bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Leading-Edge Impingement Cooling Through Racetrack Crossover Holes
Authors: Taslim M. E. , Setayeshgar L.
Published: July 2014

Proper and efficient cooling of the turbine airfoil leading edge is imperative in increasing the airfoil life and overall efficiency of the gas turbine. To enhance the heat transfer coefficient in the leading-edge cavities, they are often roughened on three walls with ribs of different geometries. The cooling flow for these geometries usually enters the cavity from the airfoil root and flows radially to the airfoil tip or, in the most recent designs, enters the leading edge cavity from the adjacent cavity through a series of crossover holes on the partition wall between the two cavities. In the latter case, the cross-over jets impinge on a smooth leading-edge wall and exit through the showerhead film holes, “gill” film holes on the pressure and suction sides, and, in some cases, forms a cross-flow in the leading-edge cavity and is ejected through the airfoil tip hole. In this investigation, the impingement heat transfer coefficient was measured on both smooth and roughened leading-edge walls. Most reported studies cover the impingement on a flat smooth surface with round jets. This investigation dealt with two new features in airfoil leading-edge cooling concept: a curved and roughened target surface as well as impingement with racetrack shaped holes. Results of circular crossover jets impinging on the same surface geometries were reported by these authors previously. Experimental heat transfer results are presented for the impingement of racetrack shaped cross-over jets, with major hole (jet) axes at 0° and 45° angles to the cooling cavity’s radial axis, on 1) a smooth curved leading-edge wall, 2) a wall roughened with conical bumps, and 3) a wall roughened with tapered radial ribs. The tests were run for a range of inlet and exit flow arrangements and jet Reynolds numbers and the results were compared with those of round cross-over jets. The major conclusions of this study are: a) racetrack crossover holes are much more efficient than circular holes in cooling of the leading-edge surface, b) the overall heat transfer performance of 0° racetrack cross-over holes is superior to that of 45° racetrack cross-over holes, c) there is a heat transfer enhancement of up to 70% for roughening the target surface, and d) the driving factor in heat transfer enhancement is the increase in surface area.
Heat Transfer Characteristics of an Impingement Plate Used in a Turbine Vane Cooling System
Authors: Son Changmin , Gillespie David , Ireland Peter , Dailey Geoffrey M.
Published: July 2014

Detailed heat transfer coefficient distributions have been measured on both surfaces of the impingement plate of an engine-representative impingement cooling system using the thermochromic liquid crystal (TLC) transient technique. The color images of the TLC on the impingement downstream surface provide evidence of a re-impingement flow. The re-impingement flow is found to contribute to local increases in the heat transfer on the impingement plate downstream surface. It was found that the average heat transfer coefficient on the impingement downstream surface is about 50% of the average target surface heat transfer coefficient. The results are compared with a previously reported correlation.
Effect of Squealer Cavity Depth and Oxidation on Turbine Blade Tip Heat Transfer
Authors: Bunker Ronald S. , Bailey Jeremy C.
Published: July 2014

An experimental study has been performed to investigate the effect of squealer cavity depth on the detailed distribution of convective heat transfer coefficients of a turbine blade tip surface. This paper presents full surface information on heat transfer coefficients within a blade cascade which develops an appropriate pressure distribution about an airfoil blade tip and shroud model. A stationary blade cascade experiment has been run consisting of three airfoils, the center airfoil having a variable tip gap clearance. The airfoil models the aerodynamic tip section of a high pressure turbine blade with inlet Mach number of 0.21, exit Mach number of 0.74, pressure ratio of 1.41, Reynolds number of 2.8•106, and total turning of about 100 degrees. The cascade inlet turbulence intensity level is 9%. Tip surface heat transfer coefficient distributions are first shown for a flat, square-edge tip with a clearance gap of 2.03 mm. Heat transfer distributions are then shown for full-perimeter squealer tip cavities having the same clearance gap above the squealer rim, and clearance-to-cavity depth ratios from 0.67 to 2. Regionally averaged heat transfer coefficients are analyzed to discern a relationship between tip heat transfer and cavity depth. Further tests demonstrate the effect of partial squealer rim oxidation, or material loss, on the surface heat transfer distributions.
Study of Hot Streak Effects in a Counter-Rotating Turbine
Authors: Ji L. C. , Xu J. Z. , Chen J.
Published: July 2014

Based on its convection nature, some influences of the hot streak on a 1+1 (with inter-blade vane) counter-rotating turbine are studied by using a three-dimensional (3D) unsteady Euler solver. Emphasis is laid on the hot streak effect to the blade heat load and the clocking effects between hot streak and blade rows. One temperature distortion magnitude, two spanwise and four tangential positions, four clocking locations between vanes of first and second stage are examined. Results show that the effect of the hot streak on a counter-rotating turbine is nearly the same as a conventional turbine. However, clocking between the hot streak and the vane of the high pressure turbine (HPT) exerts significant influences on the heat load of the whole HPT stage. Also, clocking between the HPT vane and the vane of the low pressure turbine (LPT) affects the heat load of the LPT greatly. These effects cannot be captured with the steady flow assumption. So time accurate simulation about the hot streak/blade interaction must be used as a basis for the turbine design and optimization.
The Combined Effects of Rib Arrangements and Discrete Ribs on Local Heat/Mass Transfer in a Square Duct
Authors: Cho H. H. , Lee S. Y. , Wu S. J.
Published: July 2014

Local heat/mass transfer and friction loss in a square duct roughened with various types of continuous and discrete rib tabulators are investigated. The combined effects of the gap flows of the discrete ribs and the secondary flows are examined for the purpose of the reduction of thermally weak regions and the promotion of the uniformity of heat/mass transfer distributions as well as the augmentation of average heat/mass transfer. The rib-to-rib pitch to the rib height ratio (p/e) of 8 and the rib angles of 90 and 60 deg are selected with e/Dh=0.08. The vortical structure of the secondary flows induced by the parallel angled arrays are quite distinct from that induced by the cross angled arrays. This distinction influences on heat/mass transfer and friction loss in all the tested cases. The gap flows of the discrete ribs reduce the strength of the secondary flows but promote local turbulence and flow mixing. As a result, the fairly uniform heat/mass transfer distributions are obtained with two row gaps.
Heat Transfer Characteristics of a Flow Passage With Long Pin Fins and Improving Heat Transfer Coefficient by Adding Turbulence Promoters on a Endwall
Authors: Takeishi K. , Nakae T. , Watanabe K. , Hirayama M.
Published: July 2014

Pin fins are normally used for cooling the trailing edge region of a turbine, where their aspect ratio (height H/diameter D) is characteristically low. In small turbine vanes and blades, however, pin fins may also be located in the middle region of the airfoil. In this case, the aspect ratio can be quite large, usually obtaining values greater than 4. Heat transfer tests, which are conducted under atmospheric conditions for the cooling design of turbine vanes and blades, may overestimate the heat transfer coefficient of the pin-finned flow channel for such long pin fins. The fin efficiency of a long pin fin is almost unity in a low heat transfer situation as it would be encountered under atmospheric conditions, but can be considerably lower under high heat transfer conditions and for pin fins made of low thermal conductivity material. A series of tests with corresponding heat transfer models has been conducted in order to clarify the heat transfer characteristics of the long pin-finned flow channel. It is assumed that heat transfer coefficients can be predicted by the linear combination of two heat transfer equations, which were separately developed for the pin fin surface and for tubes in crossflow. To confirm the suggested combined equations, experiments have been carried out, in which the aspect ratio and the thermal conductivity of the pin were the test parameters. To maintain a high heat transfer coefficient for a long pin fin under high-pressure conditions, the heat transfer was augmented by adding a turbulence promoter on the pin-finned endwall surface. A corresponding equation that describes this situation has been developed. The predicted and measured values showed good agreement. In this paper, a comprehensive study on the heat transfer of a long pin-fin array will be presented.
Integration of Multi-Disciplinary Factors Into Turbine Cooling Design
Authors: Glezer Boris
Published: July 2014

The presented paper describes a multi-disciplinary cooling selection practice applied to major gas turbine engine hot section components, including turbine nozzles, blades, discs, combustors and support structures maintaining blade tip clearances. The paper demonstrates the benefits of close interaction between participating disciplines, when this interaction starts in the early phase of the hot section development. The approach targets advances in engine performance and cost by optimizing the design process, often requiring compromises within individual disciplines.
Elliptical Pin Fins as an Alternative to Circular Pin Fins for Gas Turbine Blade Cooling Applications: Part 2 — Wake Flow Field Measurements and Visualization Using Particle Image Velocimetry
Authors: Uzol Oğuz , Camci Cengiz
Published: July 2014

Extensive wake flow field measurements and visualizations are conducted using particle image velocimetry (PIV) inside the wakes of the elliptical and circular pin fin arrays in order to better understand the flow physics and the loss mechanisms of these devices. The true-mean velocity field inside the wake two diameters downstream of the pin fin arrays is obtained by collecting and ensemble averaging a large number of PIV samples in the midplane of the test section. Additional experiments are also conducted inside the very near wake of the pin fins in order to visualize instantaneous flow field features. The results of the study reveal that the circular pin fin array creates a large low momentum wake region when compared to the elliptical pin fin arrays. It is observed from the flow visualization inside the wake that this kind of a very large momentum deficit is created due to the early separation of the flow from the circular fins in the second row. In the case of elliptical fins, however, the flow stays attached to the fin surface and the separation occurs very close to the downstream stagnation point on the surface which in turn results in a very small low momentum wake region behind the elliptical pin fin arrays. The mean turbulent kinetic energy levels from the PIV measurements show very high turbulence levels in the wake of the circular fin arrays compared to the elliptical fins. However, the smaller momentum deficit inside the elliptical pin fin wakes results in higher local Reynolds numbers inside the wake when compared to the circular pin fin wakes. This in turn helps to keep the endwall heat transfer enhancement levels close to the circular fin arrays although the turbulence levels are much lower in this region.
Quasi Two-Dimensional Cyclone-Jet Cooling Configuration: Evaluation of Heat Transfer and Pressure Losses
Authors: Khalatov Artem A. , Syred Nick , Bowen Philip J. , Al-Ajmi Rashed
Published: July 2014

Heat transfer and pressure losses have been studied in a cyclone-jet chamber to evaluate its the thermal efficiency and thermal-hydraulic performance. The cyclone chamber simulates the leading edge area, it is 4.2 mm in diameter and 35 mm long and has four injecting and five discharging round-shaped holes evenly spread and facing the chamber stagnation point. Such a configuration generates a quasi two-dimensional swirl flow pattern accompanied with flow separation effects. Three test sections with various inlet and outlet hole diameter have been studied to evaluate the effect of boundary conditions. The Heating in Melted Metal (HMM) experimental technique has been employed to measure heat transfer parameters.

The local spanwise heat flux distribution has a periodical characteristic with a maximum opposite the injecting holes and a minimum in between them. The non-uniformity of the heat flux depends on the diameter of inlet holes and the air mass flow rate. The angular distribution of an averaged spanwise heat transfer is asymmetrical with respect to the chamber stagnation point; it is either actually a ‘flat curve’ or has a maximum at the stagnation point. An average heat transfer in the cyclone chamber is 2.61 – 3.54 higher compared with its axial counterpart. The basic heat transfer correlations are presented in addition to the thermal efficiency and thermal-hydraulic performance evaluation made. The proposed cyclone-jet design is as good as a serpentine cyclone cooling and some advanced cooling techniques, but more simple production technology is an undoubted advantage of this configuration.
On Turbulent Secondary Flows Inside Rotating Ducts Oriented at Certain Angles With Rotation Axis
Authors: Song B. , Amano R. S.
Published: July 2014

In the present study, the fully developed turbulent secondary flows inside rotating square duct oriented at certain angles with axis of rotation are numerically simulated using the nonlinear k – ω models. For rotating duct with θ=0° angle between sidewall plane and axis of rotation, it is noteworthy that the two vortices are generated when Ro=0.05, four vortices are presented when Ro=0.15, and only two vortices are predicted when the rotational speed is increased up to Ro=0.35. For the purpose of comparison, the linear k – ω model is also employed. It is shown that the linear and nonlinear models all produce reasonable results. However, different results are also exhibited with the two models. For example, the nonlinear model predicts less distortion region than the linear model. On the suction side, the nonlinear k – ω model produces greater gradients than the linear model. For rotating ducts with θ=30° and θ=60°, it is noticed that the stronger rotation forces the lower momentum fluid to be confined near the lower left corner, and produces larger range of high mainstream velocities.
Measurements of the Effects of Pressure-Gradient History on Separation-Bubble Transition
Authors: Yaras M. I.
Published: July 2014

In many boundary-layer situations, particularly in turbomachinery, separation-bubble transition occurs at a local pressure gradient that differs significantly from the values further upstream. Additionally, this upstream history changes substantially from case to case, with the transitioning separation bubble occurring at streamwise positions along the blade chord varying from close vicinity of the leading edge to mid-chord. In the case of low free-stream disturbances, development of instability waves prior to separation would clearly vary as a result of these differences in the history of the boundary layer prior to separation.

Measurements are presented to document the effects of pressure gradients that a laminar boundary layer experiences prior to separation on the transition process that follows in the separated region. The boundary layer development was measured on a smooth, flat plate upon which streamwise pressure gradients were imposed by a flexible, contoured wall opposite to the test plate. Only low freestream-turbulence levels were considered to isolate the effects of pressure-gradient history on the transition process. Two Reynolds numbers were considered for each pressure-gradient setting. Measured quantities consisted of velocity and turbulence intensity obtained with a single hot-wire, and of surface pressures. Observed variations in transition onset location with changes in pressure-gradient history provide the basis for further development of current transition prediction schemes.
Computational and Mathematical Modelling of Turbine Rim Seal Ingestion
Authors: Hills Nicholas J. , Chew John W. , Turner Alan B.
Published: July 2014

Understanding and modelling of main annulus gas ingestion through turbine rim seals is considered and advanced in this paper. Unsteady 3-dimensional computational fluid dynamics (CFD) calculations and results from a more elementary model are presented and compared with experimental data previously published by Hills et al (1997). The most complete CFD model presented includes both stator and rotor in the main annulus and the inter-disc cavity. The k-ε model of turbulence with standard wall function approximations is assumed in the model which was constructed in a commercial CFD code employing a pressure correction solution algorithm. It is shown that considerable care is needed to ensure convergence of the CFD model to a periodic solution. Compared to previous models, results from the CFD model show encouraging agreement with pressure and gas concentration measurements. The annulus gas ingestion is shown to result from a combination of the stationary and rotating circumferential pressure asymmetries in the annulus. Inertial effects associated with the circumferential velocity component of the flow have an important effect on the degree of ingestion.

The elementary model used is an extension of earlier models based on orifice theory applied locally around the rim seal circumference. The new model includes a term accounting for inertial effects. Some good qualitative and fair quantitative agreement with data is shown.
Coupled Fluid/Solid Heat Transfer Computation for Turbine Discs
Authors: Verdicchio John A. , Chew John W. , Hills Nick J.
Published: July 2014

This paper considers the coupling of a finite element thermal conduction solver with a steady, finite volume fluid flow solver. Two methods were considered for passing boundary conditions between the two codes — transfer of metal temperatures and either convective heat fluxes or heat transfer coefficients and air temperatures. These methods have been tested on two simple rotating cavity test cases and also on a more complex real engine example.

Convergence rates of the two coupling methods were compared. Passing heat transfer coefficients and air temperatures was found to give the quickest convergence. The coupled method gave agreement with the analytic solution and a conjugate solution of the simple free disc problem. The predicted heat transfer results for the real engine example showed some encouraging agreement, although some modelling issues are identified.
Thermo-Economic Optimization of a Cogeneration Plant With Below Ambient Pressure Discharge Gas Turbine
Authors: Bianchi M. , Negri di Montenegro G. , Peretto A.
Published: July 2014

The gas turbine use in cogeneration plants for thermal and electric power production is constantly increasing especially for low power requirements.

In this paper, firstly a thermodynamic analysis of a Below Ambient pressure discharge Gas Turbine (BAGT) has been evaluated and the BAGT cogenerative performance compared with those of a Brayton Cycle (BC) cogenerative power plant.

Subsequently, an economic investigation of BAGT is carried out and the benefits, with respect to BC, evaluated.

It resulted that the BAGT presents a higher electric efficiency and its employment may strongly increase the budget at disposal for the cogenerative plant investment.
Heat Recovery System Control Strategy to Meet Multiple Transient Demands
Authors: Perez-Blanco H. , Albright Paul
Published: July 2014

As increasing power generation needs are met with gas turbines, it is clear that exhaust heat recovery presents a considerable opportunity to reduce operational costs and enhance thermal efficiency. Typically, a system may provide power, process heat and cooling. However, each utility may have a daily demand curve with peaks that do not necessarily coincide in time. Hence, it is necessary to devise strategies that ensure meeting the needs of each user continually while maintaining high thermal efficiencies. To study these situations, a dynamic model of a system comprising a gas turbine, a heat recovery steam generator, and absorption machine was developed. The transient response of the system was studied to determine the effects of sudden changes in demand. Two control strategies utilizing proportional integral controls were considered. The first strategy relied on operating the turbine to meet the power required by the consumer. When power demands were low and steam and cooling demands high, a secondary control strategy operated the turbine to meet the steam demands, thus maximizing the thermal efficiency of the systemThe first strategy relied on operating the turbine to meet the power required by the consumer. When power demands were low and steam and cooling demands high, a secondary control strategy operated the turbine to meet the steam demands, thus maximizing the thermal efficiency of the system. System control and stability were tested, including simulation of a power distribution network simulating resistive, capacitance and inductive loads.
Management of High Speed Machinery Signatures to Meet Stealth Requirement in the Royal Swedish Navy Visby Class Corvette (YS 2000)
Authors: Liwång Hans , Pejlert Lars , Miller Steve , Gustavsson Jan-Erik
Published: July 2014

Over the years, the word stealth has been used more and more when discussing design and operational characteristics in military applications. New and more challenging techniques are constantly being applied to minimize signatures and thus hinder or delay detection and identification.

The Visby Class Corvette is a multipurpose combat ship with 600 tons displacement. The hull is a sandwich construction of a PVC core with carbon fiber/vinyl laminate. The propulsion system consists of two identical CODOG machinery systems, each driving a KaMeWa 125 size Water Jet Unit.

The Ship has special requirements for all signatures, i.e. Radar-, Hydro acoustics-, IR- and Magnetic Signature. The High Speed Machinery is twin Honeywell TF50A Gas Turbines, cantilever mounted side by side on the Main Reduction Gearbox housing. The Main Reduction Gearbox is a dual input high performance marine Gearbox designated MA - 107 SBS, designed and manufactured by Cincinnati Gear Co. The Low Speed Machinery is a MTU 16 V 2000 TE90 Diesel Engine connected to the MRG by a power take in shaft.

Combustion Air for the Gas Turbines is ducted from the shipside Air Inlet Screen (radar screen) via 3-stage separating filters. The Exhausts from the twin Gas Turbines are combined into one Exhaust Pipe and ducted to the ship transom above the Water Jet stream.

Very little can be changed in the Gas Turbine, but high quality such as well balanced rotating part contributes to reduce the signatures. However, the main work has to be accomplished by the building shipyard in cooperation with the Gas Turbine manufacturer. The Main Reduction Gearbox is more available for changes to reduce signatures, but even for the Gearbox the building shipyard has to take design and installation measures.

The HSM installation consist mainly of the Gas Turbine Engine, the Main Reduction Gear, Water Jets Unit and surrounding equipment such as main shaft, bearings and so on. The emphasis in this paper is on the GT, MRG and their effect on some of the more well known signatures i.e. RCS, IR, Hydro acoustics and Magnetic. Also some design measures are discussed.
Turbocompressor Revamp: A Low Cost Modification to Considerable Efficiency Improvement
Authors: Skorping Roald , Underbakke Harald
Published: July 2014

Depletion of oil and gas reservoirs will gradually reduce the wellhead pressure. Consequently, the process equipment for separation and transport of oil and gas will move into off-design operation with reduced efficiency. Turbocompressors are critical equipment used for re-compression, injection or transport of natural gas. Off-design operation may result in a major compressor efficiency drop.

Statoil operates several offshore North Sea process platforms where reduction in wellhead pressure is a challenge. This paper describes the experience with compressor revamp on one onshore and one offshore process plant covering scope of work / supply, installation, testing, operation and cost/benefit analyses.

The processing facility on Statoil’s Troll A platform in the North Sea interacts with the installations at the Kollsnes gas treatment plant near Bergen, where natural gas is transported to the European Continent by the world’s largest variable speed electrical drive pipeline compressors. Changes in gas inlet conditions required revamping in order to adapt the compressor performance to existing process conditions. In addition, a high performance 3 dimensional rotor design was installed in the old compressor casing.

Sleipner East and Sleipner West lie in the Norwegian North Sea. The first of these gas and condensate fields came on stream in October 1993. After gradually reduction of the wellhead pressure on the Sleipner A processing platform, it was decided to modify the processing facilities and revamping of two gas turbine driven re-compressors were required.
Gearbox Failure of a Turbogenerator Set
Authors: Rao J. S. , Peraiah K. Ch.
Published: July 2014

A 6 MW Turbogenerator suffered a catastrophic failure on 26th December 1999 due to a ground fault in the line. The turbine along with the transmission unit and both the couplings failed in this accident.

The turbogenerator set is modeled for torsional vibration analysis as a multi degree of freedom system. The natural frequencies and mode shapes are obtained. The system is next modeled as an equivalent four rotor system and a short circuit analysis is made to determine the magnification factor in this period. A complete gear box analysis has been made for its fatigue life and it was shown that it is just not capable of withstanding even a single alternating stress arising from the short circuit. The pinion will fail under short circuit condition.
Dynamics of Labyrinth Gas Seals With Air Injection
Authors: Kwanka K.
Published: July 2014

Exciting forces generated in gas seals and blading of turbo-machinery can lead to vibrations of the rotor with unacceptably high amplitudes (Thomas [1958], Alford [1965]). It is important to predict in an early design stage the stability limit of the rotor so as to avoid the occurrence of self-excited vibrations. In the field, there are only few possibilities to stabilize the rotor. One way minimizing the cross-forces is by injecting air into the seal and counteracting the exciting mechanisms.

The paper will present experimental dynamic coefficients of a gas seal of the teeth on stator type with eight cavities. The coefficients will be compared to the values obtained with a tangential injection of air into the first cavity in co-rotating and in counter-rotating direction. It seems that the impact of air injection is not as effective as swirl brakes or honeycomb stators.
A Hydrostatic Bearing With Compressible Fluid for Broad Application
Authors: Jacob John S. , Bently Donald E. , Yu John J.
Published: July 2014

The use of relatively inviscid, compressible fluids in externally-pressurized bearings has interesting possibilities for both OEM and retrofit applications. The chance to dramatically reduce mechanical losses and bearing heating, the elimination of oil from the process and installation, and the utilization of compressible process fluids as the supporting medium all have potential economic and environmental benefits. An experimental gas bearing rig was constructed to investigate the feasibility of some general applications. Clearance and orifice dimensions were selected based on a fairly simple gas flow model. Bently-Muszynska model parameters for the hydrostatic gas bearing were obtained through static-pull and non-synchronous perturbation testing.
Imbalance Response of a Rotor Supported on Flexure Pivot Tilting Pad Journal Bearings in Series With Integral Squeeze Film Dampers
Authors: San Andrés Luis , De Santiago Oscar
Published: July 2014

Measurements of the imbalance responses of a massive 45 kg rotor supported on series (flexure pivot) tilting pad bearings and integral squeeze film dampers (SFDs) are presented. The rotor-bearing configuration is of interest in compressor applications where often oil lubricated dampers are introduced in series with fluid film bearings to relocate critical speeds, enhance the overall system damping, and reduce the risks of rotordynamic instabilities due to seals and impellers, for example. Coast-down experiments from 9,000 rpm are conducted for increasing levels of rotor imbalance, and equivalent system damping coefficients identified from the peak amplitude of rotor response while traversing cylindrical mode critical speeds. The tests performed with locked (inactive) and active SFDs demonstrate the effectiveness of the flexible damped support in reducing the system critical speed and improving the overall rotor response with reduced transmitted forces to ground. The SFDs allow safe rotor operation with values of imbalance twice as large as the maximum sustained by the rotor supported on tilting pad bearings alone. The experiments reveal a linear relationship between the peak amplitude of vibration at the critical speeds and the imbalance displacement, even for rotor motions larger than 50% of the tilting pad bearing and damper clearances. The tests also show little cross-coupling effects with the shaft centerline moving along a nearly vertical path. The rotor-bearing system remained stable in the entire range of operation and without the appearance of subsynchronous vibration or non-linear damper jump response.
Numerical Investigation of Blade Flutter at or Near Stall in Axial Flow Turbomachines
Authors: Höhn Wolfgang
Published: July 2014

During the design of the compressor and turbine stages of today’s aeroengines, aerodynamically induced vibrations become increasingly important since higher blade load and better efficiency are desired. In this paper the development of a method based on the unsteady, compressible Navier-Stokes equations in two dimensions is described in order to study the physics of flutter for unsteady viscous flow around cascaded vibrating blades at stall.

The governing equations are solved by a finite difference technique in boundary fitted coordinates. The numerical scheme uses the Advection Upstream Splitting Method to discretize the convective terms and central differences discretizing the viscous terms of the fully non-linear Navier-Stokes equations on a moving H-type mesh. The unsteady governing equations are explicitly and implicitly marched in time in a time-accurate way using a four stage Runge-Kutta scheme on a parallel computer or an implicit scheme of the Beam-Warming type on a single processor. Turbulence is modelled using the Baldwin-Lomax turbulence model. The blade flutter phenomenon is simulated by imposing a harmonic motion on the blade, which consists of harmonic body translation in two directions and a rotation, allowing an interblade phase angle between neighboring blades. Non-reflecting boundary conditions are used for the unsteady analysis at inlet and outlet of the computational domain. The computations are performed on multiple blade passages in order to account for nonlinear effects. A subsonic massively stalled unsteady flow case in a compressor cascade is studied. The results, compared with experiments and the predictions of other researchers, show reasonable agreement for inviscid and viscous flow cases for the investigated flow situations with respect to the Steady and unsteady pressure distribution on the blade in separated flow areas as well as the aeroelastic damping.

The results show the applicability of the scheme for stalled flow around cascaded blades. As expected the viscous and inviscid computations show different results in regions where viscous effects are important, i.e. in separated flow areas. In particular, different predictions for inviscid and viscous flow for the aerodynamic damping for the investigated flow cases are found.
Prediction of Flutter and Inlet Distortion Driven Response of a Transonic Fan Rotor Using Phase-Lagged Boundary Conditions
Authors: Li H. D. , He L.
Published: July 2014

Prediction of blade forced response and flutter is of great importance to turbomachinery designers. However, calculations of unsteady turbomachinery flows using conventional time-domain methods typically would lead to the use of multi-passage/whole-annulus domains due to the required direct periodic condition. This makes numerical computations extremely time-consuming and is one of the major difficulties for nonlinear unsteady calculations to be applied in a blading design environment. A single-passage approach to three-dimensional unsteady Navier-Stokes calculations using the Fourier-series based Shape-Correction method has been developed, and been applied to analyze inlet distortion driven response and flutter of a transonic fan rotor (NASA Rotor-67). The key feature is that the Shape-Correction method enables a single-passage solution to unsteady flows in blade rows under influences of multiple disturbances with arbitrary inter-blade phase angles. The results show that the single-passage solution can capture deterministic unsteadiness as well as time-averaged flows in good agreement with conventional multi-passage solutions, while the corresponding computing time can be reduced dramatically.
Eigen Solutions of Grouped Turbo Blades Solved by the Generalized Differential Quadrature Method
Authors: Kuang J. H. , Hsu M. H.
Published: July 2014

The eigenvalue problems of grouped turbo blades were numerically formulated by using the generalized differential quadrature method (GDQM). Different boundary approaches accompanying the GDQM to transform the partial differential equations of grouped turbo blades into a discrete eigenvalue problem are discussed. Effects of the number of sample points and the different boundary approaches on the accuracy of the calculated natural frequencies are also studied. Numerical results demonstrated the validity and the efficiency of the GDQM in treating this type of problem.
A Parametric Study of a Cottage-Roof Damper and Comparison With Experimental Results
Authors: Jareland Martin H.
Published: July 2014

Platform dampers are commonly used in turbomachinery to reduce the vibration amplitudes of the turbine blades. A blade-to-blade platform damper is simply a piece of metal which is pressed against two adjacent blade platforms by centrifugal force. Relative motions of the platforms lead to slip in the contacts and friction damping is provided in the system. The studied platform damper is designed with inclined contact surfaces. This type of damper is often called a cottage-roof damper or wedge damper. The inclination of the contact surfaces leads to variation of the normal load, which complicates the analysis of such dampers.

In this paper, a simulation model is presented for a tuned bladed disk with cottage-roof dampers. This model includes normal load variation on the contact and a friction interface model valid for both macroslip and microslip. The elasticity of the damper body is often an important parameter for the performance of the damper and is included in the model.

A comparison between solving the equation of motion in the frequency domain and the time domain is performed. It is found that the frequency domain solution with the fundamental frequency alone gives a result close to the time domain solution. The simulation model is validated with experimental data and it is found that the reduction of the resonance amplitude agrees well for the tested dampers.

A parametric study is performed to find the optimal friction damper design. The studied parameters are the inclination of the contact surface, the coefficient of friction and the damper body stiffness. It is found that an increase in inclination of the contact surface and an increase in the coefficient of friction lead to a reduction of the optimal damper mass. An increase of the damper body stiffness results in a decrease of the resonance amplitude of the blade tip, particularly for high damper masses.
Computation of the Optimal Normal Load for a Mistuned and Frictionally Damped Bladed Disk Assembly Under Different Types of Excitation
Authors: Cha D. , Sinha A.
Published: July 2014

Using non-dimensional variables, the performances of friction dampers of a mistuned bladed disk assembly are examined for different types of excitation: white noise excitation, independent narrow band random excitation and sinusoidal excitation with unknown amplitudes. Based on the harmonic balance method, an analytical technique is developed to compute the statistics of response for sinusoidal excitation with unknown amplitudes. The performances of blade-to-blade and blade-to-ground dampers are compared under different types of excitation. It is found that non-dimensional optimal normal loads of friction dampers are almost independent of the nature of excitation. Therefore, optimal normal loads of friction dampers can be chosen without any knowledge of the nature of excitation.
Design Improvements of the EJ 200 HP Compressor: From Design Verification Engine to a Future All Blisk Version
Authors: Kosing O. E. , Scharl R. , Schmuhl H. J.
Published: July 2014

The EJ 200 engine powers the Eurofighter / Typhon combat aircraft and is being built by the four nations UK (RR), Germany (MTU), Italy (FIAT AVIO) and Spain (ITP). The engine is capable of 60 kN dry thrust and 90kN reheat thrust with a 15% built in growth potential. The specific thrust to weight ratio is ≈ 10 and the overall pressure ratio 26.

MTU’s 33% work - share package contains the development of the three stage LP Compressor, the five stage HP Compressor and the Digital Engine Control Unit.

This paper concentrates on the five stage axial HP Compressor. It describes the major design changes from the very first design verification engine (DVE) to a future all blisk version. It first provides a brief historical overview of the major design improvements which are then discussed in detail.

The rotor concept is discussed with respect to life, weight, material and repair.

The development of the casing to improve the tip clearance behaviour, the containment and the protection against titanium fire is outlined.

The stator concept is described in connection with an intense cost reduction program.

The HP Compressor has successfully completed testing and flight clearance has been approved for all standards. Thus far the HPC has accumulated more than 16500 hours total engine experience and over 1040 Eurofighter flights. The production engine manufacturing is in progress, with the first engine to be delivered in March 2001.
Theory and Test Correlation for Laminate Stacking Factor Effect on Homopolar Bearing Stiffness
Authors: Kenny Andrew , Palazzolo Alan , Montague Gerald T. , Kascak Albert F.
Published: July 2014

The effect of the laminate stacking factor on homopolar magnetic bearing performance is examined. Stacked laminates are used on the bearing rotor and in the stator. These laminate stacks have anisotropic permeability. Equations for the effect of the stacking factor on homopolar bearing position stiffness are derived. Numerical results are calculated and compared to measurements. These results provide an answer for the common discrepancy between test and theory for homopolar magnetic bearing position stiffnesses.
Clocking Effects in a 1.5 Stage Axial Turbine: Steady and Unsteady Experimental Investigations Supported by Numerical Simulations
Authors: Reinmöller U. , Stephan B. , Schmidt S. , Niehuis R.
Published: July 2014

The interaction between rotor and stator airfoils in a multistage turbomachine causes an inherently unsteady flow field. In addition, different relative circumferential positions of several stator rows and rotor rows, respectively, have an influence on the flow behaviour in terms of loss generation, energy transport and secondary flow. The objective of the presented study is to investigate the effects of stator airfoil clocking on the performance of an 1-1/2 stage axial cold air turbine. The investigated axial turbine consists of two identical stators. The low aspect ratio of the blades and their prismatic design leads to a three-dimensional outlet flow with a high degree of secondary flow phenomena. Nevertheless, the small axial gaps between the blade rows are responsible for strong potential flow interaction with the radial wake regions in the measurement planes. Consequently, parts of the wakes of the first stator are clearly detected in the rotor outlet flow.

To give an overview of the time-averaged flow field, measurements with pneumatic probes are conducted behind each blade row at ten different clocking-positions of the second stator. Further, an optimised clocking position was found due to a minimum in pressure loss behind the 2nd stator. The unsteady measurements are carried out with hot-wire probes for three selected stator-stator positions. Animations of selected flow properties show the influence of different circumferential positions of the second stator on the unsteady flow behaviour and secondary flow field. In addition and compared with experimental results three-dimensional unsteady viscous flow computations are performed.
Numerical Investigation of a 1-1/2 Axial Turbine Stage at Quasi-Steady and Fully Unsteady Conditions
Authors: Aubé Martin , Hirsch Charles
Published: July 2014

The analysis and design methods used for turbomachinery components are mostly based on steady aerodynamics, neglecting the important unsteady nature of the flow field. An improvement in performance can however be achieved with a prior understanding, evaluation and modeling of the main unsteady loss sources generated in rotor/stator interactions, through new advanced experimental data coupled to systematic and controlled numerical simulations performed at the full unsteady level of approximation. But such calculations are even nowadays challenges to the CFD community, due to their high requirement in computer resources.

To investigate the importance of unsteady loss mechanisms, a 1-1/2 axial turbine stage has been resolved at both quasi-steady and fully unsteady levels of approximation. In order to reduce the demand on computer resources, a scaling procedure can be applied to retrieve equal pitch distance on both sides of each rotor/stator interface. The space and time flow periodicity are then uncoupled and the unsteady flowfield may be resolved on a reduced number of blade passages per row without having to consider any time periodicity in the boundary treatment. The grid scaling however affects the turbine total pressure ratio and the position and strength of secondary flows, as the pitch-to-chord ratio is not kept constant. This effect is analyzed in the paper, with the objective to assess the associated approximation errors.

Steady and unsteady numerical simulations are compared with the experimental data along three measuring stations placed downstream of each blade row. Even if steady results are in good agreement and allow capturing the main flow structures of the turbine stage, only the fully unsteady calculation resolves the complex loss mechanisms encountered mainly in the rotor and downstream stator components. These unsteady interactions are observed through time variations of the entropy, absolute flow angle and static pressure.
Evaluation of Unsteady CFD Methods by Their Application to a Transonic Propfan Stage
Authors: Schmitt S. , Eulitz F. , Wallscheid L. , Arnone A. , Marconcini M.
Published: July 2014

The accuracy in predicting the unsteady aerodynamic blade-row-interaction of two state-of-the-art Navier-Stokes codes is evaluated within the current paper. The general flow features of the test case — a transonic research propfan stage — are described in brief as far as necessary to understand the detailed comparisons. The calculated unsteady velocity and flow angle distributions at various axial planes of the stage are compared to data from unsteady laser measurements. The general flow features of the propfan are very well reproduced by the numerical methods and a good agreement is also obtained in comparison to the measured data. One important outcome of the comparison is the good agreement of both numerical methods with the unsteady fluctuations measured in the experiment.
A Model for Radial Flow Turbine Performance in Highly Unsteady Flows
Authors: Hu Xiao , Lawless Patrick B.
Published: July 2014

This work was focused on the development of models for turbomachinery unsteady performance that could capture the significant aspects of fluid inertia effects, and thus provide insight into performance in highly unsteady flows. The application chosen for this approach was the turbine from a pulse-turbocharged diesel engine turbocharger, where the flow unsteadiness in on the order of the mean flow. The Euler Equation with Source Terms (EEST) technique was employed, with the rotor modeled in the relative reference frame. The results of this approach showed the ability to accurately predict the dynamics of a twin-entry turbine operating in an on-engine environment. In general, the modeling approach is valid for any compression or expansion system where the reduced frequency is high enough to suggest that unsteadiness is important, while at the same time low enough that that viscous effects may be quasi-steady. Possible applications would be predictions for aircraft engine compressions systems with unsteady inlet distortions, start up transients in a broad class of turbomachines, and any radial flow systems operating with significant inlet or exit volute generated distortions.
Centrifugal Compressor Blade Trimming for a Range of Flows
Authors: Rodgers C.
Published: July 2014

Centrifugal impeller blade trimming has long been used in the turbocharger industry to adapt a single impeller casting to a series of flow capacities, but surprisingly little published literature exists on the effects of trimming to compressor performance.

This paper is presented as partial remedy, and describes the performance characteristics of a single stage centrifugal compressor designed and tested to cover a range of flow requirements by impeller blade and diffuser vane trimming.

Stage and component test performance characteristics are presented for five trimmed flowpath contours covering a flow capacity range of approximately five to one at a DeLaval number of 0.75.

The impeller tip diameter was 356mm, and the highest overall stage efficiency measured was 84.8% at an (air) pressure ratio of 1.5.
Three-Dimensional Turbulent Flow in the Tip Region of an Axial Compressor Rotor Passage at a Near Stall Condition
Authors: Ma Hongwei , Jiang Haokang
Published: July 2014

This paper presents an experimental study of the three-dimensional turbulent flow field in the tip region of an axial flow compressor rotor passage at a near stall condition. The investigation was conducted in a low-speed large-scale compressor using a 3-component Laser Doppler Velocimetry and a high frequency pressure transducer. The measurement results indicate that a tip leakage vortex is produced very close to the leading edge, and becomes the strongest at about 10% axial chord from the leading edge. Breakdown of the vortex periodically occurs at about 1/3 chord, causing very strong turbulence in the radial direction. Flow separation happens on the tip suction surface at about half chord, prompting the corner vortex migrating toward the pressure side. Tangential migration of the low-energy fluids results in substantial flow blockage and turbulence in the rear of a rotor passage. Unsteady interactions among the tip leakage vortex, the separated vortex and the corner flow should contribute to the inception of the rotating stall in a compressor.