bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Study of Hot Gas Ingestion Into an Engine Type High-Pressure Turbine Rotor-Stator Cavity
Authors: Förster Ingo , Martens Eckhard , Friedl Winfried-Hagen , Peitsch Dieter
Published: July 2014

The rims of high pressure turbines in aeroengines are sealed with air via the internal air system. This sealing is required to avoid occurrence of hot gas ingestion into the rotor-stator cavities. Due to a rapid decrease of turbine disc life at higher temperatures, such ingestion would present a hazard to the integrity of the discs and subsequently to the safety of the aircraft. One of the driving factors for ingestion is the circumferential pressure variation downstream of vanes and blades due to the aerodynamic wakes. Small ingestion cavities close to the annulus are commonly used to damp down this pressure variation. Substantial ingestion into these cavities is permitted. The actual sealing of the rotor-stator cavity itself is accomplished with a secondary seal.

A numerical simulation of the flow in an engine type rotor-stator cavity was carried out using a commercial CFD code. The cases studied comprise relevant features as rotor-stator and ingestion cavities, leakage across rotor blade shanks and circumferential pressure variation downstream of an NGV. The simulation was carried out at relevant engine temperatures and pressures.

The paper will firstly present the effects of a variation of the rim sealing mass flow on the flow field, ingestion and temperature increase in the cavity. These results were solely gained by computational means. For validation of a new air system design, engine tests on the BR715 jet engine have been performed. The data measured in these tests not only serve for certification purposes, but also may be used as input for CFD calculations. Thus, the experimental data was the baseline for comparison with the results from the present study.
Numerical Solution of Lubrication’s Compressible Bulk Flow Equations: Applications to Annular Gas Seals Analysis
Authors: Arghir Mihai , Frene Jean
Published: July 2014

The appropriate theoretical model for lubrication flows characterized by reduced Reynolds numbers greater than unity (Re*=ρVH/μ·H/L≥l) is the so-called “bulk flow” system of equations. Its solution is more difficult than for the simple Reynolds equation because one has to deal with coupled pressure and velocity fields and the equations are of mixed elliptic-hyperbolic type. Adapting some methods borrowed from CFD can develop a suitable numerical approach. In the present work we introduce a pressure-based method belonging to the family of SIMPLE algorithms where compressibility is taken into account by coupling density corrections with pressure corrections. The method is capable of handling all compressible flows and doesn’t require any specific treatment of the incompressible flow regime. It is an adaptation for the bulk flow equations of Karki and Patankar’s (1989) work and is developed in conjunction with a triangular finite volume formulation. The present paper is focused on the description of the discretized equations, of the accompanying boundary conditions and of the solution algorithm. Comparisons with analytic solutions for subsonic and supersonic channel flows prove the ability of the method to handle all compressible flow regimes. Published results for gas (air) annular seals are further used to evaluate the proposed numerical model.
Discharge Coefficients of a Pre-Swirl System in Secondary Air Systems
Authors: Dittmann M. , Geis T. , Schramm V. , Kim S. , Wittig S.
Published: July 2014

The discharge behaviour of a “direct-transfer” pre-swirl system has been investigated experimentally. The influences of the pressure ratio and the swirl ratio as well as the influence of the receiver and stator geometry were investigated. The discharge coefficients of the pre-swirl nozzles are given in the absolute frame of reference. The definition of the discharge coefficient of the receiver holes is applied to the rotating system in order to consider the work done by the rotor. Numerical calculations carried out for a free expansion through the stationary pre-swirl nozzles show very good agreement with experimental data.
Coarse Grid Modeling of Turbine Film Cooling Flows Using Volumetric Source Terms
Authors: Heidmann James D. , Hunter Scott D.
Published: July 2014

The recent trend in numerical modeling of turbine film cooling flows has been toward higher fidelity grids and more complex geometries. This trend has been enabled by the rapid increase in computing power available to researchers. However, the turbine design community requires fast turnaround time in its design computations, rendering these comprehensive simulations ineffective in the design cycle. The present study describes a methodology for implementing a volumetric source term distribution in a coarse grid calculation that can model the small-scale and three-dimensional effects present in turbine film cooling flows. This model could be implemented in turbine design codes or in multistage turbomachinery codes such as APNASA, where the computational grid size may be larger than the film hole size. Detailed computations of a single row of 35 degree round holes on a flat plate have been obtained for blowing ratios of 0.5, 0.8, and 1.0, and a density ratios of 1.0 and 2.0 using a multiblock grid system to resolve the flows on both sides of the plate as well as inside the hole itself. These detailed flow fields were spatially averaged to generate a field of volumetric source terms for each conservative flow variable. Solutions were also obtained using three coarse grids having streamwise and spanwise grid spacings of 3d, 1d, and d/3. These coarse grid solutions used the integrated hole exit mass, momentum, energy, and turbulence quantities from the detailed solutions as volumetric source terms. It is shown that a uniform source term addition over a distance from the wall on the order of the hole diameter is able to predict adiabatic film effectiveness better than a near-wall source term model, while strictly enforcing correct values of integrated boundary layer quantities.
Studies on Cooling Air Ejected Over a Corrugated Wall: Its Aerodynamic Behavior and Film Effectiveness
Authors: Funazaki K. , Igarashi T. , Koide Y. , Shinbo K.
Published: July 2014

This paper describes experimental studies on aerodynamic behaviors of the air ejected from several discrete hole rows on a corrugated wall and the resultant film effectiveness over the wall. The corrugated wall is a model of an air-cooled liner surface for aero-engine augmentors. Measurements on the aerodynamic aspects are conducted by use of a pneumatic five-hole probe in order to clarify the features of the ejected air over the corrugated wall. The temperature field is examined by traversing a thermocouple, which also reveals the behavior of the ejected air. Film effectiveness associated with the air-ejection is then determined from the extrapolation of the measured temperature profile. It is accordingly found that the air jets near the ejection holes behave like those from the holes on a flat-plate, being accompanied by upward and downward secondary flows around the jets. Close inspections on the behavior of the jets also reveal that the jet cores tend to diminish much faster than those in the flat-plate case, which is probably due to a mixing of the high-momentum jet and low-momentum air on the ‘valley’ of the corrugated wall. Such characteristics of the jets result in transversely uniform distribution of the temperature which is favorable to the liner surface protection from the extremely hot gas.
Prediction of Relaminarization Effects on Turbine Blade Heat Transfer
Authors: Boyle R. J. , Giel P. W.
Published: July 2014

An approach to predicting turbine blade heat transfer when turbulent flow relaminarizes due to strong favorable pressure gradients is described. Relaminarization is more likely to occur on the pressure side of a rotor blade. While stators also have strong favorable pressure gradients, the pressure surface is less likely to become turbulent at low to moderate Reynolds numbers. Accounting for the effects of relaminarization for blade heat transfer can substantially reduce the predicted rotor surface heat transfer. This in turn can lead to reduced rotor cooling requirements. Two dimensional midspan Navier-Stokes analyses were done for each of eighteen test cases using eleven different turbulence models. Results showed that including relaminarization effects generally improved the agreement with experimental data. The results of this work indicate that relatively small changes in rotor shape can be utilized to extend the likelihood of relaminarization to high Reynolds numbers. Predictions showing how rotor blade heat transfer at a high Reynolds number can be reduced through relaminarization are given.
Analysis of the Influence of Cooling Steam Conditions on the Cooling Efficiency of a Steam-Cooled Vane Using the Conjugate Calculation Technique
Authors: Krüger Uwe , Kusterer Karsten , Lang Gernot , Rösch Hauke , Bohn Dieter , Martens Eckhard
Published: July 2014

Closed circuit steam cooling of blades and vanes in modern gas turbines is an promising alternative instead of film-cooling using compressor air. The temperature drop across the first-stage nozzle, which is convectively steam-cooled, is reduced significantly in comparison to an intensive film-cooled vane using compressor air. Thus, the firing temperature (temperature in front of the first-stage blade row) can be increased while the combustion temperature can remain as low as necessary for low-Nox purpose.

In this paper, a steam-cooled test configuration consisting of a 3-vane cascade is numerically analysed. A computer code using a Conjugate Calculation Technique is applied. The CHTflow code has been developed at the Institute of Steam and Gas Turbines in Aachen. Due to the direct coupling of fluid flow and solid body, heat transfer boundary conditions at the external and internal surfaces become unnecessary. Validation of the code for a similar convection-cooled configuration is also given here.

The presented investigations focus on the thermal load analysis and the cooling efficiency analysis of the test configuration. It consists of a planar cascade with a convection-cooled central vane where cooling fluid can be supplied to 22 radial passages. One main aspect of the paper is to show the influence of cooling steam conditions (low-, medium & high-pressure steam supply) on the local and global cooling efficiencies. The results show that, for reaching a defined cooling efficiency level, medium steam pressure supply might be advantageous in comparison to a high-pressure level in supply. Although a lower pressure level demands an increase in steam mass flow, the overall effect on the thermal efficiency of the whole process is acceptable if one keeps in mind the advantages of handling steam at lower pressure levels. For further comparison, convective air-cooling with reasonable cooling conditions and comparable flow and heat transfer characteristics is analysed. For the given geometry of the configuration, sufficient cooling of the trailing edge becomes problematic for steam- and air-cooling application.
Heat Transfer Computations for High Pressure Turbines
Authors: Smith Graham C. , Hilditch Mary A. , Wood Nigel B.
Published: July 2014

The life of a high pressure turbine blade is strongly dependent on the operating temperature of the blade material. The gas entering the turbine is at a very high temperature and the blades must be cooled. Accurate predictions of the heat transfer to an uncooled aerofoil are an important step in predicting the blade metal temperature and designing an efficient cooling system. 3D Navier-Stokes calculations of heat transfer are presented for the vanes of two modern high pressure, shroudless turbines. The results are compared with measurements taken in a short duration test facility at engine representative conditions. The experimental dataset includes repeat measurements made using different instrumentation. These data are shown to agree within the confidence limits of the experiment. In this experiment laminar-turbulent transition is known to be a major influence on the measured heat transfer levels. However, careful modelling of this parameter, through physical reasoning and published correlations, gives predictions in reasonable agreement with the measurements.
Steady Three-Dimensional Simulation of a Transonic Axial Turbine Stage
Authors: Michelassi V. , Giangiacomo P. , Martelli F. , Dénos R. , Paniagua G.
Published: July 2014

The performance of a transonic axial turbine stage, representative of a wide class of aeroengines, is computed by a Navier-Stokes solver with a three-equation turbulence model. The stator blade has a coolant ejection slot on the pressure side close to the trailing edge. The stator-rotor interaction is modelled by a mixing plane approach. The tangential mixing strategy is discussed and analysed in terms of area or mass averaging. The computational results are compared with an experimental data set, which includes all the relevant quantities necessary to describe the stage. Both computations and experiments are carried out in four different operating conditions to allow first the effects of changes in Reynolds number and pressure ratio to be assessed and second the sensitivity of the computational model to these changes to be tested. The effect of tip leakage is investigated and CFD is used to help understand the experiments. The predictions compare favourably with experiments for most of the relevant parameters and prove the validity of the simple and fast computational model.
Elliptical Pin Fins as an Alternative to Circular Pin Fins for Gas Turbine Blade Cooling Applications: Part 1 — Endwall Heat Transfer and Total Pressure Loss Characteristics
Authors: Uzol Oğuz , Camci Cengiz
Published: July 2014

Detailed experimental investigation of the wall heat transfer enhancement and total pressure loss characteristics for two alternative elliptical pin fin arrays is conducted and the results are compared to the conventional circular pin fin arrays. Two different elliptical pin fin geometries with different major axis lengths are tested, both having a minor axis length equal to the circular fin diameter and positioned at zero degrees angle of attack to the free stream flow. The major axis lengths for the two elliptical fins are 1.67 and 2.5 times the circular fin diameter, respectively. The pin fin arrays with H/D = 1.5 are positioned in a staggered 2 row configuration with 3 fins in the first row and 2 fins in the second row with S/D = X/D = 2. Endwall heat transfer and total pressure loss measurements are performed two diameter downstream of the pin fin arrays (X/D = 2) in a rectangular cross-section tunnel with an aspect ratio of 4.8 and for varying Reynolds numbers between 10000 and 47000 based on the inlet velocity and the fin diameter. Liquid Crystal Thermography is used for the measurement of convective heat transfer coefficient distributions on the endwall inside the wake. The results show that the wall heat transfer enhancement capability of the circular pin fin array is about 25–30% higher than the elliptical pin fin arrays in average. However in terms of total pressure loss, the circular pin fin arrays generate 100–200% more pressure loss than the elliptical pin fin arrays. This makes the elliptical fin arrays very promising cooling devices as an alternative to conventional circular pin fin arrays used in gas turbine blade cooling applications.
Heat Transfer in a Two-Pass Rectangular Rotating Channel With 45° Angled Rib Turbulators
Authors: Azad Gm. S. , Uddin Mohammad J. , Han Je-Chin , Moon Hee-Koo , Glezer Boris
Published: July 2014

Experimental heat transfer results are presented in a two-pass rectangular channel (aspect ratio=2:1) with smooth and ribbed surfaces for two channel orientations (90° and 135° to the direction of rotational plane). The rib turbulators are placed on the leading and trailing sides at an angle 45° to the main stream flow. Both 45° parallel and cross rib orientations are studied. The results are presented for stationary and rotating cases at three different Reynolds numbers of 5000, 10000, and 25000, the corresponding rotation numbers are 0.21, 0.11, and 0.04. The rib height to hydraulic diameter ratio (e/D) is 0.094; the rib pitch-to-height ratio (P/e) is 10 and the inlet wall-to-coolant density ratio (Δρ/ρ) is maintained at 0.115 for all surfaces in the channel. Results show that the rotating ribbed wall heat transfer coefficients increase by a factor of 2 to 3 over the rotating smooth wall results. The heat transfer from the first pass trailing and second pass leading surfaces are enhanced by rotation. However, the first pass leading and the second pass trailing sides show a decrease in heat transfer with rotation. The result show that 45° parallel ribs produce a better heat transfer augmentation than 45° cross ribs, and a 90° channel orientation produces higher heat transfer effect over a 135° orientation.
Experimental Investigation of Transition to Turbulence as Affected by Passing Wakes
Authors: Kaszeta Richard W. , Simon Terrence W. , Ashpis David E.
Published: July 2014

This paper presents experimental results from a study of the effects of periodically passing wakes upon laminar-to-turbulent transition and separation in a low-pressure turbine passage. The test section geometry is designed to simulate unsteady wakes in turbine engines for studying their effects on boundary layers and separated flow regions over the suction surface by using a single suction surface and a single pressure surface to simulate a single turbine blade passage. Single-wire, thermal anemometry techniques are used to measure time-resolved and phase-averaged, wall-normal profiles of velocity, turbulence intensity and intermittency at multiple streamwise locations over the turbine airfoil suction surface. These data are compared to steady-state wake-free data collected in the same geometry to identify the effects of wakes upon laminar-to-turbulent transition. Results are presented for flows with a Reynolds number based on suction surface length and stage exit velocity of 50,000 and an approach flow turbulence intensity of 2.5%. While both existing design and experimental data are primarily concerned with higher Reynolds number flows (Re > 100,000), recent advances in gas turbine engines, and the accompanying increase in laminar and transitional flow effects, have made low-Re research increasingly important.

From the presented data, the effects of passing wakes on transition and separation in the boundary layer, due to both increased turbulence levels and varying streamwise pressure gradients are presented. The results show how the wakes affect transition. The wakes affect the flow by virtue of their difference in turbulence levels and scales from those of the free-stream and by virtue of their ensemble-averaged velocity deficits, relative to the free-stream velocity, and the concomitant changes in angle of attack and temporal pressure gradients. The relationships between the velocity oscillations in the freestream and the unsteady velocity profile shapes in the near-wall flow are described. In this discussion is support for the theory that bypass transition is a response of the near-wall viscous layer to pressure fluctuations imposed upon it from the free-stream flow. Recent transition models are based on that premise. The data also show a significant lag between when the wake is present over the surface and when transition begins.
On the Impact of Blade Count Reduction on Aerodynamic Performance and Loss Generation in a Three-Stage LP Turbine
Authors: Gier Jochen , Ardey Sabine
Published: July 2014

Reducing the number of blades in low pressure turbines is a desirable option for decreasing total operation costs. From an aerodynamical point of view this directly leads to an increased blade load. However, increasing the blade load above a certain level results in viscous effects like separation bubbles and finally full separation. This becomes especially significant for aero engine turbines, which operate at high altitudes and thus low Reynolds numbers. The underlying local flow phenomena and the effect on the aerodynamic performance of such configurations are addressed in this paper.

This investigation is based on a three-stage low pressure turbine typical for aero engines. Different setups are employed with different number of guide vanes in certain stages. Furthermore, the Reynolds number is varied within a wide range. These configurations are investigated numerically using a modern steady-state transitional Navier-Stokes solver and experimental results from the same turbine. Based on this information, a detailed analysis of the viscous flow phenomena is performed with focus on the influence of separation bubbles on the loss production after the transition. These results are discussed with respect to blade count reduction.
Secondary Air Systems in Aeroengines Employing Vortex Reducers
Authors: Negulescu Dimitrie , Pfitzner Michael
Published: July 2014

A secondary air system in modern aero engines is required to cool the compressor and turbine discs and make sure that no hot gas ingestion occurs into the cavities between the turbine discs, which could cause an inadvertent reduction of disc life.

A high integrity solution for guiding the air from the compressor to the turbine is through an inner bleed from the compressor platform and through the space between the disc bores and the shaft connecting the fan with the low pressure turbine.

Since strongly swirling air is taken from the compressor platforms to a much lower radius, a means of deswirling the air has to be used to avoid excessive pressure losses along the flow path.

The paper describes a system utilizing tubeless vortex reducers to accomplish this deswirl, which are compared to a more conventional air system utilizing tubes. The working principles of both types of vortex reducer and guidelines for the design of a secondary air system using vortex reducers are explained with supporting evidence from rig tests and CFD calculations. Opportunities for the aerodynamic optimisation of the tubeless vortex reducer are elaborated and the experience gained using the system during the development of the BR700 engine is described.
Development and Implementation of a Replacement Digital Gas Turbine Control for U.S. Navy Shipboard Installation
Authors: Murphy Gregory L.
Published: July 2014

Existing gas turbine control systems onboard U.S Navy ships are based on analog technology developed nearly forty years ago. In addition to being costly to maintain and provide replacement parts, these controls are not easily upgradeable. They do not allow the introduction of advanced monitoring functions and do not take advantage of improvements in control technology. Recognizing the shortcomings of these controls, the U.S. Navy has engaged in a program to introduce current technology to the fleet in order to lengthen the service life of its surface combatants.
Status of AMG (Advanced Material Gas-Generator) Research and Development Program
Authors: Kuriyama T. , Miyagawa H. , Uyama M. , Yamamoto S. , Yokoi S. , Hiromatsu M.
Published: July 2014

Research and Development program of Advanced Material Gas-Generator (AMG) was initiated in 1993 as a ten year program with a joint investment from the Japan Key Technology Center and fourteen participating Japanese companies.

The program objective is to establish basic key technologies for next generation gas-generator using advanced materials, which should have the features of significantly low fuel consumption with reduced weight and size, and should be environmentally acceptable, toward the realization of future industrial, marine and aircraft gas turbines.

In the initial phase of AMG program the conceptual study of advanced gas-generator was carried out in order to clarify technical issues and define requirements for each component. Based on the results of conceptual study, Polymer Matrix Composites (PMC), Metal Matrix Composites (MMC), Ceramic Matrix Composites (CMC) and Titanium Aluminide (TiAl) were considered as the candidate materials for the advanced material gas-generator. Then AMG is intensively proceeding R&D for next generation gas-generator using these advanced materials, and is now getting technical fruits.

This paper introduces the outline of AMG project and conceptual study, then describes some topics of each R&D themes.
Field and Application Experience of the Titan 130 Industrial Gas Turbine
Authors: Rocha George , Kurz Rainer
Published: July 2014

The two-shaft Titan 130 industrial gas turbine was introduced into commercial service in 1998 and has gained field experience in mechanical-drive and compressor-set applications. A single-shaft configuration is also available for electrical power generation applications. The 14-MW class two-shaft engine is nominally rated at 19,500 hp with a simple-cycle efficiency of more than 35% at ISO operating conditions. It is available with two combustor options: a dry, low-pollutant emissions combustion system featuring Solar’s proven SoLoNOx technology or a diffusion-flame type combustor adapted from Solar’s proven Mars gas turbine.

The Titan 130 gas turbine design is an aerodynamic scale of the existing Taurus 70 product. The unit features a modified Mars air compressor and turbine section components directly scaled from the Taurus 70, resulting in a low-risk product design well-suited for industrial service applications. A major element of the development strategy included an extended field evaluation trial in actual operating conditions to demonstrate overall product durability. The first Titan 130 mechanical-drive package was placed into service at a natural gas pipeline compressor station and successfully completed a planned 8000-hour field evaluation program. Extensive inspection and operating data have been evaluated and the unit continues to operate in normal commercial service.

A mechanical-drive package requires the successful marriage between the driver and the driven equipment. Most applications require a combination of high efficiency and high performance flexibility. Emphasis was placed on providing excellent gas compressor coverage for this product. The successful application of such a compression system is discussed and supported by site test data.

This paper provides details of the Titan 130 field evaluation program, design enhancements and typical compressor set application performance characteristics.
Power Turbine Remaining Life Assessment
Authors: deBeer Bruce , Chilcott Paul , Seib Dave
Published: July 2014

The design life of an industrial power turbine has traditionally been 100,000 hours or 5,000 starts, based on a specific set of assumed operating conditions. Actual operating conditions vary from site to site, and are often less severe than the initial assumptions used by the manufacturer. This is why Dresser-Rand has developed a Remaining Life Assessment program. The objective of this program is to assist operators in extending the life of expensive components, determining inspection intervals, developing component replacement schedules, and establishing a spare parts stocking program.

A comprehensive remaining life assessment must take into account unit operating history, a thorough non destructive examination of the components being considered for reuse, thermal and structural analyses using current analytical techniques, and material evaluations. There is some amount of variability in the input and output for each of these steps. Defects smaller than a given size are not always detected, material test results have a statistical distribution, and each operating cycle is unique. Traditionally the expected life has been based on a predetermined set of assumptions, such as stress analyses using typical dimensions, minus three sigma fatigue and creep properties, etc. The Dresser-Rand approach accounts for these inherent variations and establishes the statistical probability of successfully extending power turbine life without failure or unplanned maintenance as a function of time.
Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals: Part 2 — Smooth and Honeycomb Geometries
Authors: Dawson Matthew P. , Childs Dara W.
Published: July 2014

Results are presented from tests conducted using an experimental test facility to measure the leakage and dynamic impedance of smooth and honeycomb straight-bore annular gas seals. The test seals had a 114.3 mm bore with a length-to-diameter ratio of 0.75 and a nominal radial clearance of 0.19 mm. The honeycomb cell depth for both seals was 3.1 mm, and the cell width was 0.79 mm. Dynamic impedance and leakage measurements are reported using air at three supply pressures out to 1.72 MPa, three speeds out to 20,200 rpm, and exit-to-inlet pressure ratios of 40% and 50%. Comparisons to the predictions from the two-control-volume model of Kleynhans and Childs [1] are of particular interest. This model predicts that honeycomb seals do not fit the conventional frequency independent model for smooth annular gas seals. The experimental results verify this new theory. Numerical predictions from a computer program incorporating the new two-control-volume model of Kleynhans and Childs [1] correlate well with both measured seal leakage and dynamic impedances for the honeycomb seals.
A Harmonic Wavelets Approach for Extracting Transient Patterns From Measured Rotor Vibration Data
Authors: Chancey Valeta Carol , Flowers George T. , Howard Candice L.
Published: July 2014

Vibration analysis is a powerful diagnostic tool for rotating machinery problems. Traditional approaches to vibration signature analysis have focused on the Fourier transform, which tends to average out transient effects. Recent work in the area of wavelets has allowed for the characterization of signals in frequency and in time, which, if properly interpreted, can provide substantial insight, particularly with regard to transient behaviors. There are many different wavelets, but the harmonic wavelet was developed specifically for vibration analysis. It uses an algorithm based upon the FFT, which makes it particularly attractive to many in the vibration analysis community. This paper considers the harmonic wavelet as a tool for extracting transient patterns from measured vibration data. A method for characterizing transient behaviors using the harmonic wavelet is described and illustrated using simulation and experimental results.
Optimum Design of Squeeze Film Dampers Supporting Multiple-Mode Rotors
Authors: El-Shafei A. , Yakoub R. Y.
Published: July 2014

In this paper a study of the optimum design of squeeze film dampers for multi-mode rotors is presented. The optimum design program obtains the best possible damper parameters for a given rotor to satisfy the minimization requirements for the objective function. The objectives are to: minimize the amplitude response of the rotor at the critical speed, minimize the force transmitted to the support at the operating speed or maximize the power dissipated by the damper. A combination of these objectives can also be used, with weighting factors to weigh the importance of each of these objectives. These are the possible objectives for the design of squeeze film dampers for aircraft engine applications.

The basis of the optimum design program is an extremely fast algorithm which is able to quickly calculate the unbalance response of a rotor, for circular centered orbits of the journal in the damper. A commercial routine is used for the optimization, and is based on a complex direct search technique. The variation of the optimum clearance, length, and retainer spring stiffness are plotted against various rotor parameters. Recommendations for the design of squeeze film dampers are made. Application to an aircraft engine, illustrate the power of the developed algorithm.
Multi-Blade Row Interactions in a Transonic Axial Compressor: Part I — Stator Particle Image Velocimetry (PIV) Investigation
Authors: Sanders A. J. , Papalia J. , Fleeter S.
Published: July 2014

Multi-blade row interactions in an advanced design 1&1/2 stage axial-flow compressor are experimentally investigated at both subsonic and transonic rotor operating conditions using particle image velocimetry (PIV). Transonic rotor operation had a significant impact on the downstream stator unsteady flow field due to phenomena associated with the intra-stator transport of the chopped rotor wake segments. In the stator reference frame, the rotor wakes have a slip velocity relative to the mean flow that causes the low momentum wake fluid to migrate across the vane passage and accumulate on the stator pressure surface as the chopped wake segments are transported downstream. This results in the generation of counter-rotating vortices on each side of the chopped wake segment that convect downstream with the mean flow and act as an additional source of unsteadiness to the vane pressure surface. These interaction phenomena are not evident in the PIV data at the part-speed compressor operating condition due to the much lower velocity deficit and hence slip velocity associated with the subsonic rotor wakes.
Three-Dimensional Unsteady Flow Field due to IGV-Rotor Interaction in the Tip Region of an Axial Compressor Rotor Passage
Authors: Ma Hongwei , Jiang Haokang , Zhang Qingguo
Published: July 2014

This paper reports an experimental study of the three-dimensional unsteady flow field due to IGV-rotor interaction in the tip region of an axial compressor rotor passage. The measurements were conducted on a low-speed large-scale axial compressor using a 3-component Laser Doppler Velocimetry. Both experimental method and measurement techniques are presented in details. The results indicate that the tip corner flow of the IGV suction surface has deeper effects on the downstream flow than the IGV wake in the tip region. The interaction and the flow mixing among the IGV wake, the IGV comer flow and the rotor leading-edge flow occur at the inlet of a rotor passage, which make the rotor inlet flow three-dimensional, turbulent and unsteady. The low-energy fluids from the upstream tend to accumulate toward the rotor pressure surface after they enter a rotor passage. In the procedure, the interaction and the flow mixing among the rotor tip leakage vortex and the low-energy fluids occur in the rotor passage.
Comparative Study of Unsteady Flows in a Transonic Centrifugal Compressor With Vaneless and Vaned Diffusers
Authors: Cui Michael M.
Published: July 2014

To reduce vibration and noise level, the impeller and diffuser blade numbers inside an industrial compressor are typically chosen without common divisors. The shapes of volutes or collectors in these compressors are also not axis-symmetric. When impeller blades pass these asymmetric structures, the flow field in the compressor is time-dependent and three-dimensional. To obtain a fundamental physical understanding of these three-dimensional unsteady flow fields and assess their impact on the compressor performance, the flow field inside the compressors needs to be studied as a whole to include asymmetric and unsteady interaction between the compressor components. In current study, a unified three-dimensional numerical model was built for a transonic centrifugal compressor including impeller, diffusers, and volute. HFC 134a was used as the working fluid. The thermodynamic and transport properties of the refrigerant gas were modeled by the Martin-Hou equation of state and power laws, respectively. The three-dimensional unsteady flow field was simulated with a Navier-Stokes solver using the k-ε turbulent model. The overall performance parameters are obtained by integrating the field quantities. Both unsteady flow field and overall performance are analyzed comparatively for each component. The compressor was tested in a water chiller system instrumented to obtain both overall performance data and local flow field quantities. The experimental and numerical results agree well. The correlation between the overall compressor performance and local flow field quantities is defined. The methodology developed and data obtained in these studies can be applied to centrifugal compressor design and optimization.
A Test Case for the Numerical Investigation of Wake Passing Effects on a Highly Loaded LP Turbine Cascade Blade
Authors: Stadtmüller Peter , Fottner Leonhard
Published: July 2014

The paper presents a compilation of experimental data on the effects of wake-induced transition on a highly loaded LP turbine cascade intended to be used for further numerical work. Although the underlying physics is not yet completely understood, the benefits of wake passing are already known and employed in the design process of modern gas turbines. For further optimizations, the next step seems to be now to enable numerical simulations detailed enough to capture the major effects while being as uncomplicated as possible at the same time to be cost-effective. The experimental results constituted in this systematic investigation are available for download and should serve as a basic data set for future calculations with different turbulence and transition models, thereby shedding some light on the complexity and modeling required for a suitable numerical treatment of the wake-induced transition process.

The data introduced in this test case was acquired using a turbine cascade called T106D-EIZ with increased blade pitch compared to design point conditions in order to achieve a higher loading. A large separation bubble forms on the suction side and allows to study boundary layer development in great detail. The upstream blade row was simulated by a moving bar type wake generator. The measurements comprise hot wire data of the bar wake characteristics in the cascade inlet plane (velocity deficit and turbulence level), boundary layer surveys with surface-mounted hot films sensors and a hot wire probe at various locations and measurements of the total pressure loss coefficient. Unsteady pressure transducers are embedded into the suction side of a cascade blade and in a wake rake to resolve the local pressure distributions over time. They yield quantitative values easily comparable to the output of numerical simulations.

The objective of this paper is to enable and to invite interested researchers to validate their code on the data set. From the extensive test program, a very limited number of operating points have been selected to focus the work. The standardized data files include a “reference” case with an exit Reynolds number of 200.000 and an exit Mach number of 0.4 as well as two points with higher Mach or lower Reynolds number for constant wake passing frequencies and background turbulence levels.
Tip Clearance Effects in Radial Flow Impeller Fans Under High Temperature Working Conditions
Authors: Gür Mesut , Engin Tahsin , Çallı Ismail
Published: July 2014

Three industrial-type centrifugal fans were designed, fabricated and tested in order to investigate the effects of axial (tip) clearance between an unshrouded impeller and stationary casing, so that the flow field behavior may differ considerable from that of a shrouded centrifugal fan impeller. Tests were conducted under high temperatures of gas up to 1000 °C at six different values of tip clearance each. Test results showed that the tip leakage flow due to the tip clearance is an unavoidable factor, which deteriorates the fan performance, and therefore the impeller geometry should be designed considering the tip clearance losses.
Flow Analysis in a Transonic Centrifugal Compressor Rotor Using 3-Component Laser Velocimetry
Authors: Krain H. , Karpinski G. , Beversdorff M.
Published: July 2014

The paper describes the flow conditions found inside an optimized transonic, high pressure ratio centrifugal compressor rotor operated with a rotor tip speed of 586 m/s. The rotor was coupled with a vaned diffuser of rather small exit radius ratio. Measurements and calculations were carried out on this device. A newly developed 3-component hybrid Laser velocimeter was applied for the optical measurements inside the rotating system. For the first time the new measurement technique delivered three velocity components instead of only two for such a compact machine with very narrow flow channels. An available 3D calculation system with an embedded Navier-Stokes solver was used for the theoretical approach.

The flow field development is described with the help of optical measurement results taken at measurement planes located at the rotor inlet and exit as well as at 40% and 60% flow path length. The measured 3D effects were highest in the middle of the flow channel, where the flow is turned from axial to radial. Here the curvature effects in the meridional plane and the enhancement of secondary flow are significant. The agreement between the theoretically and experimentally obtained third velocity component is quite good, especially in the area with strong secondary flows.
Performances of Centrifugal Compressor Impellers in Steady and Unsteady Flow Regimes Under Inlet Flow Distortions
Authors: Michelassi V. , Pazzi S. , Echtner S. , Giangiacomo P. , Martelli F. , Giachi M.
Published: July 2014

The performance of a centrifugal impeller is predicted under steady ideal axial inlet conditions. The operational range is given in terms of load and flow coefficient and polytropic efficiency. The flow field at the exit of the impeller is analyzed to show how it deteriorates while moving close to the stall limit of the characteristic curve. The effect of a strong inlet distortion obtained by intentionally altering the geometry of an inlet volute on the impeller is analyzed. The investigation is carried out for two different distortions, without and with pre swirl, and for two pressure ratios, close to the design point and close to the stall limit of the operational range. The effect of the distortion is analyzed by both a quasi-steady and unsteady approaches. The first method, while faster, is found to give results in partial disagreement with the fully unsteady analysis and is therefore abandoned. The impeller under unsteady distorted inlet is found to have degraded performances in terms of efficiency and load factor, but the overall operational range seems not be significantly affected by the fluctuations of inlet total pressure and angles.
A Numerical Investigation on the Volute/Impeller Steady-State Interaction due to Circumferential Distortion
Authors: Gu Fahua , Engeda Abraham
Published: July 2014

To understand the volute/impeller interaction at off-design conditions, the steady-state interaction between volute and impeller is investigated in this paper using CFX-TASCflow’s frozen rotor model. This model is applicable to the compressor flow where the acoustic Strouhal number is close to zero. The gentle circumferential pressure distortion is confirmed at the exit of the vaneless diffuser; but the radical pressure distortion is found around the tongue, resulting from the incidence to the tongue. The circumferential pressure distortion, which is lagged in phase to the total pressure distortion, is predicted to propagate upstream over the vaneless diffuser without significant decay. It is found that the impeller exit flow pattern depends on the slope of the circumferential variation of the static pressure at exit. This explains why the impeller efficiency is reduced at off-design conditions. Therefore, this study suggests that the undersized volute is beneficial to the impeller.
Compressor Performance With Water Injection
Authors: Horlock J. H.
Published: July 2014

There has been renewed interest recently in the injection of water at inlet to gas turbine plants. As is to be expected there is a drop in temperature at the inlet face to the compressor and this obviously has an effect on compressor performance. But a second effect occurs within the early stages of the compressor itself, associated with an increase in the effective specific heat due to continuing evaporation of the water droplets. Consequently there are movements away from design operating conditions on the stage characteristics.

A one-dimensional analysis of compressor off-design performance is developed to illustrate these effects, which appear to be appreciable, even for very small quantities of water injection.
3D Transonic Flow in a Compressor Cascade With Shock-Induced Corner Stall
Authors: Weber Anton , Schreiber Heinz-Adolf , Fuchs Reinhold , Steinert Wolfgang
Published: July 2014

An experimental and numerical study of the transonic flow through a linear compressor cascade with endwalls was conducted. The cascade with a low aspect ratio of 1.34 was tested at an inlet Mach number of 1.09 and a Reynolds number of 1.9×106. Detailed flow visualizations on the surfaces and 5-hole probe measurements inside the blading and in the wake region showed clearly a 3-dimensional boundary layer separation on the blade surface and the sidewall, and a severe corner stall induced by a strong 3D shock system at blade passage entrance.

The experimental data has been used to validate and improve the 3D Navier-Stokes code TRACE. Results showed an excellent resolution of the complex flow field. Surface pressure distributions on the entire blade surface and the endwalls, flow angle and total pressure contours within the blade passage and the wake are compared with the experimental results. An analysis of the secondary flow of this highly staggered cascade did not show the classical corner vortex. Instead, a severe flow deviation and partly reverse flow near the walls is seen. The flow solver helped to identify a weak ring vortex that originates from the passage sidewall. Surface oil flow pictures on the blade contour and the sidewall are in qualitatively good agreement to numerical surface streaklines. A considerable improvement of the numerical results could be achieved by a gradual grid refinement especially in the corner region and by successive code development.
Automised Calibration of Empirical Loss- and Deviation Models for Compressor Blade Rows
Authors: Hansen Andreas , Kappis Wolfgang
Published: July 2014

Within a project of German research co-operation AG Turbo, the operational behaviour of a 15-stage transonic compressor rig was experimentally and numerically investigated. The rig is geometrically scaled from an existing advanced heavy-duty gas turbine compressor with CDA-blading.

The development and validation of a process for automatic calibration of empirical loss and deviation correlations implemented in a compressor map calculation program for multistage axial compressors (mean section performance calculation), based on existing compressor map measurement data is the target of this project.

In Order to calibrate the empirical loss- and deviation models 1D-data as overall pressure ratio, mass flow and polytropic efficiency was extracted from the measurement data.

Subsequently the coupling of an optimisation algorithm, the compressor map calculation program and the extracted measurement data had to be realised for the automised process of calibration as the second step.

Due to different targets for the parameterised loss- and deviation models they were adjusted separately with different objectives as mass flow for the deviation model and as efficiency for the loss model. Following the cumulative calibration was carried out with a combined target of mass flow and efficiency deviations.

The process for the automatic calibration of the empirical loss and deviation correlations implemented in a compressor map calculation program has been successfully developed and validated for different speed lines based on the measurement data of a 15-stage compressor rig.