Flow Control Investigations of Steady and Pulsed Jets in Bowed Compressor Cascades

2016 ◽  
Author(s):  
Longting Li ◽  
Yanping Song ◽  
Fu Chen ◽  
Huaping Liu
Keyword(s):  
Flow Control ◽  
Secondary Flow ◽  
Control Method ◽  
Vortex Generator ◽  
Actuation Frequency ◽  
Single Vortex ◽  
Pulsed Jets ◽  
Blowing Ratio ◽  
Passage Vortex ◽  
Flow Loss

Based on the previous research about the combined flow control method which was carried out by applying the endwall steady VGJ to the bowed compressor cascades to reduce the secondary flow loss, for the consideration that the pulsed jets may save the mass flow required for control, therefore the unsteady VGJs over the different actuation frequencies and blowing ratios were investigated in detail. Under the conditions of same jet geometry parameters, the improvements to the fluid fields in the bowed compressor cascades caused by the pulsed jets are less than that induced by the steady cases. With the pulsed VGJ, for the positively bowed blade, the enhancement of the time-averaged aerodynamic performance can be achieved when the blowing ratio is greater than 0.6, but all of the unsteady conditions in this research can improve the flow field in the negatively bowed blade. The time-averaged total losses decrease by 1.6% and 7.0% at most for the positively and negatively bowed blades, respectively. The mechanisms by which the endwall pulsed vortex generator jets delay flow separation and reduce loss were explored. The results show that, being different from the single vortex produced in steady VGJ, the pulsed case generates a pair of streamwise vortices with the opposite sense of rotation. One vortex suppresses the development of the secondary flow, but the other one increases the size of the passage vortex. Furthermore, for the endwall pulsed VGJ, the changes of the blowing ratio plays a more important role in improving the flow fields in the bowed cascades than that of the actuation frequency.

Effect of Blade Aspiration Slot Configuration on the Aerodynamic Performance of a Highly Loaded Aspirated Compressor Cascade

2017 ◽  
Author(s):  
Longxin Zhang ◽  
Le Cai ◽  
Bao Liu ◽  
Jun Ding ◽  
Songtao Wang
Keyword(s):  
Flow Control ◽  
Flow Rate ◽  
Control Method ◽  
Active Flow Control ◽  
Experimental Studies ◽  
Aerodynamic Performance ◽  
Flow Path ◽  
Compressor Cascade ◽  
Flow Loss ◽  
Highly Loaded

As a promising active flow control method, boundary layer suction (BLS) can be used to enhance the aerodynamic performance of the highly-loaded compressor effectively, and due to this reason, extensive studies have been carried out on it. However, contrast to those abundant studies focusing on the flow control effects of BLS, little attention has been paid on the design method of the aspiration flow path. This work presents a 3-D steady numerical simulation on a highly-loaded aspirated compressor cascade. The aspiration slot is implemented at its best location based on the previous experimental studies and the aspiration flow rate is fix to 1.5% of the inlet massflow. The plenum configuration follows the blade shape and remains unchanged. One-side-aspiration manner is adopted to simplify the aspiration devices. Two critical geometry parameters, slot angle and slot width, are varied to study the effects of blade aspiration slot configuration on the cascade loss, radial distribution of the aspiration flow rate and inner flow structures within the aspiration flow path. Results show that the slot configuration does affect the cascade performance. In comparison with the throughflow performance, it is especially true once the flow loss caused by the aspiration flow path is also taken into account, and higher flow loss will be generated within the aspiration flow path if an inappropriate scheme is adopted. In the present investigation, apart from the cases with larger negative slot angle, a wider slot is more preferable to a narrower one, since it could enhance the aspiration capacity near the endwall regions and lower the dissipation loss within the aspiration flow path. In terms of the slot angle, a larger negative value, i.e., the slot direction more aligned with the incoming flow, is not beneficial to improve the throughflow performance, while concerning the flow loss yield by the aspiration flow path, a proper negative slot angle is always optimal.

Steady Vortex-Generator Jet Flow Control on a Highly Loaded Transonic Low-Pressure Turbine Cascade: Effects of Compressibility and Roughness

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Chiara Bernardini ◽  
Stuart I. Benton ◽  
John D. Lee ◽  
Jeffrey P. Bons ◽  
Jen-Ping Chen ◽  
...  
Keyword(s):  
Surface Roughness ◽  
Mach Number ◽  
Flow Control ◽  
High Speed ◽  
Vortex Generator ◽  
Control Performance ◽  
Low Pressure Turbine ◽  
Blowing Ratio ◽  
Turbulent Separation ◽  
Mach Number Distribution

A new high-speed linear cascade has been developed for low-pressure turbine (LPT) studies at The Ohio State University. A compressible LPT profile is tested in the facility and its baseline performance at different operating conditions is assessed by means of isentropic Mach number distribution and wake total pressure losses. Active flow control is implemented through a spanwise row of vortex-generator jets (VGJs) located at 60% chord on the suction surface. The purpose of the study is to document the effectiveness of VGJ flow control in high-speed compressible flow. The effect on shock-induced separation is assessed by Mach number distribution, wake loss surveys and shadowgraph. Pressure sensitive paint (PSP) is applied to understand the three dimensional flow and shock pattern developing from the interaction of the skewed jets and the main flow. Data show that with increasing blowing ratio, the losses are first decreased due to separation reduction, but losses connected to compressibility effects become stronger due to increased passage shock strength and jet orifice choking; therefore, the optimum blowing ratio is a tradeoff between these counteracting effects. The effect of added surface roughness on the uncontrolled flow and on flow control behavior is also investigated. At lower Mach number, turbulent separation develops on the rough surface and a different flow control performance is observed. Steady VGJs appear to have control authority even on a turbulent separation but higher blowing ratios are required compared to incompressible flow experiments reported elsewhere. Overall, the results show a high sensitivity of steady VGJs control performance and optimum blowing ratio to compressibility and surface roughness.

scholarly journals Effect of the Radial Pressure Gradient on the Secondary Flow Generated in an Annular Turbine Cascade

2012 ◽  
Vol 2012 ◽  
pp. 1-14 ◽  
Author(s):  
Hesham M. El-Batsh
Keyword(s):  
Pressure Gradient ◽  
Secondary Flow ◽  
Stokes Equations ◽  
Three Dimensional ◽  
Radial Pressure ◽  
Navier Stokes ◽  
Pressure Probe ◽  
Passage Vortex ◽  
Flow Loss ◽  
Radial Pressure Gradient

This paper introduces an investigation of the effect of radial pressure gradient on the secondary flow generated in turbine cascades. Laboratory measurements were performed using an annular sector cascade which allowed the investigation using relatively small number of blades. The flow was measured upstream and downstream of the cascade using a calibrated five-hole pressure probe. The three-dimensional Reynolds Averaged Navier Stokes equations were solved to understand flow physics. Turbulence was modeled using eddy-viscosity assumption and the two-equation Shear Stress Transport (SST)k-ωmodel. The results obtained through this study showed that the secondary flow is significantly affected by the pressure gradient along blade span. The experimental measurements and the numerical calculations predicted passage vortex near blade hub which had larger and stronger values than that predicted near blade tip. The loss distribution revealed that secondary flow loss was concentrated near blade hub. It is recommended that attempts of reducing secondary flow in annular cascade should put emphasis on the passage vortex near the hub.

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.

A Global Approach to Turbomachinery Flow Control: Passage Vortex Control

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
Matthew J. Bloxham ◽  
Jeffrey P. Bons
Keyword(s):  
Flow Control ◽  
Pressure Loss ◽  
Total Pressure ◽  
Vortex Generator ◽  
Total Pressure Loss ◽  
Turbine Cascade ◽  
Combined System ◽  
Vortex Control ◽  
Passage Vortex ◽  
Zero Net Mass Flux

A flow control scheme was implemented in a low-pressure turbine cascade that simultaneously mitigated profile and endwall losses using midspan vortex generator jets (VGJs) and endwall suction. The combined system had an approximate zero-net mass flux. During the design, a theoretical model was used that effectively predicted the trajectory of the passage vortex using inviscid results obtained from two-dimensional computational fluid dynamics (CFD). The model was used in the design of two flow control approaches: the removal and redirection approaches. The emphasis of the removal approach was the direct application of flow control along the passage vortex (PV) trajectory. The redirection approach attempted to alter the trajectory of the PV with the judicious placement of suction holes. A potential flow model was created to aid in the design of the redirection approach. The model results were validated using flow visualization and particle image velocimetry (PIV) in a linear turbine cascade. Detailed total pressure loss wake surveys were measured while matching the suction and VGJ mass flow rates for the removal and redirection approaches at ReCx = 25,000 and blowing ratio, B, of 2. When compared with the no control results, the addition of VGJs and endwall suction reduced the wake losses by 69% (removal) and 68% (redirection). The majority of the total pressure loss reduction resulted from the spanwise VGJs, while the suction schemes provided modest additional reductions (<2%). At ReCx = 50,000, the endwall control effectiveness was assessed for a range of suction rates without midspan VGJs. Area-averaged total pressure loss reductions of up to 28% were measured in the wake at ReCx = 50,000, B = 0, with applied endwall suction (compared to no suction at ReCx = 50,000), at which point the loss core of the PV was almost completely eliminated.

Active Flow Control in Circular and Transitioning S-duct Diffusers

2006 ◽  
Vol 128 (6) ◽  
pp. 1192-1203 ◽  
Author(s):  
A. M. Pradeep ◽  
R. K. Sullerey
Keyword(s):  
Flow Control ◽  
Secondary Flow ◽  
Mass Flow Rate ◽  
Flow Rate ◽  
Pressure Loss ◽  
Total Pressure ◽  
Static Pressure ◽  
Vortex Generator ◽  
Main Flow ◽  
Separation Control

Performance enhancement of three-dimensional S-duct diffusers by secondary flow and separation control using vortex generator jets is the objective of the current experimental investigation. Two different diffuser geometries namely, a circular diffuser and a rectangular—to—circular transitioning diffuser were studied. The experiments were performed in uniform inflow conditions at a Reynolds number of 7.8×105 and the performance evaluation of the diffusers was carried out in terms of static pressure recovery and quality (flow uniformity) of the exit flow. Detailed measurements that included total pressure, velocity distribution, surface static pressure, skin friction, and boundary layer measurements were taken and these results are presented here in terms of static pressure rise, distortion coefficient, total pressure loss coefficient, and the transverse velocity vectors at the duct exit. The use of vortex generator jets resulted in around 26% in total pressure loss and about 22% decrease in flow distortion coefficients in the circular and transitioning diffusers. The mass flow rate of the air injected through the VGJ was about 0.1% of the mass flow rate of the main flow for secondary flow control and about 0.06% of the main flow for separation control. The physical mechanism of the flow control devices used has been explored. The structure of the vortices generated by the control methods are presented in the form of smoke visualization images. The method of flow control used here is perceived to have applications in turbomachinery like turbines and compressors.

Numerical investigation of vortex generators to reduce cross-passage flow phenomena in compressor stator end-walls

2011 ◽  
Vol 225 (7) ◽  
pp. 877-885 ◽  
Author(s):  
J Ortmanns ◽  
C Pixberg ◽  
V Gümmer
Keyword(s):  
Secondary Flow ◽  
Vortex Flow ◽  
Vortex Generator ◽  
Initial Study ◽  
Vortex Generators ◽  
Geometrical Parameters ◽  
Single Vortex ◽  
Stator Vane ◽  
Flow Phenomena ◽  
Generator Design

The numerical results presented in this article demonstrate the ability of single-vortex generators to reduce the cross-passage secondary flow in a high-turning stator vane passage. The sensitivities of the induced vortex flow are determined in an initial study by varying the geometrical parameters. The visualization of the flow patterns and the determination of the stator vane performance show that the efficiency and the working range can be increased by applying single-vortex generators. The vortex generator design has to achieve a balance between the magnitude of vorticity induced to reduce the secondary flow phenomena and the additional losses associated with the produced vortex flow.

Investigation of Secondary Flow Behavior in a Radial Turbine Nozzle

2006 ◽  
Author(s):  
Mohammed Alexin Putra ◽  
Franz Joos
Keyword(s):  
Secondary Flow ◽  
Flow Behavior ◽  
Single Vortex ◽  
Flow Angle ◽  
Radial Turbine ◽  
Passage Vortex ◽  
Flow Phenomena ◽  
Contour Plots ◽  
Axial Turbines ◽  
Secondary Vortices

Fundamental investigation of secondary flow phenomena in a radial turbine nozzle are presented. L2F measurements have been used for validation of numerical CFD calculations. Having a good agreement by using the Reynolds stress turbulence model (RSM) the numerical results have been used further to analyse the structure of secondary vortices. Contour plots of the flow angle with typical isoline pattern as well as the vorticity have been evaluated. It is shown that the channel of the radial nozzle similar secondary vorticity systems generates as known from the axial turbine nozzles. The formation and the development of the horse-shoe vortex and the corner vortex are discussed. The well known passage vortex of the axial turbines could not been found because of the small curvature of the streamlines. Instead of these an additional single vortex can be observed, called the “inflow” vortex caused by the unsymmetrical flow into the radial cascade from the upstream scroll.

scholarly journals Secondary Flow Control and Streamwise Vortices Formation

1994 ◽  
Author(s):  
Piotr P. Doerffer ◽  
Jochen Amecke
Keyword(s):  
Boundary Layer ◽  
Flow Control ◽  
Secondary Flow ◽  
Side Wall ◽  
Secondary Flows ◽  
Turbine Cascade ◽  
Streamwise Vortices ◽  
Wall Boundary Layer ◽  
Passage Vortex ◽  
Horse Shoe Vortex

The structure of a secondary flow in a linear turbine cascade has been investigated. In order to analyse streamwise vortices configuration and to control their formation two types of side wall boundary layer fences have been applied. Results obtained proved that the streamwise fence reduces significantly spanwise extent of secondary flows. Transverse fence has no such effect but causes very significant change of location and the losses level in a passage vortex. Presented results cast some new light on the contribution of passage vortex, horse shoe vortex and a shear plain in between, to the losses maximum where these flow elements are in direct neighbourhood.

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.

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