Oil Brush Seals in Turbomachinery: Flow Analyses and Closed-Form Solutions

2020 ◽  
Vol 142 (10) ◽  
Author(s):  
Ertuğrul Tolga Duran
Keyword(s):  
Closed Form ◽  
High Speed ◽  
Closed Form Solution ◽  
Frictional Heat ◽  
Rotor Speed ◽  
Test Rig ◽  
Lifting Force ◽  
Operation Conditions ◽  
Rotor Surface ◽  
Brush Seals

Abstract Brush seals are one of the most important dynamic seals used in oil and oil mist applications in industrial turbines and aviation. Flexible bristle structure is the main structural superiority of brush seals, which enables precise clearance control and high performance in compensating rotor transients. The viscous medium between the high-speed rotor surface and brush seal bristles generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. Shear heating at moderate and high rotor surface speeds results in an increase in temperature and stabilization of lifting force, which is known as high-speed lift stabilization. Strong temperature–viscosity dependency of lube oils possesses the need for a detailed analysis and understanding of the effect of shear heat on hydrodynamic lift of brush seals in oil applications. To provide a better understanding about the critical balance of hydrodynamic lift force with rotor speed, temperature, and pressure, this work presents an analytical study to investigate pressure profile and shear heat temperature rise in liquid sealing medium within the hydrodynamic lift clearance. A closed-form solution to pressure and temperature distribution in axial and radial directions has been obtained by solving continuity, Navier–Stokes, and thermal energy equations for brush seals. The thermal and pressure functions are evaluated for linear and nonlinear pressure drop approaches, and the results are compared with each other. Deviation in nonlinear and linear pressure, resulting temperature level differences, and effect of rotor speed are detailed within the content of this study. The provided closed-form functions for pressure and temperature profiles are useful for designers since these can be utilized for turbine operation conditions. Dynamic test rig design for high-speed leakage performance measurement of turbomachinery seals is detailed, where the test rig can also be adopted for stiffness, frictional heat, power loss, torque loss, and bucket tip stability testing in oil and air environment. The test setup can also be used for testing dynamic seals other than brush seals.

Oil Temperature Analysis of Brush Seals

2007 ◽  
Author(s):  
E. Tolga Duran ◽  
Mahmut F. Aksit ◽  
Yahya Dogu
Keyword(s):  
Pressure Distribution ◽  
High Speed ◽  
Stokes Equations ◽  
Strong Dependence ◽  
Viscous Medium ◽  
Superior Performance ◽  
Lifting Force ◽  
Continuity Equations ◽  
Rotor Surface ◽  
Brush Seals

Due to their superior performance and stable leakage characteristics, brush seals are one of the dynamic seals used in oil and oil mist applications in aero-engines and turbines. The viscous medium between the high speed rotor surface and brush seal bristles generates a hydrodynamic lifting force that determines seal clearance and leakage rate in oil sealing applications. The analytical solution to bristle lifting force can be obtained by using Reynolds formulation. However, there is a strong dependence on oil temperature and viscosity. This work presents a solution to oil temperature using nonlinear pressure distribution. Starting with continuity and Navier Stokes equations, temperature and nonlinear pressure distribution is derived by solving the thermal energy and reduced continuity equations simultaneously. Results of oil temperature estimates using nonlinear pressure analysis are compared with the results of a previous work using linear pressure assumption. Findings indicate that for low rotor surface speeds oil temperature distribution is almost the same for both linear and nonlinear pressure cases. Difference in oil temperature estimates increases with increasing rotor surface speeds.

Brush Seal Frictional Heat Generation: Test Rig Design and Validation Under Steam Environment

2016 ◽  
Author(s):  
M. Raben ◽  
J. Friedrichs ◽  
J. Flegler
Keyword(s):  
Steam Turbine ◽  
Heat Generation ◽  
Gas Turbines ◽  
Frictional Heat ◽  
Narrow Gap ◽  
Test Rig ◽  
Frictional Heat Generation ◽  
Brush Seal ◽  
Rotor Surface ◽  
Brush Seals

Sealing technology is a key feature to improve efficiency of steam turbines for both new power stations and modernization projects. One of the most powerful sealing alternatives for reducing parasitic leakages in the blade path of a turbine as well as in shaft sealing areas is the use of brush seals, which are also widely used in gas turbines and turbo compressors. The advantage of brush seals over other sealing concepts is based on the narrow gap that is formed between the brush seal bristle tips and the mating rotor surface together with its radial adaptivity. While the narrow gap between the bristle tips and the rotor leads to a strongly decreased flow through the seal compared with conventional turbomachinery seals, it is important to be aware of the tight gap that can be bridged by relative motion between the rotor and the brush seal, leading to a contact of the bristles and the rotor surface. Besides abrasive wear occurrence, the friction between the bristles and the rotor leads to heat generation which can be detrimental to turbine operation due to thermal effects, leading to rotor bending connected to increasing shaft vibrations. In order to investigate the frictional heat generation of brush seals, different investigation concepts have been introduced through the past years. To broaden the knowledge about frictional heat generation and to make it applicable for steam turbine applications, a new testing setup was designed for the steam test rig of the Institute of Jet Propulsion and Turbomachinery - TU Braunschweig, Germany, enabling temperature measurements in the rotor body under stationary and transient operation in steam by using rotor-integrated thermocouples. Within this paper, the development of the instrumented new rotor design and all relevant parts of the new testing setup is shown along with the testing ability by means of the validation of the test rig concept and the achieved measurement accuracy. First results prove that the new system can be used to investigate frictional heat generation of brush seals under conditions relevant for steam turbine shaft seals.

Brush Seal Frictional Heat Generation—Test Rig Design and Validation Under Steam Environment

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Markus Raben ◽  
Jens Friedrichs ◽  
Johan Flegler
Keyword(s):  
Steam Turbine ◽  
Heat Generation ◽  
Gas Turbines ◽  
Frictional Heat ◽  
Narrow Gap ◽  
Test Rig ◽  
Frictional Heat Generation ◽  
Brush Seal ◽  
Rotor Surface ◽  
Brush Seals

Sealing technology is a key feature to improve efficiency of steam turbines for both new power stations and modernization projects. One of the most powerful sealing alternatives for reducing parasitic leakages in the blade path of a turbine as well as in shaft sealing areas is the use of brush seals, which are also widely used in gas turbines and turbo compressors. The advantage of brush seals over other sealing concepts is based on the narrow gap that is formed between the brush seal bristle tips and the mating rotor surface together with its radial adaptivity. While the narrow gap between the bristle tips and the rotor leads to a strongly decreased flow through the seal compared with conventional turbomachinery seals, it is important to be aware of the tight gap that can be bridged by relative motion between the rotor and the brush seal, leading to a contact of the bristles and the rotor surface. Besides abrasive wear occurrence, the friction between the bristles and the rotor leads to heat generation which can be detrimental to turbine operation due to thermal effects, leading to rotor bending connected to increasing shaft vibrations. In order to investigate the frictional heat generation of brush seals, different investigation concepts have been introduced through the past years. To broaden the knowledge about frictional heat generation and to make it applicable for steam turbine applications, a new testing setup was designed for the steam test rig of the Institute of Jet Propulsion and Turbomachinery—TU Braunschweig, Germany, enabling temperature measurements in the rotor body under stationary and transient operation in steam by using rotor-integrated thermocouples. Within this paper, the development of the instrumented new rotor design and all relevant parts of the new testing setup is shown along with the testing ability by means of the validation of the test rig concept and the achieved measurement accuracy. First results prove that the new system can be used to investigate frictional heat generation of brush seals under conditions relevant for steam turbine shaft seals.

Design and Validation of a New Test Rig for Brush Seal Testing Under Engine Relevant Conditions

2011 ◽  
Author(s):  
D. Pfefferle ◽  
K. Dullenkopf ◽  
H.-J. Bauer
Keyword(s):  
High Surface ◽  
Test Rig ◽  
Friction Forces ◽  
Brush Seal ◽  
Main Emphasis ◽  
Rotor Surface ◽  
Brush Seals ◽  
Gap Height ◽  
Radial Gap ◽  
Gap Width

Brush seals play an increasing role in turbomachinery due to their improved behavior towards leakage and their capability to compensate for gap variations caused by thermal expansion and rotor excursions. The flexible bristles of brush seals are able to endure short-term reductions in gap width without severe damage. Consequently the necessary gap between the rotor and brush seal can virtually be reduced to zero, leading to a considerable reduction in air leakage of up to 80 percent. However the reduced gap height increases the probability of rubbing between the bristle package and the rotor surface. The friction forces generated can cause an unwanted heat load on the rotor, bristles and leakage air. In addition, the surfaces involved are exposed to abrasion effects. Especially in the thin and lightweight rotor structures of aircraft engines, the additional heat impact can lead to a problematic level of material stress. To study these effects and to give reliable quantitative design rules, a versatile test rig for brush seals was designed and built. The simulation of seal behavior under relevant engine conditions is the main emphasis of this rig, including high pressure drop, leakage flow and high surface speed. The key feature is the possibility to vary the axis symmetric radial gap width during the test rig operation by up to a 0.5 mm overlap. The so caused rubbing induces a transient rotor temperature rise which is measured via a set of 12 thermocouples embedded in the rotor. These temperature readings can be used to calculate the brush seal heat impact on the rotor structure. Preliminary results with moderate differential pressure and rotor speed proved the functionality of the test rig and confirmed the global approach of the project.

An Investigation of Heat Generation Characteristics of Brush Seals

2007 ◽  
Author(s):  
Mehmet Demiroglu ◽  
John A. Tichy
Keyword(s):  
Contact Force ◽  
Heat Generation ◽  
Operating Conditions ◽  
Frictional Heat ◽  
Design Parameters ◽  
Frictional Heat Generation ◽  
Operation Conditions ◽  
Seal Design ◽  
Wide Range ◽  
Brush Seals

Brush seals are considered as a category of compliant seals, which tolerate a great high level of interference between the seal and the rotor or shaft. Their superior leakage characteristics have opened many application fields in the turbo-machinery world, ranging from industrial steam turbines to jet engines. However, brush seal designers have to find a trade-off between the lower parasitic leakage but higher heat generation properties of brush seals for given operation conditions. As brush seals can maintain contact with the rotor for a wide range of operating conditions, the contact force/pressure generated at the seal-rotor interface becomes an important design parameter for sustained seal performance and longevity of its service life. Furthermore, due to this contact force at the interface, frictional heat generation is inevitable and must be evaluated for various design and operating conditions. In this paper, frictional heat generation at the sealrotor interface is studied. To capture temperature rise at the interface, a thermal image of the seal and rotor is taken with an infrared camera under various operating conditions. The temperature map of the rotor is compared to results from thermal finite element analysis of the rotor to back calculate the heat flux to the rotor. A closed form equation for frictional heat generation is suggested as a function of seal design parameters, material properties, friction coefficient and empirical factors from testing.

Exact closed-form solutions for Lamb’s problem—II: a moving point load

2020 ◽  
Vol 223 (2) ◽  
pp. 1446-1459
Author(s):  
Xi Feng ◽  
Haiming Zhang
Keyword(s):  
Point Source ◽  
Closed Form ◽  
High Speed ◽  
Moving Load ◽  
Closed Form Solution ◽  
Point Load ◽  
Form Solution ◽  
High Speed Rail ◽  
Lamb’S Problem ◽  
Homogeneous Half Space

SUMMARY In this paper, we report on an exact closed-form solution for the displacement in an elastic homogeneous half-space elicited by a downward vertical point source moving with constant velocity over the surface of the medium. The problem considered here is an extension to Lamb’s problem. Starting with the integral solutions of Bakker et al., we followed the method developed by Feng and Zhang, which focuses on the displacement triggered by a fixed point source observed on the free surface, to obtain the final solution in terms of elementary algebraic functions as well as elliptic integrals of the first, second and third kind. Our closed-form results agree perfectly with the numerical results of Bakker et al., which confirms the correctness of our formulae. The solution obtained in this paper may lay a solid foundation for further consideration of the response of an actual physical moving load, such as a high-speed rail train.

One-Shot Balancing of Rigid Rotors: A Closed Form Solution

2009 ◽  
Author(s):  
Enrique S. Gutie´rrez-Wing ◽  
Jorge E. Aguirre-Romano
Keyword(s):  
Closed Form ◽  
Experimental Test ◽  
Total Mass ◽  
Closed Form Solution ◽  
Form Solution ◽  
Modal Parameters ◽  
Test Rig ◽  
Rotor Bearing ◽  
Rigid Rotors ◽  
Bearing System

This article presents a closed-form solution to the computation of unbalance correction masses for rigid rotors mounted on flexible bearings. The solution requires measurements of the response of the rotor-bearing system to the unbalance that is to be corrected, as well as knowledge of its total mass or other stiffness or damping parameters that are readily deducible from the mounting configuration. No detailed mathematical models or information from previous balancing runs are required. The computation is based on the relationships that exist between some spatial and modal parameters of rotor-bearing systems. Such relationships are derived in this article, and their use in the computation of balancing masses is presented and verified with results from an experimental test rig. This work demonstrates the feasibility of balancing rigid rotors without trial runs, detailed models or historical balancing records.

On a Closed-Form Solution of Prandtl's System of Equations

2013 ◽  
Vol 40 (2) ◽  
pp. 106-114
Author(s):  
J. Venetis ◽  
Aimilios (Preferred name Emilios) Sideridis
Keyword(s):  
Closed Form ◽  
Closed Form Solution ◽  
Form Solution ◽  
System Of Equations
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