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Principles and Applications of Plasma Actuators
Published in Ranjan Vepa, Electric Aircraft Dynamics, 2020
In this section, the vorticity–velocity formulation is used to model the flow around an airfoil. The performance output of the stability model is chosen to be the pressure receptivity. The flow controls for maintaining the laminarity are assumed to be the suction holes that are located on the boundary in the pressure recovery region so they directly influence the normal velocity component in that region. Considering the momentum and displacement thicknesses of the boundary layer on the top surface of the airfoil with, and without, suction and the receptivity response in the absence of suction, due to the modeled flow, the N-factor distribution is established. Thus, the spatial growth of receptivity over the airfoil’s surface is obtained. To demonstrate the feasibility of laminar flow control, the suction velocities in the recovery region are constructed to ensure a desired velocity profile. This is done by adjusting the suction velocities so a desired set of displacement and momentum thicknesses are obtained. An inverse boundary layer control approach is adopted to synthesize an active control system for regulating the boundary layer. The efficacy of the control system is established by estimating the N-factor of the growth of the disturbances before and after the application of the active controller. By prescribing the shape factor in the trailing edge region, the instabilities in the laminar boundary layer, and consequently the spatial growth rates, are substantially reduced, although this form of control does not seem to influence the point of transition from laminar to turbulent flow.
More Wind Turbines
Published in Vaughn Nelson, Innovative Wind Turbines, 2019
Airfoils are now designed specifically for wind turbines to improve overall efficiency. The new airfoils have reduced the effect of surface roughness and reduced dynamic stall characteristics. Some of the commercial blades have vortex generatorsvortex generators on the root section. Active boundary layer control has been considered. WingletsWinglets have been field tested (TU Delft, The Netherlands; Alternative Energy Institute, WTAMU; and Aerovironment, U.S.) with the general result for small and medium size wind turbines that the extra cost in manufacturing can be easily offset by making the blades longer. Note that the tip brakes on the Enertech wind turbines acted as winglets, reducing tip vortices. Winglets also reduce the noise from tip vortices. ECN and LM Wind Power have tested new blade tip designs for improving efficiency and energy production [4]. One company, ObviaObvia (https://www.obvia.biz), has developed a turbine with dual winglets and a semi-shroud (Figure 6.21).
Subsonic Transport Aircraft
Published in G. Daniel Brewer, Hydrogen Aircraft Technology, 2017
Because of the importance of DOC to the airlines in their financial statements, it is obvious there would be very serious interest in hydrogen-fueled aircraft if it were possible to buy LH2 at the prices quoted for the IGT coal-based process at the proposed Barstow plant, especially if it also incorporated use of magnetic refrigeration for liquefaction. The use of cryogenic wall cooling in the aircraft design to achieve laminar flow by this method of boundary layer control would make the use of LH2 fuel even more desirable. These three technologies should be high priority candidates for development at an early date. As the price of crude oil increases in the future, due to both increasing scarcity and political pressures, the availability of such a desirable alternative as LH2 for aircraft fuel will become a very pressing issue.
Aerodynamic design optimization of an automobile car using computational fluid dynamics approach
Published in Australian Journal of Mechanical Engineering, 2021
Ravi Kumar B, Nitesh Varshan M, Kannan T
After going through literature, it is observed that separated flow regimes behind a moving body create a large amount of drag. Larger the area of rear side wake larger is the pressure drag and very few studies are focused on the rear wake effects on the aerodynamic drag. Previous studies demonstrated that pressure drag can be reduced by modifying the geometry especially near the region of the wake. This can be done by identifying the locations of flow separation on the vehicle and then implementing the boundary layer control devices such as suction/ blowing, vortex generators, spoilers, deflectors, etc. Another method to reduce the rear side wake area is to play with the under portion of the vehicle. We provide a slight rear undercut angle after rear wheels which enables the flow from the top and bottom surfaces of the vehicle to mix smoothly thereby reducing the effective wake formation area. These minor design modifications on existing car design have shown improved fuel economy and enhanced vehicle performance. A 2–3% reduction in an overall reduction in drag can lead to a fuel saving of as much as 700 to 1000 litres per year for the vehicle. The current work focuses on the design optimisation of an automobile car to improve its performance characteristics. A three-dimensional scaled-down car model is designed by using modelling software Pro-E and then a comprehensive flow analysis is carried out using Ansys Fluent. Regions of adverse pressures are identified and rear undercut modifications are implemented and flow is simulated and results are interpreted and compared with the available literature.
Adsorption of leather dyes on activated carbon from leather shaving wastes: kinetics, equilibrium and thermodynamics studies
Published in Environmental Technology, 2019
Christian Manera, Andrezza Piroli Tonello, Daniele Perondi, Marcelo Godinho
The lines corresponding to the second stage do not pass through the origin indicating that intraparticle diffusion was involved in the adsorption process but was not the only step of the mechanism [30]. This behaviour could be an indicative of some degree of boundary layer control [48]. The C values of 90.8 and 59.9 mg/g for AB210 and AR357, respectively, are relatively high when compared with other obtained in literature. Aksakal and Ucun [40] obtained a slope of 3.0 mg/g for adsorption of a textile dye (Reactive Red 195) onto an adsorbent prepared from Pinus sylvestris L. and Senthil Kumar [49] obtained a value of 0.8 mg/g for adsorption of Congo Red onto cashew nut shell. Those high values corroborate that the boundary layer has an important influence in the adsorption kinetics.
Quasi-radial wall jets as a new concept in boundary layer flow control
Published in Journal of Turbulence, 2018
Khodayar Javadi, Majid Hajipour
In many practical examples of wall jets, the jet needs to be blown in an external flow. In cases such as boundary layer control and film cooling, wall jet stream is in interaction with an external flow. Hence, mutual effect of the jet on the external flow and the external stream on the jet development is a main factor in operation of these systems. In this part of this study, arrays of 3D and QR wall jets with an external stream are investigated and the possibility of developing a combined wall jet from arrays of discrete wall jets is discussed. Numerical simulations have been performed for arrays of 3D wall jets in the presence of external stream, with jet-to-external stream velocity ratio of 2 (U0/Ustream = 2), and for three space-ratios of 10, 20 and 30. Surveying the results indicates that in presence of an external stream, normal and lateral growth rates of wall jets are severely limited, so that the jet boundaries never come close. Therefore, there is no way to form a combined wall jet by merging 3D wall jets. In other words, presence of external stream leads to the isolation of the 3D wall jets.