scholarly journals Numerical Study of Shaft-Seal Parameters for Various Geometry Configurations and Operation Regimes

2018 ◽  
Vol 180 ◽  
pp. 02100 ◽  
Author(s):  
Petr Straka
Keyword(s):  
Numerical Study ◽  
Pressure Ratio ◽  
Labyrinth Seal ◽  
Geometrical Parameters ◽  
Turbine Stage ◽  
Shaft Seal ◽  
Flow Angle ◽  
Geometric Configurations ◽  
Outlet Flow ◽  
Flow Through

The contribution deals with numerical modelling of flow through the shaft labyrinth seal for various geometric configurations and operating states. The objective is to obtain dependency of the mass flow rate through the seal and the outlet flow angle from the seal on the pressure ratio and the rotation speed for various seal clearances and other geometrical parameters. The results will be used as a background for modification of the test-rig for axial turbine stage.

scholarly journals Leakage Characteristic Identification of Labyrinth Seals on Reciprocating Piston through Transient Simulations

2019 ◽  
Vol 2019 ◽  
pp. 1-12
Author(s):  
Lingzi Wang ◽  
Jianmei Feng ◽  
Mingfeng Wang ◽  
Zenghui Ma ◽  
Xueyuan Peng
Keyword(s):  
Flow Rate ◽  
Pressure Ratio ◽  
Piston Compressor ◽  
Pressure Change ◽  
Labyrinth Seal ◽  
Relative Molecular Mass ◽  
Geometrical Parameters ◽  
Leakage Flow ◽  
Reciprocating Motion ◽  
Leakage Flow Rate

In the reciprocating labyrinth piston compressor, the characteristic of the internal leakage is crucial for the leakage management and performance improvement of the compressor. However, most of the published studies investigated the rotor-stator system, and those who study the reciprocating piston-cylinder system basically focus on the effects of the geometrical parameters. These conclusions could not directly be applied to predict the real-time leakage flow rate through the labyrinth seal because of the fast reciprocating motion of the piston, which will cause continually pressure change in two compression chambers, and then the pressure fluctuation will affect the flow through the labyrinth seal. A transient simulation model employing the multiscale dynamic mesh, which considers the effect of the reciprocating motion of the piston in the cylinder, is established to identify the characteristics of the internal leakage. This model was verified by a specially designed compressor, and the influence of various parameters was analyzed in detail. The sealing performance decreased linearly with the increase in the pressure ratio, and higher pressure inlet leads to higher leakage flow under the same pressure ratio. The labyrinth seal performance positively correlated to the increase of the rotational speed. Leakage characteristics of five working mediums were carried out, and the results indicated that the relative leakage decreased with an increase in the relative molecular mass. From this study, the realistic internal leakage flow rate under different operating parameters in the reciprocating labyrinth piston compressor could be predicated.

A Numerical Study of Secondary Flow in Axial Turbines With Application to Radial Transport of Hot Streaks

2000 ◽  
Author(s):  
Dilip Prasad ◽  
Gavin J. Hendricks
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Numerical Study ◽  
Angle Distribution ◽  
Turbine Stage ◽  
Radial Transport ◽  
Numerical Work ◽  
Flow Angle ◽  
Axial Turbines ◽  
Hot Streak

The flow field in a low-speed turbine stage with a uniform inlet total pressure is studied numerically. A circular hot streak is superposed on the vane inlet flow. In agreement with previous experimental and numerical work, it is observed that while the streak passes through the vane unaltered, significant radial transport occurs in the rotor. Furthermore, despite the unsteady nature of the flow field, the steady theory of Hawthorne (1974) is found to predict the radial transport velocity well. Making use of this theory, it is shown that the secondary vorticity in the rotor may be attributed to the effects of density stratification, the spatial variation of the vane exit flow angle and the relative eddy. It then follows that the extent of radial transport in the rotor may be influenced by altering the vane exit flow angle distribution. The present study examines one means by which this may be effected, viz., varying the vane twist across the span. It is shown that a “reverse” twist, wherein the flow angle at the vane exit is larger near the tip than it is at mid-span reduces the secondary flow (and consequently, radial transport) in the blade passage. On the other hand, “positive” twist, in which the vane exit flow angle decreases with span is found to markedly worsen the radial transport in the blade. It is to be noted that varying the vane twist is but one method to obtain the desired exit flow angle; possibilities for altering other aspects of the vane geometry also exist.

A Numerical Study of Secondary Flow in Axial Turbines With Application to Radial Transport of Hot Streaks

2000 ◽  
Vol 122 (4) ◽  
pp. 667-673 ◽  
Author(s):  
Dilip Prasad ◽  
Gavin J. Hendricks
Keyword(s):  
Flow Field ◽  
Secondary Flow ◽  
Numerical Study ◽  
Angle Distribution ◽  
Turbine Stage ◽  
Radial Transport ◽  
Numerical Work ◽  
Flow Angle ◽  
Axial Turbines ◽  
Hot Streak

The flow field in a low-speed turbine stage with a uniform inlet total pressure is studied numerically. A circular hot streak is superposed on the vane inlet flow. In agreement with previous experimental and numerical work, it is observed that while the streak passes through the vane unaltered, significant radial transport occurs in the rotor. Furthermore, despite the unsteady nature of the flow field, the steady theory of Hawthorne (1974) is found to predict the radial transport velocity well. Making use of this theory, it is shown that the secondary vorticity in the rotor may be attributed to the effects of density stratification, the spatial variation of the vane exit flow angle, and the relative eddy. It then follows that the extent of radial transport in the rotor may be influenced by altering the vane exit flow angle distribution. The present study examines one means by which this may be effected, viz., varying the vane twist across the span. It is shown that a “reverse” twist, wherein the flow angle at the vane exit is larger near the tip than it is at midspan, reduces the secondary flow (and consequently, radial transport) in the blade passage. On the other hand, “positive” twist, in which the vane exit flow angle decreases with span, is found to worsen the radial transport in the blade markedly. It is to be noted that varying the vane twist is but one method to obtain the desired exit flow angle; possibilities for altering other aspects of the vane geometry also exist. [S0889-504X(00)00104-5]

Boundary Layer Suction via a Slot in a Transonic Compressor: Numerical Parameter Study and First Experiments

2004 ◽  
Author(s):  
K. Hubrich ◽  
A. Bo¨lcs ◽  
P. Ott
Keyword(s):  
Boundary Layer ◽  
Shock Wave ◽  
Mach Number ◽  
Numerical Study ◽  
Pressure Ratio ◽  
Parameter Study ◽  
Flow Angle ◽  
Boundary Layer Suction ◽  
Transonic Compressor ◽  
Shock Mach Number

In the present paper a numerical and experimental study aiming at the enhancement of the working range of a transonic compressor via boundary layer suction (BLS) is presented. The main objective of the investigation is to study the influence of BLS on the interference between shock wave and boundary layer and to identify the possible benefit of BLS on the compressor working characteristics. An extensive numerical study has been carried out for the DATUM blade and for 2 different suction location configurations for one speed line and varying back-pressure levels, ranging from choked conditions to stall. It was found that the working range of the transonic compressor with a nominal inlet Mach number of 1.2 and a nominal pre-shock Mach number of 1.35 could be increased by sucking 2% of flow on the SS away, in such a way that the maximum pressure ratio and maximum diffusion could both be increased by 10%, when compared to the DATUM case. For smaller pressure ratios with respect to the design pressure ratio, the BLS is located in a supersonic flow region and thus creates additional losses due to a more divergent flow channel, which additionally accelerates the flow and results in a higher pre-shock Mach number creating higher losses. First measurements carried out in LTTs annular cascade, do show reasonable agreement with the computations in terms of inlet Mach number, flow angle, main shock location and stall limit. The most pronounced difference between measurements and computations is the occurrence of a terminal normal channel shock behind a bowed detached shock wave and a separation on the SS of the blade, which were both not predicted by the CFD.

Performance Evaluation of Contra-Rotating Fans Operating Under Different Speed Combinations

2019 ◽  
Author(s):  
Navjot Joshi ◽  
Manas Madasseri Payyappalli ◽  
A. M. Pradeep
Keyword(s):  
Numerical Study ◽  
Pressure Ratio ◽  
Axial Direction ◽  
Flow Coefficient ◽  
Suction Surface ◽  
Flow Angle ◽  
Tip Leakage Vortex ◽  
Stall Inception ◽  
Tip Leakage ◽  
Flow Mechanisms

Abstract One of the advantages of a contra-rotating fan is its possibility to operate both the rotors at different speeds. Owing to this possibility, the performance of a contra-rotating fan can be controlled by operating it at different speed combinations. A numerical study of a low aspect ratio contra-rotating fan in low subsonic regime is carried out under various speed combinations of the rotors. Both steady state and Nonlinear Harmonic (NLH) simulations are performed to identify the important flow mechanisms in the contra-rotating fan. The results show that the diffusion factor of rotor-2 is significantly high towards the hub region which implies that large separations are likely to occur at the hub. The wake of rotor-1 is observed to impinge on the suction surface of rotor-2. Rotor-2 generates a strong suction effect at high rotational speeds and thereby delays the stall inception in the whole stage and shows an improvement in the stage pressure ratio. The upstream effect strongly influences the performance of rotor-1. When rotor-2 rotates at higher rotational speed, due to the suction effect, the flow angle at the exit of rotor-1 decreases which allows the fan to operate at lower flow coefficient. When the suction effect is very strong, it pulls the tip leakage vortex of rotor-1 towards the axial direction. Due to the suction effect, the location of the appearance of tip-leakage vortex moves further downstream. The tip-leakage vortex makes a higher angle with the blade chord at near stall conditions for speed combination Nd – 1.5Nd in contrast to a lower angle for speed combination Nd – 0.5Nd. In summary, the paper describes the performance changes, flow physics and the rotor-rotor interaction mechanisms for different speed combinations of a contra-rotating fan.

An Experimental Study of Compressible Flow Through Convergent-Conical Nozzles, Including a Comparison With Theoretical Results

1972 ◽  
Vol 94 (4) ◽  
pp. 926-930 ◽  
Author(s):  
R. L. Thornock ◽  
E. F. Brown
Keyword(s):  
Flow Field ◽  
Pressure Ratio ◽  
Internal Flow ◽  
Thrust Coefficient ◽  
Local Flow ◽  
Flow Angle ◽  
Propulsive Performance ◽  
Nozzle Shape ◽  
Flow Through ◽  
Theoretical Results

Despite the widespread use of convergent-conical nozzles as propulsion nozzles in turbojet aircraft, little attention has been given to the effect of nozzle shape on their propulsive performance. This paper presents the results of an experimental investigation in which the effect of nozzle angle on the internal characteristics of the flow field and on the propulsive performance of convergent conical nozzles was investigated. In addition, a theoretical solution is described which was developed as a part of this investigation. Fifteen, twenty-five, and forty-degree nozzles were tested at pressure ratios from 1.4 to 7.0. Measurements were made of the nozzle discharge coefficient, thrust coefficient, local flow angle, and wall static pressure. The properties of the internal flow field were seen to be affected by the nozzle angle and at pressure ratios less than the choked pressure ratio by the pressure ratio as well. The results of the theoretical analysis substantiate this behavior and are in reasonable agreement with the experimental data.

Effects of Labyrinth Seal Variation on Multistage Axial Turbine Flow

2003 ◽  
Author(s):  
J. Schlienger ◽  
A. Pfau ◽  
A. I. Kalfas ◽  
R. S. Abhari
Keyword(s):  
Secondary Flow ◽  
Suction Side ◽  
Labyrinth Seal ◽  
Flow Profile ◽  
Cavity Volume ◽  
Turbine Stage ◽  
Flow Angle ◽  
Seal Design ◽  
Turbine Efficiency ◽  
Passage Vortex

The need to increase overall turbine efficiency is always a driving force for redesigning a turbine stage. In particular, the labyrinth leakage flows in the endwall regions contribute to an increase of the overall loss generation. In order to asses this mechanism, a detailed study of the effects of labyrinth seal geometry variation on the blade performance is presented. Two different shroud seal geometries have been experimentally investigated in a two stage low speed turbine facility. The seal geometries differ in the size and shape of the re-entry cavity. The baseline seal is designed with a large rectangular re-entry cavity volume in order to dissipate the kinetic energy of the accelerated leakage flow after the seal gap. The re-entry cavity volume of the alternative seal design is reduced in size and a spline shaped contour is added to the endwall using annular inserts. This modification alters the gas path of the leakage jet and changes the incidence angles on the downstream blade rows. The measurements are performed with state of the art pneumatic and fast response pressure probes at various planes within the turbine stage. It is found that the inserts improved the flow profile uniformity at the endwalls. The measurements within the stator passage reveal the origin of the tip passage vortex formation at the blade suction side, already at the inlet to the stator passage. This result does not conform to the classical secondary flow theory, which suggests that the passage vortex migrates from the pressure to the suction side within the stator passage. The origin and formation of the secondary flow passage vortices at rotor hub and stator tip is described in a flow schematic. The generation of streamwise and tangential vorticity at the interaction area of leakage and main flow field also is studied and discussed. The measured overall polytropic turbine efficiency for the second seal configuration, relative to the baseline case, is reduced by 0.3%. The change in the re-entry flow angle of the leakage gas path reduces the negative incidence angle on the rotor hub and increases it at the stator tip leading edge. The secondary flow and mixing loss is reduced at the hub and increased at the tip in the second test case with the smaller cavity volume. Hence, the combination of small clearances and inserts in the re-entry cavities shows no beneficial effect on the overall turbine efficiency.

Time-Resolved Numerical Study of Axial Gap Effects on Labyrinth-Seal Leakage and Secondary Flow in a LP Turbine

2013 ◽  
Author(s):  
Marc H.-O. Biester ◽  
Florian Wiegmann ◽  
Yavuz Guendogdu ◽  
Joerg R. Seume
Keyword(s):  
Secondary Flow ◽  
Numerical Study ◽  
Flow Direction ◽  
Labyrinth Seal ◽  
Flow Structures ◽  
Leakage Flow ◽  
Labyrinth Seals ◽  
Time Resolved ◽  
Flow Angle ◽  
Blade Row

One of the most promising ways to improve the efficiency of modern turbomachinery is the reduction of secondary flow-structures and associated losses. A widely spread approach is the usage of shrouded airfoils in combination with labyrinth-seals. The disadvantage of this arrangement is a small but inevitable labyrinth-leakage flow that tends to increase the secondary-flow structures. The present work investigates how the axial gap of the blade rows and the corresponding shift of the labyrinth’s inlet and outlet influences leakage related effects on the flow-field and loss-generation. In order to capture the inter-blade and leakage interaction properly, time-resolved RANS computations of a 1 1/2 stage low pressure turbine have been performed. Besides accounting for labyrinth seals, fillets have been modeled. The axial gap is varied from 20% to 80% axial chord length. Clocking-effects induced by the axial gap variation are compensated. The leakage flow nearly retains the flow direction of the flow entering the blade row. In case of the largest axial gap, mixing causes the flow-angle of the leakage to tend towards that of the main-flow, thus reducing the incidence on the downstream blade row. Therefore, the turning of the low-momentum flow is increased compared to a small axial gap. This leads to a higher loading in the affected region and an increased passage vortex can be observed. By comparing the entropy generation of computations with and without labyrinth seals, the regions where leakage-related losses occur are identified and the relevant mechanisms are distinguished.

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