The Effects of Unsteadiness and Compressibility on the Interaction Between Hub Leakage and Mainstream Flows in High-Pressure Turbines

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Ivan Popović ◽  
Howard P. Hodson ◽  
Erik Janke ◽  
Torsten Wolf
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Leakage Flow ◽  
Average Flow ◽  
Linear Cascade ◽  
Low Speed ◽  
Present Test ◽  
Blade Row ◽  
Time Average ◽  
Unsteady Effects

This paper investigates the effects of compressibility and unsteadiness due to the relative blade row motion and their importance in the interaction between hub leakage (purge) and mainstream flows. First, the challenges associated with the blade redesign for low-speed testing are described. The effects of Mach number are then addressed by analyzing the experiments in the low-speed linear cascade equipped with the secondary airflow system and computations performed on the low- and high-speed blade profiles. These results indicate that the compressibility does not significantly affect the interaction between the leakage and mainstream flows despite a number of compromises made during the design of the low-speed blade. This was due to the fact that the leakage–mainstream interaction takes place upstream of the blade throat where the local Mach numbers are still relatively low. The analysis is then extended to the equivalent full-stage unsteady computations. The periodic unsteadiness resulting from the relative motion of the upstream vanes appreciably affected the way in which the leakage flow is injected and the rotor flow field in general. However, the time-average flow field was still found to be dominated by the rotor blade's potential field. For the present test arrangement, the unsteady effects were not very detrimental and caused less than a 10% increase in the losses due to the leakage injection relative to the steady calculations.

The Effects of Unsteadiness and Compressibility on the Interaction Between Hub Leakage and Mainstream Flows in HP Turbines

2011 ◽  
Author(s):  
I. Popovic´ ◽  
H. P. Hodson ◽  
E. Janke ◽  
T. Wolf
Keyword(s):  
Mach Number ◽  
Relative Motion ◽  
High Speed ◽  
Leakage Flow ◽  
Linear Cascade ◽  
Low Speed ◽  
Present Test ◽  
Blade Row ◽  
Time Average ◽  
Unsteady Effects

This paper investigates the effects of compressibility and unsteadiness due to the relative blade row motion and their importance in the interaction between hub leakage (purge) and mainstream flows. First, the challenges associated with the blade redesign for low-speed testing are described. The effects of Mach number are then addressed by analyzing the experiments in the low-speed linear cascade equipped with the secondary airflow system and computations performed on the low- and high-speed blade profiles. These results indicate that the compressibility does not significantly affect the interaction between the leakage and mainstream flows despite a number of compromises made during the design of the low-speed blade. This was due to the fact that the leakage-mainstream interaction takes place upstream of the blade throat where the local Mach numbers are still relatively low. The analysis is then extended to the equivalent full-stage unsteady computations. The periodic unsteadiness resulting from the relative motion of the upstream vanes appreciably affected the way in which the leakage flow is injected and the rotor flowfield in general. However, the time-average flowfield was still found to be dominated by the rotor blade’s potential field. For the present test arrangement, the unsteady effects were not very detrimental, and caused less than a 10% increase in the losses due to the leakage injection relative to the steady calculations.

Evaluation of a Flow Measurement Probe Influence on the Flow Field in High Speed Axial Compressors

2021 ◽  
Author(s):  
Ryosuke Seki ◽  
Satoshi Yamashita ◽  
Ryosuke Mito
Keyword(s):  
Flow Field ◽  
Approximation Method ◽  
High Speed ◽  
Static Pressure ◽  
Axial Compressor ◽  
Pressure Change ◽  
Operating Point ◽  
Blade Row ◽  
Probe Insertion ◽  
Probe Geometry

Abstract The aerodynamic effects of a probe for stage performance evaluation in a high-speed axial compressor are investigated. Regarding the probe measurement accuracy and its aerodynamic effects, the upstream/downstream effects on the probe and probe insertion effects are studied by using an unsteady computational fluid dynamics (CFD) analysis and by verifying in two types of multistage high-speed axial compressor measurements. The probe traverse measurements were conducted at the stator inlet and outlet in each case to evaluate blade row performance quantitatively and its flow field. In the past study, the simple approximation method was carried out which considered only the interference of the probe effect based on the reduction of the mass flow by the probe blockage for the compressor performance, but it did not agree well with the measured results. In order to correctly and quantitatively grasp the mechanism of the flow field when the probe is inserted, the unsteady calculation including the probe geometry was carried out in the present study. Unsteady calculation was performed with a probe inserted completely between the rotor and stator of a 4-stage axial compressor. Since the probe blockage and potential flow field, which mean the pressure change region induced by the probe, change the operating point of the upstream rotor and increase the work of the rotor. Compared the measurement result with probe to a kiel probe setting in the stator leading edge, the total pressure was increased about 2,000Pa at the probe tip. In addition, the developed wake by the probe interferes with the downstream stator row and locally changes the static pressure at the stator exit. To evaluate the probe insertion effect, unsteady calculations with probe at three different immersion heights at the stator downstream in an 8-stage axial compressor are performed. The static pressure value of the probe tip was increased about 3,000Pa in the hub region compared to tip region, this increase corresponds to the measurement trend. On the other hand, the measured wall static pressure showed that there is no drastic change in the radial direction. In addition, when the probe is inserted from the tip to hub region in the measurement, the blockage induced by the probe was increased. As a result, operating point of the stator was locally changed, and the rise of static pressure of the stator increased when the stator incidence changed. These typical results show that unsteady simulations including probe geometry can accurately evaluate the aerodynamic effects of probes in the high-speed axial compressor. Therefore, since the probe will pinpointed and strong affects the practically local flow field in all rotor upstream passage and stator downstream, as for the probe measurement, it is important to pay attention to design the probe diameter, the distance from the blade row, and its relative position to the downstream stator. From the above investigations, a newly simple approximation method which includes the effect of the pressure change evaluation by the probe is proposed, and it is verified in the 4-stage compressor case as an example. In this method, the effects of the distance between the rotor trailing edge (T.E.) and the probe are considered by the theory of the incompressible two-dimensional potential flow. The probe blockage decreases the mass flow rate and changes the operating point of the compressor. The verification results conducted in real compressor indicate that the correct blockage approximation enables designer to estimate aerodynamic effects of the probe correctly.

scholarly journals On Scaling Method to Investigate High-Speed Over-Tip-Leakage Flow at Low-Speed Condition

2018 ◽  
Vol 140 (6) ◽  
Author(s):  
Hongmei Jiang ◽  
Li He ◽  
Qiang Zhang ◽  
Lipo Wang
Keyword(s):  
High Speed ◽  
Turbine Blades ◽  
Flow Distribution ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Scaling Method ◽  
Low Speed ◽  
Tip Leakage ◽  
Speed Condition

Modern high-pressure turbine blades operate at high-speed conditions. The over-tip-leakage (OTL) flow can be high-subsonic or even transonic. From the consideration of problem simplification and cost reduction, the OTL flow has been studied extensively in low-speed experiments. It has been assumed a redesigned low-speed blade profile with a matched blade loading should be sufficient to scale the high-speed OTL flow down to the low-speed condition. In this paper, the validity of this conventional scaling approach is computationally examined. The computational fluid dynamics (CFD) methodology was first validated by experimental data conducted in both high- and low-speed conditions. Detailed analyses on the OTL flows at high- and low-speed conditions indicate that, only matching the loading distribution with a redesigned blade cannot ensure the match of the aerodynamic performance at the low-speed condition with that at the high-speed condition. Specifically, the discrepancy in the peak tip leakage mass flux can be as high as 22%, and the total pressure loss at the low-speed condition is 6% higher than the high-speed case. An improved scaling method is proposed hereof. As an additional dimension variable, the tip clearance can also be “scaled” down from the high-speed to low-speed case to match the cross-tip pressure gradient between pressure and suction surfaces. The similarity in terms of the overall aerodynamic loss and local leakage flow distribution can be improved by adjusting the tip clearance, either uniformly or locally.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low-Speed Turbine Blade Cascade With Moving End Wall

2007 ◽  
Vol 130 (1) ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage ◽  
End Wall

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110deg and blade chord of 1.0m. Data were obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0×105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle image velocimetry was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip end-wall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the undertip flow near the end wall due to the moving wall is observed and the effect on the tip leakage vortex examined.

Optimization of Non-Axisymmetric End Wall Contours for the Rotor of a Low Speed, 1 1/2 Stage Research Turbine With Unshrouded Blades

2012 ◽  
Author(s):  
Jonathan Bergh ◽  
Glen Snedden ◽  
Christiaan Meyer
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Recent Work ◽  
Specific Design ◽  
Established Method ◽  
Linear Cascade ◽  
Low Speed ◽  
End Wall

Non-axisymmetric end wall contouring has become an established method for the reduction of the losses associated with secondary flow. To date, the majority of designs have been produced by the aeroengine manufacturing community and as a result access to specific design and methodological details is often limited [1]. In contrast, whilst the details of non-embargoed work are more freely available, much of this work has been carried out in simplified environments, with the most common of these being 2-dimensional, linear cascades, and therefore do not include a number of features which are present in the flow field of a real turbine [2]. Recent work by Snedden et al [3] involved the introduction of “generic”, non-axisymmetric end wall contours, originally designed for a linear cascade (the so-called Durham cascade), into the rotor row of a low speed, 1 1/2 stage research turbine. While an increase in rotor performance was noted, a detailed inspection of the flow results suggested that even greater improvements could be obtained through the design of custom end walls for the turbine. This investigation therefore covers the design of custom non-axisymmetric end wall contours for the rotor row of an annular turbine rig with unshrouded blades (the same rig as that used by Snedden), using a modified version of an end wall design routine originally developed for the production of non-axisymmetric end walls for a linear cascade environment.

The Simulation of Turbomachinery Blade Rows in Asymmetric Flow Using Actuator Disks

1997 ◽  
Vol 119 (4) ◽  
pp. 723-732 ◽  
Author(s):  
W. G. Joo ◽  
T. P. Hynes
Keyword(s):  
Supersonic Flow ◽  
Flow Field ◽  
Boundary Conditions ◽  
High Speed ◽  
Axial Position ◽  
Numerical Implementation ◽  
Asymmetric Flow ◽  
Actuator Disk ◽  
Blade Row ◽  
Flow Through

This paper describes the development of actuator disk models to simulate the asymmetric flow through high-speed low hub-to-tip ratio blade rows. The actuator disks represent boundaries between regions of the flow in which the flow field is solved by numerical computation. The appropriate boundary conditions and their numerical implementation are described, and particular attention is paid to the problem of simulating the effect of blade row blockage near choking conditions. Guidelines on choice of axial position of the disk are reported. In addition, semi-actuator disk models are briefly described and the limitations in the application of the model to supersonic flow are discussed.

Experimental and Numerical Verification of the Core-Flow in a New Low-Pressure Turbine

2016 ◽  
Author(s):  
Michael Henke ◽  
Lars Wein ◽  
Tim Kluge ◽  
Yavuz Guendogdu ◽  
Marc Heinz-Otto Biester ◽  
...  
Keyword(s):  
Flow Field ◽  
Low Pressure ◽  
Numerical Verification ◽  
Two Dimensional ◽  
Core Flow ◽  
Low Pressure Turbine ◽  
The Core ◽  
Blade Row ◽  
Unsteady Effects ◽  
Blade Row Interaction

The flow field in modern axial turbines is non-trivial and highly unsteady due to secondary flow and blade row interaction. In recent years, existing design-tools like two-dimensional flow solvers as well as fully three-dimensional CFD methods have been validated for the assumption of a quasi-steady flow field. Since the inevitable unsteadiness of the flow field has a direct impact on unsteady loss generation and work transfer, existing design methods stand in need of validation for local unsteady effects within the flow field. In order to clearly separate end-wall losses from those generated by blade row interaction within the blade passage, a two-dimensional core-flow is essential for the investigation. Hence, a new 1.5-stage high aspect ratio low pressure turbine has been designed to determine the intensity of core-flow blade row interaction for different axial gaps. First, inlet and outlet conditions of the test rig are evaluated with regard to homogeneity of the flow parameters in their radial and circumferential distributions. Secondly, the measurement data gained from rig tests have been applied as boundary conditions to time-averaged numerical computations. The flow field analysis for two different axial gaps focuses on the verification of the core flow. The authors show that the new turbine has been successfully verified using both test data and the numerical predictions, serving as a precondition for the validation of the numerical model for unsteady effects within the core-flow.

scholarly journals On Scaling Method to Investigate High-Speed Over-Tip-Leakage Flow at Low-Speed Condition

2017 ◽  
Author(s):  
Hongmei Jiang ◽  
Li He ◽  
Qiang Zhang ◽  
Lipo Wang
Keyword(s):  
High Speed ◽  
Flow Distribution ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Scaling Method ◽  
Low Speed ◽  
Aerodynamic Loss ◽  
Tip Leakage ◽  
Speed Condition

Modern High Pressure Turbine (HPT) blades operate at high speed conditions. The Over-Tip-Leakage (OTL) flow, which plays a major role in the overall loss generation for HPT, can be high-subsonic or even transonic. In practice from the consideration of problem simplification and cost reduction, the OTL flow has been studied extensively in low speed experiments. It has been assumed a redesigned low speed blade profile with a matched blade loading should be sufficient to scale the high speed OTL flow down to the low speed condition. In this paper, the validity of this conventional scaling approach is computationally examined. The CFD methodology was firstly validated by experimental data conducted in both high and low speed conditions. Detailed analyses on the OTL flows at high and low speed conditions indicate that, only matching the loading distribution with a redesigned blade cannot ensure the match of the aerodynamic performance at the low speed condition with that at the high-speed condition. Specifically, the discrepancy in the peak tip leakage mass flux can be as high as 22.2%, and the total pressure loss at the low speed condition is 10.7% higher than the high speed case. An improved scaling method is proposed hereof. As an additional dimension variable, the tip clearance can also be “scaled” down from the high speed to low speed case to match the cross-tip pressure gradient between pressure and suction surfaces. The similarity in terms of the overall aerodynamic loss and local leakage flow distribution can be improved by adjusting the tip clearance, either uniformly or locally. The limitations of this proposed method are also addressed in this paper.

PIV Maps of Tip Leakage and Secondary Flow Fields on a Low Speed Turbine Blade Cascade With Moving Endwall

2005 ◽  
Author(s):  
P. Palafox ◽  
M. L. G. Oldfield ◽  
J. E. LaGraff ◽  
T. V. Jones
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Field Measurements ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Leakage Flow ◽  
Tip Leakage Flow ◽  
Tip Leakage Vortex ◽  
Low Speed ◽  
Tip Leakage

New, detailed flow field measurements are presented for a very large low-speed cascade representative of a high-pressure turbine rotor blade with turning of 110 degrees and blade chord of 1.0 m. Data was obtained for tip leakage and passage secondary flow at a Reynolds number of 4.0 × 105, based on exit velocity and blade axial chord. Tip clearance levels ranged from 0% to 1.68% of blade span (0% to 3% of blade chord). Particle Image Velocimetry (PIV) was used to obtain flow field maps of several planes parallel to the tip surface within the tip gap, and adjacent passage flow. Vector maps were also obtained for planes normal to the tip surface in the direction of the tip leakage flow. Secondary flow was measured at planes normal to the blade exit angle at locations upstream and downstream of the trailing edge. The interaction between the tip leakage vortex and passage vortex is clearly defined, revealing the dominant effect of the tip leakage flow on the tip endwall secondary flow. The relative motion between the casing and the blade tip was simulated using a motor-driven moving belt system. A reduction in the magnitude of the under-tip flow near the endwall due to the moving wall is observed and the effect on the tip leakage vortex examined.

Design of Flow Adjusting Device in Diffuser of Open-Circuit Wind Tunnel with Low Speed Based on CFX

2015 ◽  
Vol 799-800 ◽  
pp. 640-644
Author(s):  
Xiao Yi Wang ◽  
Chong Gao ◽  
Fu Qiang Chen ◽  
Yu Hua Zhang ◽  
Zhi Zhen Qiu
Keyword(s):  
Wind Tunnel ◽  
Flow Field ◽  
High Speed ◽  
Reference Frames ◽  
Open Circuit ◽  
Analysis Model ◽  
Low Speed ◽  
Guide Plate ◽  
Study Results ◽  
Field Quality

The diffuser in wind tunnel plays a vital role to improve flow field quality. Many flow adjusting devices in diffuser were studied by lots of researchers in the world to inhibit flow separation. However, most of them were applied on closed-circuit wind tunnel with high speed. It is necessary to design appropriate flow adjusting device for diffuser in open-circuit wind tunnel with low speed which was increasingly used in aerodynamic experiment. The structure of a new open-circuit wind tunnel with low speed was firstly introduced in this paper. The flow adjusting device was designed, which was composed of three parts, namely contracting cone, air guide plate and screen. On the basis of analysis model for diffuser, the influences of contracting cone, air guide plate and screen on flow field quality were respectively given by CFX simulation that was using multiple reference frames and RNG k-ε turbulence model. Case study showed that the role of single part was limited, combined effect of three parts in flow adjusting device could greatly improve quality of flow field in diffuser. The study results mentioned above are useful for designing flow adjusting device in diffuser of practical open-circuit wind tunnel with low speed.

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