bluuebunny/crossref_metadata_2025_split huggingface dataset:
Low Pressure Steam Turbine Exhaust Flow: Part 2 — Investigation of the Condenser Neck Flow Field and 1D Modelling
Authors: Telschow Dirk , Stein Peter , Wolf Hartwig , Sgambati Alessandro 
Published: September 2016

Since many years the diffuser and exhaust of low pressure (LP) turbines are in focus of turbine development and accordingly broadly discussed within the scientific community. The pressure recovery gained within the diffuser significantly contributes to the turbine performance and therefore care is taken in flow investigation as well as optimization within this part of the turbine. However, on a plant level the component following the LP turbine is the condenser, which is connected by the condenser neck. Typically the condenser neck is not designed to provide additional enthalpy recovery. For plant design reasons, often numerous built-ins like stiffening struts, extraction pipes, steam dump devices and others are placed into the neck. Here it is vital to keep the pressure losses low, in order not to deteriorate performance, previously gained within the diffuser. Each mbar of total pressure loss in a condenser can reduce the plant power output up to 0.1%.
As discussed in the first publication (Part 1), 3D CFD enables a deep insight into the flow field, which is costly with respect to computational time and resources. But there are phases during project execution, when geometry and/or boundary conditions are not fixed and quick estimation of pressure loss and recovery in the condenser neck is needed for benchmark of designs or design changes (e.g. tender phase). Here 1D modelling approaches can help to close the gap.
Analysis of available 1D correlation of flow around obstacles has shown that these need to be adapted to the flow conditions in a condenser neck of a steam, nuclear or combined-cycle power plant. Therefore, the fluid fields, calculated and discussed in the first publication (Part 1), were analyzed regarding pressure loss created by single obstacles and interaction of built-ins of different size, number and shape. Furthermore, a 1D velocity to be used for 1D calculation was derived from the 3D velocity field. In addition, vacuum-correction-curves were implemented to cover the range of possible operating conditions.
This publication discusses the development of a 1D model for calculation of pressure loss in a condenser neck and the validity of such calculations against measurement and 3D CFD data.
Effect of Air-Curtains on Labyrinth Seal Performance
Authors: Rai Aakash C. , Prabhudharwadkar Deoras , Murthy Sunil , Giametta Andrew , Johns David 
Published: September 2016

Labyrinth seals are used in many key sealing locations in gas turbines to control various leakage flows, e.g., to control the secondary air-flow from the compressor (bypassing the combustor), the turbine inter-stage leakages and blade tip leakages. This study was performed to assess the improvement in the performance of a labyrinth seal by using an air-curtain (cross-flow jet(s)) from the stator. Detailed parametric studies were performed to study the effect of the air-curtain jet pressure, location, and the number of jets on the seal performance with respect to the leakage flow. The analysis was done using 2-dimensional axisymmetric CFD simulations.
It was found that in the case of a labyrinth seal with a flat stator (without a honeycomb attached to the stator) the air-curtain design can reduce the seal leakage by about 30% over the baseline seal design without air-curtains. This reduction happened because the air-curtain jet deflected the main seal jet away from the seal clearance. A similar conclusion was also obtained in case of a labyrinth seal with a honeycombed stator. Furthermore, our parametric studies with different air-curtain designs parameters implemented over a honeycombed labyrinth seal showed that the air-curtain jet pressure, location, and the number of jets were crucial factors governing the seal leakage. Amongst the air-curtain designs studied, it was found that implementing three air-curtains in the 1st pocket gave the maximum leakage reduction (by about 50%) over the baseline design.
Investigation of Cross Flow in Double Entry Turbocharger Turbines
Authors: Lückmann Dominik , Stadermann Max , Aymanns Richard , Pischinger S. 
Published: September 2016

The downsizing of combustion engines has become the major strategy within the automotive industry to meet the increasing demands in terms of fuel economy and harmful emissions. Furthermore, it is important to fulfil the customers expectations in terms of drivability by increasing the power density and transient performance of the engines. The key technology to reach these ambitious targets is the enhanced utilization of exhaust pulses on turbocharged engines. In four cylinder gasoline engine applications this is mainly realized by the use of double entry turbines or variabilities in the exhaust valve train. During the designing and matching process of double entry turbines it is still a major challenge to predict the turbine power output and accurately model its interaction with the engine. In the past few years, several authors have published measurement and simulation technologies aimed at enhanced modelling quality. Most of these approaches are based on the introduction of different flow conditions which help to describe the thermodynamic performance under various pulsating boundary conditions. Within an average engine cycle, the turbine operates under equal, single and unequal admissions. Furthermore, the evaluation of a turbine interacting with a four cylinder gasoline engine shows that cross flow between both turbine scrolls can occur during the blow-down phase of the cylinders. In this phase, the temperature and pressure upstream of the turbine reach their peak values within the complete engine cycle. Therefore, this phase is most crucial for the conversion of the exhaust energy into mechanical energy, which drives the compressor impeller of the turbocharger.
This work focuses on the results of stationary hot gas measurements and 3D CFD simulations of the cross flow phenomena to gain a deeper understanding of the scroll interaction in double entry turbines and its impact on engine performance. The findings were used to improve the modeling quality of double entry turbines in 1D engine process simulations, especially during the exhaust blow down where cross flow between the dividing wall and the turbine wheel occurs. The new methodology to quantify the amount of cross flow with a hot gas test has shown that the cross flow rate of a twin scroll turbine can reach values as high as 35% of the overall flow rate entering the turbine housing, whereas this value can be significantly reduced by using a segment turbine housing. The new map based turbine model, which enables predictive simulations, covers all engine relevant flow conditions of the turbine including cross flow. This is important because the cross flow has a large impact on the exhaust pulse separation and thus on the residual gas fraction of the cylinders after the gas exchange.
Experimental Investigation of a Low Pressure Model Steam Turbine With Supporting Rib in Close Vicinity to the Last Stage Rotor Blades at Varying Operating Conditions
Authors: Müller Fabian F. , Schatz Markus , Vogt Damian M. , Rehnsch Andreas 
Published: September 2016

Steam turbine retrofits often result in an increase of turbine size, aiming for more power and higher efficiency. As the existing LP steam turbine exhaust hoods are generally not modified, the last stage rotor blades frequently move closer to installations within the exhaust hood, such as baffles or ribs.
To assess the influence of supporting ribs on the vibration behavior of the last stage rotor blades, tests with two rib configurations were performed in a single stage LP model steam turbine at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) at the University of Stuttgart, Germany.
At design load and overload operating conditions no significant change in blade vibration amplitudes is observed in case of a supporting rib in close vicinity to the rotor blades compared to the reference case without installations. However, at part load operating conditions a remarkable reduction in blade amplitudes is found rather unexpectedly.
The present work shows that changes in the pattern and the frequency content of the flow within the diffuser, caused by the interaction between supporting rib and steam flow is evidently responsible for this.
Estimation of the Particle Deposition on a Subsonic Axial Compressor Blade
Authors: Suman Alessio , Morini Mirko , Kurz Rainer , Aldi Nicola , Brun Klaus , Pinelli Michele , Spina Pier Ruggero 
Published: September 2016

The quality and purity of the air entering a gas turbine is a significant factor influencing its performance and life. Foulants in the ppm range which are not captured by the air filtration system usually cause deposits on blading, which results in a severe drop in the performance of the compressor.
Through the interdisciplinary approach proposed in this paper, it is possible to determine the evolution of the fouling phenomenon through the integration of studies in different research fields: (i) numerical simulation, (ii) power plant characteristics and (iii) particle-adhesion characteristics. In fact, the size of the particles, their concentrations and adhesion ability, and filtration efficiency represent the major contributors to performing a realistic quantitative analysis of fouling phenomena in an axial compressor. The aim of this work is the estimation of the actual deposits on the blade surface in terms of location and quantity. This study combines the impact/adhesion characteristic of the particles obtained through a CFD and the real size distribution of the contaminants in the air swallowed by the compressor.
The blade zones affected by deposits are clearly reported by using easy-to-use contaminant maps realized on the blade surface, in terms of contaminant mass.
The analysis has shown that particular fluid-dynamic phenomena and airfoil shape influence the pattern deposition. The use of a filtration system decreases the contamination of the blade and the charge level of the electrostatic seems to be less important than the air contaminant concentration. From these analyses, some guidelines for proper installation and management of the power plant (in terms of filtration systems and washing strategies) can be drawn up. Characterization of the air contaminants in the power plant location represents the most important step in improving the management of the gas turbine power plant.
Increased Load Carrying Capacity of Large Tilting-Pad Journal Bearings by Injection of Cold Oil
Authors: Buchhorn Nico , Kukla Sebastian , Bender Beate 
Published: September 2016

In this paper a theoretical study with the aim to achieve higher load capacity of large tilting-pad turbine bearings is presented. The main focus is set on the reduction of thermal gradients inside the pad and thus, of adverse thermomechanical deformations. This allows for the increase of either the load carrying capacity, minimum film thickness hmin, and/or decrease maximum pad temperature Tmax.
Subject of the investigation is a 5-pad tilting-pad bearing with rocker pivots. Each pad arc measures 56° and the pivot is positioned at 60 %. By having a 500mm inner diameter the 350mm long bearing features a relative clearance of 1.28% and nominal preload of 0.23.
It is shown that the axial pad bending Δh (crowning) has a major impact on film thickness and pressure distributions and thus on the operational safety parameters.
In order to reduce this effect, radial bores through the pad supplying pressurized cold oil (Tinj = 50 °C) are simulated. Despite the evident increase in oil film pressure, the primary purpose of the injection is to rinse away the layer of hot oil sticking to the pad surface. The maximum pad temperature and the overall pad temperature gradients are thereby decreased.
The code used for simulation solves Reynolds and energy equations and computes thermomechanical deformations simultaneously. However, the simulations are carried out for one single pad only and are therefore supported by boundary conditions taken from experiments.
In order to determine the impact of the approach on the static bearing characteristics, diameter and location of the bores are varied (0.3mm ≤ db ≤ 0.5mm). It is shown that pad crowing can be reduced significantly: The axial deviation of the film thickness Δh can be decreased from Δh = 47 μm to Δh = 31 μm, while the maximum temperature Tmax can be decreased by 20 K. Further, the minimum film thickness hmin can be increased by 16 μm. Subsequently, allowing the same limits for hmin and Tmax for the new design, the load capacity can be raised by up to 1.21MPa ≙ 44 %.
An Academic Test Rig for Industrial Centrifugal Compressor Stages: A Design Approach
Authors: Bianchini Alessandro , Ferrari Lorenzo , Ferrara Giovanni 
Published: September 2016

Due to the huge amount of power connected to centrifugal compressors’ applications, even small rangeability increases of the stages would provide significant energy and money savings. In particular, industrial manufacturers pay lot of interest in better understanding the instabilities that in many cases define the minimum flow limit of their stages, but they are often hampered in the research by the short time-to-market. On the other hand, academia has historically found difficulties in approaching the problem due to the lack of dedicated experimental facilities.
In this study, the concept design of a new research test rig is presented. The rig will be able to test impellers in field-like conditions (original mass flow and peripheral Mach numbers up to 0.7), operating in open-loop configuration with ambient inlet conditions. In view of systematic test campaigns, a modular design will allow to easily replace any component of the asset and even to modify the flowpath after the impeller, so that the influence of each component can be estimated. As a research academic facility, the rig is characterized by some new design solutions, oriented to minimize the mechanical complexity, the energy consumption, the overall dimensions, and, finally, the cost. Moreover, it will be equipped with advanced experimental measurement instrumentation, e.g. a PIV system or fast response aerodynamic pressure probes.
The paper illustrates the conceptual design of the rig, including the selection of the best architecture and layout, the drivetrain assessment and the rotordynamic verification. Computational fluid-dynamic analyses are also presented, aimed at verifying the flow uniformity in the discharge sections and the thermal stability of the system during the tests.
Unsteady Effects in the Heat Load Predictions for a Two-Stage Compressor Turbine
Authors: Farhanieh Arman , Mau Christoph , Annerfeldt Mats , Nadali Najafabadi Hossein , Karlsson Matts 
Published: September 2016

Heat load analysis play an important role in the estimation of hot gas components’ lifetime. To achieve a high level of accuracy in heat load analysis, predicting the temperature distribution on the vane and blades is one area where further development is needed. Due to strong flow unsteadiness and mixing effects from blade row interactions and cooling injections, accurate heat load predictions have become an engineering challenge. This study uses both steady and time-accurate computational fluid dynamics (CFD) simulations to investigate the unsteady and mixing effects in a two-stage compressor turbine. The commercial code ANSYS CFX-15 is utilized to evaluate the performance of the steady state, mixing plane (MP) method, versus time-accurate, profile transformation (PT) and time transformation (TT) methods. The presence or absence of the rotor-stator cavities from which purge or cooling air is entering the main flowpath can also play an important role in the unsteadiness and mixing properties. Therefore the unsteady effects have been examined for two cases; a simplified model without any cavity and a detailed geometry with all the cavities included. In the simplified case, the cooling has been implemented as local patches. The results are then compared with gas temperature measurements from the real engine tests using thermo-crystals. The measurements include temperature profiles in front of the leading edge of each stator and rotor for both stages.
The findings suggest that including cooling cavities may not improve the results in steady state simulations, however their presence in transient simulations can lead to mixing prediction improvements. Moreover, the results indicate that the transient simulations will improve the mixing predictions mainly in the second stage of the turbine. The results also indicate that in transient simulations, number of passages and pitch ratio between the stators of consecutive stages directly affect the results regardless of which transient method is used.
Acoustically Induced Vibration Mitigations in Compressor Piping Systems
Authors: Allison Timothy C. , Bennett Jeffrey 
Published: September 2016

Acoustically induced vibration (AIV) is a high-frequency vibration phenomenon that can occur downstream of pressure-reducing devices such as control valves, restriction orifices, and pressure relief or safety valves in compressor piping systems. These vibrations can lead to high cycle fatigue failures of downstream piping at side branches or welded supports. Existing methods for screening and analyzing acoustically induced vibration are not well-grounded in the underlying physics and thus do not provide a methodology for evaluating a variety of mitigation strategies. Modeling of acoustically induced vibration is computationally challenging, as it requires the interaction between tens or hundreds of higher-order acoustic modes with a similar number of piping shell modes.
In order to obtain better insight into the underlying physics of AIV and to characterize the effectiveness of several mitigation methods, full-scale blow-down testing was performed at Southwest Research Institute. Tests were performed using 20 MPa nitrogen gas vented at 28 kg/s through a 3×4” pressure safety valve and multiple header pipe sizes ranging from 12” to 36”. Test configurations included baseline piping geometry at each size and several AIV mitigations including stiffening rings, viscous damping wrap, and internal acoustic mode disruptors. Test results from strain gauges, accelerometers, and dynamic pressure transducers show a broadband multimodal response with dynamic stresses up to 3 kHz near the safety valve tailpipe connection to the test header, and various mitigations reduced dynamic stresses by 8–52% depending on the piping and type of mitigation.
Acoustic and structural finite element models were analyzed in order to determine the coincident modes that match in both axial/circumferential shape and natural frequency and compare coincident frequencies with measure stresses. The results show that observed peak stress frequencies do not generally correlate well with predicted coincident modes, and that flow-induced turbulence excites frequencies below piping shell modes that can also result in significant stresses that combine with AIV.
Numerical Study on Flow and Heat Transfer of a Cooled First Stage Vane of a Gas Turbine
Authors: Ye Lv , Liu Zhao , Wang Xiangyu , Feng Zhenping 
Published: September 2016

This paper presents a numerical simulation of composite cooling on a first stage vane of a gas turbine, in which gas by fixed composition mixture is adopted. To investigate the flow and heat transfer characteristics, two internal chambers which contain multiple arrays of impingement holes are arranged in the vane, several arrays of pin-fins are arranged in the trailing edge region, and a few arrays of film cooling holes are arranged on the vane surfaces to form the cooling film. The coolant enters through the shroud inlet, and then divided into two parts. One part is transferred into the chamber in the leading edge region, and then after impinging on the target surfaces, it proceeds further to go through the film cooling holes distributed on the vane surface, while the other part enters into the second chamber immediately and then exits to the mainstream in two ways to effectively cool the other sections of the vane. In this study, five different coolant flow rates and six different inlet pressure ratios were investigated. All the cases were performed with the same domain grids and same boundary conditions.
It can be concluded that for the internal surfaces, the heat transfer coefficient changes gradually with the coolant flow rate and the inlet total pressure ratio, while for the external surfaces, the average cooling effectiveness increases with the increase of coolant mass flow rates while decreases with the increase of the inlet stagnation pressure ratios within the study range.
Experimental Investigation of Fluid Structure Interaction of Impeller Like Disks in Super Critical Carbon Dioxide
Authors: Pereboom H. P. , van Beek P. J. G. , Smeulers J. P. M. 
Published: September 2016

In radial compressors working with high density gases, such as super critical carbon dioxide, strong interactions between the fluid and the impeller can cause large dynamic loads that can lead to damage or even failure. Acoustic resonances in the compressor cavities couple strongly with the vibration modes of the impeller.
The coupled acoustic-structural modes can be predicted by means of complex models that need to be validated. To this end a test rig has been developed in which impeller like structures can be tested under high density gas conditions. In this paper the experimental setup is described with which the required data for the validation of the models is generated. The focus of this paper is not on data analysis and comparisons with models since this is part of two separate PhD projects. To demonstrate the relevance of the results a short preliminary comparison with finite element modeling is made.
The present test rig has been operated with (super critical) carbon dioxide in a pressure range from atmospheric pressure to 200 bar and temperatures between 40 and 60 degrees C.
Two types of simplified impellers have been tested: a single disk and a double disk with ribs. The latter mimics the shape of an impeller. The diameter of the impeller disk is comparable to a real impeller. The disks are mounted in a housing that represents the compressor stator including a diffuser. The housing is placed inside a specially designed pressure vessel. Several parameters can be varied, such as the width of the cavities, the clearance between the impeller and the diffuser, etc. In the test set up multiple pressure transducers are installed to measure the acoustic modes. To identify the modal deformation of the impeller, glass fiber sensors (so-called FBG’s) have been installed at 38 of points on the impeller. The transfer functions from fluid to structure are measured by means of acoustic excitation. Vice versa the transfer function from structure to fluid is measured by means of impulse excitation of the disk. In this paper the test rig is described and preliminary results are presented.