bluuebunny/crossref_metadata_2025 huggingface dataset:
Pump Grooved Seals: A CFD Approach to Improve Bulk-Flow Model Predictions
Authors: Wu Tingcheng , San Andrés Luis
Published: November 2019

In multiple stage centrifugal pumps, balance pistons, often comprising a grooved annular seal, equilibrate the full pressure rise across the pump. Grooves in the stator break the evolution of fluid swirl and increase mechanical energy dissipation; hence, a grooved seal offers a lesser leakage and lower cross-coupled stiffness than a similar size uniform clearance seal. To date bulk-flow models (BFMs) expediently predict leakage and rotor dynamic force coefficients of grooved seals; however, they lack accuracy for any other geometry besides rectangular. Note scalloped and triangular (serrated) groove seals are not uncommon. In these cases, computational fluid dynamics (CFD) models seals of complex shape to produce leakage and force coefficients. Alas CFD is not yet ready for routine engineer practice. Hence, an intermediate procedure presently takes an accurate two-dimensional (2D) CFD model of a smaller flow region, namely a single groove and adjacent land, to produce stator and rotor surface wall friction factors, expressed as functions of the Reynolds numbers, for integration into an existing BFM and ready prediction of seal leakage and force coefficients. The selected groove-land section is well within the seal length and far away from the effects of the inlet condition. The analysis takes three water lubricated seals with distinct groove shapes: rectangular, scalloped and triangular. Each seal, with length/diameter L/D = 0.4, has 44 grooves of shallow depth dg ∼ clearance Cr, and operates at a rotor speed equal to 5,588 rpm (78 m/s surface speed) and with a pressure drop of 14.9 MPa. The method validity is asserted when 2D (single groove-land) and 3D (whole seal) predictions for pressure and velocity fields are compared against each other. The CFD predictions, 2D and 3D, show the triangular groove seal has the largest leakage, 41% greater than the rectangular groove seal does, albeit producing the smallest cross-coupled stiffnesses and whirl frequency ratio. On the other hand, the triangular groove seal has the largest direct stiffness and damping coefficients. The scalloped groove seal shows similar rotordynamic force coefficients as the rectangular groove seal but leaks 13% more. For the three seal groove types, the modified BFM predicts leakage that is less than 6% away from that delivered by CFD, whereas the seal stiffnesses (both direct and cross-coupled) differ by 13%, the direct damping coefficients by 18%, and the added mass coefficients are within 30%. The procedure introduced extends the applicability of a BFM to predict the dynamic performance of grooved seals with distinctive shapes.
High Temperature Oxidation Lifetime Modeling of Thin-Walled Components
Authors: Pillai R. , Dryepondt S. , Pint B. A.
Published: November 2019

High temperature material solutions for future power generation applications require longer component lifetimes at higher temperatures to improve durability and efficiency. From a research and development point of view, the lifetimes are too long for experimental verification. Thus, accurate lifetime models are needed. Examples are provided where modeling is being applied to lifetime prediction of thin-walled NiCr wrought alloy components. Specific laboratory experiments have been conducted for alloy X at 900°–950°C in dry air and air with water vapor with cycle times from 1 to 500 h. Along with microstructure characterization, comparisons are made between experiment and model predictions. The eventual goal is to predict both oxidation and mechanical behavior.
Boundary Layer Flashback Prediction for Turbulent Premixed Jet Flames: Comparison of Two Models
Authors: Kalantari Alireza , Auwaijan Nicolas , McDonell Vincent
Published: November 2019

Lean-premixed combustion is commonly used in gas turbines to achieve low pollutant emissions, in particular nitrogen oxides. But use of hydrogen-rich fuels in premixed systems can potentially lead to flashback. Adding significant amounts of hydrogen to fuel mixtures substantially impacts the operating range of the combustor. Hence, to incorporate high hydrogen content fuels into gas turbine power generation systems, flashback limits need to be determined at relevant conditions. The present work compares two boundary layer flashback prediction methods developed for turbulent premixed jet flames. The Damköhler model was developed at University of California Irvine (UCI) and evaluated against flashback data from literature including actual engines. The second model was developed at Paul Scherrer Institut (PSI) using data obtained at gas turbine premixer conditions and is based on turbulent flame speed. Despite different overall approaches used, both models characterize flashback in terms of similar parameters. The Damköhler model takes into account the effect of thermal coupling and predicts flashback limits within a reasonable range. But the turbulent flame speed model provides a good agreement for a cooled burner, but shows less agreement for uncooled burner conditions. The impact of hydrogen addition (0 to 100% by volume) to methane or carbon monoxide is also investigated at different operating conditions and flashback prediction trends are consistent with the existing data at atmospheric pressure.
The Influence of Turbulence and Reynolds Number on Slot Film Cooling Over the Downstream Pressure Surface
Authors: Soma L. W. , Ames F. E. , Acharya S.
Published: November 2019

Pressure surface film cooling from discrete holes can often be challenging due to higher than optimum coolant to surface pressure ratios, effects of high levels of flow field turbulence, and the potential for clogging. Double wall cooling methods can be designed to collect spent cooling air and distribute the film cooling downstream through a slot. Incremental impingement is a new internal cooling method designed for cooling the leading edge region and pressure surface. Internally, incremental impingement includes high solidity pedestals to conduct heat and transmit thermal stresses due to temperature variations between cold and hot side surfaces. Subsequently, the flow is collected downstream from the last row of pedestals and discharged through a slot. Experimental and computational research from mesh slots, which have dense arrays of pedestals upstream from the discharge, and slots downstream from high solidity pedestal arrays have shown that turbulence and vorticity generated inside a film cooling plenum can have a significant impact on downstream film cooling. This impact of plenum flow disturbances is in addition to the film cooling dissipation caused by external flow field turbulence. Incremental impingement, in addition to high solidity pedestals, has impingement jets integrated behind the last row of pedestals which may cause further disruption to the film discharge and flow field interaction. The present measurements document the film cooling effectiveness distributions downstream from a slot located at 62% arc along the pressure surface of a vane. The plenum has been designed to include high solidity pedestals and impingement jets consistent with an incremental impingement geometry. Blowing ratios of 0.4, 0.7 and 1.0 have been investigated at vane exit chord Reynolds numbers of 500,000, 1,000,000 and 2,000,000 at density ratios a little over 1. These conditions have been run at 5 independent turbulence levels ranging from 0.7% to over 17%. The results provide a consistent picture of pressure surface slot film cooling downstream from incremental impingement.
Film Cooling of Compound Angle Upstream Sister Holes
Authors: Abd Alsalam Sana , Jubran Bassam
Published: November 2019

This study introduces a novel and simple strategy; compound angle upstream sister holes (CAUSH) to increase film cooling performance of the cylindrical hole by combining two techniques: Sister holes; (two small round holes placed upstream the primary hole) and compound angle hole. Whereas the upstream sister holes were injected at several compound angles β = 0°, 45°, 75°, and 90°, while the main hole was injected to the streamwise direction at 35° on a flat plate. FLUENT-ANSYS code was used to perform the simulation by solving the 3D Reynolds Averaged Navier-Stokes Equations. The capability of three types of k-ε turbulence modeling combined with the enhanced wall treatment is investigated to predict the film cooling performance of sister holes. A detailed computational analysis of the cooling performance of the (CAUSH) and the flow field was done at a density ratio equal to two (D.R = 2) and four blowing ratios M = 0.25, 0.5, 1.0 and 1.5 to predict the centerline and laterally averaged film cooling performance. The centerline effectiveness results showed that the highest cooling performance from the examined (CAUSH) was obtained at β = 0°, 45°, and 90° for low and high blowing ratio, the highest laterally averaged film cooling performance was captured at β = 0° and 90° for all tested blowing ratios. Also, the results indicated that the upstream sister hole with 90° compound angle holes has the best overall film cooling effectiveness while the worst performance is attained at β = 75°.
NOx Emissions Predictions for a Hydrogen Micromix Combustion System
Authors: Babazzi Giulia , Gauthier Pierre Q. , Agarwal Parash , McClure Jonathan , Sethi Vishal
Published: November 2019

Being free from carbon content, hydrogen has been considered as a promising candidate to reduce pollutant emissions in Gas Turbine Combustion Systems. Due to hydrogen’s significantly different burning characteristics, its implementation requires adjustments to the design philosophies of traditional combustion chambers. The micromix concept offers an alternative diffusive combustion injection system, improving the mixing characteristics without the risk associated with pre-mixing, thereby reducing the likelihood of hotspots forming.

The importance of turbulence-chemistry interaction modelling, particularly for highly diffusive flames such as hydrogen, has been widely addressed. A turbulence-chemistry interaction study on such a micromix injector was performed investigating the coupling between the Flamelet Generated Manifold (FGM) combustion model and different hydrogen reaction mechanisms. This methodology correctly reproduces the typical micromix micro-flame behaviour and the analysed mechanisms are shown to be in good agreement in terms of flow characteristics prediction.

A comparative study between two reduced order emissions prediction models was then carried out: a CFD post-processing technique for NOx emissions calculations and a hybrid CFD-CRN approach were explored. Due to the coupling between accurate turbulence-chemistry interaction modelling and the ability to handle detailed chemistry, the hybrid CFD-CRN approach gives valuable results with a modest computational cost and it could be used as an optimising tool during the injector geometry design process.
Involving Students in the Learning Process: Using Team Competition to Teach Gas Turbine Cycle Design
Authors: Van Treuren Kenneth
Published: November 2019

Active learning is an important part of modern engineering education. It directly engages students in the learning process, helping them think and creatively solve problems. Often this is done in the context of a team project involving group activities both inside and outside the classroom. Analysis and Design of Propulsion Systems is an elective course that has been a traditional lecture course at Baylor University, teaching gas turbine engines using cycle design. In an effort to involve the students more in the learning process, active learning modules were introduced to make the course more interactive.

The active learning modules involved assigning students into teams of four that were formed using the Comprehensive Assessment of Team Member Effectiveness (CATME) software. Each team was to operate as a commercial company which included picking a name, developing a logo, and writing a mission statement similar to actual commercial companies. The point of having each team become a commercial company was to foster competition. The companies were tasked to eventually design the lowest cost, most efficient high bypass turbofan engine to replace the existing engines on the B-52H bomber. Each company wrote a persuasive position paper on whether or not the B-52H should be re-engined and a Request for Proposal (RFP) for the re-engined B-52H.

Gas turbine cycle design occurred using a three part design project. The engine cycle of choice for this re-design was the high bypass turbofan. Phase one was a detailed mission analysis incorporating the requirements from the RFP and leading to the selection of a design point, the calculation of the required installed thrust for each leg (and consequently the uninstalled thrust for each leg), as well as an average uninstalled specific fuel consumption for the mission. On-design, the next phase in the design process, used an on-design analysis at the design point which resulted in a selection of a fan pressure ratio, an overall pressure ratio, and a bypass ratio. The last phase examined the chosen engine at off-design mission points and the final fuel was calculated using actual uninstalled specific fuel consumption values to assure the fuel reserve was met. All phases were incorporated into a final report.

To conclude the process, each team presented their engine as if they were a company seeking to sell their product to a customer. The customer, the professor, then picked an overall winner based on the information presented. Assessment of the course showed that the students appreciated the competitive environment giving them insight into how a gas turbine company might operate. In conclusion, the active learning modules and team competition with the design project were effective in challenging and exciting the students about the design of gas turbine engines. The company context for teams prepares students for what to expect should they work in the gas turbine industry.
Multi-Objective Design of a Transonic Turbocharger Compressor With Reduced Noise and Increased Efficiency
Authors: Wang Peng , Zangeneh Mehrdad , Heyes Francis , Roach Paul
Published: November 2019

In marine diesel engines, transonic centrifugal compressors are widely used due to their capabilities to: 1) downsize engines by increasing output power; 2) cause less fuel consumption; 3) enhance the combustion efficiency. Apart from the traditional requirements such as good choke and stall margin, high boosting pressure ratio, and high stage efficiency, it is also necessary to reduce the turbocharger noise as much as possible for a more comfortable working environment. The most effective way is to reduce the compressor noise at the source, i.e. the compressor impeller itself must produce less aerodynamic noise rather than using any silencers. In this paper, we present a redesign work for an existing impeller wheel using the 3D inverse method with an in-house aeroacoustic code. The CFD simulations for the compressor characteristics and internal flow field details, the numerical predictions of aeroacoustic sound emissions, and FEA analysis for the structure integrity have all been attempted to thoroughly assess the performances of baseline and optimised impellers. The computational results found that the new impeller can lead to better performances in all three aspects, which are supported by the experimental measurements conducted for both impellers using the same test configurations. The experimental data confirmed that the inversely redesigned impeller wheel provides a wider compressor operating range, higher efficiency at large rotating speed, and a few dB(A)s lower noise emissions in the upstream radiation direction.
Experimental Study of Flow Inside a Centrifugal Fan Using Magnetic Resonance Velocimetry
Authors: Hoffman Davis W. , Villafañe Laura , Elkins Christopher J. , Eaton John K.
Published: November 2019

Three-dimensional, three-component time-averaged velocity fields have been measured within a low-speed centrifugal fan with forward curved blades. The model investigated is representative of fans commonly used in automotive HVAC applications. The flow was analyzed at two Reynolds numbers for the same ratio of blade rotational speed to outlet flow velocity. The flow patterns inside the volute were found to have weak sensitivity to Reynolds number. A pair of counter-rotating vortices evolve circumferentially within the volute with positive and negative helicity in the upper and lower regions, respectively. Measurements have been further extended to capture phase-resolved flow features by synchronizing the data acquisition with the blade passing frequency. The mean flow field through each blade passage is presented including the jet-wake structure extending from the blade and the separation zone on the suction side of the blade leading edge.
Novel Approaches for sCO2 Axial Turbine Design
Authors: Sathish Sharath , Kumar Pramod , Namburi Adi Narayana , Swami Lokesh , Fuetterer Carsten , Gopi Pramod Chandra
Published: November 2019

The axial sCO2 turbine design for shaft power above 10 MW can be approached in a manner similar to the High Pressure (HP), backpressure steam turbine. Starting from the overall performance specification, the detailed turbine design is carried out in steps; 1-Dimensional (1D) meanline design, Quasi 3D (Q3D) throughflow design, cascade blade-to-blade design, 3-Dimensional (3D) blade design, stress and vibration analysis. These design steps are well established and validated, using dedicated test rigs and field performance measurements, for the steam turbines. Even though detailed validation tests are not available for axial sCO2 turbines, there exists a scope to utilize the established steam turbine design principles. This paper highlights sCO2 turbine design procedure through a 10 MW turbine design case study for Waste Heat Recovery (WHR) power plant. The focus areas are blade-to-blade design and stress analysis for which the challenges and novel approaches to design are elucidated.

Classical blade design typically relies on expert knowledge where the 2D blade profile geometry is successively iterated to minimize the profile loss. Automated optimization routines are also employed by geometry parametrization techniques such as Bezier or B-Spline control points. This paper introduces a novel approach to 2D blade design as applied to a sCO2 turbine through a combination of Kulfan Class Shape Transformation (CST) for blade parametrization and unique optimization constraints to mimic the expert knowledge.

The high power density of sCO2 turbomachinery while advantageous for weight and footprint reduction poses significant challenge in mechanical design. The overall power is distributed among few stages resulting in higher blade stress compared to an equivalent steam turbine. Increasing the blade chord, alternative root design are some of the mitigation methods to deal with the increased stress. They however lead to compromise in aerodynamic performance due to reduced blade aspect ratio. This necessitates novel approaches to balance mechanical and aerodynamic design, which are considered in this paper.

Through a 10 MW sCO2 axial turbine design case study, this paper brings to the fore certain design challenges as compared to a conventional steam turbine and puts forth novel approaches to overcome the identified challenges.
Optimized SGT-A35 (GT61) for Improved Emissions and Enhanced Efficiency Across the Load Range
Authors: Thirumurthy Deepak , Ruggiero Barry , Chhibber Gautam , Singh Jaskirat
Published: November 2019

The RT61 is a three-stage industrial power turbine which couples with the SGT-A35 aeroderivative gas generator (formerly named Industrial RB211). It was designed for improved efficiency and modular construction for ease in maintainability. The aeroderivative SGT-A35 (GT61) product serves both oil & gas and power generation market with a fleet size of greater than 90 units.

In recent years, there has been increased emphasis on clean energy, only complemented by the regulatory changes and market conditions. The power generation and oil & gas customers (upstream, midstream, and downstream) are continuously looking for opportunities to decrease their greenhouse gas emissions and reduce fuel consumption by improving the gas turbine cycle efficiency.

The SGT-A35 (GT61) power turbine has > 93% isentropic efficiency and industry standard overhaul schedule of 100,000 hours. However the potential for further cycle efficiency improvements and reduction in emissions exist by optimizing the power turbine capacity to a specific load range. This served as the main motivation for this technical work.

This paper discusses the engineering efforts taken in implementing the above stated improvement and further optimizing the product for reduced emissions. The improvements are discussed on the product level and on the TransCanada Pipelines fleet level.

A new power turbine variant was developed on a demanding timeline driven by the customer project. A detailed development project was undertaken to establish the new operating point, aerodynamic design, and the new geometry. It was optimized to the customer project-specific load range. During the manufacturing phase, novel rapid prototyping methods were used to achieve desired lead times. Flow path change was limited to the first stage vane to minimize the introduction of new risks and uncertainties.
Assessment of Calibration Approaches for the Stress Relaxation Test
Authors: Pellicotte Jacob , Cotto Mario , Stewart Calvin
Published: November 2019

Advanced manufacturing technologies are enabling the next generation of superalloys for extreme temperatures, pressures, and longevity. There is a need for Accelerated Creep Test (ACT) methods to reduce the time needed to implement new creep resistant superalloys. Without the development of ACTs, the qualification of new superalloys using conventional creep tests can take 11+ years corresponding to the 100,000-hour service life of long-lived turbomachinery components. A refined stress relaxation test (SRT) is introduced to succeed real-time conventional creep tests (CCTs). The stress relaxation test generates extensive stress versus creep-strain-rate data within a single specimen. Since the specimen is held below the elastic limit and relatively little creep deformation has occurred, several SRTs at different temperatures can be performed using a single specimen. To obtain data, specimens are rapidly loaded in force-control to just below the elastic limit. The specimen is switched to displacement-control and held at a fixed displacement while stress relaxation occurs. This generates a stress versus time curve that must be converted into stress versus creep-strain-rate. The stress versus creep-strain-rate curves are utilized to calculate creep activation energy and produce a creep-strain-rate master curve. The objective of this study is to determine the best calibration approach for SRT: regression of stress, regression of creep strain, and the finite difference of creep strain. It is recommended that the differentiation be applied; however, finite difference applied to the raw data produces inconsistent calculations of the creep-strain-rate. In this study, a MATLAB algorithm is written to evaluate all three calibration options where, stress and creep deformation are regressed into natural logarithm functions. The resulting creep-strain-rate curves are compared to determine the most reliable and consistent method. Analyzing and evaluating the results the regression of stress and regression or creep strain calibration methods prove to provide accurate results. These methods will help replace CCTs by conducting less expensive ACTs, while increasing the overall efficiency of the development of new materials.
Application of the Wilshire Stress-Rupture and Minimum-Creep-Strain-Rate Prediction Models for Alloy P91 in Tube, Plate and Pipe Form
Authors: Cano Jaime A. , Stewart Calvin M.
Published: November 2019

There exists a challenge in predicting the long-term creep of materials (3 105 hours) where 11+ years of continuous testing is required to physically collect creep data. As an alternative to physical testing, constitutive models are calibrated to short-term data (< 104 hours) and employed to extrapolate the long-term creep behavior. The Wilshire model was introduced to predict the stress-rupture and minimum-creep-strain-rate behavior of materials and the model is well-accepted due to the explicit description of stress- and temperature-dependence allowing predictions across isotherms and stress levels. There is an ongoing effort to determine how alloy form affects the long-term creep predictions of the Wilshire model. In this study, stress-rupture and minimum-creep-strain-rate predictions are generated for alloy P91 in tube, plate, and pipe form. Data is gathered from the National Institute of Materials Science (NIMS) material database for alloy P91 at multiple isotherms. Following the establish calibration method for the Wilshire model, post-audit validation is performed using short-term data from NIMS to vet the extrapolations accuracy of each form at different isotherms. The Wilshire model demonstrates successful extrapolative techniques for the stress-rupture and minimum-creep-strain-rate of tube, plate, and pipe forms across multiple isotherms. Overall the form with the highest extrapolative accuracy for both stress-rupture and minimum-creep-strain-rate is the plate and the lowest one is the pipe. Stress-rupture design maps are provided where stress and temperature are axes and rupture-time is in contour. The design maps can be applied to: (a) given the boundary conditions, determine the design life (b) given the design life, determine the acceptable range of a boundary conditions. The latter is more useful in turbomachinery design.
Analysis of Statistical Characteristics and Global Sensitivity for Forced Response of Bladed Disks Mistuned by Material Anisotropy
Authors: Rajasekharan Rahul , Petrov E. P.
Published: November 2019

High-pressure turbines of modern gas-turbine engines use single crystal blades that exhibit material anisotropy. Due to manufacturing tolerances, each blade in the bladed disk will have different crystal anisotropy axis orientation, thereby creating mistuning in the structure. In this paper, the blade anisotropy angles are considered as uncertain design parameters to study the variation in forced response of a mistuned bladed disk. For realistic, high fidelity model of a bladed disk, linear bonded contact conditions at blade roots and shrouds are considered. The following two kinds of analysis are performed: (a) statistical analysis using polynomial chaos expansion and (b) global sensitivity analysis using Sobol indices. An effective strategy based on gradient information is used to minimize the computational cost involved in statistical and sensitivity analysis. For the first time, the possibility of introducing intentional blade material anisotropy mistuning to reduce the amplification of forced response is investigated.
Numerical Simulation and Design Optimization of an Electrical Submersible Power Recovery Turbine
Authors: Rutter Risa , Hepp Tony , McManus David
Published: November 2019

In oilfield applications, an Electrical Submersible Pump (ESP) comprised of centrifugal pump, seal, and motor is placed inside a well to provide energy to lift reservoir fluids from the formation to the surface when the reservoir’s natural lift energy is insufficient. The use of an ESP as an Electrical Submersible Power Recovery Turbine (ESPRT) is the focus of this paper. As fluid is injected from the well surface to the pump discharge, through the pump stages, and out the pump intake, the ESPRT shaft rotates in reverse (counterclockwise from an uphole vantage point), compared to an ESP shaft. The moving fluid in the stages transmits energy to the impellers, which turns the motor shaft; the induction motor thereby becomes a generator. We simulated and optimized the performance of a conventional ESP stage using Computational Fluid Dynamics (CFD) and single-phase water.

Before any laboratory or field testing, we simulated ESPRT performance at various speeds and flow rates to predict the performance of the turbine. The CFD prediction of the turbine follows the performance in the third quadrant of a typical four-quadrant pump curve. During the pre-field test CFD study, we did not attempt to predict the stage thrust. Later field trial results, however, showed the impellers operated in up thrust due to fluid flow through the turbine stages producing an upward reaction force on the impellers. We used the field test results to improve the CFD model and, afterwards, the stage design in order to reduce up thrust. The turbine, and pump upon which it is based, are designed to operate in down thrust.

We investigated the effects of changing the diameter of the impeller balance holes and impeller-to-diffuser clearance at the impeller’s skirt and balance ring. Through several CFD iterations, we identified the optimum balance hole and clearance sizes; decreasing the size of the former feature and increasing the latter feature moved the impeller into the down thrust regime. Neither change reduced the stage head and corresponding power output.
Effect of Blade Secular Change on Unsteady Flows in Middle Pressure First-Stage Steam Turbines
Authors: Uemura Akihiro , Miyazawa Hironori , Furusawa Takashi , Yamamoto Satoru , Yonezawa Koichi , Umezawa Shuichi
Published: November 2019

This paper presents the effect of blade secular changes in stator and rotor blade passages on unsteady flows through the first-stage in a middle pressure steam turbine. The scales from the boilers may collide with the stator and rotor blade surfaces, and the blades could become gradually thinned or adhered over time because of the collision. The secular-changed blades influence the performance of steam turbines and may further induce unexpected accidents. Therefore, the maintenance, repair, and overhaul (MRO) of steam turbines is essential. The optimization of MRO scheduling is quite crucial for electric power companies. We simulated unsteady steam flows through an actual middle pressure steam turbine working at a coal-fired power plant while setting manufactured and secular-changed blades. The shape of the secular-changed blades was measured from actual blades during overhaul. The numerical method developed at Tohoku University was employed for the simulation. The difference in the results between the manufactured and secular-changed blades is shown, and the effect of secular changes on unsteady flows is investigated. In addition, the possibility of utilizing the results in the MRO of real turbines is highlighted.
Experimental Study on Analogy Principle of Overall Cooling Effectiveness for Composite Cooling Structures With Both Internal Cooling and Film Cooling
Authors: Xie Gang , Liu Cun-liang , Wang Rui , Ye Lin , Niu Jiajia
Published: November 2019

The previous theoretical work showed the matching principles of analogy parameters for effusion-impingement cooling model. The mismatch of temperature ratios Tg/Tc may result in different matching performance in laboratory condition. Thus, the analogy principles of overall cooling effectiveness were evaluated by experiments in different laboratory conditions for effusion-impingement cooling model. The film plate had 8 rows of cylinder film holes with staggered arrangement and the impingement holes was also employed staggered pattern. Four kinds of cases with different temperature ratios, varied from 1.1 to 2, were tested under three momentum flux ratios and corresponding blowing ratios. The 2D contours of overall cooling effectiveness were measured by using IR thermography. The results for cases with the same mainstream side Biot number and momentum flux ratio show similar contours and values of overall cooling effectiveness, although temperature ratios of these cases are different. And the maximum deviation of overall cooling effectiveness is within 0.02 for these cases. However, there were 0.04∼0.08 difference in the overall cooling effectiveness when the blowing ratios were matched. The overall cooling effectiveness significantly decreases under each blowing ratios with the increase of temperature ratios.
Predictions of Impingement Heat Transfer With Dimples, Pin-Fins and Zig-Zag Rib Obstacles: Conjugate Heat Transfer Computational Fluid Dynamics Predictions
Authors: El-Jummah Abubakar M. , Andrews Gordon E. , Staggs John E. J.
Published: November 2019

Regenerative cooling of low NOx gas turbine combustors was investigated using impingement heat transfer with all the combustion air used for wall cooling prior to passing to the flame stabiliser. 10 rows of impingement holes were modelled. Three obstacles were compared with smooth wall impingement heat transfer. The CHT/CFD methodology used was that validated against experimental results in previous publications of the authors. The impingement heat transfer enhancement geometries investigated were circular pin-fins, dimples and zig-zag ribs, which were aligned transverse to the direction of the cross-flow on the impingement target surface. The obstacles were equally spaced on the centre-line between each row of impingement jets transverse to the cross-flow. One heat transfer enhancement obstacle was used per impingement jet air hole. The CFD calculations were carried out for an air mass flux G of 1.08, 1.48 and 1.94 kg/sm2bara, which are the high flow rates used for regenerative combustor wall cooling. Comparison of the current CFD predictions and previous CFD work, that have experimental data, were made for the flow pressure loss and the surface and locally X2 average HTC, h. It was concluded that none of the obstacles in the impingement gap a significant increase in the surface averaged heat transfer coefficient (HTC). The impact of the obstacles was to increase the flow maldistribution due to the increased pressure loss. This resulted is less heat transfer from the reduced air mass flow in the first 4 holes and increased heat transfer in the last 4 holes, relative to the smooth wall results. The main effect of the obstacles was to increase the heat transfer to the impingement jet surface. The dimpled surface was predicted to have a very poor performance, with significantly reduced impingement heat transfer. This was due to the impingement jets being deflected away from the target surface by the shape of the dimples and this reduced the surface heat transfer.
High Amplitude Combustion Instabilities in an Annular Combustor Inducing Pressure Field Deformation and Flame Blow-Off
Authors: Vignat Guillaume , Durox Daniel , Renaud Antoine , Candel Sébastien
Published: November 2019

This article reports experiments carried out in the laboratory scale annular combustor MICCA-Spray equipped with multiple swirling spray injectors. The experimental setup consists in an air plenum connected to a combustion chamber formed by two concentric cylindrical quartz tubes, allowing full optical access to the flames. A new injection system is introduced and characterized. For a wide range of operating conditions, strong combustion instabilities are observed, but the focus of this article is placed on very high amplitude combustion instabilities coupled by a standing azimuthal mode. It is found that the frequency decreases as the amplitude of the thermoacoustic oscillation grows. New results are obtained using a higher order reconstruction method for the pressure field: its shape is shown to be modified during high amplitude oscillation, leading to asymmetries of the pressure distribution in the system. Flame blow-off occurs near the pressure nodal line when a critical level of oscillation is reached. A method is proposed to reconstruct the acoustic velocity field just before blow-off occurs. Both the velocity field and the blow-off pattern are skewed. The effect of flame blow-off on the frequency of the oscillation is discussed, and it is shown that it leads to the distortion of the pressure field. A new result is also that the phase of the flame response to acoustic perturbation can vary among flames on the same side of the nodal line.
Steam Injected Gas Turbine (STIG) for Load Flexible CHP: Aspects of Dynamic Behaviour, Control and Water Recovery
Authors: Lutsch Thorsten , Gampe Uwe , Buchheim Guntram
Published: November 2019

Industrial combined heat and power (CHP) plants are often faced with highly variable demand of heat and power. Demand fluctuations up to 50% of nominal load are not uncommonly. The cost and revenue situation in the energy market represents a challenge, also for cogeneration of heat and power (CHP). More frequent and rapid load changes and a wide operating range are required for economic operation of industrial power plants.

Maintaining pressure in steam network is commonly done directly by a condensation steam turbine in a combined cycle or indirectly by load changes of the gas turbine in a gas turbine and heat recovery steam generator arrangement. Both result in a change of the electric output of the plant. However, operating cost of a steam turbine are higher than a single gas turbine.

The steam injected gas turbine (STIG) cycle with water recovery is a beneficial alternative. It provides an equivalent degree of freedom of power and heat generation. High process efficiency is achieved over a wide operating range. Although STIG is a proven technology, it is not yet widespread.

The emphasis of this paper is placed on modeling the system behavior, process control and experiences in water recovery. A dynamic simulation model, based on OpenModelica, has been developed. It provides relevant information on system response for fluctuating steam injection and helps to optimize instrumentation and control. Considerable experience has been gained on water recovery with respect to condensate quality, optimum water treatment architecture and water recovery rate, which is also presented.
Asymptotic Description of Forced Response Vibration Saturation by Friction Forces
Authors: Martel Carlos , Martín Juan A.
Published: November 2019

The estimation of the final vibration amplitude of a turbomachinery bladed disk is of extreme practical importance; it is an essential information for the prediction of the level of high cycle fatigue of the blades, and for the subsequent estimation of its operative life span. The forced response vibration is saturated by the nonlinear damping introduced by the friction forces at the interfaces between blade and disk (and/or at the included dampers). The computation of the final amplitude of the limit cycle oscillation requires to solve a quite complicated nonlinear problem. In the case of a tuned bladed disk, this problem can be reduced to a single sector calculation with phase lag boundary conditions. The solution of this one-sector problem requires to consider many harmonics in order to capture the details of the nonlinear time periodic oscillation that sets in. If the small unavoidable differences among blades (mistuning) are also taken into account, then the situation becomes even more complicated because the solution of the mistuned vibration problem requires to consider not only a single sector but the complete bladed disk. The possibility of applying multiple scales techniques to drastically simplify this problem is explored in this paper. The idea is to exploit the fact that all relevant effects present (forcing, nonlinear friction, and mistuning) are, in most practical situations, small effects that develop in a time scale that is much longer than that associated with the natural elastic vibration frequency of the tuned system. A mass-spring model with microslip nonlinear friction is used to represent the forced bladed disk. The multiple scales method is used to asymptotically derive simplified models for both tuned and mistuned configurations. The results of the asymptotic model are compared with those from the mass-spring system, and used to analyze the particular characteristics of the nonlinear friction effects on the final vibration states.
Numerical Investigation on the Effect of Rotation and Holes Arrangement in Cold Bridge Type Impingement Cooling Systems
Authors: Paccati S. , Cocchi L. , Mazzei L. , Andreini A.
Published: November 2019

This work presents the results of a numerical analysis performed on a gas turbine leading edge cooling system. The investigation was carried out in order to provide a detailed interpretation of the outcomes of a parallel experimental campaign. The cooling geometry consists of a cold bridge type impingement system: a radial channel feeds an array of holes, which in turn generate impingement jets cooling down the inner side of the leading edge surface. Coolant is extracted by five rows of holes, replicating film cooling and showerhead systems. Two impingement geometries were considered, presenting different holes arrangements and diameters but sharing the same overall passage area, in order to highlight the effect of different coolant distributions inside the leading edge cavity.

For both geometries a single test point was investigated in static and rotating conditions, with an equivalent slot Reynolds number of around 8200 and feeding conditions corresponding to the midspan radial section of the blade. Both steady RANS approach and Scale Adaptive Simulation (SAS) were tested. Due to the strong unsteadiness of the flow field, the latter proved to be superior: as a consequence, SAS approach was adopted to study every case. A fairly good agreement was observed between the measured and computed heat transfer distributions, which allowed to exploit the numerical results to get a detailed description of the phenomena associated with the different cases.

Results reveal that the two holes arrangements lead to strongly different heat transfer patterns, related to the specific flow phenomena occurring inside the leading edge cavity and to the mutual influence of the various system features. Rotational effects also appear to interact with the supply condition, altering the jet lateral spreading and the overall heat transfer performance.
Reduced Order Models for Nonlinear Dynamic Analysis With Application to a Fan Blade
Authors: Balmaseda Mikel , Jacquet-Richardet G. , Placzek A. , Tran D.-M.
Published: November 2019

In the present work reduced order models (ROM) that are independent from the full order finite element models (FOM) considering geometrical non linearities are developed and applied to the dynamic study of a fan. The structure is considered to present nonlinear vibrations around the pre-stressed equilibrium induced by rotation enhancing the classical linearised approach. The reduced nonlinear forces are represented by a polynomial expansion obtained by the Stiffness Evaluation Procedure (STEP) and then corrected by means of a Proper Orthogonal Decomposition (POD) that filters the full order nonlinear forces (StepC ROM). The Linear Normal Modes (LNM) and Craig-Bampton (C-B) type reduced basis are considered here. The latter are parametrised with respect to the rotating velocity. The periodic solutions obtained with the StepC ROM are in good agreement with the solutions of the FOM and are more accurate than the linearised ROM solutions and the STEP ROM. The proposed StepC ROM provides the best compromise between accuracy and time consumption of the ROM.
Modeling of CO Emissions in Multi-Burner Systems With Fuel Staging
Authors: Klarmann Noah , Zoller Benjamin Timo , Sattelmayer Thomas
Published: November 2019

This work presents a novel strategy to numerically predict CO emissions in gas turbines that operate under part-load conditions employing fuel-staging concepts. In multi-burner systems, fuel can be redistributed to solely run a fraction of the available burners. The situation of active burners interacting with air from adjacent cold burners may lead to quenching effects. Our group recently published a flamelet-based combustion model for low-reactive conditions. Furthermore, a model was proposed for the prediction of CO beyond the assumption of thin reaction zones. These models are adopted in this work and further extended in order to capture quenching. All models are implemented and applied to a simple geometry for the purpose of demonstrating basic mechanisms that are relevant for fuel-staged gas turbines operating at part load conditions. Furthermore, validation is performed in a silo combustor that comprises 37 burners. Here, burner groups are switched off during part load, leading to intense interaction between hot and cold burners. Major improvement in comparison to CO predictions from the flamelet-based combustion model is achieved. It is demonstrated that the model is able to predict the correct values of global CO emissions. Furthermore, the models capacity of handling fuel-staging mechanisms like the CO drop during a burner switch-off event is shown.
Experimental and Computational Methods for the Evaluation of Double-Wall, Effusion Cooling Systems
Authors: Murray Alexander V. , Ireland Peter T. , Romero Eduardo
Published: November 2019

Further improvements in gas turbine efficiency can be sought through more advanced cooling systems — such as the double-wall, effusion system — which provide high cooling effectiveness with low coolant utilisation. The double-wall system, as described here, comprises two walls, one with a regular array of impingement holes, the other with a closely-packed, regular array of film holes (characteristic of effusion systems). These walls are mechanically and thermally connected to one another via a bank of pedestals which increase coolant wetted area and turbulent flow features. However, a lack of data exists in the open literature on these systems.

This study presents a novel experimental heat transfer facility designed with the intent of investigating flat plate versions of such double-wall geometries. Key features of the facility are presented including the use of recirculation to increase mainstream-to-coolant temperature ratio and the use of infrared thermography to obtain thermal measurements. Some rig commissioning characteristics are also provided which demonstrate well-conditioned, uniform flow. Both coolant and mainstream Reynolds numbers are matched to engine conditions, with Biot number within around 15% of engine conditions.

The facility is used to assess the cooling performance of four double-wall effusion geometries which incorporate various geometrical features. Both overall effectiveness and film effectiveness measurements are presented at a range of coolant mass flows with conclusions drawn as to preferable features from a cooling perspective. The results from a fully conjugate CFD model of the facility are presented which utilised boundary conditions obtained during experimental runs. Additionally, a computationally efficient decoupled conjugate method developed previously by the authors was adapted to assess the experimental geometries with the results comparing favourably.