Geometrical Modification of the Unsteady Pressure to Reduce Low-Pressure Turbine Flutter

2017 ◽  
Vol 139 (9) ◽  
Author(s):  
Christian Peeren ◽  
Konrad Vogeler
Keyword(s):  
Turbine Blade ◽  
Local Stability ◽  
Free Standing ◽  
Unsteady Pressure ◽  
Low Pressure Turbine ◽  
Physical Mechanisms ◽  
Local Modification ◽  
Blade Section ◽  
Turbine Design ◽  
The Impact

In this work, the impact of the airfoil shape on flutter is investigated. Flutter occurs when the blade structure is absorbing energy from its surrounding fluid leading to hazardous amplification of vibrations. The key for a more stable design is the local modification of the blade motion induces unsteady pressure, which is responsible for local stability. Especially for free-standing blades, where most exciting aerodynamic work transfer is found at the upper tip sections, a reshaping of the airfoil is expected to beneficially influence stability. Two approaches are pursued in this work. This first approach is based on flow physics considerations. The unsteady pressure field is decomposed into four physical mechanisms or effects and each effect investigated. The second approach is used to validate the conclusions made in the theoretical part by numerical optimizing the geometry of a representative turbine blade. Selected optimized designs are picked and compared with each other in terms of local stability, aerodynamics, and robustness with respect to the boundary conditions. Both approaches are applied for a freestanding and interlocked turbine blade section. The found design potential is discussed and the link to the differences mechanisms, introduced in the first part, established. Based on the observations made, design recommendations are made for a flutter-reduced turbine design.

Numerical Investigation of Pin-Fin Influences on Cooling Air Flow Characteristics in Blade Trailing Edge Region

2019 ◽  
Author(s):  
Weilong Wu ◽  
Huazhao Xu ◽  
Jianhua Wang ◽  
Xiangyu Wu ◽  
Lei Wang
Keyword(s):  
Turbine Blade ◽  
Flow Characteristics ◽  
Baseline Model ◽  
Trailing Edge ◽  
Performance Function ◽  
Pin Fin ◽  
Low Pressure Turbine ◽  
Pin Fins ◽  
Turbine Design ◽  
Cooling Air

Abstract This paper numerically investigated the influences of pin-fin size and layout on the flow characteristics of cooling air in the trailing edge of a real low pressure turbine blade. The discussion was given first for the baseline model without pin fins (denoted as M0) under a turbine design condition and two off design conditions. Then a comparison of the flow fields in the turbine blade especially in the trailing edge region was performed with three more trailing edge models, with the purpose of discovering the benefits of using pin fin configurations in a real low pressure turbine blade. The other three models (denoted as M1, M2, M3) have pin fins in different diameters and arrangements. The M1 model has a row of 13 pin fins with a diameter of 2mm, and the M2 and M3 models have two rows of pin fins arranged in a staggered pattern with a diameter of 1.2mm. Compared to the baseline model M0, it is shown that an addition of pin fin configurations helps greatly to improve cooling flow distributions and to mitigate the blockage of coolant in trailing slots. Meanwhile, the adoption of pin fins has not only affected significantly the flow field in the trailing passage but also has moderately affected flow fields in the middle and forward cooling passages. Increasing pressure ratio can increase total mass flow rate with no significant change in flow patterns. The baseline blade Model M0 shows a high value of 6 for a friction loss related performance function at the turbine design condition. However, only a moderate increase in the value of the performance function is discovered for all the three blades with pin fins.

Numerical Investigation of Contrasting Flow Physics in Different Zones of a High-Lift Low-Pressure Turbine Blade

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
Jiahuan Cui ◽  
V. Nagabhushana Rao ◽  
Paul Tucker
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Low Pressure ◽  
The State ◽  
Suction Surface ◽  
Flow Physics ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Flow Features ◽  
The Impact

Using a range of high-fidelity large eddy simulations (LES), the contrasting flow physics on the suction surface, pressure surface, and endwalls of a low-pressure turbine (LPT) blade (T106A) was studied. The current paper attempts to provide an improved understanding of the flow physics over these three zones under the influence of different inflow boundary conditions. These include: (a) the effect of wakes at low and high turbulence intensity on the flow at midspan and (b) the impact of the state of the incoming boundary layer on endwall flow features. On the suction surface, the pressure fluctuations on the aft portion significantly reduced at high freestream turbulence (FST). The instantaneous flow features revealed that this reduction at high FST (HF) is due to the dominance of “streak-based” transition over the “Kelvin–Helmholtz” (KH) based transition. Also, the transition mechanisms observed over the turbine blade were largely similar to those on a flat plate subjected to pressure gradients. On pressure surface, elongated vortices were observed at low FST (LF). The possibility of the coexistence of both the Görtler instability and the severe straining of the wakes in the formation of these elongated vortices was suggested. While this was true for the cases under low turbulence levels, the elongated vortices vanished at higher levels of background turbulence. At endwalls, the effect of the state of the incoming boundary layer on flow features has been demonstrated. The loss cores corresponding to the passage vortex and trailing shed vortex were moved farther from the endwall with a turbulent boundary layer (TBL) when compared to an incoming laminar boundary layer (LBL). Multiple horse-shoe vortices, which constantly moved toward the leading edge due to a low-frequency unstable mechanism, were captured.

The Impact of Blade Loading and Unsteady Pressure Bifurcations on Low-Pressure Turbine Flutter Boundaries

2015 ◽  
Author(s):  
Joshua J. Waite ◽  
Robert E. Kielb
Keyword(s):  
Mode Shape ◽  
Pressure Ratio ◽  
Low Pressure ◽  
Forced Response ◽  
Blade Loading ◽  
Unsteady Pressure ◽  
Aerodynamic Damping ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
The Impact

The three major aeroelastic issues in the turbomachinery blades of jet engines and power turbines are forced response, non-synchronous vibrations, and flutter. Flutter primarily affects high-aspect ratio blades found in the fan, fore high-pressure compressor stages, and aft low-pressure turbine (LPT) stages as low natural frequencies and high axial velocities create smaller reduced frequencies. Often with LPT flutter analyses, physical insights are lost in the exhaustive quest for determining whether the aerodynamic damping is positive or negative. This paper underlines some well known causes of low-pressure turbine flutter in addition to one novel catalyst. In particular, an emphasis is placed on revealing how local aerodynamic damping contributions change as a function of unsteady (e.g. mode shape, reduced frequency) and steady (e.g. blade torque, pressure ratio) parameters. To this end, frequency domain RANS CFD analyses are used as computational wind tunnels to investigate how aerodynamic loading variations affect flutter boundaries. Preliminary results show clear trends between the aerodynamic work influence coefficients and variations in exit Mach number and back pressure, especially for torsional mode shapes affecting the passage throat. Additionally, visualizations of qualitative bifurcations in the unsteady pressure phases around the airfoil shed light on how local damping contributions evolve with steady loading. Final results indicate a sharp drop in aeroelastic stability near specific regions of the pressure ratio indicating a strong correlation between blade loading and flutter. Passage throat shock behavior is shown to be a controlling factor near the trailing edge, and like critical reduced frequency, this phenomenon is shown to be highly dependent on the vibratory mode shape.

scholarly journals Turbine Blade of Gas Turbine Engine Additional Unloading by Changing the Layout of the Gravity Centre of the Shroud Shelf

2019 ◽  
Vol 7 (1) ◽  
pp. 14-23
Author(s):  
Ēriks Ozoliņš ◽  
Ilmārs Ozoliņš ◽  
Līga Ramāna
Keyword(s):  
Stress Distribution ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Critical Points ◽  
Gas Turbine Engine ◽  
Blade Profile ◽  
Turbine Engine ◽  
Low Pressure Turbine ◽  
Gravity Centre ◽  
The Impact

Abstract The article describes the impact of the gas turbine engine low-pressure turbine blade shroud shelf on the blade profile stress position. Attention is focused directly on the impact of the location of the gravity centre of the shroud shelf on blade stress distribution at the three most critical points of the profile. The paper describes the details of the calculation and the required expressions provided, as well as the results of the calculation example with clear graphical dependencies.

Numerical Investigation of Contrasting Flow Physics in Different Zones of a High-Lift Low Pressure Turbine Blade

2015 ◽  
Author(s):  
J. Cui ◽  
V. Nagabhushana Rao ◽  
P. G. Tucker
Keyword(s):  
Boundary Layer ◽  
Turbine Blade ◽  
Low Pressure ◽  
The State ◽  
Suction Surface ◽  
Flow Physics ◽  
Pressure Surface ◽  
Low Pressure Turbine ◽  
Flow Features ◽  
The Impact

Using a range of high fidelity large eddy simulations, the contrasting flow physics on the suction surface, pressure surface and endwalls of a low pressure turbine blade (T106A) was studied. The current paper attempts to provide an improved understanding of the flow physics over these three zones under the influence of different inflow boundary conditions. These include: (a) the effect of wakes at low and high turbulence intensity on the flow at mid-span and (b) the impact of the state of the incoming boundary layer on endwall flow features. On the suction surface, the pressure fluctuations on the aft portion significantly reduced at high Free-Stream Turbulence (FST). The instantaneous flow features revealed that this reduction at high FST is due to the dominance of ‘streak-based’ transition over the ‘Kelvin-Helmholtz’ based transition. Also, the transition mechanisms observed over the turbine blade were largely similar to those on a flat plate subjected to pressure gradients. On pressure surface, elongated vortices were observed at low FST. The possibility of the co-existence of both the Görtler instability and the severe straining of the wakes in the formation of these elongated vortices was suggested. While this was true for the cases under low turbulence levels, the elongated vortices vanished at higher levels of background turbulence. At endwalls, the effect of the state of the incoming boundary layer on flow features has been demonstrated. The loss cores corresponding to the passage vortex and trailing shed vortex were moved farther from the endwall with a turbulent boundary layer when compared to an incoming laminar boundary layer. Multiple horse-shoe vortices, which constantly moved towards the leading edge due to a low-frequency unstable mechanism, were captured.

The Impact of Blade Loading and Unsteady Pressure Bifurcations on Low-Pressure Turbine Flutter Boundaries

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Joshua J. Waite ◽  
Robert E. Kielb
Keyword(s):  
Mode Shape ◽  
Pressure Ratio ◽  
Low Pressure ◽  
Forced Response ◽  
Blade Loading ◽  
Unsteady Pressure ◽  
Aerodynamic Damping ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
The Impact

The three major aeroelastic issues in the turbomachinery blades of jet engines and power turbines are forced response, nonsynchronous vibrations, and flutter. Flutter primarily affects high-aspect ratio blades found in the fan, fore high-pressure compressor stages, and aft low-pressure turbine (LPT) stages as low natural frequencies and high axial velocities create smaller reduced frequencies. Often with LPT flutter analyses, physical insights are lost in the exhaustive quest for determining whether the aerodynamic damping is positive or negative. This paper underlines some well-known causes of the LPT flutter in addition to one novel catalyst. In particular, an emphasis is placed on revealing how local aerodynamic damping contributions change as a function of unsteady (e.g., mode shape, reduced frequency) and steady (e.g., blade torque, pressure ratio) parameters. To this end, frequency domain Reynolds-averaged Navier–Stokes (RANS) CFD analyses are used as computational wind tunnels to investigate how aerodynamic loading variations affect flutter boundaries. Preliminary results show clear trends between the aerodynamic work influence coefficients and variations in exit Mach number and back pressure, especially for torsional mode shapes affecting the passage throat. Additionally, visualizations of qualitative bifurcations in the unsteady pressure phases around the airfoil shed light on how local damping contributions evolve with steady loading. Final results indicate a sharp drop in aeroelastic stability near specific regions of the pressure ratio, indicating a strong correlation between blade loading and flutter. Passage throat shock behavior is shown to be a controlling factor near the trailing edge, and as with critical reduced frequency, this phenomenon is shown to be highly dependent on the vibratory mode shape.

Assessment of Unsteady Flows in Turbines

1992 ◽  
Vol 114 (1) ◽  
pp. 79-90 ◽  
Author(s):  
O. P. Sharma ◽  
G. F. Pickett ◽  
R. H. Ni
Keyword(s):  
Unsteady Flow ◽  
Three Dimensional ◽  
Flow Simulation ◽  
Experimental Investigations ◽  
Flow Parameters ◽  
Research Activities ◽  
Flow Features ◽  
Computational Fluid Dynamics Cfd ◽  
Turbine Design ◽  
The Impact

The impacts of unsteady flow research activities on flow simulation methods used in the turbine design process are assessed. Results from experimental investigations that identify the impact of periodic unsteadiness on the time-averaged flows in turbines and results from numerical simulations obtained by using three-dimensional unsteady Computational Fluid Dynamics (CFD) codes indicate that some of the unsteady flow features can be fairly accurately predicted. Flow parameters that can be modeled with existing steady CFD codes are distinguished from those that require unsteady codes.

An Experimental Investigation of the Effect of Freestream Turbulence on the Wake of a Separated Low-Pressure Turbine Blade at Low Reynolds Numbers

1999 ◽  
Vol 122 (2) ◽  
pp. 431-433 ◽  
Author(s):  
C. G. Murawski ◽  
K. Vafai
Keyword(s):  
Reynolds Number ◽  
Turbine Blade ◽  
Turbulence Intensity ◽  
Reynolds Numbers ◽  
Low Pressure ◽  
Freestream Turbulence ◽  
Suction Surface ◽  
Low Reynolds Numbers ◽  
Low Pressure Turbine ◽  
Flow Reynolds Number

An experimental study was conducted in a two-dimensional linear cascade, focusing on the suction surface of a low pressure turbine blade. Flow Reynolds numbers, based on exit velocity and suction length, have been varied from 50,000 to 300,000. The freestream turbulence intensity was varied from 1.1 to 8.1 percent. Separation was observed at all test Reynolds numbers. Increasing the flow Reynolds number, without changing freestream turbulence, resulted in a rearward movement of the onset of separation and shrinkage of the separation zone. Increasing the freestream turbulence intensity, without changing Reynolds number, resulted in shrinkage of the separation region on the suction surface. The influences on the blade’s wake from altering freestream turbulence and Reynolds number are also documented. It is shown that width of the wake and velocity defect rise with a decrease in either turbulence level or chord Reynolds number. [S0098-2202(00)00202-9]

scholarly journals Sensitivity of Supersonic ORC Turbine Injector Designs to Fluctuating Operating Conditions

2015 ◽  
Author(s):  
Elio A. Bufi ◽  
Paola Cinnella ◽  
Xavier Merle
Keyword(s):  
Method Of Characteristics ◽  
Organic Rankine Cycle ◽  
Design Procedure ◽  
Rankine Cycle ◽  
Operating Conditions ◽  
Real Gas ◽  
Real Gas Effects ◽  
Nozzle Shape ◽  
Turbine Design ◽  
The Impact

The design of an efficient organic rankine cycle (ORC) expander needs to take properly into account strong real gas effects that may occur in given ranges of operating conditions, which can also be highly variable. In this work, we first design ORC turbine geometries by means of a fast 2-D design procedure based on the method of characteristics (MOC) for supersonic nozzles characterized by strong real gas effects. Thanks to a geometric post-processing procedure, the resulting nozzle shape is then adapted to generate an axial ORC blade vane geometry. Subsequently, the impact of uncertain operating conditions on turbine design is investigated by coupling the MOC algorithm with a Probabilistic Collocation Method (PCM) algorithm. Besides, the injector geometry generated at nominal operating conditions is simulated by means of an in-house CFD solver. The code is coupled to the PCM algorithm and a performance sensitivity analysis, in terms of adiabatic efficiency and power output, to variations of the operating conditions is carried out.

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