Study of Airflow Features Through Step Seals in the Presence of Dis-Engagement Due to Axial Movement

2004 ◽  
Author(s):  
Yi Wang ◽  
Colin Young ◽  
Guy Snowsill ◽  
Tim Scanlon
Keyword(s):  
Engine Performance ◽  
Turbulence Models ◽  
Labyrinth Seal ◽  
Radial Clearance ◽  
Numerical Predictions ◽  
Axial Movement ◽  
Flow Through ◽  
Aero Engines ◽  
Cooling Air ◽  
Step Distance

Step seals are a particular design variant of the basic labyrinth seal configuration which is widely used to limit leakage from the space between rotating and stationary components. Seals of this type are employed in aero-engines to prevent oil leakage from bearing chambers and to control the flow of secondary cooling air and it follows that the design of step seals is of great importance in the achievement of optimal aero-engine performance. In this paper, numerical modelling of the flow through stepped seals has been carried out in order to gain an insight into the behaviour of the flow in the presence of dis-engagement. In the context of this work, dis-engagement would be deemed to have occurred when to the axial movement between the rotor and stator results in a clear line of sight through the step seal. The flows through the seals were calculated using the commercial CFD package Fluent and the numerical predictions were validated by comparison with test data previously presented in the literature. The model predictions were initially obtained using a number of alternative two-equation turbulence models and the RNG k-ε turbulence model with the non-equilibrium wall function was found to be in closest agreement with the measured data. It was noted that for a given radial clearance the step seal’s flow characteristic is largely dictated by the fin tip to step distance. It was found that there are two distinct stages of step seal dis-engagement. The first stage of dis-engagement occurs when the seal fin is displaced axially from its nominal position, but the seal fin still remains within the axial extent of the corresponding seal step. In this case the flow through the seal only deviates slightly from that of the fully engaged seal. The second stage occurs when the fin is subjected to a larger axial displacement and as a result assumes a position beyond the corresponding seal step. This results in a much larger seal clearance and the flow through the seal increases significantly with the fin tip to step distance in the case.

Influence of a Honeycomb Facing on the Flow Through a Stepped Labyrinth Seal

2000 ◽  
Vol 124 (1) ◽  
pp. 140-146 ◽  
Author(s):  
V. Schramm ◽  
K. Willenborg ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Theoretical Work ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Experimental Investigations ◽  
Labyrinth Seals ◽  
Numerical Predictions ◽  
Flow Through ◽  
Aero Engines

This paper reports numerical predictions and measurements of the flow field in a stepped labyrinth seal. The theoretical work and the experimental investigations were successfully combined to gain a comprehensive understanding of the flow patterns existing in such elements. In order to identify the influence of the honeycomb structure, a smooth stator as well as a seal configuration with a honeycomb facing mounted on the stator wall were investigated. The seal geometry is representative of typical three-step labyrinth seals of modern aero engines. The flow field was predicted using a commercial finite volume code with the standard k-ε turbulence model. The computational grid includes the basic seal geometry as well as the three-dimensional honeycomb structures.

Influence of a Honeycomb Facing on the Flow Through a Stepped Labyrinth Seal

2000 ◽  
Author(s):  
V. Schramm ◽  
K. Willenborg ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Flow Field ◽  
Three Dimensional ◽  
Theoretical Work ◽  
Labyrinth Seal ◽  
Honeycomb Structure ◽  
Experimental Investigations ◽  
Labyrinth Seals ◽  
Numerical Predictions ◽  
Flow Through ◽  
Aero Engines

This paper reports numerical predictions and measurements of the flow field in a stepped labyrinth seal. The theoretical work and the experimental investigations were successfully combined to gain a comprehensive understanding of the flow patterns existing in such elements. In order to identify the influence of the honeycomb structure, a smooth stator as well as a seal configuration with a honeycomb facing mounted on the stator wall were investigated. The seal geometry is representative of typical three-step labyrinth seals of modern aero engines. The flow field was predicted using a commercial finite-volume code with the standard-k-ε-turbulence model. The computational grid includes the basic seal geometry as well as the three-dimensional honeycomb structures.

Experimental Analysis of Abradable Labyrinth Seal Leakage With Simulated Groove: Part 2

2013 ◽  
Author(s):  
Luca Innocenti ◽  
Stefania Ricupero ◽  
Rajeev Kumar Pandit ◽  
Nuo Sheng
Keyword(s):  
Pressure Ratio ◽  
Test Sample ◽  
Labyrinth Seal ◽  
Axial Position ◽  
Radial Clearance ◽  
Pressure Drops ◽  
Flow Physics ◽  
Main Requirement ◽  
Numerical Predictions ◽  
Mass Leakage

In the secondary flow path of centrifugal compressors, abradable seals are in high demand when higher efficiency is the main requirement. This is because abradable seals can maintain very tight clearances between static and rotating components compared to other sealing technology. However, due to the rubbing of the teeth into the abradable material, some grooves can form. The flow physics and mass leakage of abradable seals are strongly dependent on the presence of these grooves and their shape. For cases where no grooves are present, seal leakage is mainly a function of inlet pressure, pressure ratio across the seal and tooth radial clearance. Once grooves are formed, the flow physics and seal leakage also are a function of groove dimensions, tooth clearance and tooth axial position inside the groove. The scope of the present paper is to describe the experimental campaign that has been performed to validate the numerical analysis of part 1 of the paper [1]. The experimental test matrix investigates the groove and teeth positioning effects on seal leakages. To achieve higher accuracy, the key geometric parameters, such as radial and axial gaps, were controlled in the test sample during the tests. For cases where grooves are present the experimental measurements reveal that flow field strongly depends on groove dimensions, tooth radial clearance and tooth axial position. The authors, finally, found generally a good agreement between numerical predictions and measured data, both in terms of leakage and pressure drops across the teeth.

scholarly journals Relative Performance Comparison Between Baseline Labyrinth and Dual Brush Compressor Discharge Seals in a T-700 Engine Test

1994 ◽  
Author(s):  
Robert C. Hendricks ◽  
Thomas A. Griffin ◽  
Teresa R. Kline ◽  
Kristine R. Csavina ◽  
Arvind Pancholi ◽  
...  
Keyword(s):  
High Pressure ◽  
Engine Performance ◽  
Labyrinth Seal ◽  
Performance Comparison ◽  
Engine Test ◽  
Engine Operation ◽  
Pressure Drops ◽  
Airflow Distribution ◽  
Brush Seal ◽  
Cooling Air

In separate series of YT-700 engine tests, direct comparisons were made between the forward-facing labyrinth and dual-brush compressor discharge seals. Compressor speeds to 43 000 rpm, surface speeds to 160 m/s (530 ft/s), pressures to 1 MPa (145 psi), and temperatures to 680 K (765°F) characterized these tests. The wear estimate for 46 hr of engine operations was less than 0.025 mm (0.001 in.) of the Haynes 25 alloy bristles running against a chromium-carbide-coated rub runner. The pressure drops were higher for the dual-brush seal than for the forward-facing labyrinth seal and leakage was lower-with the labyrinth seal leakage being 2½ times greater-implying better seal characteristics, better secondary airflow distribution, and better engine performance (3 percent at high pressure to 5 percent at lower pressure) for the brush seal. (However, as brush seals wear down (after 500 to 1000 hr of engine operation), their leakage rates will increase.) Modification of the secondary flow path requires that changes in cooling air and engine dynamics be accounted for.

scholarly journals SHOCK INDUCED SEPARATING FLOWS IN SCRAMJET INTAKES

2012 ◽  
Vol 19 ◽  
pp. 73-82
Author(s):  
YUFENG YAO ◽  
DANIEL RINCON ◽  
YAO ZHENG
Keyword(s):  
Flow Separation ◽  
Engine Performance ◽  
Turbulence Models ◽  
Lower Surface ◽  
Wall Pressure ◽  
Oblique Shock Wave ◽  
Mesh Topology ◽  
Numerical Predictions ◽  
Compression Ramps ◽  
Separating Flows

Shock induced separating flows in a scramjet intake has been studied by using a computational fluid dynamics approach. A configuration of scramjet intake geometry consisting of two exterior compression ramps, followed by a subsequent inlet and interior isolator/diffuser assembly, is chosen. The flow conditions are incoming Mach 7 with free-stream static temperature of 46.3K and wall temperature of 300K, respectively. Consequently, oblique shock wave will be formed and its interaction with viscous boundary layers will lead to flow separation that is responsible for the loss of mass flow, total pressure and several other effects. Simulations confirmed that it is necessary to include the cowl wedge in order to predict wall pressure distributions along the lower surface of the intake walls. It is also shown that mesh topology has some influences on prediction results with structured mesh gives better predictions than that of hybrid mesh. A total of eight turbulence models have been applied and results have shown reasonably good agreement with the experimental measurements and other numerical predictions, with small differences occur in localized regions particularly after shock reflection inside the intake channel. Not surprisingly, shock induced flow separation occurs and it correlates well with higher wall pressure and heating downstream. This phenomenon will have significant impact on deteriorating boundary layer property and consequently the engine performance.

On LES Methods Applied to Seal Geometries

2012 ◽  
Author(s):  
James Tyacke ◽  
Richard Jefferson-Loveday ◽  
Paul Tucker
Keyword(s):  
Maximum Error ◽  
Labyrinth Seal ◽  
Navier Stokes ◽  
Final Solution ◽  
Complex Flow ◽  
Eddy Simulation ◽  
Wide Range ◽  
Large Eddy ◽  
Rans Models ◽  
Flow Through

Nine Large Eddy Simulation (LES) methods are used to simulate flow through two labyrinth seal geometries and are compared with a wide range of Reynolds-Averaged Navier-Stokes (RANS) solutions. These involve one-equation, two-equation and Reynolds Stress RANS models. Also applied are linear and nonlinear pure LES models, hybrid RANS-Numerical-LES (RANS-NLES) and Numerical-LES (NLES). RANS is found to have a maximum error and a scatter of 20%. A similar level of scatter is also found among the same turbulence model implemented in different codes. In a design context, this makes RANS unusable as a final solution. Results show that LES and RANS-NLES is capable of accurately predicting flow behaviour of two seals with a scatter of less than 5%. The complex flow physics gives rise to both laminar and turbulent zones making most LES models inappropriate. Nonetheless, this is found to have minimal tangible results impact. In accord with experimental observations, the ability of LES to find multiple solutions due to solution non-uniqueness is also observed.

Numerical Prediction of Flow in a Nuclear Fuel Bundle With Various Turbulence Models

2002 ◽  
Author(s):  
Wang Kee In ◽  
Dong Seok Oh ◽  
Tae Hyun Chun
Keyword(s):  
Turbulent Flow ◽  
Nuclear Fuel ◽  
Turbulence Models ◽  
Convective Transport ◽  
Stress Model ◽  
Convergence Criteria ◽  
Mean Flow ◽  
Numerical Predictions ◽  
Viscosity Models ◽  
Fuel Bundle

The numerical predictions using the standard and RNG k–ε eddy viscosity models, differential stress model (DSM) and algebraic stress model (ASM) are examined for the turbulent flow in a nuclear fuel bundle with the mixing vane. The hybrid (first-order) and curvature-compensated convective transport (CCCT) schemes were used to examine the effect of the differencing scheme for the convection term. The CCCT scheme was found to more accurately predict the characteristics of turbulent flow in the fuel bundle. There is a negligible difference in the prediction performance between the standard and RNG k-ε models. The calculation using ASM failed in meeting the convergence criteria. DSM appeared to more accurately predict the mean flow velocities as well as the turbulence parameters.

Numerical Characterization of Hot Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Author(s):  
Riccardo Da Soghe ◽  
Cosimo Bianchini ◽  
Carl M. Sangan ◽  
James A. Scobie ◽  
Gary D. Lock
Keyword(s):  
Flow Rate ◽  
Numerical Study ◽  
Axial Flow ◽  
Radial Clearance ◽  
Buffering Effect ◽  
Hot Gas ◽  
Numerical Predictions ◽  
Wide Range ◽  
Thermal Buffering

This paper deals with a numerical study aimed at the characterization of hot gas ingestion through turbine rim seals. The numerical campaign focused on an experimental facility which models ingress through the rim seal into the upstream wheel-space of an axial-turbine stage. Single-clearance arrangements were considered in the form of axial- and radial-seal gap configurations. With the radial-seal clearance configuration, CFD steady-state solutions were able to predict the system sealing effectiveness over a wide range of coolant mass flow rates reasonably well. The greater insight of flow field provided by the computations illustrates the thermal buffering effect when ingress occurs: for a given sealing flow rate, the effectiveness on the rotor was significantly higher than that on the stator due to the axial flow of hot gases from stator to rotor caused by pumping effects. The predicted effectiveness on the rotor was compared with a theoretical model for the thermal buffering effect showing good agreement. When the axial-seal clearance arrangement is considered, the agreement between CFD and experiments worsens; the variation of sealing effectiveness with coolant flow rate calculated by means of the simulations display a distinct kink. It was found that the “kink phenomenon” can be ascribed to an over-estimation of the egress spoiling effects due to turbulence modelling limitations. Despite some weaknesses in the numerical predictions, the paper shows that CFD can be used to characterize the sealing performance of axial- and radial-clearance turbine rim seals.

Influence of Marine Propeller Geometry on Turbulence Model Selection for CFD Simulations

2021 ◽  
Vol 55 (2) ◽  
pp. 150-164
Author(s):  
Mohamed R. Shouman ◽  
Mohamed M. Helal
Keyword(s):  
Turbulent Flows ◽  
Small Diameter ◽  
Turbulence Models ◽  
Dynamics Simulation ◽  
Geometrical Parameters ◽  
Test Case ◽  
Transition Model ◽  
Transient Flows ◽  
Marine Propellers ◽  
Numerical Predictions

Abstract One of the big challenges yet to be addressed in the numerical simulation of wetted flow over marine propellers is the influence of propellers' geometry on the selection of turbulence models. Since the Reynolds number is a function of the geometrical parameters of the blades, the flow type is controlled by these parameters. The majority of previous studies employed turbulence models that are only appropriate for fully turbulent flows, and consequently, they mostly caused high discrepancy between numerical predictions and corresponding experimental measurements specifically at geometrical parameters generating laminar and transient flows. The present article proposes a complete procedure of computational fluid dynamics simulation for wetted flows over marine propellers using ANSYS FLUENT 16 and employing both transition-sensitive and fully turbulent models for comparison. The K-Kl-ω transition model and the fully turbulent standard K-ε model are suggested for this purpose. The investigation is carried out for two different propellers in geometrical features: the INSEAN E779a model and the Potsdam Propeller Test Case (PPTC) model. The results demonstrate the effectiveness of the K-Kl-ω transition model for the INSEAN E779a propeller rather than the PPTC propeller. This can be interpreted as the narrow-bladed and small-diameter propellers have more likely laminar and transient flows over its blades.

Leakage flow analysis in the gas turbine shroud gap

2019 ◽  
Vol 91 (8) ◽  
pp. 1077-1085 ◽  
Author(s):  
Filip Wasilczuk ◽  
Pawel Flaszynski ◽  
Piotr Kaczynski ◽  
Ryszard Szwaba ◽  
Piotr Doerffer ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Gas Turbine ◽  
Mass Flow ◽  
Labyrinth Seal ◽  
Leakage Flow ◽  
Original Design ◽  
Reference Case ◽  
Content Type ◽  
Flow Through ◽  
The Impact

Purpose The purpose of the study is to measure the mass flow in the flow through the labyrinth seal of the gas turbine and compare it to the results of numerical simulation. Moreover the capability of two turbulence models to reflect the phenomenon will be assessed. The studied case will later be used as a reference case for the new, original design of flow control method to limit the leakage flow through the labyrinth seal. Design/methodology/approach Experimental measurements were conducted, measuring the mass flow and the pressure in the model of the labyrinth seal. It was compared to the results of numerical simulation performed in ANSYS/Fluent commercial code for the same geometry. Findings The precise machining of parts was identified as crucial for obtaining correct results in the experiment. The model characteristics were documented, allowing for its future use as the reference case for testing the new labyrinth seal geometry. Experimentally validated numerical model of the flow in the labyrinth seal was developed. Research limitations/implications The research studies the basic case, future research on the case with a new labyrinth seal geometry is planned. Research is conducted on simplified case without rotation and the impact of the turbine main channel. Practical implications Importance of machining accuracy up to 0.01 mm was found to be important for measuring leakage in small gaps and decision making on the optimal configuration selection. Originality/value The research is an important step in the development of original modification of the labyrinth seal, resulting in leakage reduction, by serving as a reference case.

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