Numerical Investigation on the Static and Rotordynamic Characteristics for Two Types of Novel Mixed Helical Groove Seals

2020 ◽  
Author(s):  
Zhi Fang ◽  
Zhigang Li ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Reference Frame ◽  
Rotational Speed ◽  
Power Loss ◽  
Frame Theory ◽  
Sealing Capacity ◽  
Helical Groove ◽  
Groove Seal ◽  
Rotordynamic Forces ◽  
Multiple Reference ◽  
Helical Grooves

Abstract Non-contracting annular seals, such as helical groove seals, are widely used between the impeller stages in the liquid turbomachinery to reduce the fluid leakage and stabilize the rotor-bearing system. However, previous literature has expounded that the helical groove seals possess the poor sealing property at low rotational speed condition and face the rotor instability problem inducing by negative stiffness and damping, which is undesirable for liquid turbomachinery. In this paper, to obtain the high sealing performance and the reliable rotordynamic capability for full operational conditions of the machine, two novel mixed helical groove seals, which possess a hole-pattern/pocket-damper stator matching with a helically-grooved rotor, were designed and assessed for a multiple-stage high-pressure centrifugal liquid pump. In order to assess the static and rotordynamic characteristics of these two types of mixed helical groove seals, a three-dimensional (3D) steady CFD-based method with the multiple reference frame theory was used to predict the seal leakage and drag power loss. Moreover, a proposed 3D transient CFD-based perturbation method, based on the multi-frequency one-dimensional stator whirling model, the multiple reference frame theory and a mesh deformation technique, was utilized for the predictions of seal rotordynamic characteristics. The accuracy of the numerical methods was demonstrated based on the experiment data of leakage and rotordynamic forces coefficients of published helical groove seals and hole-pattern seal. The leakage and rotordynamic forces coefficients of these two mixed helical groove seals were presented at five rotational speeds (0.5 krpm, 2.0 krpm, 4.0 krpm, 6.0 krpm, 8.0 kpm) with large pressure drop of 25MPa, and compared with three types of conventional helical groove seal (helical grooves on rotor, stator or both), and two types of damper seals (hole-pattern seal, pocket damper seal with smooth rotor). Numerical results show that the mixed groove seals possess generally better sealing capacity than the conventional helical groove seals, especially at low rotational speed conditions. The circumferentially-isolated cavities (hole or pocket) on the stator enhance the “pumping effect” of the helical grooves for mixed helical groove seals, what is more, the helical grooves also strengthen the dissipation of kinetic energy in the isolated cavities, thus the mixed helical groove seal offers less leakage. Although the mixed helical groove seals possess a slightly larger drag power loss, it is acceptable in consideration of reduced leakage for the high-power turbomachinery. The present novel mixed helical groove seals have pronounced stability advantages over the conventional helical groove seal, due to the obvious large positive stiffness and increased damping. The mixed helical groove seal with the hole-pattern stator and the helically-grooved rotor (HPS/GR) possesses the lowest leakage and the largest effective damping, especially for the high rotational speeds. From the viewpoint of sealing capacity and rotor stability, the novel mixed groove seals are better seal concepts for liquid turbomachinery.

Static and Rotordynamic Characteristics for Two Types of Novel Mixed Liquid Damper Seals With Hole-Pattern/Pocket-Textured Stator and Helically Grooved Rotor

2021 ◽  
Vol 143 (4) ◽  
Author(s):  
Zhigang Li ◽  
Zhi Fang ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Power Loss ◽  
Frame Theory ◽  
Sealing Capacity ◽  
Annular Seal ◽  
Helical Groove ◽  
Groove Seal ◽  
Stiffness And Damping ◽  
Multiple Reference ◽  
Helical Grooves ◽  
Liquid Pump

Abstract Noncontacting liquid annular seals, such as helical groove seals, are widely used at the impeller interstage and shaft end in the liquid turbomachinery to reduce the fluid leakage and stabilize the rotor-bearing system. However, previous literatures have expounded that the helical groove seal possesses the poor sealing property at low rotational speed condition and suffers the rotor instability problem inducing by negative stiffness and damping, which is undesirable for the liquid turbomachinery. In this paper, to obtain the high sealing performance and the reliable rotordynamic capability throughout full operational conditions of machines, two novel mixed liquid damper seals, which possess a hole-pattern/pocket-textured stator matching with a helically grooved rotor, were designed and assessed for the balance piston location in a multiple-stage high-pressure centrifugal liquid pump. To assess the static and rotordynamic characteristics of these two types of mixed liquid damper seals, a three-dimensional (3D) steady computational fluid dynamics (CFD)-based method with the multiple reference frame theory was used to predict the seal leakage and drag power loss. Moreover, a novel 3D transient CFD-based perturbation method, based on the multifrequency one-dimensional stator whirling model, the multiple reference frame theory, and the mesh deformation technique, was proposed for the predictions of liquid seal rotordynamic characteristics. The reliability and accuracy of the present numerical methods were demonstrated based on the published experiment data of leakage and rotordynamic force coefficients of a helical groove liquid annular seal and a hole-pattern liquid annular seal. The leakage and rotordynamic force coefficients of these two mixed liquid damper seals were presented at five rotational speeds (0.5 krpm, 2.0 krpm, 4.0 krpm, 6.0 krpm, and 8.0 kpm) with large pressure drop of 25 MPa, and compared with three types of conventional helical groove seals (helical grooves on rotor, stator or both), two typical damper seals (hole-pattern seal, pocket damper seal with smooth rotor), and a mixed helical groove seal. Numerical results show that two novel mixed liquid damper seals both possess generally better sealing capacity than the conventional helical groove seals, especially at lower rotational speeds. The circumferentially isolated cavities (hole/pocket types) on the stator can enhance the “pumping effect” of the helical grooves for mixed helical groove seals, by weakening the swirl flow in seal clearance (which results in the increase of the fluid velocity gradient near the helically grooved rotor). What is more, the helical grooves on rotor also strengthen the dissipation of fluid kinetic energy in the isolated cavities, so the mixed liquid damper seals offer less leakage. Although the mixed liquid damper seals possess a slightly larger (less than 40%) drag power loss, it is acceptable in consideration of the reduced (∼60%) leakage for the high-power turbomachinery, such as the multiple-stage high-pressure centrifugal liquid pump. The present novel mixed liquid damper seals have pronounced rotordynamic stability advantages over the conventional helical groove seals, due to the obviously larger positive stiffness and damping. The mixed liquid damper seal with the hole-pattern stator and the helically grooved rotor (HPS/GR) possesses the lowest leakage and the largest effective damping, especially for higher rotational speeds. From the viewpoint of sealing capacity and rotor stability, the present two novel mixed liquid damper seals have the potential to become the attractive alternative seal designs for the future liquid turbomachinery.

Second Stage Optimization of Helical Groove Seals Using Computational Fluid Dynamics to Evaluate the Dependency of Optimized Design on Preswirl

2018 ◽  
Author(s):  
Cori Watson ◽  
Houston Wood
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Power Loss ◽  
Pressure Differential ◽  
Design Parameters ◽  
Working Fluid ◽  
Second Stage ◽  
Trade Offs ◽  
Helical Groove ◽  
Groove Seal

Helical groove seals are non-contacting annular seals used in pumping machinery to increase the efficiency and, in the case of the balance drum, to manage the axial force on the thrust bearing. Prior work has shown that optimization of helical groove seals can reduce the leakage by two thirds given a desired pressure differential or, conversely, can significantly increase the pressure differential across the helical groove seal given a flow rate. This study evaluates the dependency of the optimal helical groove seal design on the inlet preswirl, which is the ratio of the inlet circumferential velocity to the rotor surface speed. To accomplish this goal, second stage optimization from the previously optimized helical groove seal with grooves on the stator and water as the working fluid were conducted at a series of preswirls ranging from −1 to 1. Optimization is performed using ANSYS CFX, a commercial computational fluid dynamics software and mesh independence is confirmed for the baseline case. For each preswirl case, design of experiments for the design parameters of groove width, groove depth, groove spacing, and number of grooves was performed using a Kennard-Stone Algorithm. The optimized solution is interpolated from the simulations run by using multi-factor quadratic regression from the 30 simulations in each optimization and the interpolated solution is simulated for comparison. In addition to evaluating the optimized solution’s dependency on preswirl, the viability of using swirl breaks or swirl promoting inlet passages to improve the overall efficiency of the seal is discussed. Finally, the power loss performance is evaluated for each of the seal designs simulated so that potential trade-offs can be evaluated. Overall, the results show that increasing preswirl can increase the efficiency of the helical groove seal both by improving power loss and by improving leakage.

The Impact of the Multiple Reference Frame Interface on Modelling the Interaction Between IGVs and the Impeller in Turbocharger Compressors

2017 ◽  
Author(s):  
Xiangjun Li ◽  
Stephen Spence
Keyword(s):  
Flow Field ◽  
Mass Flow Rate ◽  
Reference Frame ◽  
Mass Flow ◽  
Flow Rate ◽  
Rotational Speed ◽  
Axial Position ◽  
High Rotational Speed ◽  
The Impact ◽  
Multiple Reference

In this paper numerical investigations are presented of how the axial position of the multiple reference frame (MRF) stator-rotor interface between the inlet guide vanes (IGVs) and the impeller would influence the predicted flow field for a turbocharger centrifugal compressor when simulated by the steady RANS method. In the first step, a total of three different axial positions of the MRF IGV-impeller interface were considered and compared with the results of an unsteady simulation to evaluate their accuracy. The results showed that the choice of the MRF interface location significantly influenced the predicted overall performance. At the lower rotational speed, the peak efficiency varied by 1.3% and the corresponding total pressure ratio varied by 0.022. At the high rotational speed, the different axial locations of the MRF interface varied the predicted choke point by 0.012 normalized mass flow rate. The mass flow rate of the near surge (NS) point was over estimated at both the high and low rotational speed by at least 0.038 normalized mass flow rate. Consideration of the flow field suggested that the MRF interface between the IGV and the impeller should be placed towards the upstream side of the available region to avoid being unphysically influenced by its interaction with the non-uniform pressure in the downstream subsonic flow field and to enable a more accurate prediction of the extent of the inducer shock in transonic operating situations. Based on this understanding, a further improvement was made for the setting of the MRF interface by employing a polyline interface. This achieved a more accurate numerical result for the NS operating point at low rotational speeds. The position of the MRF interface for modelling IGVs in a turbocharger compressor should be suitably chosen according to the objectives of the numerical study.

Using Multiple Reference Frame Theory for Considering Harmonics in Average-Value Modeling of Diode Rectifiers

2016 ◽  
Vol 31 (3) ◽  
pp. 872-881 ◽  
Author(s):  
Hamid Atighechi ◽  
Sina Chiniforoosh ◽  
Seyyedmilad Ebrahimi ◽  
Juri Jatskevich
Keyword(s):  
Reference Frame ◽  
Frame Theory ◽  
Average Value ◽  
Value Modeling ◽  
Multiple Reference
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