bluuebunny/crossref_metadata_2025_split huggingface dataset:
Turbulence Structures of Leading Edge Film Cooling Jets
Authors: Ardey Sabine , Wolff Stefan , Fottner Leonhard 
Published: August 2014

For a better understanding of the turbulence structures attached to film cooling jets, mean flow velocities and turbulent fluctuations were measured by means of 3D hot wire anemometry in the injection zone of a linear, large scale, high pressure turbine cascade with leading edge film cooling. Near the stagnation point, the blades are equipped with one row of film cooling holes each on the suction and pressure side. Two basically different coolant jet situations are compared: On the suction side the jet features the ordinary kidney vortex. On the pressure side, the jet separates completely from the blade surface since it is located above a large recirculation zone created by a locally adverse pressure gradient and a flow separation near the pressure side injection. The measured Reynolds stresses were analyzed with regard to turbulence production and diffusion. The Bousinesque Hypothesis was tested and could not be confirmed. It was found that the turbulence is highly anisotropic.
In addition to the brief description of the experimental set up and the acquired data, given in this paper, the complete information are published as a test case (Ardey and Fottner, 1998) that is directly accessible via internet at: http://www.unibw-muenchen.de/campus/LRT12/welcome.html
Effects of Reynolds Number and Free-Stream Turbulence on Boundary Layer Transition in a Compressor Cascade
Authors: Schreiber Heinz-Adolf , Steinert Wolfgang , Küsters Bernhard 
Published: August 2014

An experimental and analytical study has been performed on the effect of Reynolds number and free-stream turbulence on boundary layer transition location on the suction surface of a controlled diffusion airfoil (CDA). The experiments were conducted in a rectilinear cascade facility at Reynolds numbers between 0.7 and 3.0×106 and turbulence intensities from about 0.7 to 4%. An oil streak technique and liquid crystal coatings were used to visualize the boundary layer state.
For small turbulence levels and all Reynolds numbers tested the accelerated front portion of the blade is laminar and transition occurs within a laminar separation bubble shortly after the maximum velocity near 35–40% of chord. For high turbulence levels (Tu > 3%) and high Reynolds numbers transition propagates upstream into the accelerated front portion of the CDA blade. For those conditions, the sensitivity to surface roughness increases considerably and at Tu = 4% bypass transition is observed near 7–10% of chord. Experimental results are compared to theoretical predictions using the transition model which is implemented in the MISES code of Youngren and Drela. Overall the results indicate that early bypass transition at high turbulence levels must alter the profile velocity distribution for compressor blades that are designed and optimized for high Reynolds numbers.
Separation Bubbles Under Steady and Periodic-Unsteady Main Flow Conditions
Authors: Lou Weiliang , Hourmouziadis Jean 
Published: August 2014

Based on an experimental investigation carried out in a low speed test facility at the Berlin University of Technology, this paper describes the formation of separation bubbles under steady and periodic-unsteady main flow conditions. The aim of the investigation was to understand the mechanism of separation, transition and reattachment and the effect of main flow unsteadiness on it.
Separation bubbles for various main flow conditions were generated over a large flat plate, which experienced a similar pressure distribution to that on the suction surface of blades in turbomachines. The pressure distribution was generated by a contoured wall opposite the plate. Aimed at separating the effect of the velocity and the turbulence wake, this paper considers only the influence of the velocity wake. To this effect, a rotating flap was mounted downstream of the test section to produce periodic oscillations of the main flow.
The overall flow field under steady main flow conditions was obtained by hot-wire measurements. Pressure taps were used to measure the pressure distribution over the plate. The Reynolds number effects were determined and compared to the measurement results in the literature. Results for periodic-unsteady separation bubbles are shown using different Strouhal numbers, oscillation amplitudes and Reynolds numbers. Ensemble averaged mean velocity profiles and the Ensemble averaged rms velocity profiles are used to demonstrate the development of the periodic boundary layer. Time-space diagrams are plotted to show the development of the periodic-unsteady boundary layers. The characteristic instability frequencies in the free shear layer are identified. The impact of the major parameters, Strouhal number and amplitude, on the bubble formation are discussed.
Flow and Heat Transfer in a Rotating Cavity With a Stationary Stepped Casing
Authors: Jaafar Abdul A. , Motallebi Fariborz , Wilson Michael , Owen J. Michael 
Published: August 2014

In this paper, new experimental results are presented for the flow in a co-rotating disc system with a rotating inner cylinder and a stationary stepped outer casing. The configuration is based on a turbine disc-cooling system used in a gas turbine engine. One of the rotating discs can be heated, and cooling air is introduced through discrete holes angled inward at the periphery of this disc. The cooling air leaves the system through axial clearances between the discs and the outer casing. Some features of computed flows, and both measured and computed heat transfer, were reported previously for this system. New velocity measurements, obtained using Laser Doppler Anemometry, are compared with results from axisymmetric, steady, turbulent flow computations obtained using a low-Reynolds-number k-ε turbulence model.
The measurements and computations show that the tangential component of velocity is invariant with axial location in much of the cavity, and the data suggest that Rankine (combined free and forced) vortex flow occurs. The computations fail to reproduce this behaviour, and there are differences between measured and computed details of secondary flow recirculations. Possible reasons for these discrepancies, and their importance for the prediction of associated heat transfer, are discussed.
A Method for Correlating the Influence of External Crossflow on the Discharge Coefficients of Film Cooling Holes
Authors: Rowbury D. A. , Oldfield M. L. G. , Lock G. D. 
Published: August 2014

An empirical means of predicting the discharge coefficients of film cooling holes in an operating engine has been developed. The method quantifies the influence of the major dimensionless parameters, namely hole geometry, pressure ratio across the hole, coolant Reynolds number, and the freestream Mach number.
The method utilises discharge coefficient data measured on both a first-stage high-pressure nozzle guide vane from a modern aero-engine and a scale (1.4 times) replica of the vane. The vane has over 300 film cooling holes, arranged in 14 rows.
Data was collected for both vanes in the absence of external flow. These non-crossflow experiments were conducted in a pressurised vessel in order to cover the wide range of pressure ratios and coolant Reynolds numbers found in the engine. Regrettably, the proprietary nature of the data collected on the engine vane prevents its publication, although its input to the derived correlation is discussed.
Experiments were also conducted using the replica vanes in an annular blowdown cascade which models the external flow patterns found in the engine. The coolant system used a heavy foreign gas (SF6/Ar mixture) at ambient temperatures which allowed the coolant-to-mainstream density ratio and blowing parameters to be matched to engine values. These experiments matched the mainstream Reynolds and Mach numbers and the coolant Mach number to engine values, but the coolant Reynolds number was not engine representative (Rowbury et al., 1997 and 1998).
A correlation for discharge coefficients in the absence of external crossflow has been derived from this data and other published data. An additive loss coefficient method is subsequently applied to the cascade data in order to assess the effect of the external crossflow. The correlation is used successfully to reconstruct the experimental data. It is further validated by successfully predicting data published by other researchers.
The work presented is of considerable value to gas turbine design engineers as it provides an improved means of predicting the discharge coefficients of engine film cooling holes.
Real-Time On-Line Performance Diagnostics of Heavy-Duty Industrial Gas Turbines
Authors: Gülen S. Can , Griffin Patrick R. , Paolucci Sal 
Published: August 2014

This paper describes the results of real-time, on-line performance monitoring of two gas turbines over a period of five months in 1997. A commercially available software system is installed to monitor, analyze and store measurements obtained from the plant’s distributed control system. The software is installed in a combined-cycle, cogeneration power plant, located in Mass., USA, with two Frame 7EA gas turbines in April 1997.
Vendor’s information such as correction and part load performance curves are utilized to calculate expected engine performance and compare it with measurements. In addition to monitoring the general condition and performance of the gas turbines, user-specified financial data is used to determine schedules for compressor washing and inlet filter replacement by balancing the associated costs with lost revenue. All measurements and calculated information are stored in databases for real-time and historical trending and tabulating. The data is analyzed ex post facto to identify salient performance and maintenance issues.
Inverted Brayton Cycle Employment for Low Temperature Cogenerative Applications
Authors: Bianchi M. , Negri di Montenegro G. , Peretto A. 
Published: August 2014

The employment of cogeneration plants for thermal and electric power production is constantly increasing especially for low power requirements. In most cases, to match these low power needs, the cogeneration plant is built up with diesel or gasoline engine or with gas turbine units.
In this paper, the performance, in terms of the most utilized cogenerative indexes, of an Inverted Brayton Cycle working with the gas exhausted by the open power plant have been evaluated.
Subsequently, the analysis of a cogenerative gas turbine equipped with IBC was carried out and the benefits numerically calculated.
It resulted that the IBC employment may increase of about 5 percentage points the plant electric efficiency, making this solution particularly attractive for cogenerative applications.
Performance Prediction of Small-Scale Tri-Generation Plants Based on Integrated SOFC and Microturbine Systems
Authors: Campanari Stefano , Macchi Ennio 
Published: August 2014

The combined adoption of solid oxide fuel cells and microturbines has been recently considered for the development of small advanced plants for high efficiency distributed electric power generation. This paper investigates the application of this technology to an independent, small-capacity power plant, which operates in conjunction with a compression heat-pump/chiller system and eventually with an absorption chiller, cogenerating heating, cooling and electric power for a single user like a medium-size commercial building.
Detailed results are presented for both the application of a SOFC+microturbine system and a simple microturbine system, in terms of annual energy balances; they indicate, specially for the SOFC+microturbine systems, high primary energy savings and reduction in emissions of carbon dioxide. A preliminary economic analysis is presented, showing that, in absence of incentives, specific SOFC investment costs as low as 1200 $/kW are required to make economically attractive the adoption of this highly efficient and environmentally benign component.
Digital Controls and Modern Fuel Systems for Marine Prime Movers
Authors: Bellio Philip R. 
Published: August 2014

Digital controls and modern fuel systems for marine prime movers are beginning to populate the waterways and oceans, but long after industrial facilities recognized their benefits and standardized on them. Additionally, it is somewhat ironic that many marine prime movers, particularly aeroderivative gas turbines, still utilize aircraft or aircraft-derivative hydromechanical controls, yet require significant engine room manning.
Digital controls, electrically actuated fuel and air valves, shipboard networks, and CRT-based operator interfaces have all been proven, and are available for every marine prime mover application. It appears to be more of a mindset than anything else preventing the move to electronic controls and modern fuel systems. Additional roadblocks to change may be “comfort with the old stuff”, marine certifications, and high availability of older hardware. As demands for improved efficiency, decreased emissions, and reduced operating expense continue there will be more pressure to upgrade existing older controls and fuel systems, as well as build ships with prime movers equipped with current control technology. A modern electronic control designed for prime movers which interfaces to not only the prime mover, can also provide data to shipboard systems, as well as be configured for satellite links to off-shore facilities.
Other advantages of a digital control and modern fuel system include:
• Software configurable/dependent
• Self-diagnostics and monitoring
• Condition-based maintenance
• Elimination of hydraulics
• Reduced manning requirements
• Precise air and fuel metering
• Current technology
Sensitivity Analysis of Blade Mode Shape on Flutter of Two-Dimensional Turbine Blade Sections
Authors: Tchernycheva Olga V. , Regard Sébastien , Moyroud François , Fransson Torsten H. 
Published: August 2014

A parametric study on the flutter stability of a turbine cascade as a function of the torsion axis position, the bending direction and the reduced frequency is presented. In this process two different unsteady flow models are used in order to minimize the uncertainties of numerical modeling on the physical conclusions of the study. Comparisons are performed against available experimental data.
It was found that the comparison of the global aerodynamic damping between numerical results and experimental data was reasonably good. It was observed that the stability was more sensitive to changes in the mode shape than in the reduced frequency. Comparisons of the local unsteady pressures showed similar tendencies for the numerical models and the experimental data, while discrepancies on the blade suction surface between the models were observed around the trailing edge for the subsonic flow and close to shock location for the transonic flow. The results indicated interesting agreement of the mode shape stability maps with results obtained on a largely different low-pressure turbine blade.
A Navier-Stokes Analysis of the Stall Flutter Characteristics of the Buffum Cascade
Authors: Weber Stefan , Platzer Max F. 
Published: August 2014

Numerical stall flutter prediction methods are highly needed as modern jet engines require blade designs close to the stability boundaries of the performance map.
A Quasi-3D Navier-Stokes code is used to analyze the flow over the oscillating cascade designed and manufactured by Pratt & Whitney, and studied at the NASA Glenn Research Center by Buffum et al. The numerical method solves for the governing equations with a fully implicit time-marching technique in a single passage by making use of a direct-store, periodic boundary condition. For turbulence modeling the Baldwin-Lomax model is used. To account for transition, the criterion to predict the onset location suggested by Baldwin and Lomax is incorporated.
Buffum et al. investigated two incidence cases for three different Mach numbers. The low-incidence case at a Mach number of 0.5 exhibited the formation of small separation bubbles at reduced oscillation frequencies of 0.8 and 1.2. For this case the present approach yielded good agreement with the steady and oscillatory measurements. At high-incidence at the same Mach number of 0.5 the measured steady-state pressure distribution and the separation bubble on the upper surface was also found in good agreement with the experiment. But computations for oscillations at high-incidence failed to predict the negative damping contribution caused by the leading edge separation.
Identification of Bearing Coefficients of Flexible Rotor-Bearing Systems
Authors: Yang Tachung , Chaung Wei-Ching 
Published: August 2014

The accuracy of stiffness and damping coefficients of bearings is critical for the rotordynamic analysis of rotating machinery. However, the influence of bearings depends on the design, manufacturing, assembly, and operating conditions of the bearings. Uncertainties occur quite often in manufacturing and assembly, which causes the inaccuracy of bearing predictions. An accurate and reliable in-situ identification method for the bearing coefficients is valuable to both analyses and industrial applications.
The identification method developed in this research used the receptance matrices of flexible shafts from FEM modeling and the unbalance forces of trial masses to derive the displacements and reaction forces at bearing locations. Eight bearing coefficients are identified through a Total Least Square (TLS) procedure, which can handle noise effectively. A special feature of this method is that it can identify bearing coefficients at a specific operating speed, which make it suitable for the measurement of speed-dependent bearings, like hydrodynamic bearings. Numerical validation of this method is presented. The configurations of unbalance mass arrangements are discussed.
Analysis of Aerodynamically Induced Whirling Forces in Axial Flow Compressors
Authors: Spakovszky Z. S. 
Published: August 2014

A new analytical model to predict the aerodynamic forces in axial flow compressors due to asymmetric tip-clearance is introduced. The model captures the effects of tip-clearance induced distortion (i.e. forced shaft whirl), unsteady momentum-induced tangential blade forces and pressure induced forces on the spool. Pressure forces are shown to lag the tip-clearance asymmetry, resulting in a tangential (i.e. whirl-inducing) force due to spool pressure. This force can be of comparable magnitude to the classical Alford force. Prediction and elucidation of the Alford force is also presented.
In particular, a new parameter denoted as the blade loading indicator is deduced. This parameter depends only on stage geometry and mean flow and determines the direction of whirl tendency due to tangential blade loading forces in both compressors and turbines.
All findings are suitable for incorporation into an overall dynamic system analysis and integration into existing engine design tools.
Nozzle Cracking in Gas Turbines
Authors: Shirmohamadi Manuchehr , Bratt Shawn , Wang Difei , Ganji Ahmad , Neville Rob 
Published: August 2014

Cracking of 1st stage nozzles occurs routinely in industrial gas turbines. Such cracking, which sometimes is observed after only a few operating cycles, leads to short intervals between overhauls and expensive repairs or replacements of the nozzle sections. Despite the enormous economic costs associated with nozzle cracking; mechanisms, root causes, and optimum mitigation of such cracking has not been convincingly determined. In fact, some original equipment manufacturers (OEM) consider nozzle cracking as a “fact of life” and have only issued recommendations for their monitoring and replacements.
The objective of this work was to identify the mechanisms and the root causes for the 1st stage nozzle cracking of a Frame-3 gas turbine. In this project, we measured, monitored, modeled, and analyzed the temperature and stress response of the nozzles during actual operating practices. This work concluded that the primary mechanism of such cracking is low cycle fatigue caused by high cyclic stresses. The major source of these high stresses was determined to be related to thermal and pressure shocks caused by transonic events which occur during the unit startups. This work offers recommendations to mitigate such cracking and a testing program to verify the root cause.
A Transport Model for the Deterministic Stresses Associated With Turbomachinery Blade Row Interactions
Authors: van de Wall Allan G. , Kadambi Jaikrishnan R. , Adamczyk John J. 
Published: August 2014

The unsteady process resulting from the interaction of upstream vortical structures with a downstream blade row in turbomachines can have a significant impact on the machine efficiency. The upstream vortical structures or disturbances are transported by the mean flow of the downstream blade row, redistributing the time-average unsteady kinetic energy (K) associated with the incoming disturbance. A transport model was developed to take this process into account in the computation of time-average multistage turbomachinery flows.
The model was applied to compressor and turbine geometry. For compressors, the K associated with upstream 2-D wakes and 3-D tip clearance flows is reduced as a result of their interaction with a downstream blade row. This reduction results from inviscid effects as well as viscous effects and reduces the loss associated with the upstream disturbance. Any disturbance passing through a compressor blade row results in a smaller loss than if the disturbance was mixed-out prior to entering the blade row.
For turbines, the K associated with upstream 2-D wakes and 3-D tip clearance flows are significantly amplified by inviscid effects as a result of the interaction with a downstream turbine blade row. Viscous effects act to reduce the amplification of the K by inviscid effects but results in a substantial loss. 2-D wakes and 3-D tip clearance flows passing through a turbine blade row results in a larger loss than if these disturbances were mixed-out prior to entering the blade row.
Reduction of Secondary Flow Losses in Turbine Cascades by Leading Edge Modifications at the Endwall
Authors: Sauer H. , Müller R. , Vogeler K. 
Published: August 2014

Experimental results are presented which show the influence on the secondary flow and its losses by a profile modification of the leading edge very close to the endwall. The investigation was carried out with a well-known turbine profile that originally was developed for highly loaded low pressure turbines. The tests were done in a low speed cascade wind tunnel. The geometrical modification was achieved by a local thickness increase; a leading edge endwall bulb. It was expected that this would intensify the suction side branch of the horse-shoe (hs-) vortex with a desirable weakening effect on the passage vortex. The investigated configuration shows a reduction of secondary losses by 2.1% points that represents approximately 50% of these losses compared to the reference profile. Detailed measurements of the total pressure field behind the cascade are presented for both the reference and the modified profile.
The influence of the modified hs-vortex on the overall passage vortex can be clearly seen. The results of a numerical analysis are compared with the experimental findings.
A numerical analysis shows that the important details of the experimental findings can be reproduced. Quantitative values are locally different. The theoretical approach taken cannot yet be used for an exact prediction of the loss reduction. However the analysis of the interaction and the resulting tendencies are considered to be valid. Hence theoretical investigations as a guideline for the design of a leading edge bulb at the endwall are a valuable tool.