Hrishikesh Vishvas Deo

Compliant Plate Seals: Testing and Validation

Compliant Plate Seals are being developed for various turbomachinery sealing applications including gas turbines, steam turbines, aircraft engines and oil & gas compressors. These seals consist of compliant plates attached to a stator in a circumferential fashion around the rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter, and an intermediate plate extends inwards into this slot from stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip–clearance. Due to this self–correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and non-contact operation even in the presence of large rotor transients. In this paper, we have reported leakage test results for Compliant Plate Seals and visually demonstrated robust non-contact operation for different assembly clearances and interferences, stator deflections, high frequency rotor transients, different pressure conditions and rotational speeds.Copyright

Vortex Induced Flutter in Compliant Plate Seals

This paper investigates the possibility of vortex induced flutter in GE compliant plate seals (CPS). The CPS consists of a ring of slotted compliant plates attached circumferentially around the rotor, with an intermediate plate seated in the slot. Experiments show that the compliant plates vibrate in the flow field with amplitude that is a function of the differential pressure applied across the seal. The vibrations are caused by potentially multiple flow induced vibration mechanisms operating during different flow regimes. This work focuses on the dynamic instabilities that may be caused by the vortices shed by individual compliant plates and the intermediate plate. We model the compliant plate seal as a ring of a large number of locally coupled oscillators, with nonlinear stiffness arising from hydrostatic feedback. A two-way coupling exists between the structural and wake dynamics, leading to the phenomenon of “lock-in” between the wake and successive modes of seal vibration as the flow velocity is increased. Using eigenvalue analysis, we obtain the transition boundaries that divide the parameter space into sets of regions with positive and negative damping, corresponding to boundaries of onset and end of vortex induced flutter. Based on averaged equations, the amplitude of the limit cycles of the structure and wake dynamics and the phase between them is determined. It is found that the nonlinearities in seal stiffness and the nature of coupling between the compliant plates have a significant effect on the stability boundaries.Copyright

Flexure Design for Progressive Clearance Labyrinth Seal

Turbo-machinery sealing is a challenging problem due to the varying clearances caused by thermal transients, vibrations or bearing lift–off. Conventional labyrinth seals have to be assembled with large clearances to avoid rubbing during rotor transients and this results in large leakage and lower efficiency. In our previous work, we have proposed a Progressive Clearance Labyrinth Seal which is mounted on flexures and employs progressively tighter teeth from the upstream to the downstream direction. The clearance progression gives rise to a feedback phenomenon whereby a small tip-clearance is maintained between the seal and the rotor. The flexures play a very important role in the design of this seal. They are required to have low radial stiffness relative to the fluidic feedback stiffness, so that the seal can move freely in response to the self-correcting forces. The axial stiffness has to be high to limit the displacement in that direction. Most importantly, the flexures need to provide extremely high twist stiffness, since a small twist can cause large changes in the clearance progression necessary for the self–correcting behavior. In this paper, we propose a novel zero–twist flexure architecture which preserves radial compliance and twist stiffness. We first create a simple analytical model to illustrate the design concept. An experimental setup is built and the design is validated on representative flexure geometry.Copyright

Compliant Plate Seals: Design and Performance Simulations

Compliant Plate Seals are being developed for various turbomachinery sealing applications including gas turbines, steam turbines, aircraft engines and oil & gas compressors. These seals consist of compliant plates attached to a stator in a circumferential fashion around a rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter, and an intermediate plate extends inwards into this slot from stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip–clearance. Due to this self–correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and non–contact operation even in the presence of large rotor transients. CFD models have been developed to predict the leakage flow rates and hydrostatic lift and blowdown forces, and a design philosophy is proposed to predict the feedback phenomenon from the CFD results.Copyright

Static Testing of Compliant Plate Seals

Self–correcting Compliant Plate Seals are being developed for various turbomachinery sealing applications including gas turbines, steam turbines, aircraft engines and oil & gas compressors. These seals consist of compliant plates attached to a stator in a circumferential fashion around the rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter, and an intermediate plate extends inwards into this slot from stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip–clearance. Due to this self–correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and robust non–contact operation even in the presence of large rotor transients. In this paper we have described the testing of Compliant Plate Seals in a static leakage test rig (“shoebox” rig) to study the impact of different design parameters on leakage and vibration. A novel high–speed visualization set–up is described and the high–speed videos demonstrate robust non–contact operation for different assembly clearances, bridge–gaps and bridge–heights, for various differential pressure and pressure ratio conditions. The reported leakage results indicate that the leakage is relatively insensitive to assembly clearances due to the self–correcting behavior.Copyright

Progressive Clearance Labyrinth Seal for Turbo-Machinery Applications

Turbomachinery sealing is a challenging problem due to the varying clearances caused by thermal transients, vibrations, bearing lift-off etc. Leakage reduction has significant benefits in improving engine efficiency and reducing emissions. Conventional labyrinth seals have to be assembled with large clearances to avoid rubbing during large rotor transients. This results in large leakage and lower efficiency. In this paper, we propose a novel Progressive Clearance Labyrinth Seal that is capable of providing passive fluidic feedback forces that balance at a small tip-clearance. A modified packing ring is supported on flexures and employs progressively tighter teeth from the upstream to the downstream direction. When the tip-clearance reduces below the equilibrium clearance, fluidic feedback forces cause the packing ring to open. Conversely, when the tip-clearance increases above the equilibrium clearance, the fluidic feedback forces cause the packing ring to close. Due to this self-correcting behavior, the seal provides high differential pressure capability, low leakage and non-contact operation even in the presence of large rotor transients. Theoretical models for the feedback phenomenon have been developed and validated by experimental results.Copyright

Compliant Plate Seals for Turbomachinery Applications

In this paper, a novel GE Compliant Plate Seal is proposed that consists of compliant plates attached to a stator in a circumferential fashion around a rotor. The compliant plates have a slot that extends radially inwards from the seal outer diameter, and an intermediate plate extends inwards into this slot from stator. This design is capable of providing passive hydrostatic feedback forces acting on the compliant plates that balance at a small tip-clearance. When the tip-clearance reduces below the equilibrium clearance, the hydrostatic lift forces cause the compliant plates to lift away from the rotor. Conversely when the tip-clearance increases above the equilibrium clearance, the hydrostatic blowdown forces cause the compliant plates to blow down towards the rotor. Due to this self-correcting behavior, this seal is capable of providing high differential pressure capability and low leakage within a limited axial span, and non-contact operation even in the presence of large rotor transients. Simplified CFD models have been developed to predict the leakage flow rates and hydrostatic lift and blowdown forces, and a design philosophy is proposed to predict the feedback phenomenon from the CFD models. The proposed models are validated and self-correcting behavior is demonstrated through experimental testing.Copyright