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Principles and Applications of Plasma Actuators
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
The occurrence of flow separation is related to the wall shear stress, which is obtained from the product of the viscosity and the transverse velocity gradient. Flow separation occurs if the velocity gradient at the wall is zero i.e. when the wall shear stress is zero and a separation bubble develops at the rear of the airfoil. Trailing edge stall occurs in thick airfoils at high Reynolds numbers when the laminar to turbulent flow transition occurs at a point along the airfoil’s surface towards the trailing edge. In this case, separation is determined by the ability of the flow to cope with the suction pressure at the trailing edge, which leads to trailing edge separation at a high angle of attack. Passive flow separation control is based on either directly increasing the momentum in the boundary layer, or by creating flow structures such as vortices for transporting higher momentum in the free stream flow to within the boundary layer, but without the use of any external source of energy to aid the flow. Increasing the momentum of a boundary layer will generally increase the ability to overcome the adverse pressure gradient. In practice one would like to achieve this by using a minimum external energy input.
Theoretical background – hydraulics
Published in P. Novak, V. Guinot, A. Jeffrey, D.E. Reeve, Hydraulic Modelling – an Introduction, 2010
P. Novak, V. Guinot, A. Jeffrey, D.E. Reeve
If the flow over a boundary is in a situation of decreasing pressure in the direction of flow, the fluid will accelerate, the boundary layer will become thinner and the flow will be stable (e.g. flow between convergent boundaries). In the opposite case of a positive pressure gradient (e.g. in divergent flow) boundary layer separation will occur after a stagnation point (a point where the transverse velocity profile begins to exhibit an inflexion) has been reached. Flow separation is characterized by increased energy losses, with the flow being inherently unstable.
Numerical simulation for the differences between FTN/WPN engine models aerodynamic influence on BWB300 airframe
Published in Engineering Applications of Computational Fluid Mechanics, 2020
From the abovementioned aerodynamic force curve analysis, it was known that the powered influence makes WPN configuration stall characteristics were different from the FTN and Clean configurations. In order to clearly identify the flow separation changes in space, the flow separation is analyzed by using the pressure ratio (PR) distribution, because the flow separation leads to the decrease of PR. PR is the ratio of local total pressure to free stream total pressure. From the PR distribution, the total pressure loss in space can be well known. Figure 22 shows the upper surface PR distribution of the three configurations at large angles of attack (Alpha above 11°) (takeoff condition). In this figure from left to right, the WPN, FTN, and Clean configurations, respectively, are shown.
Effect of slenderness ratio and aft fins on the hydrodynamic forces for an underwater body in oblique flows
Published in Ships and Offshore Structures, 2018
Praveen Perumpulissery Chandran, Krishnankutty Parameswaran, Panigrahi Prasanna Kumar
The pressure and wall shear stress distribution along circumferential direction for model-E0 at different incidence angles are presented in Figures 22 and 23, respectively. The flow separation occurs at the location of local minimum skin friction at the leeward side and reattachment occurs at the location of local maximum skin friction (Jeans et al. 2009). Flow separation occurs due to adverse pressure gradients and the separated region can be identified by the plateau in the pressure plot.
Numerical investigation of convective cooling in a rectangular vented cavity with two inlets and a hot obstacle
Published in Numerical Heat Transfer, Part A: Applications, 2023
Jeseema Nisrin Jamal Mohamed, Velkennedy Rathinasamy, Kalidasan Karuppan, Rajeshkanna Parthasarathy
The discussion above shows that there are only limited studies that deal with the mixed convective flow in a multiported rectangular open cavity and no studies that report the combined effect of multiple inlets and exit ports along with the presence of a hot block. The presence of multiple ports in a vented cavity will enhance the efficiency of heat transfer. Any heat sources mounted in an enclosure are normally assumed and modeled as a geometrical block. Hence, finding the thermal and fluid flow performance of an open cavity with different sizes of a block will be helpful in many engineering applications like designing displacement ventilation in buildings, various solar heat exchangers, and cooling of electronic gadgets. This study also helps in understanding the behavior of multiple ports in cooling the interior of a cavity. The present manuscript reports a numerical study on a rectangular ventilated cavity with two inlets and a single outlet. The block encounters both the inlets. The buoyancy resulted from the side wall temperature and hot block mounted in the bottom wall. The presence of a block will influence the hydrodynamics behavior of inlet fluid. Flow separation, boundary layer formation, reattachment, and flow recirculation are the major flow characteristics that will be examined under various conditions. The study analyzes the effect of Rayleigh’s number and the dimensionless block height and width. The effect of the block is compared with the absence of the block condition. The results are presented in the form of streamlines, isotherms, velocity components, and heat transfer rates. Correlations are derived for different Ra, block sizes, and Nusselt numbers. The flow range is within the laminar region, which uses the buoyancy effect apart from the flow induced by air in inlets. The flow range is within the laminar region, which uses the buoyancy effect apart from the flow induced by air in inlets.