Experimental and Computational Analysis of a Gas Compressor Windback Seal

2007 ◽  
Author(s):  
G. L. Morrison ◽  
Adnan Al-Ghasem
Keyword(s):  
Standard Deviation ◽  
Gas Flow ◽  
Computational Analysis ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Screw Thread ◽  
Shaft Speed ◽  
Flow Paths ◽  
Carry Over

A gas windback seals is similar to a labyrinth seal except the cavity is one continuous channel which winds around the shaft like a screw thread. One application is in gas compressors to isolate lubrication oil from the gas flow paths. A CFD based study of clearance, pressure ratio, and shaft speed has been performed. One seal geometry was experimentally studied to provide verification of the CFD accuracy. An empirical model for the leakage rate has been developed which fits the data with a standard deviation of 0.8%. The effects of pressure ratio and shaft speed upon the leakage rate are independent of each other. Analysis of the CFD results indicate that the kinetic energy carry over coefficient is substantially less for the windback seal operating at low differential pressures and gas densities than for a labyrinth seal operating under typical conditions.

Experimental and Numerical Investigation of a Gas Compressor Windback Seal

2006 ◽  
Vol 129 (1) ◽  
pp. 129-134
Author(s):  
Adnan Al-Ghasem ◽  
G. L. Morrison ◽  
John P. Platt
Keyword(s):  
Pressure Ratio ◽  
Experimental Tests ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Rectangular Cavity ◽  
Screw Thread ◽  
Cfd Simulations ◽  
Commercial Code ◽  
Purge Gas ◽  
Gas Face Seal

The effectiveness of a computational fluid dynamics (CFD) commercial code to accurately predict the leakage rate for a windback seal was evaluated. The windback seal under consideration has a rectangular cavity and is similar in design to a gas tooth on stator annular labyrinth seal. The main difference is the windback seal has only one tooth, which continuously winds around the shaft like a screw thread. These seals are used in gas compressors to isolate the gas face seal from bearing oil. A purge gas is passed through the seal into the bearing housing. The helical design allows the seal to clear itself of any oil contamination. The objective is to determine if CFD simulations can be used along with a few experimental tests to study windback seals of this design. Comparison of measurement and predictions for a simple rectangular cavity windback seal shows predictions and measurements comparing very well with maximum differences of 5% for leakage rate. The variation of leakage with shaft speed and pressure ratio across the seal is accurately predicted by the CFD simulations.

Effects of Inlet Preswirl and Cell Diameter and Depth on Honeycomb Seal Characteristics

2010 ◽  
Vol 132 (12) ◽  
Author(s):  
Xin Yan ◽  
Jun Li ◽  
Zhenping Feng
Keyword(s):  
Temperature Increase ◽  
Pressure Ratio ◽  
Three Dimensional ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Navier Stokes ◽  
Cell Diameter ◽  
Total Temperature ◽  
Honeycomb Seals ◽  
Honeycomb Cell

Three-dimensional Reynolds-averaged Navier–Stokes solutions are employed to investigate the discharge and total temperature increase characteristics of the stepped labyrinth seal with honeycomb land. First, the relations between the windage heating number and the circumferential Mach number at different Reynolds numbers for different honeycomb seals are calculated and compared with the experimental data. The obtained numerical results show that the present three-dimensional periodic model can properly predict the total temperature increase in honeycomb seals. Then, a range of pressure ratios, three inlet preswirl ratios, four sizes of honeycomb cell diameter, and nine sizes of cell depth are selected to investigate the influence of inlet preswirl ratios and honeycomb geometry sizes on the discharge and total temperature increase characteristics of the stepped labyrinth seal. It shows that the leakage rate increases with the increase in cell diameter, and the cell depth has a strong influence on the discharge behavior. However, the influence of the inlet preswirl on the leakage rate is found to be little in the present study. For the total temperature increase characteristic, the inlet preswirl ratio and pressure ratio have more pronounced influence than those of cell depth and diameter. Furthermore, the relations between the leakage rate and cell depth and diameter, as well as the relations between the windage heating power and cell depth and diameter, are not monotonic functions if the pressure ratio is kept constant.

Prediction of Incompressible Flow in Labyrinth Seals

1986 ◽  
Vol 108 (1) ◽  
pp. 19-25 ◽  
Author(s):  
D. L. Rhode ◽  
J. A. Demko ◽  
U. K. Traegner ◽  
G. L. Morrison ◽  
S. R. Sobolik
Keyword(s):  
Numerical Model ◽  
Incompressible Flow ◽  
Computer Code ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Labyrinth Seals ◽  
New Approach ◽  
Cpu Time ◽  
Carry Over ◽  
Good Agreement

A new approach was developed and tested for alleviating the substantial convergence difficulty which results from implementation of the QUICK differencing scheme into a TEACH-type computer code. It is relatively simple, and the resulting CPU time and number of numerical iterations required to obtain a solution compare favorably with a previously recommended method. This approach has been employed in developing a computer code for calculating the pressure drop for a specified incompressible flow leakage rate in a labyrinth seal. The numerical model is widely applicable and does not require an estimate of the kinetic energy carry-over coefficient for example, whose value is often uncertain. Good agreement with measurements is demonstrated for both straight-through and stepped labyrinths. These new detailed results are examined, and several suggestions are offered for the advancement of simple analytical leakage as well as rotordynamic stability models.

Optimization of Labyrinth Seal for Screw Compressor

2007 ◽  
Author(s):  
M. Selvaraji ◽  
Sam P. Joseph ◽  
N. Nirmal
Keyword(s):  
Heat Transfer ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Heat Transfer Analysis ◽  
Lubricating Oil ◽  
Screw Compressor ◽  
Labyrinth Seals ◽  
Gas Leakage ◽  
Working Medium

There is a growing demand for compressed air in the industry for various applications. Majority of industrial requirements is in line with screw compressor operating range. Design and construction of screw compressors are demanding tasks that require advanced calculations and theoretical knowledge. Clearances play a major role in the performance and reliability aspects of a screw compressor. Seals are provided in compressors to fit around rotor shafts in order to prevent the leakage of lubricating oil and working medium. However there is a small clearance between the seal and rotor shaft, which can cause potential leakage of the working medium. The performance of the compressor is directly related to the leakage rate through the seals. The labyrinth seal is a special type of seal, used in screw compressors and turbo-machinery for sealing purpose. Labyrinth seal is a non-contacting type seal that uses a tortuous path to minimize the gas leakage. The pressure drop occurs at each labyrinth tooth as the medium is squeezed between the labyrinth tooth and the rotor. The leakage through the seal is directly related to the labyrinth profile and also the clearance between the rotor and the labyrinth tooth. The present work is carried out to reduce the leakage through the labyrinth seal by optimising the tooth profile and operating clearances. Heat transfer analysis is carried out on the housing of the labyrinth seal to find out the boundary temperature of the seal. Also the heat transfer analysis on the labyrinth seal followed by Thermo-structural analysis is carried out to find out the accurate operating clearance of the seal. By using CFD as a tool, the optimisation is carried out on different design configurations of labyrinth seal by comparing the deviation in leakage rates. Effect of rotor speed, width of seal and pressure ratio on air leakage rate is also investigated. A set of labyrinth seals has been designed based on the above optimisation and tested in the compressor. The results have been compared with the CFD prediction.

scholarly journals Novel Method of the Seal Aerodynamic Design to Reduce Leakage by Matching the Seal Geometry to Flow Conditions

Energies ◽  
2021 ◽  
Vol 14 (23) ◽  
pp. 7880
Author(s):  
Damian Joachimiak
Keyword(s):  
Kinetic Energy ◽  
Design Method ◽  
Pressure Ratio ◽  
Leakage Rate ◽  
Relative Reduction ◽  
Flow Conditions ◽  
Labyrinth Seals ◽  
Flow Phenomena ◽  
Novel Method ◽  
Carry Over

This paper presents a novel method of labyrinth seals design. This method is based on CFD calculations and consists in the analysis of the phenomenon of gas kinetic energy carry-over in the seal chambers between clearances. The design method is presented in two variants. The first variant is designed for seals for which it is impossible to change their external dimensions (length and height). The second variant enables designing the seal geometry without changing the seal length and with a slight change of the seal height. Apart from the optimal distribution of teeth, this variant provides for adjusting chambers geometry to flow conditions. As the result of using both variants such design of the seal geometry with respect to leakage is obtained which enables achieving kinetic energy dissipation as uniform as possible in each chamber of the seal. The method was developed based on numerical calculations and the analysis of the flow phenomena. Calculation examples included in this paper show that the obtained reduction of leakage for the first variant ranges from 3.4% to 15.5%, when compared with the initial geometry. The relation between the number of seal teeth and the leakage rate is also analyzed here. The second variant allows for reduction of leakage rate by 15.4%, when compared with the geometry with the same number of teeth. It is shown that the newly designed geometry reveals almost stable relative reduction of leakage rate irrespective of the pressure ratio upstream and downstream the seal. The efficiency of the used method is proved for various heights of the seal clearance.

Simulation of Subsonic Flow Through a Generic Labyrinth Seal

1986 ◽  
Vol 108 (4) ◽  
pp. 674-680 ◽  
Author(s):  
D. L. Rhode ◽  
S. R. Sobolik
Keyword(s):  
Subsonic Flow ◽  
Computer Code ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Labyrinth Seals ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Flow Through ◽  
Carry Over ◽  
Single Cavity

A new method for predicting the leakage through labyrinth seals has been developed and is shown to provide realistic results which agree with measurements. It utilizes a finite-difference computer code which was developed in order to compute the pressure drop across a single cavity of the seal. This quantity is obtained at several leakage flow Mach numbers to be used subsequently in predicting the leakage rate. The model is widely applicable and does not require an estimate of the kinetic energy carry-over coefficient, whose value is often uncertain for many untested configurations. Detailed cavity distributions of basic flowfield quantities are also presented and examined. Specifically, the predicted results of four seal leakage mass flow rates at given cavity inlet pressure and temperature are compared, and important variations are examined. Also, realistic approximations of flow variable distributions within a single cavity are made from the included figures to assist in the development of analytical methods.

Labyrinth Seal Discharge Coefficient for Rectangular Cavities

2009 ◽  
Author(s):  
Saikishan Suryanarayanan ◽  
Gerald L. Morrison
Keyword(s):  
Discharge Coefficient ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Prediction Equation ◽  
Prediction Algorithm ◽  
Expansion Factor ◽  
Clearance Ratio ◽  
Compressibility Effect ◽  
Tooth Width ◽  
Carry Over

A labyrinth seal leakage prediction equation can be developed by considering the seal as a series of orifices and cavities. CFD simulations are used to investigate the discharge coefficient’s dependence of each tooth upon the seal geometry and flow conditions for multi-toothed, teeth on stator, straight through labyrinth seals with rectangular cavities. The discharge coefficient for the first tooth of the labyrinth seal was found to be a function of tooth width to clearance ratio and Reynolds number. It was found that the ratio of the discharge coefficients of a downstream tooth of the labyrinth seal to that of the inlet tooth is a function of the carry over coefficient. The carry over coefficient is a measure of the amount of kinetic energy entering a cavity that is dissipated by turbulence in the cavity. It was observed that the expansion factor (compressibility effect) is a function of tooth pressure ratio. The models developed in this paper for discharge coefficient and expansion factor coupled with the carry over coefficient model presented in our earlier work provide a leakage prediction algorithm that is validated against prior experiments.

Numerical Investigations on the Leakage Flow Characteristics of Pocket Damper Seals

2011 ◽  
Author(s):  
Zhigang Li ◽  
Jun Li ◽  
Zhenping Feng ◽  
Jiandao Yang ◽  
Rui Yang ◽  
...  
Keyword(s):  
Flow Rate ◽  
Rotational Speed ◽  
Pressure Ratio ◽  
Flow Characteristics ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Numerical Results ◽  
Flow Coefficient ◽  
Leakage Flow ◽  
Leakage Flow Rate

The effects of pressure ratios, rotational speeds and sealing clearances on the leakage flow characteristics of pocket damper seals (PDS) were numerically investigated using Reynolds-Averaged Navier-Stokes (RANS) solutions. The leakage flow rate of the experimental PDS with the eight-bladed and eight-pocket was conducted at three different pressure drops and three different rotational speeds. The numerical results were in agreement with the experimental data. Six pressure ratios, four rotational speeds and four sealing clearances were utilized to study the effects of theses factors on the leakage flow characteristics of the PDS. Numerical results show that the leakage rate of the PDS increases with decreased pressure ratio. The leakage rate decreases with the increasing rotational speed, and this phenomenon is more pronounced at higher rotational speed. At the highest rotational speed 20200rpm, the flow coefficient is up to 4.4% less than that of the non-rotating case. The leakage rate increases linearly with sealing clearance increasing. The comparison of the leakage flow rate shows that the PDS leaks slightly less than that of the labyrinth seal at the same pressure ratio, rotational speed and sealing clearance, especially at the higher rotational speed case. Furthermore, the circumferential partition wall can significantly decrease the circumferential flow in the PDS cavity. At the highest rotational speed with 20200rpm, the swirl ratio in the active and inactive cavity of the PDS is reduced by 94.5% and 46% compared to the labyrinth seal, respectively.

A method for shock train leading edge detection based on differential pressure

2016 ◽  
Vol 231 (1) ◽  
pp. 61-71 ◽  
Author(s):  
B Xiong ◽  
Z-G Wang ◽  
X-Q Fan ◽  
Y Wang
Keyword(s):  
Standard Deviation ◽  
Edge Detection ◽  
Detection Method ◽  
Pressure Ratio ◽  
Leading Edge ◽  
Differential Pressure ◽  
Shock Train ◽  
Pressure Method ◽  
Operational Application ◽  
Deviation Method

In order to make the shock train leading edge detection method more possible for operational application, a new detection method based on differential pressure signals is introduced in this paper. Firstly, three previous detection methods, including the pressure ratio method, the pressure increase method, and the standard deviation method, have been examined whether they are also applicable for shock train moving at different speeds. Accordingly, three experimental cases of back-pressure changing at different rates were conducted in this paper. The results show that the pressure ratio and the pressure increase method both have acceptable detection accuracy for shock train moving rapidly and slowly, and the standard deviation method is not applicable for rapid shock train movement due to its running time window. Considering the operational application, the differential pressure method is raised and tested in this paper. This detection method has sufficient temporal resolution for rapidly and slowly shock train moving, and can make a real-time detection. In the end, the improvements brought by the differential pressure method have been discussed.

Sharper Labyrinth Seal Edges to Allow Greater Clearance Without Increased Leakage

1995 ◽  
Author(s):  
David L. Rhode ◽  
M. J. Guidry
Keyword(s):  
Numerical Study ◽  
Energy Generation ◽  
Labyrinth Seal ◽  
Leakage Rate ◽  
Turbulence Energy ◽  
Resistance Increase ◽  
Leakage Resistance ◽  
Edge Sharpness ◽  
Damage Susceptibility

Abstract A numerical study was undertaken to examine the effects of utilizing sharper edges for increasing the leakage resistance of advanced labyrinth seal configurations. Such an increase allows the designer to enlarge the extremely small knife clearance, providing a seal with less damage susceptibility at the same leakage rate. The maximum possible leakage resistance increase from changing three cavity edges to perfectly sharp ones was estimated from the present computations. In addition, previous measurements of the edge sharpness effect on the leakage through orifices are appropriately utilized to obtain a rough estimate of the resistance increase for generic seals. The latter allows consideration of a broader range of application. Further, turbulence energy generation contours reveal that only one particular cavity edge needs to be sharpened in order to obtain a significantly increased leakage resistance.

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