Evolution of a Pulsed Vortex Generator Jet in a Turbulent Boundary Layer

2002 ◽  
Author(s):  
Hamid Johari ◽  
Gregory Rixon
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Vortex Generator ◽  
Vortex Generator Jet

Development of a Steady Vortex Generator Jet in a Turbulent Boundary Layer

2003 ◽  
Vol 125 (6) ◽  
pp. 1006-1015 ◽  
Author(s):  
Gregory S. Rixon ◽  
Hamid Johari
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flow Direction ◽  
Vortex Generator ◽  
Streamwise Vortex ◽  
Freestream Velocity ◽  
Local Boundary ◽  
Image Velocimetry ◽  
Particle Image Velocimetry Method ◽  
Vortex Generator Jet

The development of a vortex generator jet within a turbulent boundary layer was studied by the particle image velocimetry method. Jet velocities ranging from one to three times greater than the freestream velocity were examined. The jet was pitched 45 deg and skewed 90 deg with respect to the surface and flow direction, respectively. The velocity field in planes normal to the freestream was measured at four stations downstream of the jet exit. The jet created a pair of streamwise vortices, one of which was stronger and dominated the flow field. The circulation, peak vorticity, and wall-normal position of the primary vortex increased linearly with the jet velocity. The circulation and peak vorticity decreased exponentially with the distance from the jet source for the jet-to-freestream velocity ratios of 2 and 3. The wandering of the streamwise vortex can be as much as ±30% of the local boundary layer thickness at the farthest measurement station.

scholarly journals The effects of minute vortex generator jet in a turbulent boundary layer with adverse pressure gradient

2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110232
Author(s):  
Mohammad Javad Pour Razzaghi ◽  
Cheng Xu ◽  
Yue Liu ◽  
Yasin Masoumi
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Turbulent Flows ◽  
Velocity Ratio ◽  
Vortex Formation ◽  
Vortex Generator ◽  
Adverse Pressure Gradient ◽  
Passive Flow Control ◽  
Vortex Generator Jet

Experimental and numerical analysis of active and passive flow control is an important topic of practical value in the study of turbulent flows. This paper numerically analyzed the effects of an air microjet on an adverse pressure gradient turbulent boundary layer over a flat plane. Experimental data were employed to verify the numerical modeling. Vortex formation and development were then studied by changing the microjet to inflow velocity ratio (VR) and microjet angles. According to the results, the best values of the angles [Formula: see text] and [Formula: see text] for various velocities were found to be 30° and from 60° to 90°, respectively. Moreover, at VRs = 1, 2, and 4, the [Formula: see text] values (the distance at which the complete vortex persisted in the flow) were 0.058, 0.078, and 0.18, respectively. Compared to VR = 1, the vortex strength for VRs = 2 and 4 grew by 3.5 and 6.8 times, respectively. When the microjet was added to the flow, the highest variation in the Reynolds stress along the x-direction from VR = 1–4 was 10%. The corresponding values along the y and z- directions were 15% and 2.7 times, respectively.

scholarly journals Karakteristik Wake Area Akibat Efek Penggunaan Vortex Generator di Belakang Wing Airfoil Naca 43018

2019 ◽  
Vol 4 (1) ◽  
pp. 55-63
Author(s):  
Setyo Hariyadi S.P ◽  
Wawan Aries Widodo
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Flat Plate ◽  
Drag Force ◽  
Lift Force ◽  
Vortex Generator ◽  
Leading Edge ◽  
O 15 ◽  
O 19 ◽  
Wing Airfoil

Pada aliran yang melintasi suatu airfoil terdapat fenomena separasi, yakni ketika momentum aliran sudah tidak mampu lagi mengatasi adverse pressure gradien. Selanjutnya separasi ini akan diikuti dengan timbulnya daerah wake pada daerah di belakang airfoil yang mengakibatkan naiknya drag force dan menurunnya lift force. Untuk mengurangi hal tersebut maka vortex generator diletakkan pada sisi atas airfoil untuk mempercepat terbentuknya turbulent boundary layer sehingga dapat menunda separasi dan memperkecil daerah wake. Efektivitas dari vortex generator dipengaruhi oleh penempatan, ketinggian, dan interval antar vortex generator. Untuk mendapatkan hasil yang optimal, drag yang dihasilkan oleh vortex generator itu sendiri harus dikurangi. Untuk itu profil dari vortex generator yang digunakan harus sedemikian rupa sehingga drag yang dihasilkan dapat dikurangi tanpa menurunkan performasi dari airfoil tersebut. Oleh karena itu, penelitian ini dilakukan untuk melihat pengaruh penambahan vortex generator terhadap unjuk kerja airfoil melalui metode eksperimen. Tujuan penelitian ini adalah membandingkan karakteristik aliran fluida plain wing dan dengan penambahan vortex generator. Profil vortex generator yang digunakan adalah flat plate vortex generator dengan konfigurasi straight dan ditempatkan pada x/c = 10% dan 20% arah chord line dari leading edge. Variasi yang digunakan adalah bilangan Reynolds (Re), sudut serang (α) dan peletakan vortex generator pada airfoil. Kecepatan freestream yang digunakan yaitu kecepatan 12 m/s atau Re = 7,65 x 105 dan kecepatan 17 m/s atau Re = 9 x 105, dan pada sudut serang (α) 0o, 3 o, 6 o, 9 o, 12 o, 15 o, 19 o, dan 20 o. Hasil penelitian ini menunjukkan bahwa terjadi peningkatan performansi dari airfoil NACA 43018 dengan penambahan vortex generator dibandingkan dengan tanpa vortex generator. Adanya vortex generator, mempercepat perubahan dari aliran laminar ke turbulen. Separasi dapat tertunda dengan adanya vortex generator.

Combined Flow Control of Positively Bowed Blade and Vortex Generator Jet on a Compressor Cascade

2020 ◽  
Vol 37 (2) ◽  
pp. 95-109
Author(s):  
Longting Li ◽  
Yanping Song ◽  
Fu Chen
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Control Method ◽  
Vortex Generator ◽  
Separation Region ◽  
Loss Reduction ◽  
Compressor Cascade ◽  
Control Effect ◽  
Combined Flow ◽  
Vortex Generator Jet

AbstractA combined flow control method based on positively bowed blade and endwall vortex generator jet (VGJ) was performed to a compressor cascade under three kinds of inlet conditions. The results show that the endwall VGJ can further decrease the total losses in positively bowed cascades. At 0° incidence with zero inlet boundary layer, the separation type in the positively bowed blade is open, with the VGJ, the loss reduction is 2.7 %. As the inlet boundary layer thickens at 0° incidence, the separation region increases with the separation type keeping unchanged, the loss reduction increasing to 11.73 %. As the incidence rises to +7° with zero inlet boundary layer, the separation type converts into closed and the flow separation is the severest in the three cases, with the VGJ, however, the loss reduction is just 7.4 %, which means that the control effect of endwall VGJ not only depends on the size of separation region but also relies on the type of separation mode. If the separation type is open, as the size of separation region expands, the control effectiveness of endwall VGJ increases; if the separation type converts into closed with the further aggravation of flow field, that control effect will decrease.

scholarly journals STUDI EKSPERIMEN OIL FLOW VISUALIZATION PADA AIRFOIL NACA 0012 DENGAN TRAPEZOIDAL VORTEX GENERATOR MENGGUNAKAN OPEN CIRCUIT SUBSONIC WIND TUNNEL

2019 ◽  
Vol 4 (4) ◽  
pp. 1-9
Author(s):  
Setyo Hariyadi ◽  
Habibie Aldo putra
Keyword(s):  
Boundary Layer ◽  
Wind Tunnel ◽  
Turbulent Boundary Layer ◽  
Vortex Generator ◽  
Leading Edge ◽  
Open Circuit ◽  
Subsonic Wind Tunnel ◽  
Oil Flow ◽  
Oil Flow Visualization ◽  
Naca 0012

Pada pembuatan suatu pesawat terbang, suatu analisis sebelum terbang terhadap kinerja aerodinamika dari pesawat tersebut sangat diperlukan, terutama untuk daerah dimana metoda analitik/empirik tidak dapat menjangkaunya seperti perkiraan CLmax, karakteristik stall dan lain-lainnya. Satu hal penting yang harus diperhatikan dalam pendesainan suatu pesawat yaitu pemilihan airfoil dan modifikasinya. Modifikasi airfoil dilakukan untuk menunda separasi aliran dan meningkatkan performa airfoil, salah satunya dengan vortex generator. Hal ini dapat diindikasikan dengan tertundanya separasi aliran yang melintasi permukaan atas dari airfoil. Topik yang dikaji dalam penelitian ini adalah aliran melintasi airfoil NACA 0012 dengan penambahan vortex generator. Tujuan penelitian ini adalah untuk membandingkan karakteristik aliran fluida dengan dan tanpa penambahan vortex generator. Profil vortex generator yang digunakan adalah trapezoidal vortex generator dengan konfigurasi straight dan ditempatkan pada x/c = 20% arah chord line dari leading edge. Variasi yang digunakan adalah bilangan Reynolds (Re) dan sudut serang (α) pada airfoil. Kecepatan freestream yang digunakan yaitu kecepatan 10 m/s dan 20 m/s, pada sudut serang (α) 0°, 4°, 10°, 12°, 15°,dan 17°. Dari penelitian ini didapatkan performa aerodinamika dan fenomena aliran di sekitar airfoil. Perihal ini ada peningkatan performa aerodinamika pesawat dari sudut serang 0° sampai sudut serang 12° terbukti dengan meningkatnya kecepatan transisi dari laminar boundary layer menjadi turbulent boundary layer.

Instantaneous Behavior of Streamwise Vortices for Turbulent Boundary Layer Separation Control

2006 ◽  
Vol 129 (2) ◽  
pp. 226-235 ◽  
Author(s):  
K. P. Angele ◽  
F. Grewe
Keyword(s):  
Boundary Layer ◽  
Turbulent Boundary Layer ◽  
Separation Bubble ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Separation Control ◽  
Streamwise Vortices ◽  
Layer Separation ◽  
Vortex Size ◽  
The Mean

The present study investigates turbulent boundary layer separation control by means of streamwise vortices with focus on the instantaneous vortex behavior. A turbulent boundary layer is exposed to a pressure gradient that generates a separation bubble with substantial backflow. The separation bubble is controlled by conventional passive vortex generators creating pairs of counterrotating vortices. Quantitative information is achieved by applying Particle Image Velocimetry (PIV) to the cross-stream plane of the vortices. The characteristics of a pair of counter-rotating vortices shed from a vortex generator is investigated in the near-field downstream of the vortex generator. The vortices were found to grow with the boundary layer in the downstream direction, and the maximum vorticity decreases as the circulation is conserved. The vortices are nonstationary, and the movements in the spanwise direction are larger than those in the wall-normal direction, due to the presence of the wall. The vortices fluctuate substantially and move over a spanwise distance, which is approximately equal to their size. The most probable instantaneous separation between the two vortices shed from one vortex generator equals the difference between their mean positions. The unsteadiness of the vortices contributes to the observed maxima in the Reynolds stresses around the mean vortex centers. The instantaneous vortex size and the instantaneous maximum vorticity are also fluctuating properties, and the instantaneous vortex is generally smaller and stronger than the mean vortex. A correlation was found between a large instantaneous vortex size and a low instantaneous maximum vorticity (and vice versa), suggesting that the vortices are subjected to vortex stretching.

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