bluuebunny/crossref_metadata_2025 huggingface dataset:
Coupling of Endwall and Aerofoil Optimisation on a Low-Speed Compressor Tandem Stator
Authors: Straccia Mattia , Gümmer Volker
Published: September 2021

The scope of this paper is to provide clarity over fundamental effects of non-axisymmetric endwall contouring in a highly-loaded compressor tandem stator. Specifically, the focus of the research will be the influence that aerofoil optimization and end-wall contouring have on each other, and how a combined optimization of the two simultaneously affects the final design of the optimized geometry. The reference geometry used in this research is a standard tandem vane arrangement with smooth axi-symmetric endwalls and designed to represent a datum stage configuration for future investigations of such blade geometries, experimental work on a low-speed research compressor being a next step. The optimization was performed using an in-house developed routine coupled with Auto-Opti, an automated optimizer based on an evolutionary strategy algorithm, developed by the DLR Institute of Propulsion Technology. The entire optimization was conducted solely on the stator, modeled as an annular cascade. This paper reports about a thorough flow field analysis of the optimized geometry in order to understand local mechanisms occurring with non-axisymmetric contouring in the tandem stator passage flow field and its overall performance. Furthermore, it describes and explains the effect that the aerofoil optimization has on the contoured hub surface shape, compared to an optimization process, which is only applied to the hub contouring. In particular, the results clarify how endwall flow field improvements reduce the degree of required aerofoil deformation, and show that the new blade shape is better adapted to the contoured endwall. The 3D endwall flow field has been investigated in order to understand how the optimized geometry modifies the magnitude of the cross-passage flow and reduces the size of the trailing edge corner vortex of the front and rear tandem vane. The paper concludes with some guidelines on how endwall contouring and near endwall aerofoil section design and optimization can be applied most effectively.
Inlet Flow Distortion in an Advanced Civil Transport Boundary Layer Ingesting Engine Installation
Authors: Hall D. K. , Greitzer E. M. , Uranga A. , Drela M. , Pandya S. A.
Published: September 2021

This paper presents first-of-a-kind measurements, and complementary computations, of the flow through the propulsion system of a boundary layer ingesting, twin-engine advanced civil transport aircraft configuration. The experiments were carried out in the NASA Langley 14- by 22-foot Subsonic Tunnel, using a 1:11 scale model of the D8 “double-bubble” aircraft with electric ducted fans providing propulsive power. Overall force and moment measurements and flow field surveys at the inlet and nozzle exit planes were obtained. The computations were carried out with the NASA OVERFLOW code. The measurements and computations were conducted for a range of aircraft angles of attack and propulsor powers representing operating points during the aircraft mission. Velocity and pressure distributions at the propulsor inlet and exit, and integral inlet distortion metrics, are presented to quantify the flow non-uniformity due to boundary layer ingestion. The distorted inflow exhibits qualitative and quantitative changes over the mission, from a unidirectional stratified stagnation pressure at cruise to a streamwise vortex structure at climb conditions. The computations capture these flow features and reveal the interactions between airframe and propulsor that create these three-dimensional flow variations.
Dynamic Mesh Adaption for Scale-Resolving Reacting Flow Simulations
Authors: Xia Yu , Stopford Phil , Sharkey Patrick , Verma Ishan
Published: September 2021

In this paper, a dynamic adaptive mesh refinement method is used in conjunction with a hybrid scale-resolving turbulence model to solve industrial combustion problems. The objective of the adaption method is to track and resolve characteristic turbulent structures arising from swirlers, pilot injectors and flame propagation in industrial burner configurations. By employing Polyhedral Unstructured Mesh Adaption (PUMA)® within Ansys Fluent® solver, local regions of mesh are refined to capture gradients in temperature, velocity and other key variables. For Scale-Resolving Simulations (SRS), highly refined meshes are required to resolve a sufficient range of turbulent scales. In this work, a strategy is proposed to evaluate the scale-resolving quality of the mesh and to refine it dynamically in a transient simulation. The condition used for adapting the mesh is based on the gradients of key variables such as temperature and velocity, whilst the large-scale eddies are resolved using an approach based on the LES mesh resolution index. This strategy is then applied to a series of test cases (a diffusion jet flame, a bluff-body premixed flame and a swirl stabilized flame), using the hybrid Stress-Blended Eddy Simulation (SBES) turbulence model and a Flamelet Generated Manifold (FGM) combustion model. The numerical results are compared with available experimental data, and the accuracy of the solutions is discussed.
Evaluating the Influence of Rotor-Casing Eccentricity on Turbine Efficiency Including Time-Resolved Flow Field Measurements
Authors: DeShong Eric T. , Siroka Shawn , Berdanier Reid A. , Thole Karen A.
Published: September 2021

The clearance that exists between the casing and turbine blade tips is one of the key drivers of efficiency in gas turbine engines. For this reason, engine manufacturers utilize precise manufacturing techniques and may employ clearance control systems to minimize tip clearances to reduce associated losses. Despite these efforts, turbines typically exhibit some nominal casing ovality or rotor-casing eccentricity, and changes to blade tip clearance during operation commonly occur due to thermal and mechanical stresses. The present study investigates non-axisymmetric tip clearance effects by creating a rotor-casing eccentricity in a one-stage axial test turbine operating in a continuous-duration mode at engine relevant conditions with engine representative hardware. A magnetic levitation bearing system was leveraged to move the turbine shaft to vary the rotor-casing eccentricity without test section disassembly. The results of this study indicate that rotor-casing eccentricity does not affect overall turbine efficiency over the range that was tested, but does locally influence efficiency and the rotor exit flow field. Comparisons of flow angle and secondary flow kinetic energy agreed with previous studies and existing analytical methods, respectively. Collectively, these results indicate that tip clearance can be studied locally on an eccentric rotor.
Selecting a Compressor Meridional Topology: Axial, Mixed, Radial
Authors: Smyth Jonathan M. , Miller Robert J.
Published: September 2021

This paper proposes a new duty-based Smith Chart as part of an improved method of selecting the geometric topology of compressors (axial, mixed or radial) in the earliest stage of design. The method has a number of advantages over previous methods: it is based on the non-dimensional flow and the non-dimensional work, which aligns with the aerodynamic function of the compressor and is therefore more intuitive than specific speed and specific diameter. It is based on a large number of consistently designed compressor rotors which have been computationally predicted using RANS CFD. Most importantly, it provides the designer not only with a choice of topology but also with the complete meridional geometry of the compressor, its blade design and the number of blades. This fidelity of geometry at the very early stage of design allows the designer to undertake a true systems design optimization (noise, manufacturing, packaging constraints and cost). This has the major advantage of significantly reducing early stage design times and costs and allows the designer to explore completely new products more quickly.
Investigation of Mistuned Oscillating Cascade Using Fully-Coupled Method
Authors: Phan H. M. , He L.
Published: September 2021

The uncoupled phase-shifted single-passage simulation is commonly used for turbomachinery aeroelastic problems. However, it has difficulties in dealing with unconventional phenomena such as strong fluid-structure interaction effects as well as blade mistuning effects. Regarding mistuning effects, structural mistuning has been studied extensively while aerodynamic mistuning has received far less attention. There seems to be a lack of clear and systematic understanding of physical behaviour and mechanisms of mistuned bladerows, particularly in the context of the aerodynamic mistuning versus structural one. In the present work, direct fully-coupled method is adopted to investigate the dynamics mechanism of a mistuned oscillating cascade. Both structurally and aerodynamically mistuned cascades show that the blades would couple and oscillate at a unique frequency and a constant inter-blade phase angle regardless of the individual blade’s eigen-frequency. The vibration amplitudes of blades of a mistuned row are different when excited. For structural mistuning, the mode localization effect is seen to be responsible for a monotonic increase of cascade aeroelastic stability with mistuning. On the other hand, the aerodynamically mistuned cascade shows a stabilizing effect at small amount of mistuning but exhibits a destabilizing effect at large mistuning. Such non-monotonic tendency could be explained using the aero-damping decomposition by the influence coefficient approach. At low reduced frequency, there is a striking difference between the tuned and aero-mistuned cascade. Although the tuned cascade is stable, the aero-mistuned cascade may experience flutter. A close inspection of the aero-mistuned cascade flutter reveals that there are two oscillating waves forming a beating signal.
Influence of Surface Roughness on the Flat-Plate Boundary Layer Transition Under a High-Lift Airfoil Pressure Gradient and Low Freestream Turbulence
Authors: Jeong Heechan , Song Seung Jin
Published: September 2021

Effects of surface roughness on the transition of flat-plate boundary layers under a high-lift airfoil pressure gradient with low incoming freestream turbulence level have been investigated. Time-resolved streamwise and wall-normal velocity fields with surface roughness values of Ra/C = 0.065·10−5, 4.417·10−5 and 7.428·10−5 have been measured at a fixed Reynolds number of 5.2·105 and freestream turbulence intensity of 0.2%. For the reference Smooth surface of Ra/C = 0.065·10−5, a laminar separation bubble forms from about 64% to 83% of the chord length. Displacement thickness increases downstream of separation and then decreases during the transition (reattachment), and momentum thickness increases due to the vortices shed from the separation bubble. Increasing surface roughness has little impact on the laminar boundary layer separation onset but reduces the height and length of the separation bubble and induces earlier transition. For Ra/C = 4.417·10−5, displacement thickness during transition is slightly thinner and the overall momentum deficit is slightly lower than those for Ra/C = 0.065·10−5. For Ra/C = 7.428·10−5, the separation bubble becomes hardly visible as the transition mode approaches the attached mode, and turbulent mixing by the wall-bounded turbulence becomes dominant. In addition, the portion of turbulent wetted area increases due to earlier transition, and momentum deficit increases more rapidly in the turbulent wetted area. Thus, the overall momentum deficit for Ra/C = 7.428·10−5 is larger than that for Ra/C = 0.065·10−5.
Thermodynamic Analysis of Waste Heat Recovery Systems in Large Waste Heat Generating Industries
Authors: Thada Shantanu , Rajan Yash T. , Pradeep A. M. , Sridharan Arunkumar
Published: September 2021

The accelerating growth of electricity demand necessitates looking for potential waste heat recovery solutions in production industries. Significant potential for efficient waste heat recovery is observed in the cement manufacturing industry. Based on the waste heat source temperatures in a cement plant, two potential candidates, the supercritical CO2 Brayton (S-CO2) cycle or the Organic Rankine cycle (ORC), promises low capital cost and enhanced thermodynamic performance. The current study focuses on modelling and optimization of the S-CO2 and ORC cycles for a 1 MTPA cement plant, with the raw-clinker preheater as the waste-heat source. The primary objective is to maximize the net-power output using genetic algorithms. A comparative performance analysis of the two ORCs with working fluids: R134a and Propane, the simply recuperated S-CO2 cycle (RC) and recompressed-recuperated S-CO2 cycle (RRC) configurations is presented with varying number of preheaters. For all cases, ORC-R134a yields more power than the ORC-Propane, RC, and RRC configurations. In terms of the waste heat recovered, ORC-Propane marginally outperforms ORC-R134a. The ORC configurations recover 32%–38% of the available heat, while the S-CO2 configurations recover, at maximum, 25%–30% of the available heat.
Bayesian Inference of Experimental Data for Axial Compressor Performance Assessment
Authors: Cruz Gonçalo G. , Babin Cedric , Ottavy Xavier , Fontaneto Fabrizio
Published: September 2021

As the next generation of turbomachinery components becomes more sensitive to instrumentation intrusiveness, a reduction of the number of measurement devices required for the evaluation of performance is a possible and cost-effective way to mitigate the arising of non-mastered experimental errors. A first approach to a data assimilation methodology based on Bayesian inference is developed with the aim of reducing the instrumentation effort. A numerical model is employed to provide an initial belief of the flow, that is then updated based on experimental observations, using an ensemble Kalman filter algorithm for inverse problems. Validation of the algorithm is achieved with the usage of experimental measurements not used in the data assimilation process. The methodology is tested for a low aspect ratio axial compressor stage, showing a good prediction of the corrected compressor map, as well as a promising prediction of the inter-row radial pressure distribution and 2D flow field.
A Numerical Study on the Influence of Hydrogen Addition on Soot Formation in a Laminar Aviation Kerosene (Jet A1) Flame at Elevated Pressure
Authors: Sun Mingshan , Gan Zhiwen
Published: September 2021

The hydrogen addition is a potential way to reduce the soot emission of aviation kerosene. The current study analyzed the effect of hydrogen addition on aviation kerosene (Jet A1) soot formation in a laminar flame at elevated pressure to obtain a fundamental understanding of the reduced soot formation by hydrogen addition. The soot formation of flame was simulated by CoFlame code. The soot formation of kerosene-nitrogen-air, (kerosene + replaced hydrogen addition)-nitrogen-air, (kerosene + direct hydrogen addition)-nitrogen-air and (kerosene + direct nitrogen addition)-nitrogen-air laminar flames were simulated. The calculated pressure includes 1, 2 and 5 atm. The hydrogen addition increases the peak temperature of Jet A1 flame and extends the height of flame. The hydrogen addition suppresses the soot precursor formation of Jet A1 by physical dilution effect and chemical inhibition effect, which weaken the poly-aromatic hydrocarbon (PAH) condensation process and reduce the soot formation. The elevated pressure significantly accelerates the soot precursor formation and increases the soot formation in flame. Meanwhile, the ratio of reduced soot volume fraction to base soot volume fraction by hydrogen addition decreases with the increase of pressure, indicating that the elevated pressure weakens the suppression effect of hydrogen addition on soot formation in Jet A1 flame.
Improved CFD Predictions of Pyrolysis Oil Combustion Using Advanced Spray Measurements and Numerical Models
Authors: van Beurden Eva , Pozarlik Artur , Putra Bima , Brem Gerrit , Bouten Thijs , Withag Jan , Axelsson Lars-Uno
Published: September 2021

In search of an economical and environmentally friendly manner of power generation the industry is forced to find fuels which can replace conventional fossil fuels. During the last years this has led to significant developments in the production of alternative fuels, whereby these fuels became a more reliable and more efficient source of energy. Fast pyrolysis oil (FPO) is considered as a promising example of one of the alternative fuels.

This research focuses on the application of FPO in a gas turbine combustion chamber. For the OPRA OP16 gas turbine, a numerical approach using advanced CFD simulations has been applied to a real scale gas turbine combustor. The simulations are supported by full-scale combustor tests and atomizer spray experiments. Hereby it has been shown numerically and experimentally that the gas turbine combustion chamber can operate on FPO in the 30–100% load range.

The droplet Sauter Mean Diameter (SMD) has been investigated by means of a Particle Droplet Image Analysis to visualize the sprays in the near field of the atomizer. The effects of the spray pattern are of key importance to the flame structure in the gas turbine combustion chamber. Therefore the results from this dedicated test experiment have been used as input for dedicated CFD simulations.

A dedicated combustion model of fast pyrolysis oil has been developed for the OpenFOAM code, considering both the evaporation of the oil and the burnout of the char. In the simulations the gas turbine electrical load, the cone angle and the droplet SMD of the spray were varied. These simulations provide a detailed insight and description on the evaporation of the pyrolysis oil and the flame characteristics in the low calorific fuel combustor of OPRA’s OP16.
On Choosing the Optimal Impeller Exit Velocity Triangles in Preliminary Design
Authors: Lou Fangyuan , Key Nicole L.
Published: September 2021

Impeller discharge flow plays an important role in centrifugal compressor performance and operability for two reasons. First, it determines the work factor and relative diffusion for the impeller. Second, it sets the flow into the downstream stationary diffusion system. The choice made in the preliminary design phase for the impeller exit velocity triangle is crucial for a successful design. The state-of-the-art design approach for determining the impeller exit velocity triangle in the preliminary design phase relies on several empirical guidelines, i.e. maximum work factor and diffusion ratio for an impeller, the optimal range of absolute flow angle, etc. However, as modern compressors continue pushing toward higher efficiency and higher work factor, this design approach falls short in providing exact guidance for choosing an optimal impeller exit velocity triangles due to its empirical nature as well as the competing mechanism of the two trends. In light of this challenge, this paper introduces a reduced-dimension, deterministic approach for the design of the impeller exit velocity triangle. The method gauges the design of the impeller exit velocity triangle from a different design philosophy using a relative diffusion effectiveness parameter and is validated using 6 impeller designs, representative of applications in both turbochargers and aero engines. Furthermore, with the deterministic method in place, optimal impeller exit velocity triangles are explored over a broad design space, and a one-to-one mapping from a selection of impeller total-to-total pressure ratios and backsweep angles to a unique optimal impeller exit velocity triangle is provided. This new approach is demonstrated, and discussions regarding the influences of impeller total-to-total pressure ratio, isentropic efficiency, and backsweep angle on the optimal impeller exit velocity triangle are presented.
Influence of Flow Coefficient on Ingress Through Turbine Rim Seals
Authors: Graikos Dimitrios , Carnevale Mauro , Sangan Carl M. , Lock Gary D. , Scobie James A.
Published: September 2021

Rim seals are critical in terms of limiting the temperature of highly-stressed engine components but function with a penalty to the power output and contribute to entropy gain stemming from mixing losses in the turbine. Ingress through rim seals is influenced by the presence of rotor blades and stator vanes, and the mainstream flow coefficient in the annulus that determines the corresponding swirl.

This paper presents an experimental study of ingress upstream and downstream of the rotor disc in a 1.5-stage rig with double radial clearance rim seals. Two rotor discs were used, one with blades and one without, and two platforms were used downstream of the rotor, one with vanes and one without. Tests were conducted at two rotational speeds and a range of flow conditions was achieved by varying the annulus and sealing mass flow rates. Concentration effectiveness, swirl and steady pressure measurements separated, for the first time, the influence of the blades and vanes on ingress over a wide range of flow conditions. Measurements on the downstream stator platform provide added insight into the complex interaction between the egress and the mainstream. Measurements of unsteady pressure revealed the presence of large-scale structures, even in the absence of blades. The number and speed of the structures was shown to depend on the flow coefficient and the purge flow rate.
Thermal Characterization of a Steam Turbine Casing Including Measuring of Adiabatic Wall Temperatures Using Proprietary Sensors
Authors: Weigel Bernhard Valerian , Odenbach Stefan , Uffrecht Wieland , Polklas Thomas
Published: September 2021

Modern steam turbines must increasingly be designed for flexible operation. However an increasing amount of cold starts and load changes have a massive impact on fatigue resistance of the material. So the monitoring of thermal parameters of the casing is significant for checking thermally induced stresses and furthermore lifetime calculation. Additionally the measurement data is helpful for CFD validation reasons.

This paper presents a new proprietary developed sensor setup and measurement results. The sensors are flush mounted into a steam turbine at different axial and circumferential locations in the recirculation area between the intermediate and the lower pressure turbine. Hence it is possible to detect temperatures, temperature gradients and heat flux in the part of the wall near the fluid. Moreover the field of temperature within the sensor can be modulated by powering an installed heater. So the adiabatic wall temperature can be identified. For measuring the temperature gradient, seven equidistant spaced thermocouples were used in difference circuit. Therefore two different types of thermocouples were applied. Both types have better transfer characteristics compared to a thermocouple of type K. High amplification enables monitoring of small differences in temperature. The temperature measures an integrated resistor thermometer.

The sensors are applied on a real 12 MW industrial steam turbine with maximal live steam parameters of 400 °C and 30 bar. The measurements show various operation points and load changes.
Development of a Multi-Shaker-Control to Investigate the Influence of the Interblade Phase Angle on Frictionally Damped Turbine Blades
Authors: Jäger Florian , Kaptan Ferhat , Panning-Von Scheidt Lars , Wallaschek Jörg
Published: September 2021

Constructive damper concepts are developed and integrated in turbomachinery to reduce vibration amplitudes generated by dynamic loads. The potential damping effectiveness of friction-based damper concepts is strongly dependent on the relative motion between adjacent blades, besides other factors such as normal force. In cyclic symmetric structures the phase difference is determined by the excited nodal diameter, which leads to different damper movements and efficiencies for given mode shapes. Several studies on the investigation of the damper performance of different underplatform damper geometries have been carried out on non-rotating test stands consisting usually of two blades in order to reduce the experimental effort before setting up rotational tests. Based on the existing modes of the two blades and the application of commonly just one shaker, the investigations are limited to the in-phase and out-of-phase modes. In this paper an experimental approach is developed to reduce the gap of transferability between non-rotating and rotational tests to analyze the effects of a variable interblade phase angle on the damping effect of underplatform dampers. For this purpose, a cascaded control system using two shakers is being developed to control the force amplitudes and the phase difference between the response of the two blades. The control algorithm is designed in a model-based way by using a two degrees of freedom oscillator with friction contact and is subsequently integrated in the non-rotating test stand.
Unsteady Turbine Rim Sealing and Vane Trailing Edge Flow Effects
Authors: Monge-Concepción Iván , Siroka Shawn , Berdanier Reid A. , Barringer Michael D. , Thole Karen A. , Robak Christopher
Published: September 2021

Hot gas ingestion into the turbine rim seal cavity is an important concern for engine designers. To prevent ingestion, rim seals use high pressure purge flow but excessive use of the purge flow decreases engine thermal efficiency. A single stage test turbine operating at engine-relevant conditions with real engine hardware was used to study time-resolved pressures in the rim seal cavity across a range of sealing purge flow rates. Vane trailing edge (VTE) flow, shown previously to be ingested into the rim seal cavity, was also included to understand its effect on the unsteady flow field. Measurements from high-frequency response pressure sensors in the rim seal and vane platform were used to determine rotational speed and quantity of large-scale structures (cells). In a parallel effort, a computational model using Unsteady Reynolds-averaged Navier-Stokes (URANS) was applied to determine swirl ratio in the rim seal cavity and time-resolved rim sealing effectiveness. The experimental results confirm that at low purge flow rates, the VTE flow influences the unsteady flow field by decreasing pressure unsteadiness in the rim seal cavity. Results show an increase in purge flow increases the number of unsteady large-scale structures in the rim seal and decreases their rotational speed. However, VTE flow was shown to not significantly change the cell speed and count in the rim seal. Simulations point to the importance of the large-scale cell structures in influencing rim sealing unsteadiness, which is not captured in current rim sealing predictive models.
Low Reynolds Number Effects on the Separation and Wake of a Compressor Blade
Authors: Liu Qiang , Ager Will , Hall Cesare , Wheeler Andrew P. S.
Published: September 2021

This paper investigates the surface boundary layer and wake development of a compressor blade at a range of low Reynolds number from 45000 to 120000. Experiments in a miniature linear compressor cascade facility have been performed with detailed surface pressure measurements and flow visualization to track variations in the separation bubble size. These have been combined with high resolution pneumatic pressure and hot wire probe traverses in the downstream wake. High fidelity DNS simulations have been completed on the same compressor blade section across the same range of operating conditions.

The results show that large laminar separation bubbles exist on both blade surfaces. As Reynolds number increases, these separation bubbles shorten in length and reduce in thickness. Correspondingly, the downstream wake narrows, although the peak wake loss coefficient remains approximately constant. As the Reynolds number is increased from 45000 to 120000 the bubble length on the suction side reduced from 48% to 28% chord and on the pressure side reduced from 35% to 20% chord, while the loss coefficient reduced from 9% to 5%. The flow features are examined further within the high-fidelity computations, which reveal the dependence of the wake turbulence on the laminar separation bubbles. The separation bubbles are found to generate turbulent kinetic energy, which convects downstream to form the outer part of wake. As Re increases, a shorter bubble produces less turbulence in the outer part of the boundary layer leading to a narrower wake. However, the trailing edge separation is largely independent of Reynolds number, leading to the constant peak loss coefficient observed. The overall loss is shown to vary linearly with the total turbulence production, and this depends on the size of the separation bubbles.

Overall, this research provides new insight into the connection between the blade surface flow field and the wake characteristics at low Reynolds number. The findings suggest that changes that minimize the extent of the blade separation bubbles could provide significant improvements to both the steady and unsteady properties of the wake.
Numerical Investigation of the Low-Swirl Flow in an Aeronautical Combustor With Angular Air Supply
Authors: Hoffmann Sven , Koch Rainer , Bauer Hans-Jörg
Published: September 2021

Civil air traffic is predicted to further grow in the near future. Hence, the development of aeronautical combustors will face major challenges to meet future stringent environmental regulations. In the present study, an innovative gas turbine combustor with angular air supply called Short Helical Combustor (SHC) is investigated. The main feature of this concept is the helical arrangement of the fuel injectors around the turbine shaft. Aiming at the implementation of a lean-burn concept, a low-swirl lifted flame is adopted. This flame is lifted off and not anchored to the injector which opens the potential of low NOx emissions due to a high degree of premixing within the combustor.

In this work, isothermal flow characteristics of such a generic SHC combustor are studied by use of RANS predictions with special emphasis on the interaction of adjacent low-swirl flows. For evaluating the influence of injector parameters on the flow field, a parametric study based on single sector simulations is performed. It is shown that the asymmetrically confined swirling jet flow is strongly deflected towards the sidewall of the staggered SHC dome. The deflection of the flow is associated with an asymmetric pressure field in the vicinity of the burner which is generally known as Coandă effect. As a consequence of the deflected flow, the angular momentum flux at combustor outlet is increased.

The interaction of the low-swirl jet and the SHC sidewall is investigated with regards to backflow momentum and residence time in the recirculation zone. It is concluded that by modifying the momentum of the air flow through the injector, the amount of recirculating air flowing back along combustor walls is strongly affected. The present work establishes an understanding of the underlying aerodynamics of the SHC concept which is essential for matching the requirements of lean lifted flames.
Achieving Better Power Plant Guarantees Through a New Exergy-Based Approach for the HRSG
Authors: Smith Raub W.
Published: September 2021

The best assurance an owner has to maximize the performance of the entire combined cycle power plant is perfect alignment of HRSG performance guarantee metrics to this goal. Currently, HRSG equipment performance guarantees include steam generation rates and steam temperature at each pressure level plus draft loss and reheater pressure drop. This profusion of guaranteed parameters with multiple bonus/LD rates is not always well correlated to the customer’s ultimate goal of delivering MW from the bottoming cycle since the behavior of each steam generation circuit is a complex function of steam pressure, steam turbine performance, and GT exhaust temperature.

This paper proposes a solution that normalizes and combines all HRSG performance measurements into a single value directly and reliably tied to the customer value metric (which may be different for fired and unfired operation or other load points). This is achieved by expressing the HRSG performance guarantee in terms of exergy recovered to steam and plant exergy loss attributable to the HRSG (gas side draft loss).

This will be shown, with examples, to serve the goals of the customer to confirm by test that an HRSG delivers the promised steam exergy consistent with the plant level performance requirement.
High-Performance Computing Probabilistic Fracture Mechanics Implementation for Gas Turbine Rotor Disks on Distributed Architectures Including Graphics Processing Units (GPUs)
Authors: Gajjar Mrugesh , Amann Christian , Kadau Kai
Published: September 2021

We present an efficient Monte Carlo based probabilistic fracture mechanics simulation implementation for heterogeneous high-performance (HPC) architectures including CPUs and GPUs. The specific application focuses on large heavy-duty gas turbine rotor components for the energy sector. A reliable probabilistic risk quantification requires the simulation of millions to billions of Monte Carlo (MC) samples. We apply a modified Runge-Kutta algorithm in order to solve numerically the fatigue crack growth for this large number of cracks for varying initial crack sizes, locations, material and service conditions. This compute intensive simulation has already been demonstrated to perform efficiently and scalable on parallel and distributed HPC architectures including hundreds of CPUs utilizing the Message Passing Interface (MPI) paradigm. In this work, we go a step further and include GPUs in our parallelization strategy. We develop a load distribution scheme to share one or more GPUs on compute nodes distributed over a network. We detail technical challenges and solution strategies in performing the simulations on GPUs efficiently. We show that the key computation of the modified Runge-Kutta integration step speeds up over two orders of magnitude on a typical GPU compared to a single threaded CPU. This is supported by our use of GPU textures for efficient interpolation of multi-dimensional tables utilized in the implementation. We demonstrate weak and strong scaling of our GPU implementation, i.e., that we can efficiently utilize a large number of GPUs/CPUs in order to solve for more MC samples, or reduce the computational turn-around time, respectively. On seven different GPUs spanning four generations, the presented probabilistic fracture mechanics simulation tool ProbFM achieves a speed-up ranging from 16.4x to 47.4x compared to single threaded CPU implementation.
Effect of Spanwise Hole to Hole Spacing on Overall Cooling Effectiveness of Effusion Cooled Combustor Liners for a Swirl Stabilized Can Combustor
Authors: Ahmed Shoaib , Wahls Benjamin H. , Ekkad Srinath , Lee Hanjie , Ho Yin-Hsiang
Published: September 2021

One of the most effective ways to cool the combustor liner is through effusion cooling. Effusion cooling (also known as full coverage effusion cooling) involves uniformly spaced holes distributed throughout the combustor liner wall. Effusion cooling configurations are preferred for their high effectiveness, low-pressure penalty, and ease of manufacturing. In this paper, experimental results are presented for effusion cooling configurations for a realistic swirl driven can combustor under reacting (flame) conditions. The can-combustor was equipped with an industrial engine swirler and gaseous fuel (methane), subjecting the liner walls to engine representative flow and combustion conditions. In this study, three different effusion cooling liners with spanwise spacings of r/d = 6, 8, and 10 and streamwise spacing of z/d = 10 were tested for four coolant-to-main airflow ratios. The experiments were carried out at a constant main flow Reynolds number (based on combustor diameter) of 12,500 at a total equivalence ratio of 0.65. Infrared Thermography (IRT) was used to measure the liner outer surface temperature, and detailed overall effectiveness values were determined under steady-state conditions. The results indicate that decreasing the spanwise hole-to-hole spacing (r/d) from 10 to 8 increased the overall cooling effectiveness by 2–5%. It was found that reducing the spanwise hole-to-hole spacing further to r/d = 6 does not affect the cooling effectiveness implying the existence of an optimum spanwise hole-to-hole spacing. Also, the minimum liner cooling effectiveness on the liner wall was found to be downstream of the impingement location, which is not observed in existing literature for experiments done under non-reacting conditions.
Design and Validation of a Large Steam Turbine End-Stage Blade to Meet Current and Future Market Demands
Authors: Lübbe Bertold , Aschenbruck Jens , Pütz Oliver , Theidel Mira
Published: September 2021

To meet today’s and future market needs, large end-stage blades are obliged to fulfill high flexibility regarding the operational range and high efficiency goals while being prepared for daily start-stop cycles.

The end-stage total efficiency can be maximized by enlarging the steam turbine exhaust area and thereby reducing the exhaust losses. Therefore, a new Low Pressure (LP) backend featuring an increased freestanding 41″ steel blade has been developed and is presented here, which is optimized for maximum efficiency over a wide range of operation conditions.

To allow for such a large steel-blade to operate at 60Hz rotational speed and to meet the daily cycling demand, various aspects of the blade design were optimized. A new high strength blade steel was developed (Teuber [1]), which gives the designer freedom for aerodynamical optimizations, while keeping the mechanical utilization within the predefined, allowable limits. To maximize the cycling capability, a new fir tree root was developed which minimizes the static as well as the dynamic loading. To verify the success of the new fir-tree root design and to verify the natural frequencies for the relevant modes, an extensive validation measurement campaign was setup with a full-scale blade row in a spin-pit. Here, the airfoil, root and steeple of the end-stage blade were equipped with strain gauges. Additionally, the blade row was monitored using tip-timing sensors. The results of this validation measurement campaign are presented in this paper. They show a close agreement between the design calculations and the measured static strains and vibration responses in terms of natural frequencies as well as displacement and strain amplitudes.

Additionally, a test turbine has been set-up featuring a direct scaling of the new LP backend with the new high strength steel and a pre-stage to simulate realistic operation conditions over the complete operation range. The blade performance was tested up to high mass-flows, condenser pressures of up to 300 mbar and at varying load points covering all potential load points from extreme part load to full load with minimal and maximal condenser pressure. Strain gauges as well as tip-timing are used to measure the vibration response of the end-stage blade during the measurement campaign. The results presented here show, that throughout the complete measurement campaign the blade experienced minimal excitation which led to vibration levels that allowed unrestricted operation in the complete, tested operation range. In summary this paper shows the main design features of a large full-speed freestanding end-stage blade and the validation measures that were performed to ensure that the design targets and the market requirements are fully met.
Experimental Development of On-Line Flame Transfer Function Measurements for Fielded Gas Turbines
Authors: Matthews Austin , Cobb Anna , Adhikari Subodh , Wu David , Lieuwen Tim , Blust Jim , Emerson Benjamin
Published: September 2021

Understanding thermoacoustic instabilities is essential for the reliable operation of gas turbine engines. To complicate this understanding, the extreme sensitivity of gas turbine combustors can lead to instability characteristics that differ across a fleet. The capability to monitor flame transfer functions in fielded engines would provide valuable data to improve this understanding and aid in gas turbine operability from R&D to field tuning. This paper presents a new experimental facility used to analyze performance of full-scale gas turbine fuel injector hardware at elevated pressure and temperature. It features a liquid cooled, fiber-coupled probe that provides direct optical access to the heat release zone for high-speed chemiluminescence measurements. The probe was designed with fielded applications in mind. In addition, the combustion chamber includes an acoustic sensor array and a large objective window for verification of the probe using high-speed chemiluminescence imaging. This work experimentally demonstrates the new setup under scaled engine conditions, with a focus on operational zones that yield interesting acoustic tones. Results include a demonstration of the probe, preliminary analysis of acoustic and high speed chemiluminescence data, and high speed chemiluminescence imaging. The novelty of this paper is the deployment of a new test platform that incorporates full-scale engine hardware and provides the ability to directly compare acoustic and heat release response in a high-temperature, high-pressure environment to determine the flame transfer functions. This work is a stepping-stone towards the development of an on-line flame transfer function measurement technique for production engines in the field.
Experimental Characterization of Losses in Bladeless Turbine Prototype
Authors: Renuke Avinash , Reggio Federico , Traverso Alberto , Pascenti Matteo
Published: September 2021

Multi-disk bladeless turbines, also known as Tesla turbines, are promising in the field of small-scale power generation and energy harvesting due to their low sensitivity to down-scaling effects, retaining high rotor efficiency. However, low (less than 40%) overall isentropic efficiency has been recorded in the experimental literature. This article aims for the first time to a systematic experimental characterization of loss mechanisms in a 3-kW Tesla expander using compressed air as working fluid and producing electrical power through a high speed generator (40krpm). The sources of losses discussed are: stator losses, stator-rotor peripheral viscous losses, end wall ventilation losses and leakage losses. After description of experimental prototype, methodology and assessment of measurement accuracy, the article discusses such losses aiming at separating the effects that each loss has on the overall performance. Once effects are separated, their individual impact on the overall efficiency curves is presented. This experimental investigation, for the first time, gives the insight into the actual reasons of low performance of Tesla turbines, highlighting critical areas of improvement, and paving the way to next generation Tesla turbines, competitive with state of the art bladed expanders.
Design Performance Analysis of Supercritical CO2 Cycle for CSP Application With Sensible Heat Thermal Storage
Authors: Thanganadar Dhinesh , Fornarelli Francesco , Camporeale Sergio , Gillard Jonathon , Patchigolla Kumar
Published: September 2021

Supercritical CO2 (sCO2) cycles can achieve higher efficiencies than steam Rankine cycles at a higher temperature with a compact plant footprint. Concentrated solar power plants are capital intensive, as there is no fuel-related operating cost, the capital cost must be reduced to realise a reduction in the levelised cost of electricity. Power cycle efficiency and the temperature difference between the hot and cold storage tanks are the critical thermodynamic parameters to reduce the size and the cost of solar field and two-tank storage system whilst the power cycle specific power has also to be maximised to lower the power block cost. With these objectives, three potential cycle configurations were selected for detail assessment; a recompression cycle, partial cooling cycle and a partial heating cycle. A set of performance maps are presented using multi-objective optimisation, which maximises the efficiency and the specific power is explored for five different compressor inlet temperature of 35°C, 40°C, 45°C, 50°C, 55°C and two turbine inlet temperatures of 600°C and 700°C. The overnight capital cost across the Pareto front are estimated and the economic performance map is presented, which guides in selecting an optimal design for different boundary conditions.
Adjoint Optimization of Film Cooling Hole Geometry
Authors: Jones Fraser B. , Oliver Todd , Bogard David G.
Published: September 2021

This paper is part of a two paper series on optimization methods for film cooling which seek to address the limitations of experimental optimization by utilizing advances in RANS based CFD to quickly optimize film cooling hole geometries. In the companion paper [1] on parametric optimization the optimum hole was experimentally demonstrated to have > 40% improvement in spatially averaged effectiveness compared to a baseline 7-7-7 hole, and was developed by leveraging RANS as a proxy for experimental data. In this paper adjoint based optimization was used to develop unique film cooling hole geometries. Adjoint optimization moves beyond using RANS as a proxy for experimental data instead utilizing the derivatives available in RANS to fully optimize the geometry of a shaped film cooling hole. The resulting geometry was experimentally validated to further increase performance by over 80% compared to the baseline 7-7-7 shaped hole. The study also show that further increases in performance are predicted when expanding the optimization target region. Furthermore, these new optimized geometries are readily manufactured by Additive Manufacturing (AM) processes and significantly less time consuming to generate than an equivalent parametrically optimized hole shape. These methods provide the tools necessary to fully utilize the large design space offered by AM and will be dramatically shift the future of film cooling hole design.
Modeling of Combustor-Turbine Vane Interaction Using Stress-Blended Eddy Simulation
Authors: Verma Ishan , Rida Samir , Zori Laith , Basani Jaydeep , Kamrath Benjamin , Brandt Dustin
Published: September 2021

Modeling the interaction between gas turbine engine modules is complex. The compact nature of modern engines makes it difficult to identify an optimal interface location between components, especially in the hot section. The combustor and high-pressure turbine (HPT) are usually modeled separately with a one-way boundary condition transfer to the turbine inlet. This approach is not ideal for capturing all the intricate flow details that travel between the combustor and the turbine and for tracking hot streak migration that determines turbine durability. Modeling combustor-turbine interaction requires a practical methodology that can be leveraged during the engine design process while ensuring accurate, fast, and robust CFD solutions.

The objective of this paper is to assess the effectiveness of joint simulation versus co-simulation in modeling combustor and turbine interaction. Co-simulations are performed by exchanging information between the combustor and the turbine stator at the interface, wherein the combustor is solved using Stress-Blended Eddy Simulation (SBES) while the stator is solved using RANS. The joint combustor-stator simulations are solved using SBES. The benefits of using SBES versus LES are explored. The effect of the combustor-stator interaction on the flow field and hot streak migration is analyzed. The results suggest that the SBES model is more accurate than LES for heat transfer predictions because of the wall treatment and the joint simulation is computationally efficient and less prone to interpolation errors since both hot section components are modeled in a single domain.