Detached-Eddy Simulation Applied to the Tip-Clearance Flow in a Last Stage Steam Turbine Blade

2018 ◽  
Author(s):  
Tianrui Sun ◽  
Paul Petrie-Repar ◽  
Damian M. Vogt
Keyword(s):  
Steam Turbine ◽  
Flow Structure ◽  
Complex Structure ◽  
Tip Clearance ◽  
Steam Turbines ◽  
Detached Eddy Simulation ◽  
Tip Clearance Flow ◽  
Eddy Simulation ◽  
Clearance Flow ◽  
Last Stage

Prediction of the aerodynamic stability of rotor blades at the last stage of steam turbines is of great importance and widely studied. Considering the large span and low natural frequency of these blades, flow at the tip region has a remarkable effect on blade flutter characteristics. However, the transonic tip-clearance flow in these blades has a complex structure of vortices. To obtain a deep understanding of the transonic tip-clearance flow structure in steam turbines, the Detached-Eddy Simulation (DES) is applied in this paper. DES is a hybrid LES/RANS method that activates LES in specified flow regions and applies URANS in other regions of the flow field. As far as we are aware, the tip-clearance flow structure of real-scale last stage steam turbine by high-fidelity numerical method had not been much analyzed in open literature. In this paper, the transonic tip-clearance flow structure in modern last stage of steam turbines is analyzed by both URANS and DES approaches. The open steam turbine model designed by Durham University is chosen as the research model. The flow solver applied is the commercial software ANSYS CFX. From the DES result, the tip leakage vortex and the induced vortices are presented. Based on the comparison between tip-clearance flow structure captured by the two approaches, the URANS method is not able to resolve all induced vortices. Therefore, the distribution of aerodynamic loading on the blade surface is different between URANS and DES results. The present study serves as a basis for investigating the influence of the tip-clearance flow structure on blade aeroelasticity.

scholarly journals Zonal Detached-Eddy Simulation Applied to the Tip-Clearance Flow in an Axial Compressor

AIAA Journal ◽  
2016 ◽  
Vol 54 (8) ◽  
pp. 2377-2391 ◽  
Author(s):  
W. Riéra ◽  
J. Marty ◽  
L. Castillon ◽  
S. Deck
Keyword(s):  
Axial Compressor ◽  
Tip Clearance ◽  
Detached Eddy Simulation ◽  
Tip Clearance Flow ◽  
Eddy Simulation ◽  
Clearance Flow

Detached-Eddy Simulation Applied to Aeroelastic Stability Analysis in a Last-Stage Steam Turbine Blade

2019 ◽  
Vol 141 (9) ◽  
Author(s):  
Tianrui Sun ◽  
Paul Petrie-Repar ◽  
Damian M. Vogt ◽  
Anping Hou
Keyword(s):  
Steam Turbine ◽  
Steam Turbines ◽  
Detached Eddy Simulation ◽  
Tip Leakage Flow ◽  
Aeroelastic Stability ◽  
Blade Vibration ◽  
Tip Leakage ◽  
Eddy Simulation ◽  
Blade Flutter ◽  
Last Stage

Blade flutter in the last stage is an important design consideration for the manufacturers of steam turbines. Therefore, the accurate prediction method for blade flutter is critical. Since the majority of aerodynamic work contributing to flutter is done near the blade tip, resolving the tip leakage flow can increase the accuracy of flutter predictions. The previous research has shown that the induced vortices in the tip region can have a significant influence on the flow field near the tip. The structure of induced vortices due to the tip leakage vortex cannot be resolved by unsteady Reynolds-averaged Navier–Stokes (URANS) simulations because of the high dissipation in turbulence models. To the best of author’s knowledge, the influence of induced vortices on flutter characteristics has not been investigated. In this paper, the results of detached-eddy simulation (DES) and URANS flutter simulations of a realistic-scale last-stage steam turbine are presented, and the influence of induced vortices on the flutter stability has been investigated. Significant differences for the predicted aerodynamic work coefficient distribution on the blade surface, especially on the rear half of the blade suction side near the tip, are observed. At the least stable interblade phase angle (IBPA), the induced vortices show a destabilizing effect on the blade aeroelastic stability. The motion of induced vortices during blade oscillation is dependent on the blade amplitude, and hence, the aerodynamic damping is also dependent on the blade vibration amplitude. In conclusion, the induced vortices can influence the predicted flutter characteristics of the steam turbine test case.

Inlet Condition Effects on the Tip Clearance Flow With Zonal Detached Eddy Simulation

2013 ◽  
Vol 136 (4) ◽  
Author(s):  
William Riéra ◽  
Lionel Castillon ◽  
Julien Marty ◽  
Francis Leboeuf
Keyword(s):  
Guide Vane ◽  
Tip Clearance ◽  
Tip Vortex ◽  
Inlet Guide Vane ◽  
Detached Eddy Simulation ◽  
Tip Leakage Vortex ◽  
Tip Clearance Flow ◽  
Tip Leakage ◽  
Inlet Condition ◽  
Clearance Flow

In the present study, the influence of the inlet condition on the tip clearance flow of an axial compressor is investigated. Two different zonal detached eddy simulations (ZDES) computations are carried out and compared to Reynolds-averaged Navier–Stokes (RANS) and unsteady RANS (URANS) computations as well as to experimental data. A rotating distortion map of the flow cartography is set as inlet condition for the first ZDES computation. An azimuthally averaged inlet condition is used for the second one and uncouples the rotor tip-leakage vortex flutter phenomenon, which stems from the arrival of the inlet guide vane wake from the behavior inherent to the rotor tip-leakage vortex. In the studied configuration, the inlet guide vane tip vortex reveals to lower the effects from double leakage on the rotor. The topology of the rotor tip-leakage vortex is described, and its development is analyzed.

Investigation of Unsteady Flow Field in a Low-Speed One and a Half Stage Axial Compressor: Effects of Tip Gap Size on the Tip Clearance Flow Structure at Near Stall Operation

2014 ◽  
Author(s):  
Chunill Hah ◽  
Michael Hathaway ◽  
Joseph Katz
Keyword(s):  
Unsteady Flow ◽  
Flow Structure ◽  
Flow Instability ◽  
Axial Compressor ◽  
Leading Edge ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Low Speed ◽  
Clearance Flow ◽  
Tip Clearance Vortex

The primary focus of this paper is to investigate the effect of rotor tip gap size on how the rotor unsteady tip clearance flow structure changes in a low speed one and half stage axial compressor at near stall operation (for example, where maximum pressure rise is obtained). A Large Eddy Simulation (LES) is applied to calculate the unsteady flow field at this flow condition with both a small and a large tip gaps. The numerically obtained flow fields at the small clearance matches fairly well with the available initial measurements obtained at the Johns Hopkins University with 3-D unsteady PIV in an index-matched test facility which renders the compressor blades and casing optically transparent. With this setup, the unsteady velocity field in the entire flow domain, including the flow inside the tip gap, can be measured. The numerical results are also compared with previously published measurements in a low speed single stage compressor (Maerz et al. [2002]). The current study shows that, with the smaller rotor tip gap, the tip clearance vortex moves to the leading edge plane at near stall operating condition, creating a nearly circumferentially aligned vortex that persists around the entire rotor. On the other hand, with a large tip gap, the clearance vortex stays inside the blade passage at near stall operation. With the large tip gap, flow instability and related large pressure fluctuation at the leading edge are observed in this one and a half stage compressor. Detailed examination of the unsteady flow structure in this compressor stage reveals that the flow instability is due to shed vortices near the leading edge, and not due to a three-dimensional separation vortex originating from the suction side of the blade, which is commonly referred to during a spike-type stall inception. The entire tip clearance flow is highly unsteady. Many vortex structures in the tip clearance flow, including the sheet vortex system near the casing, interact with each other. The core tip clearance vortex, which is formed with the rotor tip gap flows near the leading edge, is also highly unsteady or intermittent due to pressure oscillations near the leading edge and varies from passage to passage. For the current compressor stage, the evidence does not seem to support that a classical vortex breakup occurs in any organized way, even with the large tip gap. Although wakes from the IGV influence the tip clearance flow in the rotor, the major characteristics of rotor tip clearance flows in isolated or single stage rotors are observed in this one and a half stage axial compressor.

scholarly journals Verification and Validation of Large Eddy Simulation for Tip Clearance Vortex Cavitating Flow in a Waterjet Pump

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7635
Author(s):  
Chengzao Han ◽  
Yun Long ◽  
Mohan Xu ◽  
Bin Ji
Keyword(s):  
Large Eddy Simulation ◽  
Tip Clearance ◽  
Verification And Validation ◽  
Flow Structures ◽  
Tip Clearance Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Clearance Flow ◽  
Vorticity Transport ◽  
Waterjet Pump

In this paper, large eddy simulation (LES) was adopted to simulate the cavitating flow in a waterjet pump with emphasis on the tip clearance flow. The numerical results agree well with the experimental observations, which indicates that the LES method can make good predictions of the unsteady cavitating flows around a rotor blade. The LES verification and validation (LES V&V) analysis was used to reveal the influence of cavitation on the flow structures. It can be found that the LES errors in cavitating region are larger than those in the non-cavitating area, which is mainly caused by more complicated cavitating and tip clearance flow structures. Further analysis of the interaction between the cavitating and vortex flow by the relative vorticity transport equation shows that the stretching, dilatation and baroclinic torque terms have major effects on the generation and transport of vortex structure. Meanwhile the Coriolis force term and viscosity term also exacerbate the vorticity transport in the cavitating region. In addition, the flow loss characteristics of this pump are also revealed by the entropy production theory. It is indicated that the tip clearance flow and trailing edge wake flow cause the viscous dissipation and turbulent dissipation, and the cavitation can further enhance the instability of the flow field in the tip clearance.

Short Length-Scale Rotating Stall Inception in a Transonic Axial Compressor: Criteria and Mechanisms

2006 ◽  
Author(s):  
Chunill Hah ◽  
Jo¨rg Bergner ◽  
Heinz-Peter Schiffer
Keyword(s):  
Axial Compressor ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Stall Inception ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Eddy Simulation ◽  
Clearance Flow ◽  
Flow Mechanisms ◽  
Tip Clearance Vortex

The current paper reports on investigations aimed at advancing the understanding of the flow mechanism that leads to the onset of short-length scale rotating stall in a transonic axial compressor. Experimental data show large oscillation of the tip clearance vortex as the rotor operates near the stall condition. Inception of spike-type rotating stall is also measured in the current transonic compressor with high response pressure transducers. Computational studies of a single passage and the full annulus were carried out to identify flow mechanisms behind the spike-type stall inception in the current transonic compressor rotor. Steady and unsteady single passage flow simulations were performed, first to get insight into the interaction between the tip clearance vortex and the passage shock. The conventional Reynolds-averaged Navier-Stokes method with a standard turbulence closure scheme does not accurately reproduce tip clearance vortex oscillation and the measured unsteady pressure field. Consequently, a Large Eddy Simulation (LES) was carried out to capture more relevant physics in the computational simulation of the rotating stall inception. The unsteady random behavior of the tip clearance vortex and it’s interaction with the passage shock seem to be critical ingredients in the development of spike-type rotating stall in a transonic compressor. The Large Eddy Simulation was further extended to the full annulus to identify flow mechanisms behind the measured spike-type rotating stall inception. The current study shows that the spike-type rotating stall develops after the passage shock is fully detached from the blade passages. Interaction between the tip clearance vortex and the passage shock creates a low momentum area near the pressure side of the blade. As the mass flow rate decreases, this low momentum area moves further upstream and reversed tip clearance flow is initiated at the trailing edge plane. Eventually, the low momentum area near the pressure side reaches the leading edge and forward spillage of the tip clearance flow occurs. The flows in the affected blade passage or passages then stall. As the stalled blade passages are formed behind the passage shock, the stalled area rotates counter to the blade rotation just like the classical Emmon’s type rotating stall. Both the measurements and the computations show that the rotating stall cell covers one to two blade passage lengths and rotates at roughly 50% of the rotor speed.

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