Suppression Effect of Vortex Generator Jets With Non-Circular Orifices on Separating Flow

2003 ◽  
Author(s):  
Hiroaki Hasegawa ◽  
Kazuo Matsuuchi ◽  
Yasuhiro Komatsuzaki
Keyword(s):  
Flow Separation ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Pressure Recovery ◽  
Suppression Effect ◽  
Longitudinal Vortices ◽  
Separating Flow ◽  
Wide Range ◽  
Vortex Generator Jets ◽  
Vortex Generator Jet

Jets issuing through small holes in a wall into a freestream have proven effective in the control of boundary layer separation. Longitudinal (streamwise) vortices are produced by the interaction between the jets and the freestream. This technique is known as the vortex generator jet method of separation or stall control because it controls separation in the same general way as the well-known method using solid vortex generators. The vortex generator jet method is active control of flow separation that has the ability to provide a time-varying control action to optimize performance under wide range of flow conditions. In this study, the suppression effect of the jet orifice shape of vortex generator jets on flow separation in the diffuser is investigated for three types of jet orifice (circular, triangle and square orifices). The triangle orifice makes strong the vorticity of longitudinal vortices and effective the pressure recovery in the diffuser in comparison with the other orifice shapes. Furthermore, it is found that the orifice shape of vortex generator jets causes the different tendency of the pressure recovery in the downstream direction.

The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets

2001 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Rolf Sondergaard ◽  
Richard B. Rivir
Keyword(s):  
Boundary Layer ◽  
Duty Cycle ◽  
Separation Bubble ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Skew Angle ◽  
Suction Surface ◽  
Duty Cycles ◽  
Wide Range ◽  
Vortex Generator Jets

The effects of pulsed vortex generator jets on a naturally separating low pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 degree pitch and 90 degree skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient vs. pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies (F+) well below unity and with low (10%) duty cycles. This unexpected low frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50% duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is 5–6 times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.

Effects of Vortex Generator Jet on Flow Separations in Bowed Compressor Cascades

2015 ◽  
Author(s):  
Longting Li ◽  
Yanping Song ◽  
Fu Chen ◽  
Huaping Liu
Keyword(s):  
Flow Separation ◽  
Nodal Point ◽  
Vortex Generator ◽  
Suction Side ◽  
Loss Reduction ◽  
Flow Conditions ◽  
Combined Flow ◽  
Wide Range ◽  
Vortex Generator Jet ◽  
Corner Vortex

A combined flow control was performed by using a vortex generator jet (VGJ) in bowed compressor cascades. Loss calculations were done over a wide range of parameters including jet mass flow, jet direction and jet location, to determine their effectiveness in controlling flow separation. The topology theory is introduced in this paper to analyze the changes of separation structures in bowed cascades caused by VGJ. The results in this paper indicate that not all kinds of VGJs made up of jet parameters in any arrangement can improve the flow conditions of bowed cascades, but that there are optimal combinations of jet parameters attaining the largest total pressure loss reduction of up to 2.7% and 9.1% for positively and negatively bowed blades, respectively. The VGJ comprised of optimal jet parameters make the flow separation on the suction side of the positively bowed blade basically disappear. The VGJ in the optimal case renders flow separation on the suction side of the negatively bowed blade be relieved so that a separation line on it disappears accordingly. In addition, the mechanisms of VGJs in cases which increase the loss in bowed cascades were chosen to be analyzed in detail. The consequences show that VGJ, in that case, causes that two passage vortices are produced in the positively bowed blade, so the flow field is deteriorated. For the negatively bowed blade, the VGJ leads to the result that the flow separation on the suction side is severer and the separation nodal point corresponding to the corner vortex is transformed from a degenerately nodal point to a spiral point which means that the loss caused by the corner vortex increases.

The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets

2001 ◽  
Vol 124 (1) ◽  
pp. 77-85 ◽  
Author(s):  
Jeffrey P. Bons ◽  
Rolf Sondergaard ◽  
Richard B. Rivir
Keyword(s):  
Boundary Layer ◽  
Duty Cycle ◽  
Separation Bubble ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Skew Angle ◽  
Suction Surface ◽  
Duty Cycles ◽  
Wide Range ◽  
Vortex Generator Jets

The effects of pulsed vortex generator jets on a naturally separating low-pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high-altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 deg pitch and 90 deg skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient versus pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies F+ well below unity and with low (10 percent) duty cycles. This unexpected low-frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50 percent duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low-momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is five to six times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.

Study on Flow Separation Control by Vortex Generator Jets with Different Parameters

2012 ◽  
Vol 588-589 ◽  
pp. 1786-1789
Author(s):  
Yong Hui Xie ◽  
Zhong Yang Shen ◽  
Tao Fan
Keyword(s):  
Flow Control ◽  
Flow Separation ◽  
Vortex Generator ◽  
Separation Control ◽  
Flow Separation Control ◽  
Profound Influence ◽  
Orthogonal Analysis ◽  
Conical Diffuser ◽  
Flow Charts ◽  
Vortex Generator Jets

In order to investigate the mechanism of flow separation control in conical diffuser by vortex generator jets (VGJs) method, numerical simulations were conducted to discuss the effect of VGJs with different parameters on flow control. The aerodynamic performance in conical diffuser with angle of 14° was tested and analyzed based on Shear-Stress-Transport (SST) simulation. The flow charts at several sections were analyzed, illuminating the formation of complex vortices. Moreover, the effects of 5 VGJs parameters on the diffuser were analyzed by orthogonal analysis. It was shown that the number of jets and the pitch angle of jet showed more profound influence on the flow control by VGJs.

Separation Control on Low-Pressure Turbine Airfoils Using Synthetic Vortex Generator Jets

2003 ◽  
Author(s):  
Ralph J. Volino
Keyword(s):  
Boundary Layer ◽  
Vortex Generator ◽  
Low Pressure ◽  
Turbulent Shear ◽  
Suction Surface ◽  
Local Skin ◽  
Free Stream Turbulence ◽  
Low Pressure Turbine ◽  
Wide Range ◽  
Vortex Generator Jets

Oscillating vortex generator jets have been used to control boundary layer separation from the suction side of a low-pressure turbine airfoil. A low Reynolds number (Re = 25,000) case with low free-stream turbulence has been investigated with detailed measurements including profiles of mean and fluctuating velocity and turbulent shear stress. Ensemble averaged profiles are computed for times within the jet pulsing cycle, and integral parameters and local skin friction coefficients are computed from these profiles. The jets are injected into the mainflow at a compound angle through a spanwise row of holes in the suction surface. Preliminary tests showed that the jets were effective over a wide range of frequencies and amplitudes. Detailed tests were conducted with a maximum blowing ratio of 4.7 and a dimensionless oscillation frequency of 0.65. The outward pulse from the jets in each oscillation cycle causes a disturbance to move down the airfoil surface. The leading and trailing edge celerities for the disturbance match those expected for a turbulent spot. The disturbance is followed by a calmed region. Following the calmed region, the boundary layer does separate, but the separation bubble remains very thin. Results are compared to an uncontrolled baseline case in which the boundary layer separated and did not reattach, and a case controlled passively with a rectangular bar on the suction surface. The comparison indicates that losses will be substantially lower with the jets than in the baseline or passively controlled cases.

scholarly journals Generating Mechanism of Longitudinal Vortices Using Pulsed Vortex Generator Jets.

2001 ◽  
Vol 44 (3) ◽  
pp. 361-368
Author(s):  
Hiroaki HASEGAWA ◽  
Kazuo MATSUUCHI ◽  
Junsuke TANAKA
Keyword(s):  
Vortex Generator ◽  
Longitudinal Vortices ◽  
Vortex Generator Jets

The Response of Injection of Vortex Generator Jets to a Backward Facing Step Flow

2003 ◽  
Author(s):  
Koichi Yamagata ◽  
Manabu Saito ◽  
Tadashi Morioka ◽  
Shinji Honami
Keyword(s):  
Shear Layer ◽  
Large Scale ◽  
Flow Behavior ◽  
Velocity Ratio ◽  
Vortex Generator ◽  
Step Response ◽  
Backward Facing Step ◽  
Longitudinal Vortices ◽  
Step Flow ◽  
Vortex Generator Jets

In this paper, the flow behavior of a reattachment process over a backward facing step flow is reported. The reattachment process is controlled by injection of vortex generator jets. The injection of jets upstream of the step produces the co-rotating longitudinal vortices in a separating shear layer. The experiment of the step response of the injection jet is also conducted in order to investigate the evolution process of the longitudinal vortices. A large scale of primary and counter vortices are observed, when the velocity ratio of the free stream to injected jet is 6. The detailed structure of the longitudinal vortices is clarified. The remarkable effect of the vortices on the separating shear layer downstream of the step is observed.

Active Flow Separation Control Using Endwall Vortex Generator Jets in Highly Loaded Compressor Cascades

2015 ◽  
Author(s):  
Yanyan Feng ◽  
Yanping Song ◽  
Fu Chen ◽  
Huaping Liu
Keyword(s):  
Flow Separation ◽  
Active Flow Control ◽  
Vortex Generator ◽  
Control Technique ◽  
Flow Separation Control ◽  
Positive Effects ◽  
Loss Coefficients ◽  
Vortex Generator Jets ◽  
Active Flow ◽  
Highly Loaded

An active flow control technique of endwall vortex generator jets (VGJs) was used in two kinds of highly loaded compressor cascades. Numerical investigations were carried out on a NACA 65 profile with a large camber angle at low subsonic and high subsonic speeds, and a CDA profile at high subsonic speed respectively. The results indicate that the endwall VGJs can restrain flow separation effectively by reenergizing the boundary layer fluid and resisting the transverse movement of endwall secondary flow. At Mach number 0.23, the results of the jet blowing ratio study illustrate that the increasing jet velocity shows noteworthy potential to improve the cascade aerodynamic performance. The double jets structures were investigated yet gains weaker beneficial effects than single jet. It is probably attributed to the complex flow structure, leading to strong disturbance and large-scale mixing loss. Under −5°, 0° and +5° angles of attack, the loss coefficients are maximally reduced by 4.1%, 9.5% and 17.3% respectively. Under high subsonic conditions, the endwall VGJs still has significantly positive effects on NACA 65 profile. Considering the small separation region of CDA, the loss coefficients increase slightly although the flow separation is weakened further by VGJ.

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