bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Prediction of Combustor Heatshield Flow and Heat Transfer With Sub-Grid-Scale Modelling of Pedestals
Authors: Luff John K. , McGuirk James J.
Published: July 2014

A goal for computational analysis of combustors is to produce a tool for life prediction. An important part of this will be the prediction of the temperature field in the combustor walls. The complex geometries of combustor components make this a formidable task. In this paper a 3D coupled numerical flow/conjugate heat transfer calculation procedure is presented for a combustor heatshield. Proper account must be taken of the blockage and heat transfer effects of pedestals. A scheme has been developed to account for these effects without resolving the pedestals in the computational grid. Extra sink terms are included in the momentum equations to account for pedestal pressure drop. An extra energy equation is solved to determine the local pedestal temperature and to account for heat transfer between pedestals and fluid. This treatment has been validated against empirical data for arrays of pedestals in ducts with good agreement for friction factor and Nusselt number. The methodology is then applied to a generic heatshield geometry to indicate that a viable computational route has been developed for combustor heatshield analysis.
Film-Cooled Turbine Endwall in a Transonic Flow Field: Part I — Aerodynamic Measurements
Authors: Kost Friedrich , Nicklas Martin
Published: July 2014

Thermodynamic and aerodynamic measurements were carried out in a linear turbine cascade with transonic flow field. Heat transfer and adiabatic film-cooling effectiveness resulting from the interaction of the flow field and the ejected coolant at the endwall were measured and will be discussed in two parts. The investigations were performed in the Windtunnel for Straight Cascades (EGG) at DLR, Göttingen. The film-cooled NGV endwall was operated at representative dimensionless engine conditions of Mach and Reynolds number Ma2is=1.0 and Re2=850,000 respectively.

Part I of the investigation discusses the aerodynamic measurements. Detailed aerodynamic measurements were carried out in the vicinity of a turbine stator endwall using conventional pressure measurements and a Laser-2-Focus (L2F) device. The L2F served as a velocimeter measuring 2D-velocity vectors and turbulence quantities and as a tool to determine the concentration of coolant ejected through a slot and through holes at the endwall. Pressure distribution measurements provided information on the endwall pressure field and its variation with coolant flow rate. Pressure probe measurements delivered cascade performance data. Oil flow visualization and laser velocimetry gave a picture of the near endwall flow field and its interference with the coolant. A strikingly strong interaction of coolant air and secondary flow field could be identified. The measurement of coolant concentration downstream of the ejection locations provided a detailed picture of the coolant flow convection and its mixing with the main flow. The relative coolant concentration in the flow field is directly comparable to the adiabatic film-cooling effectiveness measured by thermal methods at the wall.
Experimental Investigation of Impingement Cooling With Turbulators or Surface Enlarging Elements
Authors: Annerfeldt Mats O. , Persson Johan L. , Torisson Tord
Published: July 2014

For the materials in modern gas turbines to survive, a considerable amount of cooling is required. In cases where large amounts of heat need to be removed, impingement cooling with its high heat transfer coefficients may be a good alternative. The possibilities of enhancing impingement cooling by introducing surface enlarging/turbulence enhancing elements are examined experimentally in this work. A technique using thin foil heaters combined with an infrared camera is used. Local temperature distribution on the target plate is measured, enabeling to separately evaluate the Nusselt number enhancement for different areas. Experiments are conducted for four different area enlarging geometries: triangle, wing, cylinder and dashed rib all made from aluminum. Comparison between each area enlarged surface and a flat plate is made in terms of Nusselt number and also pumping power in order to maximize the cooling efficiency. Overall Nusselt number enhancement factors compared to impingement on a flat plate show values of 1 to 1.3, the trend decreasing with increased jet-to-plate distance and Reynolds number. When normalizing by the spent pumping power the enhancement factors drop to 0.4 to 1.2 compared to impingement on a smooth plate. The best results were achieved with die rib geometry and when not using a too large value of enlarger height compared to jet-to-plate distance. Row-wise evaluation of Nusselt number enhancement shows an increased enhancement factor with row number and therefore crossflow ratio (Gc/Gj). The infrared camera pictures reveal that the enhancement is found in three different areas, on the enlarger base area, the area just downstream the enlarger and in diagonal streaks with increased turbulence generated by the enlargers. Tests using an enlarger material with heat conductivity scaled to represent actual gas turbine conditions show that only the enlarger base area is affected when decreasing the enlarger heat conductivity. The result is a small decrease in total Nusselt number enhancement.
An Experimental Study of Impingement on Roughened Airfoil Leading-Edge Walls With Film Holes
Authors: Taslim M. E. , Pan Y. , Spring S. D.
Published: July 2014

Airfoil leading-edge surfaces in state-of-the-art gas turbines, being exposed to very high gas temperatures, are often life-limiting locations and require complex cooling schemes for robust designs. A combination of convection and film cooling is used in conventional designs to maintain leading-edge metal temperatures at levels consistent with airfoil life requirements. Compatible with the external contour of the airfoil at the leading edge, the leading-edge cooling cavities often have complex cross-sectional shapes. Furthermore, to enhance the heat transfer coefficient in these 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 more advanced designs, enters the leading edge cavity from the adjacent cavity through a series of crossover holes in the wall separating the two cavities. In the latter case, the crossover 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. The main objective of this investigation was to study the effects that film holes on the target surface have on the impingement heat transfer coefficient. Available data in the open literature are mostly for impingement on a flat smooth surface with no representation of the film holes. This investigation involved two new features used in airfoil leading-edge cooling those being a curved and roughened target surface in conjunction with leading-edge row of film holes. Results of the crossover jets impinging on these leading-edge surface geometries with no film holes were reported by these authors previously. This paper reports experimental results of crossover jets impinging on those same geometries in the presence of film holes. The investigated surface geometries were smooth, roughened with large and small conical bumps as well as tapered radial ribs. A range of flow arrangements and jet Reynolds numbers were investigated and the results were compared to those of the previous study were no film holes were present. It was concluded that the presence of leading-edge film holes along the leading edge enhances the internal impingement heat transfer coefficients significantly. The smaller conical bump geometry in this investigation produced impingement heat transfer coefficients up to 35% higher than those of the smooth target surface. When the contribution of the increased area in the overall heat transfer is taken into consideration, this same geometry for all flow cases as well as jet impingement distances (Z/djet) provides an increase in the heat removal from the target surface by as much as 95% when compared with the smooth target surface.
Effect of Blade Tip Clearance on Turbine Shroud Heat/Mass Transfer
Authors: Rhee Dong Ho , Choi Jong Hyun , Cho Hyung Hee
Published: July 2014

This study investigates the local heat/mass transfer characteristics on the stationary shroud with blade tip clearances for flat tip geometry. A large scale linear cascade is used and the relative motion between the blade and shroud is neglected in this study. A naphthalene sublimation method is employed to determine the detailed local heat/mass transfer coefficients on the shroud surface. The geometry of blade tip used in this study is flat and the tip clearance varies from 0.66% to 2.85% of the blade chord length. The flow enters the gap between the blade tip and shroud at the pressure side due to the pressure difference. Therefore, the heat/mass transfer characteristics on the shroud are changed significantly from those for no tip clearance. High heat/mass transfer region is observed along the pressure side of blade due to the entrance effect and the acceleration of the tip gap flow. Complex heat transfer patterns on the shroud are observed in the region where the blade tip and shroud are overlapped due to the flow separation and reattachment. Then, the heat/mass transfer coefficients on the shroud increase along the suction side of blade because tip leakage vortices are generated with interacting the main flow. The experimental results show that the heat/mass transfer characteristics are changed significantly with the gap distance between the tip of turbine blade and the shroud. However, the turbulence intensity of incoming flow has little influence on the heat/mass transfer coefficients on the shroud with tip clearance.
Measurements in a Turbine Cascade Flow Under Ultra Low Reynolds Number Conditions
Authors: Van Treuren Kenneth W. , Simon Terrence , von Koller Marc , Byerley Aaron R. , Baughn James W. , Rivir Richard
Published: July 2014

With the new generation of gas turbine engines, low Reynolds number flows have become increasingly important. Designers must properly account for transition from laminar to turbulent flow and separation of the flow from the suction surface, which is strongly dependent upon transition. Of interest to industry are Reynolds numbers based upon suction surface length and flow exit velocity below 150,000 and as low as 25,000. In this paper, the extreme low end of this Reynolds number range is documented by way of pressure distributions, loss coefficients and identification of separation zones. Reynolds numbers of 25,000 and 50,000 and with 1% and 8–9% turbulence intensity of the approach flow (Free Stream Turbulence Intensity, FSTI) were investigated.

At 25,000 Reynolds number and low FSTI, the suction surface displayed a strong and steady separation region. Raising the turbulence intensity resulted in a very unsteady separation region of nearly the same size on the suction surface. Vortex generators were added to the suction surface, but they appeared to do very little at this Reynolds number.

At the higher Reynolds number of 50,000, the low-FSTI case was strongly separated on the downstream portion of the suction surface. The separation zone was eliminated when the turbulence level was increased to 8–9%. Vortex generators were added to the suction surface of the low-FSTI case. In this instance, the vortices were able to provide the mixing needed to reestablish flow attachment.

This paper shows that massive separation at very low Reynolds numbers (25,000) is persistent, in spite of elevated FSTI and added vortices. However, at a higher Reynolds number, there is opportunity for flow reattachment either with elevated freestream turbulence or with added vortices. This may be the first documentation of flow behavior at such low Reynolds numbers. Though undesirable to operate under these conditions, it is important to know what to expect and how performance may be improved if such conditions are unavoidable.
Detailed Boundary Layer Measurements on a Turbine Stator Vane at Elevated Freestream Turbulence Levels
Authors: Radomsky R. W. , Thole K. A.
Published: July 2014

High freestream turbulence levels have been shown to greatly augment the heat transfer on a gas turbine airfoil. To better understand these effects, this study has examined the effects elevated freestream turbulence levels have on the boundary layer development along a stator vane airfoil. Low freestream turbulence measurements (0.6%) were performed as a baseline for comparison to measurements at combustor simulated turbulence levels (19.5%). A two-component LDV system was used for detailed boundary layer measurements of both the mean and fluctuating velocities on the pressure and suction surfaces. Although the mean velocity profiles appeared to be more consistent with laminar profiles, large velocity fluctuations were measured in the boundary layer along the pressure side at the high freestream turbulence conditions. Along the suction side, transition occurred further upstream due to freestream turbulence.
Flow Field Simulations of a Gas Turbine Combustor
Authors: Barringer M. D. , Richard O. T. , Walter J. P. , Stitzel S. M. , Thole K. A.
Published: July 2014

The flow field exiting the combustor in a gas turbine engine is quite complex considering the presence of large dilution jets and complicated cooling schemes for the combustor liner. For the most part, however, there has been a disconnect between the combustor and turbine when simulating the flow field that enters the nozzle guide vanes. To determine the effects of a representative combustor flow field on the nozzle guide vane, a large-scale wind tunnel section has been developed to simulate the flow conditions of a prototypical combustor. This paper presents experimental results of a combustor simulation with no downstream turbine section as a baseline for comparison to the case with a turbine vane. Results indicate that the dilution jets generate turbulence levels of 15–18% at the exit of the combustor with a length scale that closely matches that of the dilution hole diameter. The total pressure exiting the combustor in the near wall region neither resembles a turbulent boundary layer nor is it completely uniform putting both of these commonly made assumptions into question.
Transient Analyses of Conjugate Heat Transfer of a First Stage Rotor Blade in Start-Up and Shut-Down
Authors: Takahashi Toshihiko , Watanabe Kazunori , Takahashi Takeshi
Published: July 2014

In order to contribute to the life assessment of the first stage rotor blade, transient analyses of heat transfer in the start-up and shut-down of a power generation gas turbine (GT) were conducted by thermal conjugation inside and outside the blade, which consist of thermal convection and heat conduction. Characteristic diagrams in a hot start and a normal shut-down that simulate an actual plant were used to set the numerical conditions.

The characteristics of the predicted blade temperature distributions were classified into two regions for load and no-load operation. In the no-load operation in which conduction heat transfer was dominant, the temperatures of the leading and the trailing edges changed drastically and the gradient of the temperature on the blade root increased substantially after ignition. In the load operation, the configuration of the blade temperature profile remained similar over half load.

It was possible to use the predictions to estimate stress and creep strain, which are demanded for the life assessment of the blade, from the start-up to the shut-down.
Fluid Flow and Heat Transfer in a Rotating Two-Pass Square Duct With In-Line 90° Ribs
Authors: Liou Tong-Miin , Chen Meng-Yu , Tsai Meng-Hsiun
Published: July 2014

Laser-Doppler velocimetry and transient thermochromic liquid crystal measurements are presented to understand local fluid flow and surface heat transfer distributions in a rotating ribbed duct with a 180° sharp turn. The in-line 90° ribs were arranged on the leading and trailing walls with rib height-to-hydraulic diameter ratio and pitch-to-height ratio of 0.136 and 10, respectively. The Reynolds number, based on duct hydraulic diameter and bulk mean velocity, was fixed at 1.0×104 whereas the rotational number varied from 0 to 0.2. Results are compared with those of the rotating smooth duct flow in terms of maximum streamwise mean velocities (Umax/Ub) and turbulence intensities (u′max/Ub), skewness of mean velocity profiles, secondary flow pattern, turn-induced separation bubble, and turbulence anisotropy. Nusselt number ratio mappings are also provided on the leading and trailing walls. The relationships between the fluid flow and local heat transfer enhancement are also documented. It is found that the rotating ribbed duct flow provides higher Umax/Ub, u′max/Ub, and stronger total averaged secondary flow and, hence heat transfer is enhanced. Comparisons with heat transfer data published by other research groups are also made. Furthermore, simple linear correlations between regional averaged Nusselt number ratio and rotation number are developed.
The Fluid Dynamics of LPT Blade Separation Control Using Pulsed Jets
Authors: Bons Jeffrey P. , Sondergaard Rolf , Rivir Richard B.
Published: July 2014

The effects of pulsed vortex generator jets on a naturally separating low pressure turbine boundary layer have been investigated experimentally. Blade Reynolds numbers in the linear turbine cascade match those for high altitude aircraft engines and industrial turbine engines with elevated turbine inlet temperatures. The vortex generator jets (30 degree pitch and 90 degree skew angle) are pulsed over a wide range of frequency at constant amplitude and selected duty cycles. The resulting wake loss coefficient vs. pulsing frequency data add to previously presented work by the authors documenting the loss dependency on amplitude and duty cycle. As in the previous studies, vortex generator jets are shown to be highly effective in controlling laminar boundary layer separation. This is found to be true at dimensionless forcing frequencies (F+) well below unity and with low (10%) duty cycles. This unexpected low frequency effectiveness is due to the relatively long relaxation time of the boundary layer as it resumes its separated state. Extensive phase-locked velocity measurements taken in the blade wake at an F+ of 0.01 with 50% duty cycle (a condition at which the flow is essentially quasi-steady) document the ejection of bound vorticity associated with a low momentum fluid packet at the beginning of each jet pulse. Once this initial fluid event has swept down the suction surface of the blade, a reduced wake signature indicates the presence of an attached boundary layer until just after the jet termination. The boundary layer subsequently relaxes back to its naturally separated state. This relaxation occurs on a timescale which is 5–6 times longer than the original attachment due to the starting vortex. Phase-locked boundary layer measurements taken at various stations along the blade chord illustrate this slow relaxation phenomenon. This behavior suggests that some economy of jet flow may be possible by optimizing the pulse duty cycle and frequency for a particular application. At higher pulsing frequencies, for which the flow is fully dynamic, the boundary layer is dominated by periodic shedding and separation bubble migration, never recovering its fully separated (uncontrolled) state.
Conditional Sampling in a Transitional Boundary Layer Under High Free-Stream Turbulence Conditions
Authors: Volino Ralph J. , Schultz Michael P. , Pratt Christopher M.
Published: July 2014

Conditional sampling has been performed on data from a transitional boundary layer subject to high (initially 9%) free-stream turbulence and strong K=ν/U∞2dU∞/dxas high as9×10-6 acceleration. Methods for separating the turbulent and non-turbulent zone data based on the instantaneous streamwise velocity and the turbulent shear stress were tested and found to agree. Mean velocity profiles were clearly different in the turbulent and non-turbulent zones, and skin friction coefficients were as much as 70% higher in the turbulent zone. The streamwise fluctuating velocity, in contrast, was only about 10% higher in the turbulent zone. Turbulent shear stress differed by an order of magnitude, and eddy viscosity was three to four times higher in the turbulent zone. Eddy transport in the non-turbulent zone was still significant, however, and the non-turbulent zone did not behave like a laminar boundary layer. Within each of the two zones there was considerable self-similarity from the beginning to the end of transition. This may prove useful for future modeling efforts.
Disintegration of Oil Jets Emerging From Axial Passages at the Face of a Rotating Cylinder
Authors: Glahn A. , Blair M. F. , Allard K. L. , Busam S. , Schäfer O. , Wittig S.
Published: July 2014

A fundamental study has been performed to examine the disintegration of oil films emerging from axial passages at the face of a rotating cylinder. The investigation has been conducted in parallel to a similar study on atomization processes at rotating radial holes (Glahn et al. 2001) and has used the same approaches in simulating one of the droplet generation sources in aero-engine lubrication systems. Both papers aim to contribute to the establishment of a database that can be used for the development of droplet generation models directly applicable to engine conditions. As with the parallel investigation, the near-term objectives of fundamental oil film disintegration studies are (i) to determine droplet sizes under relevant aero-engine bearing compartment operating conditions, and (ii) to measure individual droplet diameter/velocity relationships. The long-term objective is to incorporate this information into advanced design systems such as CFD-based tools.

In the present study, flow visualization has been used to identify the dominant disintegration processes. Droplet diameters and velocities have been obtained for relevant engine operating conditions. Data are presented in terms of both characteristic diameters and size-class resolved droplet velocities and flow angles. A comparison of droplet sprays measured in the present study with those generated by disintegration of oil films at the rim of a rotating disk (Glahn at al. 2000) has been enabled by introducing non-dimensional parameters for atomization products and operating conditions.
The Flow Structure in Rotating Hollow Shafts With Radial Inflow and Axial Throughflow
Authors: Brillert D. , Reichert A. W. , Simon H.
Published: July 2014

Modern heavy-duty gas turbines operate with high turbine inlet temperatures and thus require complex secondary air systems to ensure that blades and vanes are supplied with the necessary amount of cooling air. Low-emission gas turbines with a high thermal efficiency require minimum amounts of cooling and sealing air which means that secondary air systems must be designed with extreme accuracy.

In previous papers, the secondary air system of Siemens Vx4.3A gas turbines and the calculation method used for their design were introduced. This paper deals with the calculation of the flow in cooling air passages in rotating hollow shafts with axial throughflow. The paper starts with a derivation of basic equations and a brief review of the work on this topic described in the literature. Then on the basis of these basic equations a simple one–dimensional model is described to predict the three–dimensional flow (losses, flow deflection) in the rotating hollow shafts for different massflow rates. The calculation system is completed by matching the correlations of the simple one–dimensional model to the results of the numerical simulations.
Thermo-Economic Analysis of an Intercooled, Reheat and Recuperated Gas Turbine for Cogeneration Applications: Part II — Part-Load Operation
Authors: Bhargava R. , Negri di Montenegro G. , Peretto A.
Published: July 2014

The knowledge of off-design performance for a given gas turbine system is critical particularly in applications where considerable operation at low load setting is required. This information allows designers to ensure safe operation of the system and determine in advance thermo-economic penalty due to performance loss while operating under part-load conditions.

In this paper, thermo-economic analysis results for the intercooled, reheat (ICRH) and recuperated gas turbine, at the part-load conditions in cogeneration applications, have been presented.

Thermodynamically, a recuperated ICRH gas turbine based cogeneration system showed lower penalty in terms of electric efficiency and Energy Saving Index over the entire part-load range in comparison to the other cycles (non-recuperated ICRH, recuperated Brayton and simple Brayton cycles) investigated.

Based on the comprehensive economic analysis for the assumed values of economic parameters, this study shows that, a mid-size (electric power capacity 20 MW) cogeneration system utilizing non-recuperated ICRH cycle provides higher return on investment both at full-load and part-load conditions, compared to the other same size cycles, over the entire range of fuel cost, electric sale and steam sale values examined. The plausible reasons for the observed trends in thermodynamic and economic performance parameters for four cycles and three sizes of cogeneration systems under full-load and part-load conditions have been presented in this paper.
Multiobjective Robust Optimal Design of a Gas Turbine Cogeneration Plant Under Uncertain Energy Demands
Authors: Yokoyama Ryohei , Ito Koichi
Published: July 2014

A multiobjective robust optimal design method based on the minimax regret criterion is proposed for sizing equipment of energy supply plants so that they are robust in economic and energy saving characteristics under uncertain energy demands. Equipment capacities and utility contract demands as well as energy flow rates are determined to minimize a weighted sum of the maximum regrets in the annual total cost and primary energy consumption, and satisfy all the possible energy demands. This optimization problem is formulated as a kind of multilevel linear programming one, and its solution is derived by repeatedly evaluating lower and upper bounds for the optimal value of the weighted sum of the maximum regrets. Through a case study on a gas turbine cogeneration plant for district energy supply, the trade-off relationship between the robustness in economic and energy saving characteristics is clarified.
Effects of Anti-Icing System Operation on Gas Turbine Performance and Monitoring
Authors: Mathioudakis K. , Tsalavoutas A.
Published: July 2014

The effect of operation of compressor bleed anti-icing on the performance of an industrial gas turbine is analysed. The effect of putting this system in operation is first qualitatively discussed, while the changes on various performance parameters are derived by using a computer engine performance model. The main point of the paper is the study of the effect of anti-icing system operation on parameters used for engine condition monitoring. It is shown that operation of the anti-icing system causes an apparent modification of such parameters, which may reduce the diagnostic ability of an on-line monitoring system and produce false alarms. It is shown that by incorporating the effect of anti-icing system operation into a diagnostic engine model, such problems can be avoided and the diagnostic ability of the system is not influenced by anti-icing activation. The analysis presented is substantiated through experimental data from a twin shaft gas turbine operating in the field.
Conformable Eddy-Current Sensors and Arrays for Fleetwide Gas Turbine Component Quality Assessment
Authors: Goldfine Neil , Schlicker Darrell , Sheiretov Yanko , Washabaugh Andrew , Zilberstein Vladimir , Lovett Timothy
Published: July 2014

The conformable Meandering Winding Magnetometer (MWM™) eddy current sensors and MWM-Arrays provide new inspection capabilities for gas turbine components. The sensors provide measurements of coating thickness and absolute electrical conductivity, which can capture features of interest for a population of components, e.g., for tracking fleetwide trends in quality and aging, failure evaluations and correlating failure origins to features of specific fleet population segments. Inspection applications include metallic and nonmetallic coating thickness and porosity measurement, detection of cracks on complex surfaces, imaging and detection of small flaws, thermal degradation monitoring, and cold work quality assessment. For example, the US Air Force uses the MWM for cold work quality control on all of the C-130 propeller blades that go through the Warner Robins ALC. For P-3 and C-130 propeller blades, trend analysis is being performed fleetwide. This paper describes MWM technology advances for absolute property measurements and specific capability demonstrations. Multifrequency quantitative inversion methods used for coating characterization are also used for characterization of process-affected zones, such as shot peen quality or titanium alpha case characterization.
Heavy Fuel Operation at Limay Bataan Power Station
Authors: Basler Benno , Marx Detlef
Published: July 2014

The Limay Bataan Power station, a 600 MW combined cycle, is now in its 8th successful year of operation. Operating on this specific heavy fuel oil, which is a high viscosity, high ashbearing heavy fuel residue from the refinery at Limay, requires a skilled and experienced crew as the quality of fuel was subject to major changes which are highly relevant to the operating mode. If not treated properly, this fuel could corrode blades within a short operating period.

This paper describes the experiences gained on the fuel handling from the fuel treatment plant to the turbine and also addresses the operation of the combined cycle. Specific operating problems are discussed. The plant is fully operated and maintained by ALSTOM Power O&M Ltd with its local team that has greatly contributed to the success of the plant.
A System for Health State Determination of Natural Gas Compression Gas Turbines
Authors: Bettocchi R. , Pinelli M. , Spina P. R. , Venturini M. , Sebastianelli S.
Published: July 2014

This paper illustrates the policy and objectives in compression system maintenance and describes a system for the health state determination of natural gas compression gas turbines based on “Gas Path Analysis”. Some results of the application of the diagnostic system to gas turbines working in a natural gas compression plant are presented.
The MS 5002E: A New 2-Shaft, High Efficiency Heavy Duty Gas Turbine for Oil and Gas Applications
Authors: Aurelio Luca , Battagli Paolo , Bianchi Dino , Martin Arlie R. , Tognarelli Leonardo
Published: July 2014

In mid-’98 it was decided to develop a new high efficiency version of the very successful MS5002 (GE Frame 5 two-shaft), to satisfy the most recent Customer requirements in terms of fuel consumption and environmental impact.

The machine was conceived considering different markets, primarily mechanical drive, but also non-Oil&Gas power generation.

Power class is 30 MW, pressure ratio is 17:1, simple cycle efficiency is over 36% and combined cycle efficiency approximately 51%.

The new model retains features that contributed to the success of its predecessors. The main ones are the full heavy-duty concept for on-site maintenance, the moderate firing temperature (compared with state of the art) for highest reliability, the two-shaft design with free power turbine for mechanical drive use, the high heat recovery capability.

Achievement of high cycle efficiency with low firing temperature is possible thanks the advanced tools used for the definition, design and optimization of airfoils, clearances, leakages and distribution of cooling flows. Aero-thermal design was largely based on state of the art 3D CFD and on sophisticated airfoil cooling techniques of the same type extensively used in aircraft engine development.

The dry-low-emissions combustion system design is derived from the GEPS DLN2.6.

A thorough testing program, including the full-scale test of the axial compressor and a full load prototype test, is planned to support development and to validate the design.
Modeling and Computation of Fouling of a 36MW Multistage Centrifugal Compressor Train Operating in a Cracked Gas Environment
Authors: Haq Inam U. , Bu-Hazza Ahmed I.
Published: July 2014

Cracked gas compressor fouling, which results from polymerization and saturated heavy hydrocarbons in olefins plant, remains one of the leading factors responsible for decreasing ethylene production revenues. This key equipment performance susceptibility to fouling has been studied in this paper. An analytical technique was developed based on the measured geometrical dimensions of aerodynamic components of the compressor train. The analytical model, capable of predicting performance at clean and progressive fouling conditions, of 27 stages of compression is detailed. Simulation results derived from model are compared with in-situ measured and mechanical design data of the compressor and good correspondence was obtained. Simulated fouling revealed more drop in efficiency of latter stages as a result of fouling of early stages. Current practice to combat compressor fouling is reviewed. A better location is proposed to install additional injection nozzles in vicinity of diffusers to carry out effective washing to decelerate fouling accumulation.
Measurements Versus Predictions for the Dynamic Impedance of Annular Gas Seals: Part 1 — Test Facility and Apparatus
Authors: Dawson Matthew P. , Childs Dara W. , Holt Christopher G. , Phillips Stephen G.
Published: July 2014

An experimental facility and apparatus are described for measuring the dynamic impedance and leakage characteristics of annular gas seals. The apparatus currently has a top speed of 29,800 rpm and can accommodate seal diameters up to 114.3 mm. The air-supply system can provide up to 13.79 MPa (2,000 psi) of pressure at the seal inlet. Test seals are configured in a back-to-back arrangement inside the stator and air enters a central inlet annulus at two opposed radial positions. Labyrinth seals and bleed ports located outboard of each test seal are used to control the pressure drop across the test seals. Two orthogonal, external hydraulic shakers are used to excite the test stator at frequencies up to 400 Hz. At a given operating condition, the apparatus can measure the rotordynamic impedance of a pair of identical seals over a broad frequency range using a single pseudo-random excitation waveform. Measurements are also made of seal leakage rates and upstream and downstream temperatures and pressures.
Experimental Evaluation of a Metal Mesh Bearing Damper in Parallel With a Structural Support
Authors: Al-Khateeb Eyad M. , Vance John M.
Published: July 2014

In a previous ASME paper experiments were reported on metal mesh bearing dampers (MMD) that were tested in a power turbine rotor at speeds up to 12,000 rpm. They were made of 0.229 mm stainless steel 304 wire mesh, compressed to 57% density, which is close to the maximum density that was economically available. After balancing, a level of vibration was achieved similar to that previously observed with squeeze film dampers. These experiments showed that the MMD could suppress vibration amplitudes of the 22.7 kg rotor at critical speeds of 4,000 rpm and 9,300 rpm. Much of the testing showed the rotor having little or no response to unbalance on coastdown through the critical speeds. The donut-shaped MMD in those tests were the only bearing supports; no squirrel cages were used. A question was raised about the feasibility of using MMD in parallel with a squirrel cage bearing support so that the stiffness can be controlled independently of the damping. This paper presents experimental results for metal mesh dampers with a squirrel cage as a parallel bearing support. Experiments with copper mesh as seal elements (on another project) had indicated that copper mesh has higher damping than stainless steel, so copper was chosen for these experiments. Both a linear viscous damping model and a hysteretic damping model were investigated. Some hysteretic damping models predict that damping depends on stiffness. A different hysteretic model turned out to be useful and promising as a prediction model for two reasons: a) it fits the measured data, and b) it predicts that the damping is not lost if the MMD is put in parallel with a steel structure such as a squirrel cage bearing support. The measurements reported here support the validity of that prediction.
Experimental Evaluation of Hybrid Damper Seals With Brush Elements: Effect of the Bristles on Power Dissipation and Rotordynamics
Authors: Buchanan Steven E. , Vance John M.
Published: July 2014

A previous paper described measurements of damping and leakage of a brush hybrid seal in a nonrotating test apparatus. In those experiments most of the damping came from the brush. This paper describes further experiments with this seal in a rotordynamic rig designed to determine if the bristles will still contribute significant damping at large amplitudes after wearing in to a line-line contact. These tests continued to show much more damping and much less leakage than a labyrinth seal of the same dimensions. The damping performance is even better after the brush is worn in. In the rotating experiments it was discovered that the brush elements also produce a surprising amount of friction torque and consequent power loss, especially at high pressure drops. During the experiments it was found that the brush friction is destabilizing to backward whirl, and that support asymmetry suppresses the instability.
Rotordynamic and Bearing Upgrade of a High-Speed Turbocharger
Authors: Pettinato Brian C. , DeChoudhury Pranabesh
Published: July 2014

The paper discusses the redesign of a high-speed turbocharger for improved bearing life and mechanical operation. The modifications resulted in reduced oil leakage across the end seal, reduced coke buildup at the turbine, increased thrust load capacity, and improved rotordynamics. In particular, rotordynamic stability was improved by eliminating subsynchronous vibration at the operating speed. The redesign consisted of changing the bearings from a pair of combination journal/thrust bearings to a pair of journal bearings and a double acting thrust bearing at the center of the unit. The active thrust bearing was moved away from the hot turbine end of the machine. The thrust bearing geometry was modified for increased minimum film thickness, reduced metal temperature, and increased load capacity. Inlet and drain passages were revised for better oil flow distribution. Unit rotordynamics were improved by upgrading the journal bearings from three-axial-groove to three-lobe design. The upgraded unit kept the same footprint as the original design with only piping modifications required.

Extensive analysis and testing were conducted. Testing of the original and revised turbochargers showed improvements in the redesign with reduced bearing metal temperatures and improved rotordynamic stability. Theoretical results along with test data consisting of bearing performance and vibration data of the original and modified system are presented in this paper.
Experimental Study on the Vibration Control Capability of a Hybrid Squeeze Film Damper
Authors: Zhu Changsheng
Published: July 2014

In order to improve the highly nonlinear characteristics of the conventional hydrodynamic squeeze film damper (SFD) in high journal eccentricity ratios and make its dynamic characteristics controllable, a hybrid (combination hydrostatic and hydrodynamic) squeeze film damper (HSFD) is presented. The effectiveness of the hybrid squeeze film damper in attenuating vibration of rotor systems and in improving the high non-linearity of oil film forces of the conventional hydrodynamic SFD is experimentally studied in this paper with a rigid rotor and a flexible rotor. The steady state unbalance responses of rotor-HSFD systems are compared with those of rotor-SFD systems in different radial clearance ratios. It is shown that the HSFD has very good linear dynamic characteristics and can effectively attenuate vibration of rotor systems, especially in larger rotor unbalances and large radial clearance ratios.
Investigation of Unsteady Aerodynamic Blade Excitation Mechanisms in a Transonic Turbine Stage: Part II — Analytical Description and Quantification
Authors: Laumert Björn , Mårtensson Hans , Fransson Torsten H.
Published: July 2014

This paper presents a study of the blade pressure perturbation levels and the resulting blade forces in a high-pressure transonic turbine stage based on 3D time dependent viscous computations. Globally, the blade pressure unsteadiness is quantified with the RMS of the pressure perturbations integrated in both time and along the blade surface. Operation point as well as spanwise variations are addressed. Locally, the relative strength of the pressure perturbation events on the vane and rotor blade surface is investigated. To obtain information about the relative strength of events related to the blade passing frequency and higher harmonics, the pressure field is Fourier decomposed in time at different radial positions along the blade arc-length. The amplitude peaks are then related to the pressure events in space-time maps.

With the help of the observations and results from the blade pressure study, the radial variations of the unsteady blade force and torque acting on a constant span blade profile section are investigated. The connection between the first and second vane passing frequency pressure amplitudes on the rotor blade surface and the resulting force and the torque amplitudes for three selected blade modes was investigated in detail. In this investigation the pressure was integrated over defined rotor blade regions to quantify local force contributions. Spanwise as well as operation point variations are addressed.
Excitation of Ring Vortex Production in Subsonic Jets by Sound Waves
Authors: Bohn Dieter E. , Balkowski Ingo
Published: July 2014

In many technical units pressure of gaseous fluids is reduced in turbulent jets with high subsonic velocities. In addition to broadband noise of the jets individual frequencies are sometimes observed. Those frequencies are caused by formation of periodic vortex structures in the jet. In some cases vortex formation can be influenced by sound waves which are emitted upstream of the discontinuity.

This effect is been investigated experimentally at velocities between Ma = 0.3 and Ma = 0.9 in several nozzles. The effect of the excitation on the turbulence in the jet is been measured by means of a dynamic pressure probe. It is shown that the turbulent vortex formation is influenced by the sound wave over a wide frequency range. A visualization of the density field shows regular vortex structures in the jet.

The noise emission is simultaneously investigated with condenser microphones. In addition to the frequency peak at the excitation frequency an increase of the broadband jet noise level can be observed.
CFD Investigation of Aeromechanics
Authors: Silkowski Peter D. , Rhie Chae M. , Copeland George S. , Eley James A. , Bleeg James M.
Published: July 2014

A Computational Fluid Dynamics (CFD) tool was developed and applied to a variety of aeromechanics problems, including both forced response and flutter. This 3-D non-linear, viscous, time accurate code, in conjunction with a large parallel network, is used to demonstrate the mature capability of CFD based tools for aeromechanical analysis. An example of multistage blade row interaction analysis is presented and compared against detailed experimental data highlighting the fidelity of current CFD tools. Flutter analyses of isolated blade rows are also compared to data and used to demonstrate several classical aeromechanical concepts such as influence coefficients, the destabilizing effect of neighboring blades in cascade flutter, the depiction of an aerodynamic damping map, and the flutter benefit of frequency mistuning. These two capabilities, multistage and flutter, are then combined to examine the effect of multistage interaction on the flutter problem. Finally the reasons for extending the above modeling to include full-aeroelastic capability are discussed and an example is presented.
The Coupled Longitudinal and Bending Vibrations on Stability in a Cracked Blade-Disk
Authors: Huang B. W. , Kuang J. H.
Published: July 2014

The effect of coriolis force on the stability in a rotational blade-disk with a cracked blade was presented in this paper. A disk comprising of periodically shrouded blades was used to simulate the weakly coupled periodic structure. The mode localization phenomenon introduced by the blade crack on the longitudinal and bending vibrations on the rotating blades are considered. The Galerkin method was used to derive the unperturbation equations for the system. The boundaries of instability zones of the mistuned system were approximated by employing the so called multiple scales method. The effects of coriolis force and the magnitude of crack on the variation of the dynamic stability zones in a cracked blade-disk system are investigated numerically. Numerical results indicate that the coriolis force and the coupling effect between longitudinal and bending vibrations could affect the dynamic stability in a mistuned system significantly.
Crack Propagation in Gas Turbine Rotor Disks: Comparison of Experimental Results at Real Components With Fatigue Life Prediction
Authors: Maldfeld E. , Schödel M. , Berger C.
Published: July 2014

Rotor disks of gas turbines are high stressed components and for safe life design both stress criteria and fracture mechanics are needed. Due to the forging process in rotor disks flaws have to be considered. There exists a certain detection limit, beneath no flaw size is detectable.

A comparison of predicted and observed crack propagation in a real gas turbine rotor disk with machined surface cracks is presented. The comparision of experimental crack growth behaviour and life prediction shows that the fracture mechanics analysis is conservative and that non detectable flaws within gas turbine rotor components cannot hurt safe service operation.
Local/Global Effects of Mistuning on the Forced Response of Bladed Disks
Authors: Rivas-Guerra Alejandro J. , Mignolet Marc P.
Published: July 2014

The focus of the present investigation is on the assessment and modeling of the local (spanning only a few blades) and global (encompassing the entire disk) effects of mistuning on the forced response of bladed disks. To this end, the concept of localization is first revisited and a new measure of this effect is introduced in terms of the number of blades the mistuning of which actually affects the forced response of a central blade. Using this new metric, it is demonstrated that high responding blades typically exhibit a high level of localization and that the reverse is not true. Thus, localization is not only disk dependent but also varies from blade-to-blade on the same disk.

This observation is then used to validate a partial mistuning approach to the determination of the maximum amplitude of response over the entire population of disks. The results of this study indicate that the largest amplification due to mistuning occurs at very strong blade-to-blade coupling levels, at the contrary of a general perception, but is associated with extremely large mistuning levels.

Finally, the above phenomenological observations are used to devise a modeling technique of both local and global components of mistuning. An example of application is presented that demonstrates the high accuracy of this approach through the entire blade-to-blade coupling domain.