices with the help of progressive extraction of ( λ2) iso-surfaces in a top-down fashion. This leads to a hierarchical tree representing the spatial proximity and merging relation of vortices. After separating individual vortices, their shape and orientation information is extracted. Candidate hairpin vortices are identified based on their shape and orientation information as well as their physical characteristics. An interactive visualization system is developed to aid the exploration, classification, and analysis of hairpin vortices based on their geometric and physical attributes. We also present additional use cases of the proposed system for the analysis and study of general vortices in other types of flows.

Drag reduction by a superhydrophobic surface with longitudinal grooves: the effects of the rib surface curvature

We have investigated the effects of rib surface curvature of a superhydrophobic wall in both laminar and turbulent channel flows. Direct numerical simulation is performed for laminar flows and large eddy simulation is performed for turbulent flows. The parametric study shows that a convex rib surface leads to a lower flow ratethan a flat rib for all Reynolds numbers. A concave rib surface firstly increases and then decreases the flow rate as the curvature angle becomes larger, where an optimal curvature angle exists to maximise flow rate. The value of the optimal curvature angle varies with the Reynolds number. A curved rib surface can modify the distribution of the mean velocity and turbulent statistics near the SH wall. Analysis shows that the overall effect of a curved rib surface on the flow rate is the combination of the wetted area augmentation and the change to the spanwise flow interaction, which depends on the curvature angle and the Reynolds number. The SH wall does not change the fundamental structures of near-wall vortices in turbulent flows. The ridge-groove pattern formed by the curved rib surface can provide additional drag reduction similar to that arising from the surface riblets.

Blackhole and cosmology-sink as source

The paper argues that supermassive spinning black holes at Galaxy centers are spinning whirlpools which translate impulse energy acting towards blackhole centers as cosmological expansion energy and gravitational energy,one almost balancing the other. The blackhole interiors are quantum entangled with spin coupled states high in mutual information,leading possibly to negative information,that can express as dark matter. The cosmological fluids in blackhole interiors have quantum vortex flows and turbulence,so that the ergodic boundaries can cause negative temperature states,with dark energy like effects in blackhole interiors,prior to onset of turbulent vortex flows and ultrafast thermalization of event horizons,with coalescence of white hole like entities,associated with worm holes or ER bridges as Susskind equivalents of quantum entangled states.

Investigation of numerical approaches to modeling large-scale turbulent vortex flows in the mode of vertical take-off and landing of an aircraft

The study considers the operation of an unmanned aerial vehicle in hovering mode over a flat landing platform. As a propulsion system, impellers are used, which are a system of a propeller rotating inside an air ring. The air ring is a body of revolution with an aerodynamic profile in cross section. The paper investigates the effect of unsteady interaction of vortex flows with the design of an aircraft by two alternative numerical methods, one of which is vortex-resolving. Numerical calculations are performed using the traditional turbulence modeling approach based on the averaged Navier–Stokes equations (RANS, Reynolds Averaged Navier–Stokes), where the turbulence is assumed to be isotropic, and the eddy-resolving Large Eddy Simulation method. The main feature of the latter is as follows: a turbulent flow is represented as the superposition of the motion of large-scale and small-scale turbulences. After discretizing the flow using a filtering operation, large-scale turbulence, which depends directly on the boundary conditions, is solved from the full Navier–Stokes equations. Small-scale turbulence has isotropic properties and is modeled similarly to semi-empirical RANS methods. The technique allows one to accurately calculate the vortex structure of any flow directly from the equations of motion using relatively low computing power, in contrast to the RANS models, which simulate the flow using a simplified mathematical model and can provide satisfactory accuracy only for a limited range of problems. The results indicate that eddy-resolving methods for modeling turbulence, in contrast to the methods based on averaged Navier–Stokes equations, make it possible to estimate the effect of aperiodic perturbations on the design of aircraft arising from the interaction of large eddies with each other and with the underlying surface. Such phenomena are accompanied by side impacts of a shock nature on the impeller rings, which can lead to loss of aircraft stability. Under conditions of a small propeller step, the use of an air ring results in a significant increase in the air flow passing through the rotor rotation loop, an increase in thrust due to the creation of flow circulation around the airfoil of the ring, and a decrease in the power on the propeller. Even though the effect of using an air ring disappears with a large incoming flow, this design is considered very promising for use on aircraft with vertical takeoff and landing. This mode of operation is the most energy-consuming and determines the greatest requirements for the lifting force of the power plant. The results of this work have demonstrated that numerical methods based on averaging the Navier–Stokes equations and the use of classical turbulence models of the k–ω or k–ε type, which are widely used in numerical modeling of propellers, in takeoff and landing modes fail to detect aperiodic unsteady phenomena associated with the interaction of large eddies, in contrast to eddy-resolving methods for modeling turbulence.

Spherical agglomeration of nickel-manganese-cobalt hydroxide in turbulent Batchelor vortex flow

In this study, turbulent Batchelor vortex flow, due to its periodic fluid motion, was used to produce highly dense and spherical Ni-Mn-Co (NMC) hydroxide agglomerates (microparticles) in a rotation disk crystallizer. A high shear stress (1500 rpm) in the turbulent Batchelor vortex regime, and the presence of ammonia at a pH of 12, help form spherical shaped agglomerates with a high tap density (2.1 g/m3) from irregular shaped agglomerates. The coefficient of variation (0.38) of the agglomerates also narrowed while using this approach. When sufficient ammonia was supplied to form a complex ([M(NH3)n]2+) with all M2+, the reaction rate with OH– slowed and the agglomeration process was affected by the high shear stress in a sufficient amount of time. On the contrary, when ammonia is not present in the reaction solution, free M2+ ions rapidly react with OH– ion, resulting in irregular shaped agglomerates. The pH was related to the OH– concentration and all of the [M(NH3)n]2+ complex was consumed during the agglomeration process when the OH– concentration reached a mol ratio of 1:2 ([M(NH3)n]2+:OH–). When the ammonia feeding rate was higher than 1.2 mL/min, highly dense agglomerate was obtained. However, the [M(NH3)n]2+ complex could not be generated when the pH exceeded a value of 12, according to the mass and equilibrium calculations. In addition, the residence time was significantly shorter (30 min) in the turbulent Batchelor vortex flow regime compared to previous studies (~12 to 50 h). This study suggests that the high shear stress in the turbulent Batchelor vortex flow regime can be effectively used for making highly dense and spherical NMC hydroxide, with high tap density, in a short amount of time.

The barely implicit correction algorithm for low-Mach-Number flows II: Application to reactive flows

In this paper, the Barely Implicit Correction (BIC) algorithm is applied to the simulation of low-Mach-number, reactive flows. The BIC algorithm is a solution procedure consisting of an explicit predictor step to solve the convective portion of the Navier-Stokes equations and an implicit corrector step which removes the acoustic limit on the integration time step. We show how to include reaction processes into the BIC integration procedure. The algorithm is then applied to four test problems with successively increased difficulty. First, a series of one-dimensional flames are computed, showing that BIC can reproduce the correct flame properties. Second, simulations of two-dimensional counter-flow diffusion flames show that the integration procedure can compute the structure of a strained diffusion flame. Third, triple flames are computed and the results show that BIC can compute complex and multi-dimensional heat release structures. Finally, simulations of a three-dimensional, unsteady fire whirl show that the algorithm can compute complex heat release structures in a turbulent vortex flow field. These results indicate that the algorithm is robust, stable for flows with combustion, and can be used to study a wide variety of reactive flows.

Vortices evolution in the solar atmosphere

Aims. We study vortex dynamics in the solar atmosphere by employing and deriving the analytical evolution equations of two vortex identification criteria. Methods. The two criteria used are vorticity and the swirling strength. Vorticity can be biased in the presence of shear flows, but its dynamical equation is well known; the swirling strength is a more precise criterion for the identification of vortical flows, but its evolution equation is not known yet. Therefore, we explore the possibility of deriving a dynamical equation for the swirling strength. We then apply the two equations to analyze radiative magneto-hydrodynamical simulations of the solar atmosphere produced with the CO5BOLD code. Results. We present a detailed review of the swirling strength criterion and the mathematical derivation of its evolution equation. This equation did not exist in the literature before and it constitutes a novel tool that is suitable for the analysis of a wide range of problems in (magneto-)hydrodynamics. By applying this equation to numerical models, we find that hydrodynamical and magnetic baroclinicities are the driving physical processes responsible for vortex generation in the convection zone and the photosphere. Higher up in the chromosphere, the magnetic terms alone dominate. Moreover, we find that the swirling strength is produced at small scales in a chaotic fashion, especially inside magnetic flux concentrations. Conclusions. The swirling strength represents an appropriate criterion for the identification of vortices in turbulent flows, such as those in the solar atmosphere. Moreover, its evolution equation, which is derived in this paper, is pivotal for obtaining precise information about the dynamics of these vortices and the physical mechanisms responsible for their production and evolution. Since this equation is available, the swirling strength is now the ideal quantity to study the dynamics of vortices in (magneto-)hydrodynamics.

Numerical Simulation of the Influence of Vent Conditions on Hydrogen Flame Propagation

ABSTRACT In order to reduce the damage caused by a gas explosion in a ventilation duct, a Large Eddy Simulation (LES) model was used to simulate the hydrogen/air explosion process in the ventilation duct under different side vent. The results show that in the process of flame propagation, the large size side vent near the ignition end produces a larger discharge effect, which causes more serious distortion and longer time for the flame front passing through the side vents. The influence mechanism of the side vent on the flame propagation is different at different stages of flame propagation. When the flame front is behind the side vent, the positive flow field traction on the flame front increases the contact area between the flame front and unburned gas, and thus accelerates the flame propagation. When the side vent is 1 m away from the ignition end, with the side vent diameter increasing from 40 mm to 80 mm, the peak flame propagation speed increases by 19.02% before the flame reaches the vent. When the flame front passes through the side vent, the exhaust of the side vent and the disturbance of the vertical flow field can restrain the flame propagation. However, when the flame front is in front of the vent, the synergistic effect between turbulent vortex and reverse flow field causes the flame propagation speed to fluctuate greatly. The influence of the side vent size on the explosion relief effect is restricted by the side vent position. When the side vent is located in the pressure rising section, the pressure relief effect of the side vents with different sizes is very great and is almost unaffected by the size of the side vent. When the side vent is 1 m away from the ignition end, the peak overpressure in the tube decreased by 50.75%, 52.88% and 55.43%, respectively, when the diameter of the side vent was 40 mm, 60 mm and 80 mm. On the contrary, when the side vent is outside the pressure rising section, the pressure relief effect of the side vent will be weakened, and vents with different sizes have a great alteration to pressure relief effect. For the side vent being 5 m from the ignition end, the peak overpressure in the tube decreased by 4.49%, 13.41%, and 35.51%, respectively, when the diameter of the side vent was 40 mm, 60 mm, and 80 mm.

Wave damping of a sloshing wave by an interacting turbulent vortex flow.

We report on the enhancement of the hydrodynamic damping of gravity waves at the surface of a fluid layer as they interact with a turbulent vortex flow in a sloshing experiment. Gravity surface waves are excited by oscillating horizontally a square container holding our working fluid (water). At the bottom of the container, four impellers in a quadrupole configuration generate a vortex array at moderate to high Reynolds number, which interact with the wave. We measure the surface fluctuations using different optical nonintrusive methods and the local velocity of the flow. In our experimental range, we show that as we increase the angular velocity of the impellers, the gravity wave amplitude decreases without changing the oscillation frequency or generating transverse modes. This wave dissipation enhancement is contrasted with the increase of the turbulent velocity fluctuations from particle image velocimetry measurements via a turbulent viscosity. To rationalize the damping enhancement a periodically forced shallow water model including viscous terms is presented, which is used to calculate the sloshing wave resonance curve. The enhanced viscous dissipation coefficient is found to scale linearly with the measured turbulent viscosity. Hence, the proposed scheme is a good candidate as an active surface gravity wave dampener via vortex flow reconfiguration.

Investigation of vortex flow patterns at the meniscus in a water caster mould

ABSTRACTVortices at the meniscus of the continuous casting mould can entrain mould powder into the liquid pool. The entrained globules will form slivers in the subsequent downstream processing of the slabs. This article presents a three-dimensional computational study of the vortexing at the meniscus with an emphasis on capturing flow behaviours of vortices in continuous casting mould. We have used ANSYS FLUENT 19.2 a commercial CFD package. Two turbulence models, namely standard k- model and shear stress transport (SST) k- model, are employed in this work. The performance of the two turbulence models has been evaluated by comparing the flow measurements from 0.4-scale water model experiments. Both the turbulence models could capture vortices at the top surface. The transient vortex flow characteristics such as formation, expansion (and sustenance), thinning, merging and dissipation of the rotational flow are also predicted by the numerical simulations. In general, the standard k- model and the SST k- model exhibited good capability in predicting the complex, unsteady and turbulent vortex flow phenomena at the meniscus in continuous casting mould.

A Study on Airfoil Flow and Aerodynamic Noise with Interaction of Vortices in Turbulent Flow and Boundary Layer around Airfoil Surface

A Study on Airfoil Flow and Aerodynamic Noise with Interaction of Vortices in Turbulent Flow and Boundary Layer around Airfoil Surface

Axial mixing and vortex stability to in situ radial injection in Taylor–Couette laminar and turbulent flows

Taylor–Couette flows have been widely studied in part due to the enhanced mixing performance from the variety of hydrodynamic flow states accessible. These process improvements have been demonstrated despite the traditionally limited injection mechanisms from the complexity of the Taylor–Couette geometry. In this study, using a newly designed, modified Taylor–Couette cell, axial mass transport behaviour is experimentally determined over two orders of magnitude of Reynolds number. Four different flow states, including laminar and turbulent Taylor vortex flows and laminar and turbulent wavy vortex flows, were studied. Using flow visualization techniques, the measured dispersion coefficient was found to increase with increasing $Re$, and a single, unified regression is found for all vortices studied. In addition to mass transport, the vortex structures’ stability to radial injection is also quantified. A dimensionless stability criterion, the ratio of injection to diffusion time scales, was found to capture the conditions under which vortex structures are stable to injection. Using the stability criterion, global and transitional stability regions are identified as a function of Reynolds number, $Re$.

Arc dynamics of a pulsed DC nitrogen rotating gliding arc discharge

In this study, a novel pulsed direct current (DC) rotating gliding arc (RGA) plasma reactor co-driven by an external magnetic field and a tangential gas flow has been developed. The dynamic characteristics of the rotating gliding arc have been investigated by means of numerical simulation and experiment. The simulation results show that a highly turbulent vortex flow can be generated at the bottom of the RGA reactor to accelerate the arc rotation after arc ignition, whereas the magnitude of gas velocity declined significantly along the axial direction of the RGA reactor. The calculated arc rotation frequency (14.4 Hz) is reasonably close to the experimental result (18.5 Hz) at a gas flow rate of 10 l min−1. In the presence of an external magnet, the arc rotation frequency is around five times higher than that of the RGA reactor without using a magnet, which suggests that the external magnetic field plays a dominant role in the maintenance of the arc rotation in the upper zone of the RGA reactor. In addition, when the magnet is placed outside the reactor reversely to form a reverse external magnetic field, the arc can be stabilized at a fixed position in the inner wall of the outer electrode at a critical gas flow rate of 16 l min−1.

Visualization of supersonic turbulent vortical flows with filtered Rayleigh scattering

The interactions of multiple streamwise vortices have the potential to enhance the fuel/air mixing process in the supersonic flowfields intrinsic of scramjet combustors. As part of an ongoing experimental study on the mixing enhancement capabilities of imposed streamwise vortex interactions, high quality visualizations of the resulting turbulent vortical flowfields have been obtained with the filtered Rayleigh scattering technique. By visualizing the structure and organization of the studied flowfields, which are generated by a ramped strut injector in a Mach 2.5 flow, insight into the relevant flow physics governing the vortex interactions is obtained. Filtered Rayleigh scattering is a non-intrusive laser-based diagnostic technique that images the light scattered from the constituent gas molecules of a flow, thus providing a distinct advantage over other flow visualization techniques, in that it is not required to seed the flow with gaseous or particulate flow tracers. However, because the Rayleigh scattered signal is relatively weak, it is easily obscured by light scattered from other sources, necessitating the implementation of a molecular notch filter. This fact, combined with the complex supersonic turbulent vortical flows that are of interest, makes the application of the filtered Rayleigh scattering technique challenging and non-trivial. This work will highlight the experimental considerations necessary to achieve successful visualization of the flows of interest by presenting the methods used to image a single downstream station of a non-merging vortex interaction mode. The resulting flow visualizations illustrate the highly turbulent nature of the probed flowfield while confirming the behavior observed in previous experiments.