Flow Control of Airfoil at Post-stall Conditions by Multiple Frequency Applied SAADO Jets
Author : A. Şamil Demirsöz
Publisher :
Page : 194 pages
File Size : 22,4 MB
Release : 2006
Category : Aerofoils
ISBN :
Author : A. Şamil Demirsöz
Publisher :
Page : 194 pages
File Size : 22,4 MB
Release : 2006
Category : Aerofoils
ISBN :
Author : Eray AKÇAYÖZ
Publisher : LAP Lambert Academic Publishing
Page : 88 pages
File Size : 18,67 MB
Release : 2010-05
Category :
ISBN : 9783838356013
The synthetic jet is applied over an airfoil to control the flow separation. Response Surface Methodology is employed for the optimization of synthetic jet parameters at various angles of attack. The synthetic jet parameters; the jet velocity, the jet location, the jet angle and the jet frequency are optimized to maximize the lift to drag ratio. The jet power coefficient is kept constant in the optimization. The lift to drag ratio increased significantly especially at post stall angles of attack.
Author : Kyle Donald Hipp
Publisher :
Page : 80 pages
File Size : 47,77 MB
Release : 2016
Category :
ISBN :
The performance of active flow control on a NACA 643-618 laminar airfoil at post-stall angles of attack is evaluated using discrete, wall-normal pulsed jets. Actuation is implemented near the leading edge of the airfoil. For actuation periods equal to one convective period, and two convective periods at a chord Reynolds number of 64,000, the time-average lift coefficient increases monotonically as the actuation duty cycle is reduced, for a given blowing ratio. Flow reattachment is achieved following the termination of a short duration pulse, enclosing a separation bubble. The reattachment point propagates towards the trailing edge at a rate three times slower than the convective period of the flow. Extended jet off-times can cause full separation to reoccur should the reattachment point reach the trailing edge, however optimal jet off-times can cause suction pressure to extend over much of the airfoil chord. Higher duty cycle actuation results in a phase shift of the dynamics that appears to be commensurate with the duration of the jet. A disturbance initiated by the termination of the jet causes a delay in the redevelopment of the shear layer and the reattachment of the flow, prohibiting high lift values from being attained. Data collected at multiple post-stall angles of attack show that the rate at which the reattachment point propagates downstream increases with higher angles of attack. At twice the Reynolds number, the same dynamics appear to persist however a weak suction pressure recovery over the extent of the separation bubble reduces the distinction in time-averaged lift between short and long jet pulse durations.
Author : Volkan Kamaci
Publisher :
Page : 254 pages
File Size : 22,31 MB
Release : 2005
Category : Aerofoils
ISBN :
Author : Ersin Gercek
Publisher :
Page : 180 pages
File Size : 18,47 MB
Release : 2004
Category : Base flow (Aerodynamics)
ISBN :
Author : Julie Anne Lovato
Publisher :
Page : 130 pages
File Size : 31,14 MB
Release : 1992
Category : Aerofoils
ISBN :
"This experimental analysis presents a comprehensive study of the separating boundary layer over a static airfoil under natural and actively controlled conditions. Near-surface hot-film and surface pressure measurements, as well as flow visualization are used to analyze the large-scale nature of the flow over a two-dimensional NACA-0015 airfoil and determine forcing effects. Results from the static study are then extended for an initial evaluation of unsteady airfoil control. Results show that the fundamental frequency associated with free shear layer instabilities for this case is an integral multiple of the frequency associated with wake structures. The static separating boundary layer response to active control confirms that it is a boundary layer transitioning to a free shear layer. Qualitative analyses show that significant reduction in overall static separation can be achieved under forcing conditions. Upper airfoil surface suction values are also significantly increased over the natural values. Applying tangential pulsed air control at static fundamental frequencies to a dynamic airfoil results in delay of the dynamic stall vortex formation and a delay of dynamic stall. These discoveries indicate that the developed control methodology may prove successful in increasing unsteady aircraft maneuverability. Subject terms: Static Airfoil Control; Separation Control; Unsteady Aerodynamics; Boundary Layer Control."--Report documentation page.
Author : Pau Valdepeñas Pujol
Publisher :
Page : pages
File Size : 44,24 MB
Release : 2017
Category :
ISBN :
Active flow control methods have been widely studied for more than a decade in order to improve the airfoil's efficiency. This study is focused on fluidic actuation (the addition or subtraction of momentum to/from the boundary layer by blowing and/or sucking fluid). A synthetic jet is a very particular type of fluidic actuation that involves periodic blowing and suction with zero-net-mass-flow over a the full period. Its success as an active flow control device has been extensively reported by several authors. As it can be seen synthetic jet technology provides good results on boundary layer reattachment and therefore, an improvement on the airfoil's efficiency. What is more, is a generic system that can be widespread on multiple types of airfoils such as unmanned aerial vehicles and conventional airplanes airfoils. The effectiveness of control in mitigating boundary separation depends on a number of parameters related both to the flow itself and the control input such as: frequency and amplitude of the excitation, the excitation shape, exit diameter and cavity shape. Since the synthetic jet system has several degrees of freedom and the flux is unpredictable, multiple simulations have to be done in order to assess the best configuration to achieve the maximum airfoil's efficiency. The well-known excitation of the synthetic jet is the zero-net-mass-flow that combines both expulsion and suction periodically. In this study, we also evaluate other types of excitations that imply more or less energy into the system that is characterized with the momentum coefficient. The goal is to assess thoroughly this existent trade-off between the aerodynamics performance and the momentum coefficient. And finally, extract deep conclusions and assess the best synthetic jet configuration where the aerodynamics performances are improved with a low momentum coefficient.. To extract suitably conclusions we pass through a thorough and intricate process that starts with the adapted and generic discretized surface for the synthetic jet that we use to solve the Navier-Stokes equations, then the appropriate conversions to simulate with spectral element framework Nektar++ and finally the detailed extraction of results. Moreover, we adopt to this study a practical approach with an unmanned aerial vehicle (UAV Skywalker x6) airfoil's photogrammetry that we use to simulate.
Author : Carlos San Gabriel Romero
Publisher :
Page : pages
File Size : 11,37 MB
Release : 2019
Category :
ISBN :
In a previous research Active Flow Control techniques, such as sweeping jets, applied in an ultra-low Reynolds regime (Re=1000) were found effective to reattach an already separated flow achieving lift enhancements but also inducing a large skin-friction drag increase due to the high velocities near the airfoil surface. In this study, firstly the current actuator configurations have been analyzed with the objective of determining the most important factors involved in the increase of the viscous drag. Then, several hypothesis have been done with the aim of reducing this drag penalty while keeping the lift enhancement. The decision taken in this sense has been to apply geometrical modifications to the the actuators using two control parameters, the jet width and the jet angle in which the fluid is injected. Moreover these modifications have been applied to three different actuation types; blowing, suction and synthetic jets. The simulations have been carried in a 2D NACA0012 airfoil in which a remeshing has been done in order to apply the commented modifications. The obtained results show variations depending on in which actuation type are applied. The jet angle modification has obtained interesting results for the blowing jet, since an angle that maximizes the lift coefficient has been found. The jet width has also obtained an optimum value for a specific momentum coefficient, that moreover is suitable for the three actuations. In conclusion, it has been proved that that besides the momentum coefficient and the jet location the geometrical parameters of the actuator have also a considerable impact on the overall efficiency of the actuation.
Author : John F. Donovan
Publisher :
Page : pages
File Size : 13,93 MB
Release : 1998
Category :
ISBN :
Author : Charles Strother Hynes
Publisher :
Page : 196 pages
File Size : 10,18 MB
Release : 1968
Category : Lift (Aerodynamics)
ISBN :