•Further insight into unsteady cavitating flows characteristics involved thermal effects are investigated.•Local thermal characteristics in the cavitation region around hydrofoil are ...obtained.•Dynamics evolution mechanism in thermos-sensitive fluids is addressed.•Interactions between the vortex structure and cavitation evolution are presented.
Cavitation shedding is of a great practical interest since the unsteady flow features can induce significant fluctuations around the body where cavitation occurs, especially in thermo-sensitive fluid. The present paper numerically studies the unsteady cavitating flows over a NACA0015 hydrofoil in thermo-sensitive fluid of fluoroketone with special emphasis on the cavitation shedding dynamics. Comparisons between numerical predictions and available experimental data are performed to validate the numerical framework and help us further understand the physical feature. The results show that the predicted cavity evolution and pressure distribution are in good agreement with the experimental data. It is observed that the cavitating flows over the hydrofoil undergo more complex unsteady periodic evolution, including the cavity formation, growth, break-off, collapse and shedding. Two propagation patterns of the re-entrant flow appear along the chordwise direction and the spanwise direction, which are responsible for the unsteady cavity evolution. Note that the temperature distribution around the hydrofoil is closely related to the cavity evolution. The temperature around the hydrofoil undergoes a strong evolution that is contributed by the local evaporation and condensation processes. Meanwhile, the thermal effects on cavitating flows are associated with temperature-dependent physical properties of the fluid media. Interestingly, compared to the isothermal cavitation, thermal effects suppress the intensity of cavitation and show a potential to reduce the pressure pulsation peak. Furthermore, there is a strong interaction between the complex vortex structure and cavitation evolution. In one typical cycle, the rotation effect and the shear effect co-dominate the cavity growth, break-off and shedding of the unsteady cavitating flows.
Strongly interacting topological matter
exhibits fundamentally new phenomena with potential applications in quantum information technology
. Emblematic instances are fractional quantum Hall (FQH) ...states
, in which the interplay of a magnetic field and strong interactions gives rise to fractionally charged quasi-particles, long-ranged entanglement and anyonic exchange statistics. Progress in engineering synthetic magnetic fields
has raised the hope to create these exotic states in controlled quantum systems. However, except for a recent Laughlin state of light
, preparing FQH states in engineered systems remains elusive. Here we realize a FQH state with ultracold atoms in an optical lattice. The state is a lattice version of a bosonic ν = 1/2 Laughlin state
with two particles on 16 sites. This minimal system already captures many hallmark features of Laughlin-type FQH states
: we observe a suppression of two-body interactions, we find a distinctive vortex structure in the density correlations and we measure a fractional Hall conductivity of σ
/σ
= 0.6(2) by means of the bulk response to a magnetic perturbation. Furthermore, by tuning the magnetic field, we map out the transition point between the normal and the FQH regime through a spectroscopic investigation of the many-body gap. Our work provides a starting point for exploring highly entangled topological matter with ultracold atoms
.
Display omitted
•The bubble spatial position is obtained by dual-perspective imaging technology.•The bubble distribution range in the swirl flow is expanded.•Double vortices in ever-changing ...positions prevent bubbles from converging.•Increasing Re can reduce the size and increase the distribution range of bubbles.
In the process of carbon dioxide capture by chemical absorption, swirl flow plays a positive role in enhancing mass transfer. To leverage the advantages of swirl flow in enhancing mass transfer and overcome the drawback of bubbles easily aggregating in swirl flow, a tangential inlet venturi tube is designed. This study utilized dual-perspective high-speed imaging technology to achieve clearer measurements of the spatial positions of individual bubbles and the spatial distribution of bubble clusters. By measuring the three-dimensional motion trajectories of individual bubbles in still water and at low Re, the positive effect of swirl flow in expanding the distribution range of bubbles is observed. By measuring the three-dimensional motion trajectories of bubbles of different sizes at the same Re, it is observed that smaller bubbles are less likely to be captured by the vortices. And the spatial distribution of the bubble cluster in the diffuser section is analyzed by extracting grayscale values and correlating them with the flow field using Computational Fluid Dynamics (CFD) method. Experimental results indicate that as the bubble size decreases, the number of grayscale peaks gradually increases, indicating an expansion of the spatial distribution range of the bubble cluster in the diffuser section. CFD results reveal the presence of two vortices that continuously rotate around the central axis in the diffuser section. However, these vortices attract but did not confine small-sized bubbles. The bubbles are distributed around the vortices and moved along with the rotational motion of the vortices, allowing the bubble cluster to maintain a larger spatial distribution level within the swirl flow.
•Heat transfer distributions, mean flow fields and turbulent flow structures of surface vortex structures are obtained.•DES results are compared with the corresponding RANS and experimental ...results.•Heat transfer enhancement mechanisms of surface vortex generators have been revealed.•The micro V rib-dimple significantly reduces the dead-air zone in the dimple.
Turbulent flow and heat transfer characteristics in the channels with surface vortex structures of micro V-shaped ribs, dimples, and their hybrid structures have been investigated by carrying out delayed detached eddy simulations (DDES) at the Reynolds number of 50,500. It is found that, for the micro V-shaped rib, lower turbulent mixing is produced behind the leeward rib region, while the stronger longitudinal vortex pairs induced by the V-shaped ribs enhance the convective transport of heat. For the dimple, the shed vortices and the shear-layer vortices increase the near-wall turbulent mixing. The complex secondary flows induced by the flow separation, attachment and ejection increase the convective transport of heat. However, the flow separation produces a dead-air zone limiting the further increase of heat transfer enhancement. For the micro V-shaped rib-dimple hybrid structure, the strong downwash flow induced by the micro V rib breaks the recirculation zone inside the downstream dimple and the dimple here works as a vortex amplifier, which produces much stronger longitudinal vortex pairs. This process enhances both the turbulent mixing and convective transport of heat. Therefore, the micro V-shaped rib-dimple hybrid structure provides even more pronounced heat transfer enhancement.
To investigate the design strategy of highly loaded tandem cascades at both the midspan and endwall, the overall performance and flow mechanisms of four typical tandem cascades based on the ...optimization were analyzed from multiple perspectives numerically. The results show that the interference effects on the Front Blade (FB) and Rear Blade (RB) should not be overlooked during the design phase, and the design strategies at the midspan and endwall are completely different. At the midspan, the optimization aims to increase the interference effects and the strength of the gap jet while maintaining the same load on the FB and RB. However, the endwall optimal airfoil exhibits weakening interference effects, advancement of the gap jet location, and load transfer from the FB to RB. Through further analysis of flow characteristics, the midspan optimal airfoil is beneficial for inhibiting the low-energy fluid from interacting with the suction surface of RB under the design condition, but results in earlier occurrence of corner stall. The endwall optimal airfoil helps suppress the development of the secondary flow and delay the onset of corner stall. Furthermore, by combining the benefits of these two design approaches, additional forward sweep effects are achieved, further enhancing the performance of the tandem cascade.
•Effects of the free surface on the TLV cavitation dynamics is investigated.•Influence of the free surface on the tip-leakage vortex structure is analyzed.•Flow structure considering the influence of ...free surface is examined based on a dynamic mode decomposition method.
Tip-leakage vortex (TLV) cavitation is complex and challenging multiphase flow problem in propulsion equipment. In this paper, the large-eddy method and the Schnerr–Sauer cavitation model are combined to simulate a NACA0009 hydrofoil near the free surface. The numerical method used is validated by comparing the characteristics of TLV cavitation with available experimental data. The results show that the free surface affects the evolution of the cavitation and the characteristics of the hydrodynamic load. The lift and drag coefficient of the TLV hydrofoil decreases for the near free surface case, but the pulsation frequency of the lift coefficient increases. Meanwhile, the mechanism of the TLV near the free surface is found by comparing that case to a “no free surface” scenario. Moreover, an improved dynamic mode decomposition (DMD) method is used to investigate the unsteady cavitation flow characteristic of the TLV. The results show the main flow features of the TLV cavitation including the coherent structure and energy distribution are closely related to the existence of free surfaces by analyzing the first two modes based on the DMD method.
Cavitation is of great practical interest because unsteady flow features can induce negative effects such as mechanical erosion and noise. Air injection is an important way to adjust the instability ...of the cavitation flow field. In the present study, we numerically simulate a NACA66 hydrofoil with a particular emphasis on understanding the effects of ventilation on cavitation characteristics such as cavity dynamics, vortex structure, and the wake field. Cavitation is modeled by using the Schnerr-Sauer cavitation model, and the Large Eddy Simulation (LES) method is used to calculate the unsteady natural and ventilated cavitation flow. The results of the numerical simulation are in good agreement with experiment, which verifies the effectiveness of the numerical method. The evolution of cavity dynamics and vortex structure are analyzed to clarify how multi-scale vortex structures evolve in the flow field. The results show that the shedding speed of the ventilated cloud cavity is faster than the natural cavitation. In addition, ventilation improves the pressure pulsation on the cavitation hydrofoil surface. The rotational effect in ventilated cavitation is more significant. Furthermore, ventilation causes strong, large-scale, pulsating eddy currents to rotate into small-scale eddies. An analysis of the vorticity transfer equation shows that the gas injection increases the velocity gradient and enhances the conversion of the two gas-liquid phases. The results in the wake of the hydrofoil show that ventilation can effectively reduce the turbulence intensity and turbulence integral scale, which indicates that ventilation can improve the velocity pulsation and instability. Interestingly, increasing the ventilation rate helps to improve the pressure peak on the hydrofoil surface and increases the lift and drag coefficient. Moreover, gas injection is responsible for cavity pulsation and the re-entrant jet enhances the fluctuation intensity.
•Positive effects of ventilated cavitation over hydrofoil is investigated.•Evolution of transient cavitation dynamics around hydrofoil is analyzed.•The influence of the gas injection on vortex structures is examined.•Improvement of turbulence in downstream wake of hydrofoil is evaluated.
•ECSF has a maximum total separation efficiency of 95 % and 77 % for PM10 and PM2.5.•Auxiliary airflow can remove the particles deposited in discharge pipe with its velocity no exceeding 5 m/s.•The ...diameter of underflow pipe should not be smaller than that of cone outlet.•In addition to the inner and outer vortices, there is also a reversed vortex in the ECSF.
A novel cyclone design called enhanced cyclone with split flow (ECSF) incorporates bypass flow and underflow to eliminate or suppress localized secondary flow observed in conventional cyclones. The present study aims to investigate the mechanism of ECSF in suppressing localized secondary flow and explore methods for regulating the bottom flow rate. The turbulent characteristics within the ECSF are obtained using Reynolds stress model, while the trajectory of particles is predicted using discrete phase model to derive the separation performance. The accuracy of the simulation model has been validated through experimental verification. The results demonstrated that the full separation efficiency of ECSF for PM10 and PM2.5 remained above 90 % and 70 %, respectively. Moreover, it exhibited an increasing trend with the rise in the full split ratio, eventually stabilizing at approximately 95 % and 77 %, correspondingly, when the full split ratio reached 20 %. The bypass flow and underflow effectively eliminated or suppressed the upper ash ring and processing vortex core (PVC) phenomenon, respectively. However, the exacerbation of the short-circuit flow phenomenon hindered further improvement in separation efficiency beyond a full diversion ratio of 20 %. When the full split ratio is relatively small, particles may accumulate in the discharge pipe, which can be resolved by introducing auxiliary airflow; however, it is crucial to ensure that the flow rate of auxiliary flow does not exceed 14.29 % of that of feed flow to avoid compromising the separation efficiency. Furthermore, the split flow induces an additional reversed vortex within the ECSF, which extends from the overflow pipe to conical section. Its structural characteristics are influenced by both back pressure of discharge outlet and diameter of underflow pipe. To ensure optimal performance of the ECSF, it is recommended that the underflow pipe diameter should not be smaller than that of the outlet in conical section.
•The vortex structures around moving spheres are numerically investigated.•The flow conditions include a single swaying sphere and two colliding spheres.•The direct numerical model was integrated ...with an hybrid immersed boundary method.•The simulated velocities around the spheres are validated by a laboratory experiment.
This study incorporates a hybrid Cartesian/immersed boundary (HCIB) method and the Navier-Stokes equations to simulate three-dimensional vortex flows around spheres swinging and colliding in viscous fluids. The motions of the spheres were prescribed in the model, and the simulated velocities around the spheres were validated by the results of laboratory experiments. The Reynolds number computed by the sphere diameter and the maximum swing velocity was Re = 13,500. The simulation results were examined in detail to elucidate the three-dimensional flows and pressure fields induced by the single swinging sphere and two colliding spheres. The evolution of the vortices can be divided into two parts: (i) Before the collision, the primary vortex ring induced by the swinging sphere grows in size, propagates obliquely downward, and eventually dissipates into turbulent flow. (ii) After the collision, the striking sphere transfers its momentum to the target sphere and another vortex ring is generated in front of the striking sphere owing to its impulsive deceleration. This vortex ring is separated from the sphere's boundary and the vorticity pattern is different from that of a single sphere case. After the collision, the target sphere up-swings with almost no vortical wake behind it, as observed in the experiments.
•Fluid structure is compared under subsonic-supersonic mixed and subsonic uniform inflows.•An asymmetric recirculation zone is observed under subsonic-supersonic mixing inflow.•Interaction between ...the subsonic-supersonic shear layer and the recirculation zone is discussed.•Flowfield downstream of the flameholder is divided into five regions and two stages.
Subsonic uniform and supersonic mixing flows are widely present in the combustion chamber of a multi-mode combined scramjet engine, where the significant pressure, velocity, and temperature gradients of the two impose severe limitations on flame propagation. The vortex structures downstream of an evaporative flameholder were experimentally measured under subsonic-supersonic mixing inflow and subsonic uniform inflow. Results indicate that, under subsonic-supersonic mixing inflow conditions, an asymmetric vortex structure in the recirculation zone is formed due to the presence of a subsonic-supersonic shear layer, which exerts compressive or stretching effects on the recirculation zone downstream of the flameholder, in contrast to the symmetric dual-vortex structure observed under subsonic uniform inflow conditions. The asymmetric recirculation zone displays fluid being entrained from one vortex to another, with the degree and direction of entrainment dependent on the supersonic expansion state. Additionally, a simplified flow field structure is proposed for comparing the differences between the subsonic-supersonic mixing inflow and subsonic uniform inflow, along with the introduction of five regions and two stages to describe the flow field structure downstream of the flameholder under subsonic-supersonic mixing inflow. Analysis of the flow characteristics downstream of the flameholder under subsonic-supersonic mixing inflow and subsonic uniform inflow conditions can offer design insights for the combustion scheme of aerospace-integrated propulsion systems.
