Flow separation control on a smooth ledge using an arc discharge in a magnetic field

This paper presents results of experimental study for surface MHD arc actuator as vortex generator in boundary layer of smooth ledge. The study was held at flow velocities 20 to 50 m/s. The pulsed arc discharge was organized in external magnetic field. The amplitude of current was 80 A, while pulse duration was 80 μs. The flow velocity was measured by PIV method. It was founded that the location of the arc breakdown is critically impotent. The arc must be struck just above the separation point. The operation of the actuator in a pulse-periodic mode leads to a shift in the middle position of the flow separation point at frequencies up to 700 Hz and higher. A three-dimensional analysis of the separation region structure behind the MHD actuator shows that the main effect on the flow occurs in the interelectrode gap.

Mathematical Principle Analysis of Separation Point Prediction

During the development of fluid mechanics, fluid separation is an important issue. So far, there is no mathematical formula to reveal and describe the essence of fluid separation. At the same time, due to the high cost and limitation of the experimental method, another method is urgently needed to predict the separation position of the fluid. After axiomatizing fluid mechanics and combining the principle of excited state of quantum mechanics, this paper reveals that fluid separation is a special form of fluid in an excited state, and deduces the state conditions of fluid separation. The research results of this paper provide new ideas for solving problems in fluid separation and engineering applications.

Influence of the position and energy of local rapid heating of the supersonic gas flow on the position of the separation point on the surface of airfoil

Using numerical simulation, the study of the process of rapid local energy release in supersonic flow in a two-dimensional unsteady case and the process of separation point shift by a gas-dynamic perturbation caused by the energy input into the flow were carried out. The flow around the airfoil was modeled as laminar, and local heat release as a instantaneous isochoric process without changing the gas density. The value of energy input and the place of gas heating on the surface of the airfoil were varied. The cases of initiation of energy input at a certain distance before and after the initial position of the separation point, as well as immediately before the separation point, were considered. During obtained flow patterns processing, the displacement of the separation point position downstream, the time of this displacement, the position and size of the separation region with reattachment and the lifetime of this flow zone were determined. The obtained data can help to choose a strategy for initiating energy input in a repetitively pulsed regime, as well as in a regime of a variable position of energy release on the surface of a body, streamlined by compressible gas flow.

Forward Roll Coating of a Williamson’s Material onto a Moving Web: A Theoretical Study

This paper presents a mathematical model for the thin film roll coating process of an incompressible Williamson material, passing through a closed passage between a rotating roll and a web. In light of lubrication approximation theory, the flow equations are nondimensionalized. The regular perturbation approach is used to provide solutions for the velocity profile, pressure gradient, flow rate per unit width, and shear stress at the roll surface. Important engineering quantities such as coating thickness, maximum pressure, separation point, roll/sheet separating force, and roll-transmitted power to the fluid are also obtained. The effects of several factors are graphically projected. The study shows that the material factors that are involved determine the operating variables. Coating thickness and separation point are controlled by Weissenberg’s number, therefore acting as a controlling parameter for the rate of flow, thickness in coating, power contribution, pressure, roll separating force, and separation point. In comparison to the existing results in the literature, the current results are broader and zero-order results are more accurate.

The Influence of Front Wing Pressure Distribution on Wheel Wake Aerodynamics of a F1 Car

The present study focuses on investigating the aerodynamic interaction between a three-element wing and wheel in ground effect, following the Formula One regulation change set for 2022, among which is the simplification of the front wing. This was accomplished by conducting a three-dimensional computational fluid dynamics analysis, using a Detached-Eddy Simulation approach, on a simplified one-quarter model of a Formula One racing car. The main goal was to examine how changing the front wing pressure distribution, by changing the incidence of the second flap, affected the wheel wake. The flow investigation indicated that the wheel wake is influenced by the flap configuration, which is mainly due to the fact that different flap configurations produce different upwash flow fields, leading to a variation of the separation point on top of the tire. As the separation point moves rearwards, the downwash generated in the central region (for a vertical plane) of the wheel wake increases incrementally, leading to a resultant wake that is shorter and further apart. The force investigation showed that the proximity between the region of instability (i.e., vortex breakdown) and the wing’s trailing edge influences the behavior of the transient oscillations, regarding the forces acting on the wing: detecting higher drag force fluctuations, when compared to downforce fluctuations.

Effects of the boundary layer control methods on stability and separation point

This paper concerns the benefits of the active boundary layer control methods. The main focus was studying the effectiveness of suction control for a laminar flow over an airfoil. However, injection normal to or along the wall was also approached using two numerical methods. For different values and distributions of the velocity control magnitude, a systematic comparison was done. Having the results of the laminar flow, a linear stability analysis based on the small disturbance theory was carried out obtaining both the neutral stability curves and the transition point. In the end, for each case, results were presented with the corresponding observations. Additionally, a study on the dependency of the separation point with respect to the injection velocity magnitude was done.

Modeling and experimental verification of the dead metal zone for cutting force prediction in micro milling

In micro-cutting process, ploughing phenomenon occurring due to the dead metal zone (DMZ) leads to substantial ploughing force resulting in an obvious contribution to the total cutting force. To improve accuracy of the cutting force predicted, this paper aimed to explore the DMZ geometry related to the cutting depth and tool edge radius and thereof effect on cutting force. The prominent contribution of this research is to establish a new DMZ model by employing the slip-line field theory of the plastic formation. Based on the proposed model, DMZ are divided into shearing-dominated, mixed shearing and ploughing, and pure ploughing according to the minimum uncut chip thickness (MUCT). It is firstly proposed that the inner vertex of DMZ is the separation point of shearing effect and ploughing effect during metal cutting. The shape of the DMZ is theoretically calculated by an analytical way and verified by the simulation software. Finally, a cutting force model including shear force and ploughing force is established and verified by a series of experiments. The predicted cutting forces show remarkable agreement with those measured. The result proves that the separation point model is correct and can effectively demonstrate the ploughing force to accurately predict cutting force.

Effect of Soccer Ball Panels on Aerodynamic Characteristics and Flow in Drag Crisis

The panel patterns of soccer balls that change with each World Cup have a significant impact on the balls’ aerodynamic and flight characteristics. In this study, the aerodynamic forces of eleven types of soccer ball with different panel patterns were measured in a wind tunnel experiment. We characterized the panel shapes of soccer balls by the length, cross-sectional area, and the panel grooves’ volume. The results confirmed that the drag and drag crisis characteristics are dependent on the groove length and volumes. Flow separation points were visualized by an oil film experiment and particle image velocimetry (PIV) measurement to understand the drag crisis of the soccer balls. The results showed that the panel shape of the ball significantly changes the position of the separation point near the critical region, where the drags crisis occurs. In the critical region, laminar and turbulent flows coexist on the ball. On the other hand, the effect of panel shape on the separation point position is small in subcritical and supercritical states.

Using baseball seams to alter a pitch direction: The seam shifted wake

An experimental investigation of how seams and their orientation relative to the spin axis and flight direction can alter the formation of a wake around a baseball was conducted. Particle Image Velocimetry (PIV) was used to examine the velocity field around a baseball in specific orientations and to find the boundary layer separation location, which is the location on the baseball where the wake begins to form. Certain orientations can advance the separation point on one side of the baseball, generating a pressure force on the baseball and modifying its flight path. Using this information as a guide, baseballs were launched 55 feet (a realistic pitching distance) in orientations designed to have an asymmetric separation point. These pitches were 90 mph at spin rates near 1200RPM with a vertical spin axis perpendicular to the initial flight direction. A Rapsodo 1.0 system was used to compare the pitch locations for different seam orientations. The results of this study showed a significant and repeatable difference in the path of the baseball depending on the orientation of the seams relative to the spin axis. This effect was more significant for baseballs with larger seams.