Endwall Secondary Flow Control in a High Speed Compressor Cascade With Vortex Generator Jets

2016 ◽  
Author(s):  
Huaping Liu ◽  
Deying Li ◽  
Bingxiao Lu ◽  
Menghan Yu
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Secondary Flow ◽  
High Speed ◽  
Vortex Generator ◽  
Low Energy ◽  
Incoming Flow ◽  
Compressor Cascade ◽  
Flow Angle ◽  
Vortex Generator Jets

This paper presents a numerical investigation of secondary flow control in a high speed compressor cascade for different incoming flow incidences by means of endwall vortex generator jets (VGJs). The inlet Reynolds number is 560,000 in corresponding to an inlet Mach number of 0.67. Based on the detail analysis of the flow field and cascade performance, two effect mechanisms of the vortex induced by the VGJ are proposed. The first is to enhance the mixing between the endwall boundary layer and the mainstream. The second is to block the cross flow as an air obstacle. Therefore, the low energy fluids accumulation in the corner region could be decreased significantly, weakening the separation on the suction side and reducing the losses effectively. This benefit becomes more obvious with the increase of the incidence from i = −2° to 4°. Additionally, a more uniform flow angle as well as static pressure profile along the blade height is obtained at the cascade outlet. The maximum loss reduction is up to 12.9% while i = 4° with a jet mass flow ratio of 0.2%. However, the unfavorable impact of the VGJs is also detected in the up-washed region, where the loss is increased by the mixing processes between the mainstream fluids and the low energy fluids. For the case i = −4°, a strengthened induced vortex is generated due to the increased angle between the jet and incoming flow, resulting in loss increase in the up-washed region. Besides, a more rapid corner boundary layer development appears in the rear part of the passage, contributing to severe separation and loss enhancement, which suggests that the VGJ should be switched off for this incidence. Therefore, the advice to the application of the VGJ according the incidence is further obtained.

Secondary flow control using endwall jet fence in a high-speed compressor cascade

2017 ◽  
Vol 31 (10) ◽  
pp. 4841-4852 ◽  
Author(s):  
Huaping Liu ◽  
Shuai Jiang ◽  
Yongchuan Yu ◽  
Dongfei Zhang ◽  
Huanlong Chen
Keyword(s):  
Flow Control ◽  
Secondary Flow ◽  
High Speed ◽  
Compressor Cascade

The Cost of Flow Control in a Compressor

2011 ◽  
Author(s):  
Simon W. Evans ◽  
Howard P. Hodson
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Vortex Generator ◽  
Control Methods ◽  
Compressor Cascade ◽  
Suction Surface ◽  
Boundary Layer Suction ◽  
Blade Row ◽  
Efficiency Increase ◽  
The Cost

This paper documents an analysis performed to estimate the cycle cost of flow control in a compressor. The analysis is based on a series of experiments conducted in a low-speed compressor cascade at high incidence. In these experiments, flow control was applied to delay a turbulent separation on the suction surfaces of the blades in the cascade. The flow control methods studied include boundary layer suction and both steady and pulsed vortex generator jets. Endwall control was also applied to remove corner separations. Tip gaps and endwall suction were both studied for this purpose. The flow control methods studied were able to successfully delay a separation occurring on the suction surface of the blades, reducing the loss coefficient. The mass flow rates and jet supply pressures required to achieve control in each case were used to model a single flow-controlled blade row in a typical turbofan cycle using cycle analysis software. The cost of control to the cycle was calculated as the polytropic compressor efficiency increase required to maintain thrust relative to a conventional cycle with no flow control. The results of the analysis show that the benefits of flow control significantly outweigh the cost. They also show that boundary layer suction coupled with endwall suction yields the lowest cycle cost. This is because of the small pressure difference required to drive suction, which allows reinjection of the aspirated air a short distance upstream of the flow controlled blade row.

Experimental and Computational Investigations of Low-Pressure Turbine Separation Control Using Vortex Generator Jets

2009 ◽  
Author(s):  
Ralph J. Volino ◽  
Olga Kartuzova ◽  
Mounir B. Ibrahim
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Total Pressure ◽  
Vortex Generator ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Separation Control ◽  
Airfoil Surface ◽  
Low Pressure Turbine ◽  
Vortex Generator Jets

Boundary layer separation control has been studied using vortex generator jets (VGJs) on a very high lift, low-pressure turbine airfoil. Experiments were done under low freestream turbulence conditions on a linear cascade in a low speed wind tunnel. Pressure surveys on the airfoil surface and downstream total pressure loss surveys were documented. Cases were considered at Reynolds numbers (based on the suction surface length and the nominal exit velocity from the cascade) of 25,000, 50,000 and 100,000. Jet pulsing frequency, duty cycle, and blowing ratio were all varied. In all cases without flow control, the boundary layer separated and did not reattach. With the VGJs, separation control was possible even at the lowest Reynolds number. Pulsed VGJs were more effective than steady jets. At sufficiently high pulsing frequencies, separation control was possible even with low jet velocities and low duty cycles. At lower frequencies, higher jet velocity was required, particularly at low Reynolds numbers. Effective separation control resulted in an increase in lift of up to 20% and a reduction in total pressure losses of up to 70%. Simulations of the flow using an unsteady RANS code with the four equation Transition-sst model produced good agreement with experiments in cases without flow control, correctly predicting separation, transition and reattachment. In cases with VGJs, however, the CFD did not predict the reattachment observed in the experiments.

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.

Influence of Unsteady Wakes on the Secondary Flows in the Linear T106 Turbine Cascade

2016 ◽  
Author(s):  
Ilker Kirik ◽  
Reinhard Niehuis
Keyword(s):  
Boundary Layer ◽  
Flow Field ◽  
Secondary Flow ◽  
High Speed ◽  
Base Flow ◽  
Secondary Flows ◽  
Pressure Probe ◽  
Hot Wire ◽  
Flow Angle ◽  
Secondary Flow Field

The present work extends previous investigations on the secondary flows around a steady and unsteady base flow to detailed time-averaged and time-resolved flow field measurements up- and downstream of the cascade. As a representative of modern low pressure turbine rotors of moderate aerodynamic loading, the LPT cascade T106 with parallel sidewalls was chosen for these investigations. Previous investigations have shown that the intensity of secondary flows in the endwall region within a first test set-up was fairly low due to the thin endwall boundary layer at the inlet of the cascade which impeded to study the influence of periodically incoming wakes on the temporal development of the secondary flow field. For that reason a new test-up was built providing a thicker inlet boundary. Measurements have been performed in the High-Speed Cascade Wind Tunnel of the University of the Federal Armed Forces Munich under realistic Mach and Reynolds numbers. In order to simulate real turbomachinery situtations, a wake generator is installed generating temporally representative wakes in the inlet plane of the cascade by a moving bar system. The inlet conditions were determined using a hot wire and a Pitot probe. Detailed measurements of the three-dimensional flow field were carried out downstream of the cascade with a triple hot wire probe, a conventional five hole pressure probe, and a dynamic pressure probe equipped with a single Kulite sensor. All measurements were performed with and without moving bars. Based on previous investigations, a pitch of the moving bars of 40 mm and a circumferential speed of 20 m/s was chosen as the configuration with the highest influence on the secondary flow field. It is shown that the intended increase of the inlet boundary layer was achieved by putting plates on top of each other in the inlet plane endwalls. This leads to more pronounced secondary flow parameters in the spanwise distribution of the pitchwise averaged secondary flow angle (Δβ2,sec) and the secondary losses (ζ2,sec).

Flow Control in Serpentine Inlet Duct Using Vortex Generator Jets

2008 ◽  
Author(s):  
R. K. Sullerey ◽  
S. Chandra
Keyword(s):  
Reynolds Number ◽  
Flow Control ◽  
Secondary Flow ◽  
Vortex Generator ◽  
Pulse Frequency ◽  
Combined Effect ◽  
Flow Distortion ◽  
Pulsed Jet ◽  
Constant Area ◽  
Vortex Generator Jets

The objective of the present research is to study the effectiveness of steady and pulsed vortex generator jets in reducing inlet flow distortion and in improving pressure recovery by effective secondary flow control in uniform inflow Serpentine duct diffuser. The measurements were carried out in at a test Reynolds number of 6.5×105 based on the diffuser inlet width. Serpentine duct diffuser consisted of two main portions namely square to circular constant area followed by a circular diffusing duct. Investigations show that the flow in the serpentine diffusing duct suffers from stall on the inner wall and the outflow at AIP has considerable flow distortion due the combined effect of secondary flow and the inner wall stall. It is observed that the use of vortex generator jets both in steady and pulsed modes improve the performance substantially. The number of jets, location of jets, velocity ratios and the pulse frequency are some of the variables that are studied. The results obtained so far suggest that use of pulsed jet not only gives better performance but also reduces the amount of air that need to be injected through the jets in comparison to steady jets for similar velocity ratios.

scholarly journals Control of Laminar Boundary-Layer Separation Using Steady and Harmonic Vortex Generator Jets

2018 ◽  
Author(s):  
Aria Alimi ◽  
Olaf Wünsch
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Laminar Boundary Layer ◽  
Active Flow Control ◽  
Vortex Generator ◽  
Boundary Layer Separation ◽  
Transition To Turbulence ◽  
Momentum Exchange ◽  
Layer Separation ◽  
Vortex Generator Jets

Active flow control of canonical laminar separation bubbles by steady and harmonic vortex generator jets (VGJs) was investigated using direct numerical simulations. Both control strategies were found to be effective in controlling the laminar boundary-layer separation. However, the present results indicate that using the same blowing amplitude, harmonic VGJs were more effective and efficient in reducing the separated region than the steady VGJs considering the fact that the harmonic VGJs use less momentum than the steady case. For steady VGJs, longitudinal structures formed immediately downstream of injection location led to formation of hairpin-type vortices causing an earlier transition to turbulence. Symmetric hairpin vortices were shown to develop downstream of the forcing location for the harmonic VGJs as well. However, the increased control effectiveness for harmonic VGJs flow control strategy is attributed to the fact that shear-layer instability mechanism was exploited. As a result, disturbances introduced by VGJs were strongly amplified leading to development of large-scale coherent structures, which are very effective in increasing the momentum exchange, thus, limiting the separated region.

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