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.

Numerical Characterization of Hot-Gas Ingestion Through Turbine Rim Seals

2016 ◽  
Vol 139 (3) ◽  
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, computational fluid dynamics (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 displays a distinct kink. It was found that the “kink phenomenon” can be ascribed to an overestimation of the egress spoiling effects due to turbulence modeling 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.

scholarly journals Experimental and Numerical Study on Energy Piles with Phase Change Materials

Energies ◽  
2020 ◽  
Vol 13 (18) ◽  
pp. 4699 ◽  
Author(s):  
M. M. Mousa ◽  
A. M. Bayomy ◽  
M. Z. Saghir
Keyword(s):  
Phase Change ◽  
Heat Pump ◽  
Flow Rate ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Coefficient Of Performance ◽  
Working Fluid ◽  
Numerical Predictions ◽  
Energy Piles ◽  
Discharging Capacity

Phase change materials (PCM) utilization in energy storage systems represents a point of interest and attraction for the researchers to reduce greenhouse gas emissions. PCM have been used widely on the interior or exterior walls of the building application to optimize the energy consumption during heating and cooling periods. Meanwhile, ground source heat pump (GSHP) gained its popularity because of the high coefficient of performance (COP) and low running cost of the system. However, GSHP system requires a stand-by heat pump during peak loads. This study will present a new concept of energy piles that used PCM in the form of enclosed tube containers. A lab-scaled foundation pile was developed to examine the performance of the present energy pile, where three layers of insulation replaced the underground soil to focus on the effect of PCM. The investigation was conducted experimentally and numerically on two identical piles with and without PCM. Moreover, a flow rate parametric study was conducted to study the effect of the working fluid flow rate on the amount of energy stored and released at each model. Finally, a comprehensive Computational fluid dynamic (CFD) model was developed and compared with the experimental results. There was a good agreement between the experimental measurements and the numerical predictions. The results revealed that the presence of PCM inside the piles increased not only the charging and discharging capacity but also the storage efficiency of the piles. It was found that PCM enhances the thermal response of the concrete during cooling and heating processes. Although increasing the flow rate increased charging and discharging capacity, the percentage of energy stored/released was insignificant compared to the flow rate increasing percentage.

Rotating Stall Observations in a High Speed Compressor—Part II: Numerical Study

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
J. Dodds ◽  
M. Vahdati
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Numerical Predictions ◽  
Stage 1 ◽  
Variable Stator

In this two-part paper the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (Part I) and numerically (Part II). The experimental observations reported in Part I are now explored through the use of 3D unsteady Reynolds-averaged Navier–Stokes (RANS) simulation. The objective is to both validate the computational model and, where possible, explore some physical aspects of the phenomena. Unsteady simulations are presented, performed at a fixed speed with the three rows of variable stator vanes adjusted to deliberately mismatch the front stages and provoke stall. Two families of rotating stall are identified by the model, consistent with experimental observations from Part I. The first family of rotating stall originates from hub corner separations developing on the stage 1 stator vanes. These gradually coalesce into a multicell rotating stall pattern confined to the hub region of the stator and its downstream rotor. The second family originates from regions of blockage associated with tip clearance flow over the stage 1 rotor blade. These also coalesce into a multicell rotating stall pattern of shorter length scale confined to the leading edge tip region. Some features of each of these two patterns are then explored as the variable stator vanes (VSVs) are mismatched further, pushing each region deeper into stall. The numerical predictions show a credible match with the experimental findings of Part I. This suggests that a RANS modeling approach is sufficient to capture some important aspects of part span rotating stall behavior.

scholarly journals Higher-Order Mode Electromagnetic Analysis of a Material Sample between Two Flanged Coaxial Probes for Broadband Modelling of Dielectric Measurement Setups

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Raúl V. Haro-Báez ◽  
Juan Córcoles ◽  
Jorge A. Ruiz-Cruz ◽  
José R. Montejo-Garai ◽  
Jesús M. Rebollar
Keyword(s):  
Numerical Study ◽  
Higher Order ◽  
Dielectric Measurement ◽  
Analysis Method ◽  
Higher Order Modes ◽  
Wall Boundary Conditions ◽  
Wide Range ◽  
Coaxial Probes ◽  
Material Sample

The characterization of the dielectric properties of a material requires a measurement technique and its associated analysis method. In this work, the configuration involving two coaxial probes with a material for dielectric measurement between them is analyzed with a mode-matching approach. To that effect, two models with different complexity and particularities are proposed. It will be shown how convergence is sped up for accurate results by using a proper choice of higher-order modes along with a combination of perfect electric wall and perfect magnetic wall boundary conditions. It will also be shown how the frequency response is affected by the flange mounting size, which can be, rigorously and efficiently, taken into account with the same type of approach. This numerical study is validated through a wide range of simulations with reference values from another method, showing how the proposed approaches can be used for the broadband characterization of this well-known, but with a recent renewed interest from the research community, dielectric measurement setup.

Experimental Measurements of Ingestion Through Turbine Rim Seals—Part II: Rotationally Induced Ingress

2012 ◽  
Vol 135 (2) ◽  
Author(s):  
Carl M. Sangan ◽  
Oliver J. Pountney ◽  
Kunyuan Zhou ◽  
J. Michael Owen ◽  
Mike Wilson ◽  
...  
Keyword(s):  
Experimental Results ◽  
Radial Clearance ◽  
Rotating Fluid ◽  
Flow Rates ◽  
Hot Gas ◽  
Wide Range ◽  
The Common ◽  
Axial Clearance ◽  
Better Than ◽  
Good Agreement

Part I of this two-part paper presented experimental results for externally-induced (EI) ingress, where the ingestion of hot gas through the rim seal into the wheel-space of a gas turbine is controlled by the circumferential variation of pressure in the external annulus. In Part II, experimental results are presented for rotationally-induced (RI) ingress, where the ingestion is controlled by the pressure generated by the rotating fluid in the wheel-space. Although EI ingress is the common form of ingestion through turbine rim seals, RI ingress or combined ingress (where EI and RI ingress are both significant) is particularly important for double seals, where the pressure asymmetries are attenuated in the annular space between the inner and outer seals. In this paper, the sealing effectiveness was determined from concentration measurements, and the variation of effectiveness with sealing flow rate was compared with theoretical curves for RI ingress obtained from an orifice model. Using a nondimensional sealing parameter Φ0 the data could be collapsed onto a single curve, and the theoretical variation of effectiveness with Φ0 was in very good agreement with the data for a wide range of flow rates and rotational speeds. It was shown that the sealing flow required to prevent RI ingress was much less than that needed for EI ingress, and it was also shown that the effectiveness of a radial-clearance seal is significantly better than that for an axial-clearance seal for both EI and RI ingress.

Improvement of the THD Performance of a Misaligned Plain Journal Bearing

2003 ◽  
Vol 125 (2) ◽  
pp. 334-342 ◽  
Author(s):  
J. Bouyer ◽  
M. Fillon
Keyword(s):  
Film Thickness ◽  
Flow Rate ◽  
Journal Bearing ◽  
Numerical Study ◽  
Axial Flow ◽  
Hydrodynamic Pressure ◽  
Operating Conditions ◽  
Local Defect ◽  
Minimum Film Thickness ◽  
Global Defect

This numerical study deals with the improvement of the thermohydrodynamic performance of a 100 mm plain journal bearing submitted to a constant misalignment torque under steady-state conditions. The performance of the misaligned journal bearing is improved by adding either a local or a global defect to the bearing geometry. The influence on bearing performance of the local defect, situated in the zone of minimum film thickness, is analyzed by using various widths and lengths of defect. A global defect, which is conical in shape and is located at one end of the bearing, is also studied under varying direction and magnitude of misalignment torque. Our main focus was on hydrodynamic pressure, temperature distributions at the film/bush interface, oil flow rate, power losses and film thickness. The defects significantly improved the performance of the bearing. The minimum film thickness increased by more than 60 percent and the temperature decreased, whilst the axial flow rate was barely affected. Thus, the defects can be an effective solution for misaligned bearings when they are submitted to extreme operating conditions.

Swelling characterization of photo-cross-linked gelatin methacrylate spherical microgels for bioencapsulation

e-Polymers ◽  
2014 ◽  
Vol 14 (3) ◽  
pp. 161-168 ◽  
Author(s):  
Jinmu Jung ◽  
Jonghyun Oh
Keyword(s):  
Flow Rate ◽  
Rate Ratio ◽  
Axial Flow ◽  
Microfluidic System ◽  
Low Flow ◽  
Flow Rate Ratio ◽  
Swelling Characteristics ◽  
Irradiation Apparatus ◽  
Proportional Relationship

AbstractThe swelling behavior of biocompatible and biodegradable polymers is important for the delivery and release of cells and drugs in biomedical applications. This study reported the swelling characteristics of photo-cross-linked gelatin methacrylate (GelMa) spherical microgels. Spherical microgels were generated in a microfluidic system consisting of a co-axial flow-focusing device for microdroplet generation and an ultraviolet (UV) irradiation apparatus for polymerization. At a low flow rate ratio (<0.14), the 9 wt.% GelMa spherical microgels were smaller than the 6 wt.% ones. In contrast, at a high flow rate ratio (>0.14), the results were reversed. Overall, a proportional relationship was observed between the flow rate ratio and the droplet size. The increased GelMa concentration improved the mechanical properties and increased the swelling ratios. The possibility of bioencapsulation was demonstrated, with good viability of 3T3 cells encapsulated in the spherical microgels.

Rotating Stall Observations in a High Speed Compressor: Part 2 — Numerical Study

2014 ◽  
Author(s):  
J. Dodds ◽  
M. Vahdati
Keyword(s):  
High Speed ◽  
Numerical Study ◽  
Axial Flow ◽  
Leading Edge ◽  
Rotating Stall ◽  
Tip Clearance ◽  
Tip Clearance Flow ◽  
Numerical Predictions ◽  
Stage 1 ◽  
Variable Stator

In this two part paper the phenomenon of part span rotating stall is studied. The objective is to improve understanding of the physics by which stable and persistent rotating stall occurs within high speed axial flow compressors. This phenomenon is studied both experimentally (part 1) and numerically (part 2). The experimental observations reported in Part 1 are now explored through the use of 3D unsteady RANS simulation. The objective is to both to validate the computational model and, where possible, explore some physical aspects of the phenomena. Unsteady simulations are presented, performed at a fixed speed with the three rows of variable stator stagger vanes adjusted to deliberately mismatch the front stages and provoke stall. Two families of rotating stall are identified by the model, consistent with experimental observations from Part 1. The first family of rotating stall originates from hub corner separations developing on the stage 1 stator vanes. These gradually coalesce into a multi-cell rotating stall pattern confined to the hub region of the stator and its downstream rotor. The second family originates from regions of blockage associated with tip clearance flow over the stage 1 rotor blade. These also coalesce into a multi-cell rotating stall pattern of shorter length scale confined to the leading edge tip region. Some features of each of these two patterns are then explored as the variable stator vanes are mismatched further, pushing each region deeper into stall. The numerical predictions show a credible match with the experimental findings of Part 1. This suggests that a RANS modelling approach is sufficient to capture some important aspects of part span rotating stall behavior.

Experimental Measurements of Ingestion Through Turbine Rim Seals: Part 2—Rotationally-Induced Ingress

2011 ◽  
Author(s):  
Carl M. Sangan ◽  
Kunyuan Zhou ◽  
J. Michael Owen ◽  
Oliver J. Pountney ◽  
Mike Wilson ◽  
...  
Keyword(s):  
Experimental Results ◽  
Radial Clearance ◽  
Rotating Fluid ◽  
Flow Rates ◽  
Hot Gas ◽  
Wide Range ◽  
The Common ◽  
Axial Clearance ◽  
Better Than ◽  
Good Agreement

Part 1 of this two-part paper presented experimental results for externally-induced (EI) ingress, where the ingestion of hot gas through the rim seal into the wheel-space of a gas turbine is controlled by the circumferential variation of pressure in the external annulus. In Part 2, experimental results are presented for rotationally-induced (RI) ingress, where the ingestion is controlled by the pressure generated by the rotating fluid in the wheel-space. Although EI ingress is the common form of ingestion through turbine rim seals, RI ingress or combined ingress (where EI and RI ingress are both significant) is particularly important for double seals, where the pressure asymmetries are attenuated in the annular space between the inner and outer seals. In this paper, the sealing effectiveness was determined from concentration measurements, and the variation of effectiveness with sealing flow rate was compared with theoretical curves for RI ingress obtained from an orifice model. Using a nondimensional sealing parameter, Φ0, the data could be collapsed onto a single curve, and the theoretical variation of effectiveness with Φ0 was in very good agreement with the data for a wide range of flow rates and rotational speeds. It was shown that the sealing flow required to prevent RI ingress was much less than that needed for EI ingress, and it was also shown that the effectiveness of a radial-clearance seal is significantly better than that for an axial-clearance seal for both EI and RI ingress.

Numerical and Experimental Investigations on Preload Effects in Air Foil Journal Bearings

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Marcel Mahner ◽  
Pu Li ◽  
Andreas Lehn ◽  
Bernhard Schweizer
Keyword(s):  
Friction Torque ◽  
Fluid Film ◽  
Radial Clearance ◽  
Experimental Investigations ◽  
Hysteresis Curves ◽  
Numerical Predictions ◽  
Wide Range ◽  
Reaction Forces ◽  
Bearing Stiffness ◽  
Definition Of

A detailed elastogasdynamic model of a preloaded three-pad air foil journal bearing is presented. Bump and top foil deflections are herein calculated with a nonlinear beamshell theory according to Reissner. The two-dimensional pressure distribution in each bearing pad is described by the Reynolds equation for compressible fluids. The assembly preload is calculated by simulating the assembly process of top foil, bump foil, and shaft. Most advantageously, there is no need for the definition of an initial radial clearance in the presented model. With this model, the influence of the assembly preload on the static bearing hysteresis as well as on the aerodynamic bearing performance is investigated. For the purpose of model validation, the predicted hysteresis curves are compared with measured curves. The numerically predicted and the measured hysteresis curves show a good agreement. The numerical predictions exhibit that the assembly preload increases the elastic foil structural stiffness (in particular for moderate shaft displacements) and the bearing damping. It is observed that the effect of the fluid film on the overall bearing stiffness depends on the assembly preload: For lightly preloaded bearings, the fluid film affects the overall bearing stiffness considerably, while for heavily preloaded bearings the effect is rather small for a wide range of reaction forces. Furthermore, it is shown that the assembly preload increases the friction torque significantly.

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