FIGURE 15 - uploaded by Peyman Zahedi
Content may be subject to copyright.
Source publication
In this study, tangential and perpendicular steady blowing at the trailing edge of NACA 0012 airfoil is investigated numerically to flow separation control and to study the effects of blowing amplitude and blowing coefficient on airfoil aerodynamic characteristics. Flow was fully turbulent with the Reynolds number of 5×105 and the turbulent employe...
Context in source publication
Context 1
... of blowing amplitude and blowing coefficient on the lift coefficient, drag coefficient and lift to drag ratio is indicated in figures 8, 9 and 10. In these figures, three blowing amplitude, 0.1, 0.3 and 0.5 with blowing coefficients of 0.00035, 0.00315 and 0.00875 are considered. By increasing blowing coefficient, lift coefficient increases a little and drag coefficient grows to 16 degree and then decreases, generally tangential blowing at the trailing edge of the airfoil increases the drag force. The effect of tangential blowing on lift and drag coefficients in angles of attack less than 10 degrees is so inconsiderable that by blowing coefficient of 0.00875 lift and drag coefficients increase only 0.5 and 5 percent respectively, but lift to drag ratio decreases about 5 percent which is unfavorable. In angles of attack less than 14 degrees (stall angle), tangential blowing causes reduction in lift to drag ratio and in angles of attack larger than 14 degrees it causes increasing. Because of this we focus on blowing effects on large angles of attack. Greatest increase of lift to drag ratio occurs in blowing coefficient of 0.00875 which increases around 16.5 percent in angle of attack of 18 degrees that in this situation lift coefficient increase by 7 percent and drag coefficient decrease by 9 percent. A considerable note about tangential steady blowing at the trailing edge of airfoil is that changes of amplitude of blowing and of blowing coefficient have very little effect on aerodynamic characteristics of NACA 0012 airfoil and increases of blowing amplitude from 0.1 to 0.3 and 0.5 cause changes less than 0.1 percent in lift and drag coefficient. This is also shown by Huang et al. [17] in tangential steady blowing near leading edge and in distance of 0.371 of chord length from leading edge. As we give energy to boundary layer by using tangential blowing, so contrary to suction [17 and 32], in blowing by increasing blowing coefficient changes of lift and drag coefficients and lift to drag ratio are almost stable. Another considerable note in tangential blowing is that by increasing blowing coefficient stall angle has no change and stall occur at the same angle of 14 degrees. In the airfoils it is tried to prevent sudden changes of lift coefficient after stall or sudden stall itself. Generally, airfoils with thickness of 6 to 10 percent of chord length have sudden stall and those with thickness of more than 14 percent of chord length have a gradual stall [33, 34 and 35]. Using tangential blowing results in 9 percent slower stall, however, experimental investigations show that NACA 0012 airfoil has a sudden stall [29, 30 and 31]. In our studies, lift coefficient during no-blowing situation after stall has about 10 percent decreases (lift coefficient difference percentage between angles of attack of 14 and 16 degrees), by using tangential blowing, lift coefficient has declined less than 0.4 percent. So by using steady tangent blowing as well as increasing lift to drag ratio by 16.5 percent, stall is also happening slower. On the other hand, it should be noted that by using tangential blowing separation is delayed on the airfoil. When there is no tangent blowing on the airfoil, at the angle of attack 18 degrees, separation occurs in a distance equals to 0.103 of chord length from leading edge while by using blowing coefficient of 0.00875 separations occur in distance of 0.152 of chord length from leading edge. Streamlines around the airfoil with angle of attack 18 degrees for different blowing coefficient are shown in figure 11. As it can be seen by increasing blowing coefficient or blowing amplitude, vortexes formed at the back of airfoil are decreased but not eliminated. Thereafter we study the effect of blowing amplitude and blowing coefficient on lift and drag coefficients for perpendicular steady blowing (perpendicular blowing) at the trailing edge of NACA 0012 airfoil. Lift and drag coefficient changes and lift to drag ratio changes with angles of attack in blowing amplitudes of 0.1, 0.3 and .05 are shown in figures 12, 13 and 14. In perpendicular blowing, contrary to tangential blowing, the increase of amplitude and/or blowing coefficient make the condition worse so that using blowing amplitude of 0.1 in angle of attack 14 degrees decreases lift to drag ratio by 6.5 percent and using blowing amplitude of 0.5 decreases lift to drag ratio by 17 percent. Generally, using perpendicular blowing makes the situation worse, before stall angle perpendicular blowing decrease lift to drag ratio intensively and after stall and in angle of attack of 18 degrees cause 25 percent increase in lift to drag ratio. Blowing increase the boundary layer momentum [36] and turbulence is increased by the energy added to the boundary layer by perpendicular blowing, so the more blowing amplitude or blowing coefficient increases, the larger are the turbulence of flow and vortex and eventually the more lift to drag ratio decreases. In figure 15 tangential and perpendicular steady blowing in angles of attack 16 and 18 degrees and blowing amplitude of 0.5 are compared. As it can be seen, perpendicular blowing at the trailing edge of airfoil causes larger vortexes. There is two substantial points in controlling the flow separation in perpendicular blowing at the end of the airfoil, first by using perpendicular blowing stall angle changes from 14 to 16 degrees, and second by increasing angle of attack influence percent of perpendicular blowing goes up and even in angle of attack 18 degrees results in 25 percent increase of lift to drag ratio. Changes of lift to drag ratio with blowing amplitude of 0.1 compared to no blowing status are shown in table ...
Similar publications
Citations
... At the high angles (α ˃ 20˚), the turbulence generator effect, for the wing characteristics under these conditions, becomes very small because the separation bubble size becomes a very large. (Yousefi et al. 2013) . The comparisons were done for the results of lift and drag coefficients for a wide range of the angles of attack (0 to 22) degree and constant Reynolds number of 78,000. ...
... The NACA 0012 airfoil's performance was examined numerically by Kianoosh Yousefi et al. [5] without and with the perpendicular and tangential blowing at a freestream velocity of 7.3 m/s (Re=500,000), the chord of 100 cm and different attack angles of 12, 14, 16 and 18 degree. The blowing slots were placed at 20%c from the trialing edge with different velocities (0.1, 0.3 and 0.5) percent of the freestream velocity and length of 3.5%c. ...
... The study was performed by doing an inward single dimple at different locations (75%, 50%, 25% and 10% of the chord length from the leading edge) on the airfoil ̓ s upper surface at constant air speed of 7.3 m/s and various attack angle. 5 It was concluded that the dimple presence at location of 75% of the chord increases the lift by 7% and reduces the drag 3% comparing with the smooth airfoil. ...
... The governing equations of the flow around the airfoil surface according to the assumptions mentioned in the paragraph (2) and the turbulence model (k-ω SST) are as following: - [5] i. Continuity equation: ...
This study includes a numerical simulation to investigate the aerodynamic behavior of the air flow around the NACA0012 airfoil's surface with and without a triangular rib. The triangular rib was used on the upper surface of the airfoil with size of 2% of the total chord length at different locations of 50, 70 and 90 percent of the chord length from the leading edge separately as passive control technique. Workbench-Fluent 17.2 version software was used to simulate the flow at 7 m/s freestream velocity (Re= 78,000), various attack angle (0˚ to 22˚) and chord length of 168 mm. The results indicated that presence of the triangular rib on the airfoil's upper surface, at the low angles of attack (less than 12˚), is a negative for the lift and drag results, at the angle of 12˚ is a positive only for the location of 90% while, at the higher angles is a positive for all the locations and for all the results where, the lift increases and drag decreases therefore, the NACA0012 airfoil's performance (the lift to drag ratio) significantly enhances but, at 22˚, it has a very small effect for all the results. Also, it was concluded that the rib presence at 50%c location delays the stall angle two degree (from 14˚ to 16˚).
... The NACA 0012 airfoil's performance was examined numerically by Kianoosh Yousefi et al. [5], both with and without perpendicular and tangential blowing at a freestream velocity of 7.3 m/s (Re=500,000), the chord at 100 cm and different attack angles of 12, 14, 16 and 18 degrees. ...
... The governing equations of the flow around the airfoil surface, according to the assumptions mentioned in paragraph 2 and the turbulence model (k-ω SST), are the following: [5] i. Continuity equation: ...
... Where, S is the strain rate invariant measure, 1ܨ is the function of blending, ߚ * is 0.09 and σ ߱2 is 0.856, P݇ is production limiter used in the transport turbulence model of Menter's shear stress to avoid the build-up of turbulence in areas of stagnation [5]. In addition, all of the constants are calculated by a blend from the consistent constant of the (k˗ω SST) model by σ ݇, σ ߱ & etc. [5]. ...
This study includes a numerical simulation to investigate the aerodynamic behavior of the air flow around the surface of the NACA0012 airfoil, with and without a triangular rib. The triangular rib was used on the upper surface of the airfoil with size of 2% of the total chord length and variously located at 50, 70 and 90 percent of the chord length from the leading edge, separately as a passive control technique. Workbench-Fluent 17.2 version software was used to simulate the flow at 7 m/s freestream velocity (Re = 78,000), various attack angles (0˚ to 22˚) and chord length of 168 mm. The results indicated the presence of the triangular rib on the airfoil’s upper surface, at low angles of attack (less than 12˚), was a negative for the lift and drag results, at the angle of 12˚ it was a positive only for the location of 90%, while at the higher angles it was a positive for all locations and for all results where the lift increased and drag decreased. Therefore, the NACA0012 airfoil’s performance (lift to drag ratio) was significantly enhanced but, at 22˚, it had a very small effect for all results. It was concluded that the rib’s presence at 50% location delayed the stall angle by two degrees (from 14˚ to 16˚).
... Recent developments in the flow control over the airfoil have been categorized into passive devices [2][3][4][5][6][7] and active devices. [8][9][10][11][12][13][14][15][16] Passive methods, such as altering the geometric dimensions to modify the surface pressure distribution to delay or prevent the flow separation. ...
... Further, they claimed that the blowing effectively alters the surface pressure distribution by delaying the flow separation. Later studies [12][13][14] found that increasing the amplitude of the tangential blowing further moves the separation point downstream towards airfoil trailing edge which in turn effectively increases the aerodynamic efficiency by 15%. Huang et al. 15 computationally investigated the effects of blowing on NACA0012 airfoil at 18°angle of attack and observed that in addition to stall delay characteristics it effectively reduces the drag. ...
Recent research proves that wings with leading-edge tubercles have the ability to perform efficiently in post-stall region over the conventional straight wing. Moreover, the conventional straight wing outperforms the tubercled wing at a pre-stall region which is quintessential. Even though tubercled wing offers great performance enhancement, because of the complexity of the flow, the trough region of the tubercled wing is more prone to flow separation. Henceforth, the present paper aims at surface blowing – an active flow control technique over the tubercled wing to enhance the aerodynamic efficiency by positively influencing its lift characteristics without causing any additional drag penalty. Flow parameters like blowing velocity ratios and the location of blowing were chosen to find the optimised configuration keeping the amplitude and frequency of the leading-edge tubercles constant as 0.12c and 0.25c respectively. Numerical investigations were carried out over the baseline tubercled wing and tubercled wing with surface blowing at various blowing jet velocity ratios 0.5, 1 and 2 over four different chordwise locations ranging from 0.3c to 0.8c. The results confirm that blowing at various x/c with different blowing velocity ratios performs better than the conventional tubercled wing. Comparatively, blowing velocity ratio 2 at 0.3c shows peak performance of about 28% enhancement in the lift characteristics relative to the baseline model. Particularly, in the pre-stall region, 25–50% increase in aerodynamic efficiency is evident over the tubercled wing with surface blowing compared with the baseline case. Additionally, attempts were made to delineate the physical significance of the flow separation mechanism due to blowing by visualizing the streamline pattern.
... He also mentioned that although suction has more of an effect on the increase of the stall angle, it is only recommended for use in the time of need, such as extending the range of angle of attack for aircrafts to perform the high-performance maneuvers, due to the high cost of power required to actuate the device. Later, Yousefi et al. [9] in 2013 and Yousefi and Saleh [10] in 2014 numerically investigated the effect of perpendicular and tangential blowing on NACA0012 and the impact of blowing amplitude parameters (the ratio of injection velocity to the freestream flow velocity) and blowing slot length on aerodynamic performances. They concluded that using the tangential blowing does not change the stall angle, although this deficit can be removed via the implementation of perpendicular blowing. ...
This research numerically elucidates the effects of suction and blowing on the enhancement of unsteady aerodynamic characteristics of flows and their corresponding impact on stall delay over the well-known NACA0012 airfoil at various angles of attack (\( 12 \le {\text{AOA}} \le 20 \)) under low Reynolds numbers. For this purpose, an in-house solver written in C++ is developed. The numerical code utilizes the Jameson’s cell-centered finite volume numerical method accompanied by a progressive power-law preconditioning approach to suppress the stiffness of the governing equations. Many numerical simulations are performed over the suction-blowing control parameters, namely, the slot location (\( L_{j} \)), suction/blowing amplitudes (\( A_{j} \)), and suction/blowing angle (\( \theta_{j} \)). Most of the analyses are based on the measurements of the unsteady aerodynamic characteristics behaviors (such as lift, drag, moment coefficients, and stall phenomena) over the airfoil. The numerical results confirm that the unsteady behavior of the flow (vortex shedding) is weakened or approximately removed when suction is used, especially near the leading edge. In all of the test cases, the ratio of the average lift coefficient to the average drag coefficient increases with increasing suction and blowing amplitudes, except in the case of perpendicular blowing. Furthermore, the blowing is more sensitive to the blowing angle compared to the suction. From the suction and blowing results, it is concluded that the former has a more positive impact on the lift and drag characteristics, especially in the case of incompressible flow at Low-Reynolds regimes.
... An extensive number of studies have then been conducted, tending to improve the comprehension and effectiveness of such active means. Several approaches can be performed such as steady (Chen et al. 2006;Radespiel et al. 2016) or pulsed Marom et al. 2016) fluid amounts imposed from one or multiple slots (Sun and Hamdani 2001;Zhao et al. 2015) either tangentially or perpendicularly (Yousefi et al. 2013). Kim and Sung (2003) performed direct numerical simulations of a spatially evolving turbulent boundary layer. ...
... They demonstrated the existence of a threshold momentum input where blowing becomes more effective than suction. Later, Yousefi et al. (2013) focused on tangential and perpendicular blowing and suction slot geometry optimization including jet width and amplitude effects. Chen et al. (2015) analyzed the control effectiveness on aerodynamic forces and alternate vortex shedding suppression as a function of suction holes azimuthal position, spanwise spacing and flow rate. ...
... They demonstrated that the maximum permissible angle of attack of the airfoil can be increased and the lift forces can be increased by 10%. Yousefi et al. [18] studied the flow separation control with skewed angle of blowing. Mack et al. [19] studied the fluidic oscillators that can be employed in active boundary layer control. ...
Boundary layer separation over an airfoil causes large energy losses and strong adverse pressure gradients. This in turn leads to a reduction in the lift force and an increase in the drag force. Therefore delaying or if possible, eliminating the flow separation is mandatory. The elimination of flow separation would permit higher angles of attack for many practical applications. Steady blowing on the suction side of the airfoil is found to be effective in controlling the boundary layer separation. Flow around NACA0012 and LA203A airfoils are analysed in the present study, with the position of the secondary blowing jet at 60 percent of the chord length and angles of attack ranging from 2 to 18 degree for NACA0012 and 2 to 20 degree for LA203A. The secondary blowing velocity is varied from 0 percent to 40 percent of the free stream velocity. The lift curves of all the cases studied are plotted. The results show that the secondary blowing helps to control flow separation and cause an increase in the lift and delay the stalling of airfoils in both cases.
... With the development of computational facilities in recent years, computational fluid dynamics (CFD) has been increasingly used to investigate boundary layer control. Numerous flow control studies through CFD approaches [25][26][27][28][29][30][31][32][33] have been conducted to investigate the effects of blowing, suction, and synthetic jets on the aerodynamic characteristics of airfoils. In the current study, the optimization of blowing and suction slot geometries, including suction and blowing jet widths, is numerically analyzed. ...
The effects of jet-width for blowing and suction flow control were evaluated for a NACA0012 airfoil. The RANS equations were employed in conjunction with a Menter’s shear stress turbulent model. Tangential and perpendicular blowing at the trailing edge as well as perpendicular suction at the leading edge were applied on the airfoil upper surface. The jet widths were varied from 1.5 to 4 percent of the chord length and the jet velocity was also selected 0.3 and 0.5 of freestream velocity. Results of this study demonstrated that, when blowing jet width increases, lift to drag ratio rises continuously in tangential blowing and decreases quasi-linearly in perpendicular blowing. Moreover, the jet widths of 3.5 and 4 percent of the chord length are the most effective amounts for tangential blowing, and smaller jet widths are more effective for perpendicular blowing. Furthermore, the lift to drag ratio improves when suction jet width increases and reaches to its maximum value at 2.5 percent of the chord length.
This research paper includes an investigation of the characteristics of the two-dimensional, turbulent and incompressible flow around the cambered smooth NACA 6409 airfoil numerically. CFD simulation, using Workbench-Fluent software, was performed at different attack angles (from 0° to 16°) and Reynolds number of 3.3 * 10⁵. The study results showed that the flow separation happens in the upper region of the airfoil when it is subjected to an opposite and strong pressure gradient. The highest coefficient of the lift is got at 12° an attack angle whereas, the maximum value of the aerodynamic performance of the airfoil is obtained at an angle of 4°.
Natural vortex development in double diffusive confined wall jet flow is firstly analyzed as a basic state. A consecutive vortices production and shedding processes are observed at moderated Reynolds numbers. The influence of these phenomena on combined transfers is then discussed. Strouhal number evolution was determined by spectral analysis conducted in the near-field region of the laminar wall jet. Accordingly, two critical values were found indicating the transitions between stationary, non stationary and quasi-periodic states. Uniform amounts of water are then added or extracted through a thin slot placed on the horizontal flat plate in order to control larges structures creation and growth. The main purpose is to assess the effectiveness of uniform suction or blowing on each flow state and to establish the appropriate conditions under which the natural instability disappears. An Average Nusselt and Sherwood numbers as well as skin friction coefficient dependant behavior were observed which implies that vortex dynamic directly affects thermo-solutal transfer.
