A Comparison of Tip Gap Loss Sensitivity for Shrouded vs. Unshrouded Turbine Rotors

2019 ◽  
Author(s):  
William V. Banks ◽  
Ali A. Ameri ◽  
Robert J. Boyle ◽  
Jeffrey P. Bons
Keyword(s):  
Numerical Study ◽  
Flow Characteristics ◽  
Aircraft Engine ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Blade Loading ◽  
Shrouded Rotor ◽  
Grid Independence ◽  
Stage Efficiency

Abstract A numerical study was conducted to evaluate the loss sensitivity of shrouded vs. unshrouded turbine rotor blades. Accuracy is demonstrated with a series of grid independence studies. Application of the methods is performed through various studies related to the effects of shrouding a High-Pressure Turbine (HPT) rotor blade for a NASA-specified N+3 timeframe single-aisle aircraft engine at takeoff conditions. Flat, Recessed, and Shrouded rotor configurations are evaluated at tip clearances from 0.25% to 4% of blade span. Mach # distributions, near-tip blade loading, and other flow characteristics are examined. Plots of stage efficiency vs. tip clearance are presented, with trends compared to available experimental data. It is shown that for the imposed boundary conditions, the addition of a shroud improves stage efficiency and significantly reduces sensitivity to tip clearance at higher clearance fractions. A casing recess is also shown to slightly increase sensitivity to tip clearance for tip clearances greater than 0.5%. Total pressure loss profiles vs. blade span are also compared, providing insight into the mechanisms behind the performance of the three configurations.

Numerical Study of Incidence Angles and Gap Heights in Turbine Cascades and Rotors on Tip Clearance Losses

2013 ◽  
Author(s):  
Clemens Buske ◽  
Wolfram C. Ullrich ◽  
Ingo Roehle
Keyword(s):  
Flow System ◽  
Numerical Study ◽  
Turbine Rotor ◽  
Tip Clearance ◽  
Flow Conditions ◽  
Blade Loading ◽  
Design And Optimization ◽  
Loss Coefficients ◽  
Turbine Cascades ◽  
Global Values

The design and optimization of turbines demands the use of fast low-fidelity tools. To obtain adequate results, loss correlations simplifying the complex turbine throughflow are implemented. Accounting for modern turbine designs and flow conditions, revisions of profile and secondary loss correlations were primarily focused upon, while improvements of the tip clearance loss correlations are difficult to achieve. Realistic engine-like conditions concerning variations of the tip clearance, blade loading and solidity are time- and cost-intensive to investigate. This paper is focused on an extensive numerical study, intending to support experiments on tip clearance loss correlations. The losses of a high pressure axial turbine rotor are analyzed for different tip clearance gap heights and incidence angles at cruise condition. The results are contrasted with a cascade having comparable tip profile and gap heights. The cascade’s flow is comparable to the rotor, but with respect to experimental restrictions concerning inlet and outlet conditions. Steady 3D calculations in the stationary and rotating frame were performed applying DLR’s turbomachinery CFD code TRACE using Menter’s SST k – ω turbulence model. The tip clearance loss coefficients were extracted from the flow field by post-processing data of an outlet plane and as massflow averaged global values. The findings are discussed referencing previous publications about the leakage flow system and tip clearance loss. Finally, a comparison to results from tip clearance loss correlations of Ainley-Mathieson and Dunham-Came is presented.

scholarly journals Numerical study of unsteady flow and exciting force for swept turbomachinery blades

2016 ◽  
Vol 20 (suppl. 3) ◽  
pp. 669-676
Author(s):  
Di Zhang ◽  
Ma Jiao-Bin ◽  
Qi Jing
Keyword(s):  
Boundary Layer ◽  
Unsteady Flow ◽  
Pressure Fluctuation ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Aerodynamic Performance ◽  
Rotor Blades ◽  
Stable Operation ◽  
Straight Blade ◽  
Excitation Force

The aerodynamic performance of blade affects the vibration characteristics and stable operation of turbomachinery closely. The aerodynamic performance of turbine stage can be improved by using swept blade. In this paper, the RANS method and the RNG k-? turbulence mode were adopted to investigate the unsteady flow characteristics and excitation force of swept blade stage. According to the results, for the swept blade, the fluid of boundary layer shifts in radial direction due to the influence of geometric construction. It is observed that there is similar wake development for several kinds of stators, and the wake has a notable effect on the boundary layer of the rotor blades. When compared with straight blade, pressure fluctuation of forward-swept blade is decreased while the pressure fluctuation of backward-swept blade is increased. The axial and tangential fundamental frequency excitation force factors of 15?forward-swept blade are 0.139 and 0.052 respectively, which are the least, and all excitation force factors are in the normal range. The excitation factor of the forward-swept blade is decreased compared with straight blade, and the decreasing percentage is closely related to the swept angle. As for backward-swept blades, the situation is the other way around. Additionally, the change of axial excitation factor is more obvious. So the vibration reduction performance of forward-swept blade is better.

scholarly journals Tip Leakage Flow in a Linear Turbine Cascade

1988 ◽  
Vol 110 (1) ◽  
pp. 18-26 ◽  
Author(s):  
J. Moore ◽  
J. S. Tilton
Keyword(s):  
Heat Transfer ◽  
Potential Flow ◽  
Pressure Rise ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Tip Leakage Flow ◽  
Vena Contracta

An experimental and analytical study of flow in the tip clearance gap of a linear turbine rotor blade cascade has been performed. Measurements of wall static pressures and flow velocities are used to verify a flow model involving a vena contracta, near the tip gap entrance, followed by flow mixing to fill the gap. A frequently referenced potential flow theory for flow into a tip gap is found to be in error and the correct theory is shown to model the unloading along the pressure surface of the blade and the endwall static pressure distribution up to the vena contracta accurately. A combined potential flow and mixing model accounts for the pressure rise in the tip gap due to mixing. Turbine tip heat transfer is also discussed and a correlation of local heat transfer rates for essentially incompressible flow over unshrouded turbine rotor blades is presented.

Experimental Investigations Into Pressure Field in Tip Clearance of Shrouded Rotor Blades

2002 ◽  
Author(s):  
Krzysztof Kosowski ◽  
Marian Piwowarski
Keyword(s):  
Pressure Distribution ◽  
Pressure Pulsation ◽  
Pressure Field ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Experimental Investigations ◽  
Pressure Pulsations ◽  
Blade Tip ◽  
Shrouded Rotor ◽  
Blade Tip Clearance

The experimental investigations into the pressure field in the shroud clearance were performed on a one-stage air model turbine of impulse type. Measurements of pressure distribution were carried out for different rotor eccentricities, different values of axial gap and of rotor-stator misalignment, different rotor speeds and different turbine load. The experimental investigations proved that: a) the pressure in the blade tip clearance is not stationary but it pulsates, b) the effect of nozzle trailing edge can be observed in the blade shroud clearance, c) for a given turbine output, the rotor-stator eccentricity and rotor-stator misalignment appear the most important parameters influencing the pressure distribution in the shroud clearance. Aiming to investigate the pressure pulsation transmission through the leakage flow in the blade shroud clearances, pulsations of different amplitudes and frequencies were excited in the turbine inlet duct and corresponding changes of pressure were measured along the shroud width, followed by appropriate harmonic analysis. The investigations were performed for forced pulsations with frequencies ranging from 1Hz to 8 Hz. In all the examined cases, the frequency of pressure pulsations remained unchanged, while the amplitude of the pulsation decreased gradually along the tip clearance. The frequency of these pressure pulsations in the tip clearance was equal to the frequency of the pressure pulsation at the turbine stage inlet and to the frequency of pressure pulsation at the turbine flow passage’s exit.

Tip-Shroud Labyrinth Seal Effect on the Flutter Stability of Turbine Rotor Blades

2019 ◽  
Author(s):  
Roque Corral ◽  
Michele Greco ◽  
Almudena Vega
Keyword(s):  
Rotor Blade ◽  
Labyrinth Seal ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Stability Prediction ◽  
Labyrinth Seals ◽  
Turbine Rotor Blade ◽  
The Stability ◽  
Shrouded Rotor ◽  
Tip Shroud

Abstract The effect of the tip-shroud seal on the flutter onset of a shrouded turbine rotor blade, representative of a modern gas turbine, is numerically tested and the contribution to the work-per-cycle of the aerofoil and the tip-shroud are clearly identified. The numerical simulations are conducted using a linearised frequency domain solver. The flutter stability of the shrouded rotor blade is evaluated for an edgewise mode and compared with the standard industrial approach of not including the tip-shroud cavity. It turns out that including the tip shroud significantly changes the stability prediction of the rotor blade. This is due to the fact that the amplitude of the unsteady pressure created in the inter-fin cavity, due to the motion of the airfoil, is much greater than that of the airfoil. It is concluded that the combined effect of the seal and its platform tends to stabilise the rotor blade for all the examined nodal diameters and reduced frequencies. Finally, the numerical results are shown to be consistent with those obtained using an analytical simplified model to account for the effect of the labyrinth seals.

Unsteady Forces in Last Stage LP Steam Turbine Rotor Blades With Exhaust Hood

2016 ◽  
Author(s):  
Romuald Rzadkowski ◽  
Jan Surwiło ◽  
Leszek Kubitz ◽  
Piotr Lampart ◽  
Mariusz Szymaniak
Keyword(s):  
Numerical Study ◽  
Flow Analysis ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Steam Turbines ◽  
Exhaust Hood ◽  
Low Frequencies ◽  
Unsteady Forces ◽  
Relative Contribution ◽  
Last Stage

Several high vibration amplitude problems have been reported regarding the slender last stage blades of commercial LP steam turbines. This paper presents a numerical study of unsteady forces acting on rotor blades using ANSYS CFX. A 3D transonic viscous flow through the stator and rotor blades with an exhaust hood was modelled. The last stage was modelled as a full blade annulus, so that the axial, radial and circumferential distribution of flow patterns and blade forces could be examined. An unsteady flow analysis was conducted on a typically designed last stage and exhaust diffuser, with measured and calculated downstream static pressure distribution as the outlet boundary condition. The results showed that under off-design conditions, vortices occurred in the last stage and diffuser. Unsteady aerodynamic forces were found at high frequencies (stator passing frequencies) and low frequencies (generated from asymmetric pressure distributions behind the rotor), with the relative dominance of these forces/frequencies shifting as a function of radial span. An FFT analysis was carried out. Three sections were investigated: the hub, midspan and peripheral (tip) section. The steady pressure behind the rotor blade was compared with experimental results in the LP last stage behind the rotor blades and in a specified cross-section of the exhaust hood. The lower frequency unsteady forces had a higher relative contribution towards the tip of the blade.

A Novel Cooling Method for Turbine Rotor-Stator Rim Cavities Affected by Mainstream Ingress

2004 ◽  
Vol 127 (4) ◽  
pp. 798-806 ◽  
Author(s):  
Y. Okita ◽  
M. Nishiura ◽  
S. Yamawaki ◽  
Y. Hironaka
Keyword(s):  
Gas Flow ◽  
Numerical Study ◽  
Turbine Rotor ◽  
Rotor Blades ◽  
Significant Advance ◽  
Axial Distribution ◽  
Cooling Effectiveness ◽  
Cooling Flow ◽  
Cooling Method ◽  
Flow Phenomena

A combined experimental and numerical study of interaction between cooling flow and mainstream gas flow in a turbine rotor-stator rim cavity is reported. Particular emphasis is put on the flow phenomena in a rim cavity downstream of rotor blades. The experiments are conducted on a rig simulating an engine HP-turbine in which cooling effectiveness distributions as well as velocities, turbulence quantities, pressure, and temperature profiles are measured. Numerical calculation, especially at a full 3D, unsteady solution level, can lead to satisfactory predictions in fluid and mass transfer inside the cavity. Both experimental and numerical results indicate that large turbulence stresses near the rotor disk intensify turbulent diffusion across the cavity and consequently axial distribution of the cooling effectiveness inside the cavity becomes uniform. In order to obtain an adequate distribution of cooling effectiveness across the rim cavity and to suppress the turbulence level near the rotor surface for more efficient cooling, a novel cooling method is developed using numerical simulation. The disk-front and -rear cavities are then redesigned according to the new cooling strategy and integrated in the test rig. Experimental results verify a significant advance in cooling performance with the new method.

Mechanism of Nonsynchronous Blade Vibration in a Transonic Compressor Rig

2016 ◽  
Vol 139 (1) ◽  
Author(s):  
Daniel Möller ◽  
Maximilian Jüngst ◽  
Felix Holzinger ◽  
Christoph Brandstetter ◽  
Heinz-Peter Schiffer ◽  
...  
Keyword(s):  
Numerical Study ◽  
Stability Limit ◽  
Rotor Blades ◽  
Tip Clearance ◽  
Structural Vibration ◽  
Blade Vibration ◽  
Tip Clearance Flow ◽  
Transonic Compressor ◽  
Clearance Flow ◽  
Fluctuation Pattern

This paper presents a numerical study on blade vibration for the transonic compressor rig at the Technische Universität Darmstadt (TUD), Darmstadt, Germany. The vibration was experimentally observed for the second eigenmode of the rotor blades at nonsynchronous frequencies and is simulated for two rotational speeds using a time-linearized approach. The numerical simulation results are in close agreement with the experiment in both cases. The vibration phenomenon shows similarities to flutter. Numerical simulations and comparison with the experimental observations showed that vibrations occur near the compressor stability limit due to interaction of the blade movement with a pressure fluctuation pattern originating from the tip clearance flow. The tip clearance flow pattern travels in the backward direction, seen from the rotating frame of reference, and causes a forward traveling structural vibration pattern with the same phase difference between blades. When decreasing the rotor tip gap size, the mechanism causing the vibration is alleviated.

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