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Climb and descent
Published in Mohammad H. Sadraey, Aircraft Performance, 2017
The glide with a maximum ground distance (range) occurs when an aircraft flies with the minimum glide angle (γmin). At this situation, the maximum ground distant (i.e., maximum range) is covered. This glide operation is suitable for a powered aircraft with all engines inoperative. Pilots must maximize their horizontal distance, to find an appropriate place to land safely. An interesting parameter in this flight operation is the glide ratio, that is, the horizontal distance covered with each unit of lost altitude. The higher the glide ratio, the longer the horizontal distance covered with losing each unit of altitude that the aircraft is losing. This ratio is about 10–15 for majority of modern aircraft, but for gliders, the ratio is about 30–40.
Feasibility of Adaptive Micro Air Vehicles
Published in Norman M. Wereley, Inderjit Chopra, Darryll J. Pines, Twelfth International Conference on Adaptive Structures and Technologies, 2017
Felipe Bohorquez, Chris Cadou, Darryll Pines
Figures 6 thru 9 illustrate these geometric scaling relationships for small birds and how they compare to three current MAV designs. Although approximate, these scaling relationships illustrate that most MAV designs have shorter wingspans and lower aspect ratios than their biological counterparts, suggesting a higher maneuverability than the equivalent size bird. However, higher maneuverability for the same mass also implies higher bandwidth control for these systems. Another important property of winspan and aspect ratio is its connection to the aerodynamic properties of an aircraft. As the wingspan and aspect ratio increases, the lift to drag ratio also increases affecting the glide ratio of the aircraft. Thus, birds with long wingspans and high aspect ratios are more akin to dynamic soaring. Since most MAVs have short wingspans and low aspect ratios, one would not expect for these vehicles to have great glide or soaring properties. Finally, Figure 8 displays the average wing loading (N/m2) values for birds as a function of body mass. Specific birds are displayed by the ‘x’ symbol. The wing loading for three MAVs is also displayed in this figure with the ‘o’ symbol. Notice that the wing loading for MAVs is significantly higher than the equivalent size bird. This suggests that MAVs must fly faster in comparison to birds of comparable geometric size, aerodynamic properties and weight to stay aloft. To accomplish this goal MAVs must expend more power to overcome the induced aerodynamic drag. Another interesting aspect of nature is that the wing and aspect ratio for hummingbirds tends to be independent of body mass while their wingspan increases monotonically with mass. Figure 9 summarizes these geometric scaling laws for birds on a single chart and indicates that nature has figured out more efficient ways of achieving flight at low Reynolds number than humans.
The Feasibility Study
Published in William H. Middendorf, Richard H. Engelmann, Design of Devices and Systems, 2017
William H. Middendorf, Richard H. Engelmann
A search through Jane’s All the World’s Aircraft [2] revealed that the Swiss Neukom AN-66 sail plane has the lowest minimum sinking speed of any aircraft and the highest glide ratio. (Glide ratio is the ratio of horizontal distance covered in unit time to the altitude lost in the same time in still air.) Since this seems to be the optimum for the state of the art in 1967, this aircraft was used as the basis for the study. Pertinent data for the aircraft are:
Aerodynamic shape integrated design of wind turbine airfoils and vortex generators
Published in International Journal of Green Energy, 2022
Quan Wang, Shuyi Yang, Huanjun Wang, Jun Wang
Recently, some researchers have introduced VGs technology to wind turbine blades. Lee and Kwon (2019) introduced that VGs are installed in the place near to the blade root in order to improve the lift of the wind turbine blade. Mereu, Passoni, and Inzoli (2019) modeled the post-stall behavior at high Reynolds number based on CFD scale-resolving methods. The results indicated that scale-resolving method showed a better accuracy for stall simulation compared to RANS model. Stall angle of attack could be well captured and the VGs were reproduced in a more rigorous way. Wang et al. (2017) analyzed the influence of VGs on the aerodynamic performance of S809 airfoil. It was found that the VGs could delay the boundary layer separation. Moreover, the double VGs could demonstrate better performance in terms of the flow separation control. Zhang et al. (2016) investigated the effects of height, chord-wise position, and span-wise spacing between two VGs. The results showed that the maximum lift coefficient was increased with VGs installed toward the leading edge of airfoils; however, the lift at small angles of attack was decreased as the chord-wise position of VGs is smaller than 20% chord. Nematollahi et al. (2019) studied the effect of the acicular VGs on the vortex diameters, the position of vortex breakdown, and the separation by using particle image velocimetry technology. The results showed that the acicular VGs had positive effects on the aerodynamic performance of the wing. Furthermore, compared with a smooth wing, the acicular VGs delayed the vortex breakdown and increased the flow momentum near the upper wing surface and behind the wing. Martinez-Filgueira, Fernandez-Gamiz, and Zulueta et al. (2017) investigated the trajectory and size of the primary vortex produced by low-profile VGs on a plate. The studied cases showed that the conventional height VGs with the major drag produced the largest positive circulation, while the case h4 (h4 = 0.2δ, δ is boundary layer thickness) produced the lowest circulation and the lowest associated drag as well. Skrzypiński, Gaunaa, and Bak (2014)studied the possible advantages of mounting VGs on a 10 MW wind turbine blade. The results indicated that the optimal VGs configuration could increase the annual energy production. Kundu, Sarkar, and Nagarajan (2019) studied the performance of S1210 hydrofoil with VGs. The results showed that the lift coefficient was increased by 17% by mounting VGs near the trailing edge of the foil. The combination of VGs and rounded trailing edge could increase the glide ratio significantly. Zhu et al. (2019) present unsteady RANS simulations of dynamic stall of NREL S809 airfoil with and without rectangular VGs. VGs were found to delay the onset of dynamic stall and greatly elevate the maximum lift coefficient by almost 40%. The above studies which included the parameters selection, the size determined and wind tunnel experiment of VGs have made an important contribution to improve the aerodynamic performances of wind turbine blades.