Aerodynamic Free Lunch: VGs increase L/D ratio up to 880%. Does it work for flaps too?
I understand this research was for a wing without flaps.
I understand this reduction in drag with VGs works only for the alpha range past the max Cl point of the wing without VGs, eg. 8-18 deg, increasing the L/D by 880% at 18 deg AOA as shown in the table and graph below.
Would a wing with 20% chord NON-SLOTTED flaps see a similar 84% reduction in drag for each flap setting eg 10,20,30 deg?
Would a wing with 20% chord SLOTTED flaps see a similar 84% reduction in drag for each flap setting eg 10,20,30 deg?
Why does the drag almost stay the same even thought the lift goes up? My intuition is that the VG wing drag value stays close to the 8 deg drag value w/o VGs, as that is the local AOA the wing is seeing due to the VGs, instead of the drag at 18 deg, even though the lift is increasing. Is that correct?
Experimental and Numerical Analysis of the Effect of Vortex Generator Height on Vortex Characteristics and Airfoil Aerodynamic Performance Xinkai Li 1,2,3,* , Ke Yang 1,2,3,4 and Xiaodong Wang 5 1 2 3 4 5 102206, China; [email protected] * Correspondence: [email protected]; Tel.: +86-010-8254-3038 Received: 29 January 2019; Accepted: 7 March 2019; Published: 12 March 2019 Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China; [email protected] Key Laboratory of Wind Energy Utilization, Chinese Academy of Sciences, Beijing 100190, China Dalian National Laboratory for Clean Energy, CAS, Beijing 100190, China Graduate School, University of Chinese Academy of Sciences, Beijing 100049, China College of Energy, Power and Mechanical Engineering, North China Electric Power University, Beijing Abstract: To explore the effect of the height of vortex generators (VGs) on the control effect of boundary-layer flow, the vortex characteristics of a plate and the aerodynamic characteristics of an airfoil for VGs were studied by both wind tunnel experiments and numerical methods. Firstly, the ratio of VG height (H) to boundary layer thickness (δ) was studied on a flat plate boundary layer; the values of H are 0.1δ, 0.2δ, 0.5δ, 1.0δ, 1.5δ, and 2.0δ. Results show that the concentrated vortex intensity and VG height present a logarithmic relationship, and vortex intensity is proportional to the average kinetic energy of the fluid in the height range of the VG. Secondly, the effects of height on the aerodynamic performance of airfoils were studied in a wind tunnel using three VGs with H = 0.66δ, 1.0δ, and 1.33δ. The stall angle of the airfoil with and without VGs is 18◦ and 8◦, respectively, so the VGs increase the stall angle by 10◦. The maximum lift coefficient of the airfoil with VGs increases by 48.7% compared with the airfoil without VGs, and the drag coefficient of the airfoil with VGs is 84.9% lower than that of the airfoil without VGs at an angle of attack of 18◦. The maximum lift–drag ratio of the airfoil with VGs is lower than that of the airfoil without VGs, so the VGs do not affect the maximum lift–drag ratio of the airfoil. However, a VG does increase the angle of attack of the best lift–drag ratio.
Source: www.researchgate.net › publication › 331712096