Showing papers on "Starting vortex published in 2020"
TL;DR: In this article, an advanced potential flow method is used to study the aerodynamic interactions between small rotors of quadrotor configurations and the impact on the overall flight performance of the quadrotors.
Abstract: An advanced potential flow method is used to study the aerodynamic interactions between small rotors of quadrotor configurations and the impact on the overall flight performance. The aerodynamic an...
17 citations
TL;DR: By tracking trajectories of typical virtually color-dyed fluid parcels, clear visualizations of the entrainment and detrainment processes by the vortex ring, the advection transport of the trailing jet and the adventus transport of trailing shear layer, during the longitudinal propagation of the vortexRing are obtained.
Abstract: We carry out experiments on vortex ring flows submerged underwater which are generated by a pulsatile circular jet with the stroke ratio of 10. The pulsatile Reynolds number, based on centerline exit velocity and jet diameter, is a cosinusoidal function of time with a mean part of 2000 and an oscillating part of 820. This axisymmetric flow field is measured in a meridian symmetry plane by time-resolved planar particle image velocimetry. For revealing the interaction among the starting vortex ring, the trailing jet and the ambient quiescent fluid, we apply finite-time Lyapunov exponent in the Lagrangian framework to the Eulerian-based PIV dataset. By tracking trajectories of typical virtually color-dyed fluid parcels, we obtain clear visualizations of the entrainment and detrainment processes by the vortex ring, the advection transport of the trailing jet and the advection transport of trailing shear layer, during the longitudinal propagation of the vortex ring.
9 citations
TL;DR: In this article, a phase-lock image Schlieren technique and a pressure-field microphone were used to investigate the formation mechanism of the induced pressure wave induced by an asymmetrical Alternating Current (AC) Dielectric Barrier Discharge (DBD) plasma actuator which is under the influence of residual charge on the dielectric surface.
7 citations
TL;DR: In this article, phase-locked tomographic particle image velocimetry measurements are performed to obtain the complex three-dimensional vortex system created by the interaction of plasma synthetic jets with external crossflow.
Abstract: In the present study, phase-locked tomographic particle image velocimetry measurements are performed to obtain the complex three-dimensional vortex system created by the interaction of plasma synthetic jets with external crossflow. Three orifice configurations (round, transverse slot, and longitudinal slot) are investigated. For the round orifice case, the vortex system consists of a starting vortex ring surrounding the jet head, a hanging vortex pair residing in the two lateral sides of the jet body, several shear layer vortices bridging the two legs of the hanging vortex pair, and a hairpin vortex induced by the low-speed secondary jet. For the slot orifice cases, the above vortex system is also present; nevertheless, the interconnections of the vortices are further intersected by the rib vortices that are branched out of the elongated vortex ring during axis switching. The counter-rotating vortex pair observed in the far field is essentially evolving from the hanging vortex pair in the near field.
6 citations
TL;DR: In this paper, the development of laminar thermals and the formation of buoyant vortex rings in thermals were studied by performing direct numerical simulations, where the boundary of non-occurrence and occurrence of the secondary vortex ring was determined in a space of Richardson number (Ri) and injection duration.
Abstract: The development of laminar thermals and the formation of buoyant vortex rings in thermals are studied by performing direct numerical simulations. The formation number of buoyant vortex rings in thermals is also analysed. We find that the development of thermals can be classified into three modes: the starting vortex ring dominated mode; the mode with the occurrence of a secondary vortex ring with breakup; and the mode with the occurrence of a secondary vortex ring without breakup. For the latter two modes, owing to the stretching of the thermal cap, the fluid at the leading edge rolls up, and a secondary vortex ring occurs, grows and replaces the starting vortex ring. The boundary of non-occurrence and occurrence of the secondary vortex ring is determined in a space of Richardson number (Ri) and injection duration ( larger than the critical value (approximates to 1. 95 × 105) for the occurrence of the secondary vortex ring. The formation number of buoyant vortex rings in thermals is beyond the universal formation number of 4 for non-buoyant vortex rings, and increases with the increase of the Richardson number and the injection duration. The switching between the thermal modes by changing the Richardson number and the injection duration has no significant effect on the value of the formation number.
4 citations
TL;DR: The spectral proper orthogonal decomposition method, which extracts spatially and temporally coherent modes in stationary flowfields, is used in the current paper to analyze high-speed broadband channels.
Abstract: The spectral proper orthogonal decomposition method, which extracts spatially and temporally coherent modes in stationary flowfields, is used in the current paper to analyze high-speed broadband ch...
4 citations
TL;DR: In this paper, the authors presented direct numerical simulations of accelerated viscous flow past an infinite wedge with a focus on the effect of the accelerating rate on vortex dynamics and material transport near the wedge tip.
Abstract: This paper presents direct numerical simulations of accelerated viscous flow past an infinite wedge with a focus on the effect of the accelerating rate on vortex dynamics and material transport near the wedge tip. The wedge angle ranges π/3 ≤ βπ ≤ 5π/6 and the acceleration rate is 0 ≤ p ≤ 1. Since the wedge is infinite, the inviscid self-similar analysis predicts that the solution of one viscosity at a time is the same as the solution of a different viscosity at a scaled time. This theoretical prediction is numerically verified in the current work. Evolution of the vorticity, streamlines, and streaklines is shown in great detail. In the vorticity field, hierarchical vortex separations at the wedge tip are observed, which associate with multiple circulating regions in the streamlines. We also compare the solution at varying acceleration rates and wedge angles and explore the scaling laws in the solution. Streaklines are used to illustrate material transport in the fluid flow. The streaklines form two spirals, a major one that corresponds to the starting vortex and a second one that appears near the wedge tip. The formation of both the major and secondary spirals are investigated and diagnosed using the strain rate in the fluid flow.This paper presents direct numerical simulations of accelerated viscous flow past an infinite wedge with a focus on the effect of the accelerating rate on vortex dynamics and material transport near the wedge tip. The wedge angle ranges π/3 ≤ βπ ≤ 5π/6 and the acceleration rate is 0 ≤ p ≤ 1. Since the wedge is infinite, the inviscid self-similar analysis predicts that the solution of one viscosity at a time is the same as the solution of a different viscosity at a scaled time. This theoretical prediction is numerically verified in the current work. Evolution of the vorticity, streamlines, and streaklines is shown in great detail. In the vorticity field, hierarchical vortex separations at the wedge tip are observed, which associate with multiple circulating regions in the streamlines. We also compare the solution at varying acceleration rates and wedge angles and explore the scaling laws in the solution. Streaklines are used to illustrate material transport in the fluid flow. The streaklines form two spira...
4 citations