Mode Shape Sensitivity of the High Pressure Turbine Rotor Excitation Due to Upstream Stators

2002 ◽  
Author(s):  
Markus Jo¨cker ◽  
Torsten H. Fransson
Keyword(s):  
High Pressure ◽  
Mode Shape ◽  
Rotor Blade ◽  
High Sensitivity ◽  
Turbine Rotor ◽  
Mode Shapes ◽  
Navier Stokes ◽  
Shape Sensitivity ◽  
High Pressure Turbine ◽  
Unsteady Aerodynamic

The excitability of single rotor blade mode shapes due to the excitations by upstream stators in high-pressure turbine stages is subject of the present work. An evaluation of unsteady aerodynamic analyses of the stator-rotor interaction towards their sensitivity to the rotor blade mode shape is presented and applied. The unsteady aerodynamic analyses were performed at midspan sections with a well validated 2D/Q3D hybrid Euler/Navier Stokes non-linear flow solver (UNSFLO). The mode shape is parametrized by a torsion axis location in the plane of the blade section, which allows the construction of excitability maps as a function of 2D rigid body mode shapes. Excitability itself is derived from a generalized force analysis. The evaluation demonstrates the high sensitivity of excitability to the mode shape, which suggests that only small modifications in mode shape can significantly change the risk of blade mode excitation. It also highlights the central importance of the relative phase of unsteady blade pressure harmonic. Changes in axial gap can significantly modify the excitability and transform highly excited modes to less excited modes and vice versa. The variation of rotational speed (−5% to +10%) did not show remarkable changes in the mode excitability of the investigated rotor.

Aerodynamic Performance of an Unlocated High Pressure Turbine Rotor With Worn Tip Seal Fins

2017 ◽  
Author(s):  
Lucas Pawsey ◽  
David John Rajendran ◽  
Vassilios Pachidis
Keyword(s):  
High Pressure ◽  
Rotor Blade ◽  
Turbine Rotor ◽  
Aerodynamic Performance ◽  
Axial Displacement ◽  
High Pressure Turbine ◽  
Design Modification ◽  
Turbine Casing ◽  
Secondary Air ◽  
Shaft Failure

An unlocated shaft failure in the high pressure turbine spool of an engine may result in a complex orbiting motion along with rearward axial displacement of the high pressure turbine rotor sub-assembly. This is due to the action of resultant forces and limitations imposed by constraints such as the bearings and turbine casing. Such motion of the rotor following an unlocated shaft failure, results in the development of multiple contacts between the components of the rotor sub-assembly, the turbine casing, and the downstream stator casing. Typically, in the case of shrouded rotor blades, the tip region is in the form of a seal with radial protrusions called ‘fins’ between the rotor blade and the turbine casing. The contact between the rotor blade and the turbine casing will therefore result in excessive wear of the tip seal fins, resulting in changes in the geometry of the tip seal domain that affects the characteristics of the tip leakage vortex. The rotor sub-assembly with worn seals may also be axially displaced rearwards, and consequent to this displacement, changes in the geometry of the rotor blade may occur because of the contact between the rotor sub-assembly and the downstream stator casing. An integrated approach of structural analyses, secondary air system dynamics, and 3D CFD is adopted in the present study to quantify the effect of the tip seal damage and axial displacement on the aerodynamic performance of the turbine stage. The resultant geometry after wearing down of the fins in the tip seal, and rearward axial displacement of the rotor sub-assembly is obtained from LS-DYNA simulations. 3D RANS analyses are carried out to quantify the aerodynamic performance of the turbine with worn fins in the tip seal at three different axial displacement locations i.e. 0 mm, 10 mm and 15 mm. The turbine performance parameters are then compared with equivalent cases in which the fins in the tip seal are intact for the same turbine axial displacement locations. From this study it is noted that the wearing of tip seal fins results in reduced turbine torque, power output and efficiency, consequent to changes in the flow behaviour in the turbine passages. The reduction in turbine torque will result in the reduction of the terminal speed of the rotor during an unlocated shaft failure. Therefore, a design modification that can lead to rapid wearing of the fins in the tip seal after an unlocated shaft failure holds promise for the management of a potential over-speed event.

Experimental Investigation of Mode Shape Sensitivity of an Oscillating LPT Cascade at Design and Off-Design Conditions

2006 ◽  
Author(s):  
Damian M. Vogt ◽  
Torsten H. Fransson
Keyword(s):  
Mode Shape ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Turbine Rotor ◽  
Shape Sensitivity ◽  
Aeroelastic Stability ◽  
Turbine Rotor Blade ◽  
Reduced Frequency ◽  
Lp Turbine ◽  
Bending Modes

The effect of negative incidence operation on mode shape sensitivity of an oscillating low pressure (LP) turbine rotor blade row has been studied experimentally. An annular sector cascade has been employed in which the middle blade has been made oscillating in controlled three-dimensional rigid-body modes. Unsteady blade surface pressure data were acquired at midspan on the oscillating blade and two pairs of non-oscillating neighbor blades and reduced to aeroelastic stability data. The test program covered variations in reduced frequency, flow velocity and inflow incidence; at each operating point a set of three orthogonal modes was tested such as to allow for generation of stability plots by mode recombination. At nominal incidence it has been found that increasing reduced frequency has a stabilizing effect on all modes. The analysis of mode shape sensitivity yielded that the most stable modes are of bending type with axial to chordwise character whereas high sensitivity has been found for torsion-dominated modes. Negative incidence operation caused the flow to separate on the fore pressure side. This separation was found to have a destabilizing effect on bending modes of chordwise character whereas an increase in stability could be noticed for bending modes of edgewise character. Variations of stability parameter with inflow incidence have hereby found being largely linear within the range of conditions tested. For torsion-dominated modes the influence on aeroelastic stability was close to neutral.

Unsteady Boundary Layer Transition on a High Pressure Turbine Rotor Blade

1999 ◽  
Author(s):  
Maik Tiedemann ◽  
Friedrich Kost
Keyword(s):  
Boundary Layer ◽  
High Pressure ◽  
Rotor Blade ◽  
Suction Side ◽  
Turbine Rotor ◽  
Boundary Layer Transition ◽  
Unsteady Boundary Layer ◽  
High Pressure Turbine ◽  
Layer Transition ◽  
Turbine Rotor Blade

This investigation is aimed at the experimental determination of the location, the extent, and the modes of the laminar-to-turbulent transition processes in the boundary layers of a high pressure turbine rotor blade. The results are based on time-resolved, qualitative wall shear stress data which was derived from surface hotfilm measurements. The tests were conducted in the “Windtunnel for Rotating Cascades” of the DLR in Göttingen. For the evaluation of the influence of passing wakes and shocks on the unsteady boundary layer transition, a test with undisturbed rotor inlet flow was conducted in addition to full stage tests. Two different transition modes led to a periodic-unsteady, multi-moded transition on the suction side. In between two wakes, transition started in the bypass mode and terminated as separated-flow transition. Underneath the wakes, plain bypass transition occurred. The weak periodic boundary layer features on the pressure side indicate that this surface was not significantly affected by passing wakes or shocks. The acquired data reveals that the periodically disturbed suction side boundary layer is less susceptible to bubble bursting than the undisturbed flowfield. Thus, these blades may be subjected to higher aerodynamic loads. Accordingly, as in low pressure turbines, the unsteady effects in high pressure turbines may allow for a reduction of the number of rotor blades, with respect to the original design.

Experimental Investigation of Mode Shape Sensitivity of an Oscillating Low-Pressure Turbine Cascade at Design and Off-Design Conditions

2006 ◽  
Vol 129 (2) ◽  
pp. 530-541 ◽  
Author(s):  
Damian M. Vogt ◽  
Torsten H. Fransson
Keyword(s):  
Mode Shape ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Low Pressure ◽  
Turbine Rotor ◽  
Shape Sensitivity ◽  
Aeroelastic Stability ◽  
Low Pressure Turbine ◽  
Reduced Frequency ◽  
Bending Modes

The effect of negative incidence operation on mode shape sensitivity of an oscillating low-pressure turbine rotor blade row has been studied experimentally. An annular sector cascade has been employed in which the middle blade has been made oscillating in controlled three-dimensional rigid-body modes. Unsteady blade surface pressure data were acquired at midspan on the oscillating blade and two pairs of nonoscillating neighbor blades and reduced to aeroelastic stability data. The test program covered variations in reduced frequency, flow velocity, and inflow incidence; at each operating point, a set of three orthogonal modes was tested such as to allow for generation of stability plots by mode recombination. At nominal incidence, it has been found that increasing reduced frequency has a stabilizing effect on all modes. The analysis of mode shape sensitivity yielded that the most stable modes are of bending type with axial to chordwise character, whereas high sensitivity has been found for torsion-dominated modes. Negative incidence operation caused the flow to separate on the fore pressure side. This separation was found to have a destabilizing effect on bending modes of chordwise character, whereas an increase in stability could be noted for bending modes of edgewise character. Variations of stability parameter with inflow incidence have hereby found being largely linear within the range of conditions tested. For torsion-dominated modes, the influence on aeroelastic stability was close to neutral.

Influence of Hot Streak Temperature Ratio on Low Pressure Stage of a Vaneless Counter-Rotating Turbine

2007 ◽  
Author(s):  
Qingjun Zhao ◽  
Fei Tang ◽  
Huishe Wang ◽  
Jianyi Du ◽  
Xiaolu Zhao ◽  
...  
Keyword(s):  
Shock Wave ◽  
High Pressure ◽  
Secondary Flow ◽  
Low Pressure ◽  
Turbine Rotor ◽  
Temperature Ratio ◽  
High Pressure Turbine ◽  
Pressure Stage ◽  
Low Pressure Turbine ◽  
Hot Streak

In order to explore the influence of hot streak temperature ratio on low pressure stage of a Vaneless Counter-Rotating Turbine, three-dimensional multiblade row unsteady Navier-Stokes simulations have been performed. The predicted results show that hot streaks are not mixed out by the time they reach the exit of the high pressure turbine rotor. The separation of colder and hotter fluids is observed at the inlet of the low pressure turbine rotor. After making interactions with the inner-extending shock wave and outer-extending shock wave in the high pressure turbine rotor, the hotter fluid migrates towards the pressure surface of the low pressure turbine rotor, and the most of colder fluid migrates to the suction surface of the low pressure turbine rotor. The migrating characteristics of the hot streaks are predominated by the secondary flow in the low pressure turbine rotor. The effect of buoyancy on the hotter fluid is very weak in the low pressure turbine rotor. The results also indicate that the secondary flow intensifies in the low pressure turbine rotor when the hot streak temperature ratio is increased. The effects of the hot streak temperature ratio on the relative Mach number and the relative flow angle at the inlet of the low pressure turbine rotor are very remarkable. The isentropic efficiency of the Vaneless Counter-Rotating Turbine decreases as the hot streak temperature ratio is increased.

Impact of Individual High-Pressure Turbine Rotor Purge Flows on Turbine Center Frame Aerodynamics

2017 ◽  
Author(s):  
S. Zerobin ◽  
C. Aldrian ◽  
A. Peters ◽  
F. Heitmeir ◽  
E. Göttlich
Keyword(s):  
High Pressure ◽  
Pressure Loss ◽  
Turbine Rotor ◽  
Flow Conditions ◽  
High Pressure Turbine ◽  
Reference Case ◽  
University Of Technology ◽  
Purge Flow ◽  
Generation Mechanisms ◽  
The Impact

This paper presents an experimental study of the impact of individual high-pressure turbine purge flows on the main flow in a downstream turbine center frame duct. Measurements were carried out in a product-representative one and a half stage turbine test setup, installed in the Transonic Test Turbine Facility at Graz University of Technology. The rig allows testing at engine-relevant flow conditions, matching Mach, Reynolds, and Strouhal number at the inlet of the turbine center frame. The reference case features four purge flows differing in flow rate, pressure, and temperature, injected through the hub and tip, forward and aft cavities of the high-pressure turbine rotor. To investigate the impact of each individual cooling flow on the flow evolution in the turbine center frame, the different purge flows were switched off one-by-one while holding the other three purge flow conditions. In total, this approach led to six different test conditions when including the reference case and the case without any purge flow ejection. Detailed measurements were carried out at the turbine center frame duct inlet and outlet for all six conditions and the post-processed results show that switching off one of the rotor case purge flows leads to an improved duct performance. In contrast, the duct exit flow is dominated by high pressure loss regions if the forward rotor hub purge flow is turned off. Without the aft rotor hub purge flow, a reduction in duct pressure loss is determined. The purge flows from the rotor aft cavities are demonstrated to play a particularly important role for the turbine center frame aerodynamic performance. In summary, this paper provides a first-time assessment of the impact of four different purge flows on the flow field and loss generation mechanisms in a state-of-the-art turbine center frame configuration. The outcomes of this work indicate that a high-pressure turbine purge flow reduction generally benefits turbine center frame performance. However, the forward rotor hub purge flow actually stabilizes the flow in the turbine center frame duct and reducing this purge flow can penalize turbine center frame performance. These particular high-pressure turbine/turbine center frame interactions should be taken into account whenever high-pressure turbine purge flow reductions are pursued.

Linear Deterministic Source Terms for Hot Streak Simulations

2000 ◽  
Author(s):  
Paul D. Orkwis ◽  
Mark G. Turner ◽  
John W. Barter
Keyword(s):  
Boundary Condition ◽  
High Pressure ◽  
Source Term ◽  
Aircraft Engine ◽  
Turbine Rotor ◽  
High Pressure Turbine ◽  
Order Of Accuracy ◽  
Time Average ◽  
Hot Streak ◽  
Unsteady Effects

Steady state surface rothalpy results obtained with a lumped deterministic source term are compared with results obtained from a traditional nonlinear inviscid unsteady solution for an aircraft engine first stage high-pressure turbine rotor configuration. Boundary condition/potential field effects and the order of accuracy of the available schemes are shown to have a significant effect on surface rothalpy results. However, the new technique demonstrates a significant potential for including unsteady effects in time average calculations with minimal computer effort.

Unsteady Aerodynamics and Interactions Between a High Pressure Turbine Vane and Rotor

2004 ◽  
Author(s):  
Ryan M. Urbassik ◽  
J. Mitch Wolff ◽  
Marc D. Polanka
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Potential Field ◽  
Rotor Blade ◽  
Second Harmonic ◽  
Unsteady Aerodynamics ◽  
Pressure Measurements ◽  
High Pressure Turbine ◽  
Turbine Vane ◽  
Unsteady Pressure Measurements

A set of experimental data is presented investigating the unsteady aerodynamics associated with a high pressure turbine vane (HPV) and rotor blade (HPB). The data was acquired at the Turbine Research Facility (TRF) of the Air Force Research Laboratory. The TRF is a transient, blowdown facility generating several seconds of experimental data on full scale engine hardware at scaled turbine operating conditions simulating an actual engine environment. The pressure ratio and freestream Reynolds number were varied for this investigation. Surface unsteady pressure measurements on the HPV, total pressure traverse measurements downstream of the vane, and surface unsteady pressure measurements for the rotor blade were obtained. The unsteady content of the HPV surface was generated by the rotor potential field. The first harmonic decayed more rapidly than the second harmonic with a movement upstream causing the second harmonic to be most influential at the vane throat. The blade unsteadiness appears to be caused by a combination of shock, potential field, and vane wake interactions between the vane and rotor blade. The revolution averaged data resulted in higher unsteadiness than a passing ensemble average for both vane and rotor indicating a need to understand each passage for high cycle fatigue (HCF) effects.

Using CFD to Reduce Resonant Stresses on a Single-Stage, High-Pressure Turbine Blade

2002 ◽  
Author(s):  
J. P. Clark ◽  
A. S. Aggarwala ◽  
M. A. Velonis ◽  
R. E. Gacek ◽  
S. S. Magge ◽  
...  
Keyword(s):  
High Pressure ◽  
Turbine Blade ◽  
Guide Vane ◽  
Turbine Blades ◽  
Suction Side ◽  
Lessons Learned ◽  
Single Stage ◽  
Navier Stokes ◽  
High Pressure Turbine ◽  
Time Resolved

The ability to predict levels of unsteady forcing on high-pressure turbine blades is critical to avoid high-cycle fatigue failures. In this study, 3D time-resolved computational fluid dynamics is used within the design cycle to predict accurately the levels of unsteady forcing on a single-stage high-pressure turbine blade. Further, nozzle-guide-vane geometry changes including asymmetric circumferential spacing and suction-side modification are considered and rigorously analyzed to reduce levels of unsteady blade forcing. The latter is ultimately implemented in a development engine, and it is shown successfully to reduce resonant stresses on the blade. This investigation builds upon data that was recently obtained in a full-scale, transonic turbine rig to validate a Reynolds-Averaged Navier-Stokes (RANS) flow solver for the prediction of both the magnitude and phase of unsteady forcing in a single-stage HPT and the lessons learned in that study.

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