bluuebunny/crossref_metadata_2025 huggingface dataset:
Transient Analysis of Rotating Stall Development in a Centrifugal Compressor With Vaned Diffuser
Authors: Fujisawa Nobumichi , Takahashi Masaki , Ohta Yutaka
Published: November 2019

The transient process of the rotating stall development in a centrifugal compressor with a vaned diffuser was investigated by experimental and numerical analyses. Previous studies show that a diffuser stall triggers a stage stall, which rotates through rotor and stator passages. The vortex evolution at the diffuser throat represents the key factor in diffuser stall development. The developed diffuser stall cell blocked the impeller exit, causing an impeller passage stall. This paper focused on two aspects regarding the transient process of the diffuser stall development. The first aspect is the process by which the vortex at the diffuser throat near the hub side, develops in the circumferential direction. Secondly, we investigated the mechanism of the diffuser stall expansion into impeller passages. The transient analysis of the diffuser stall development was conducted experimentally and numerically by closing the throttle valve abruptly. The hub side blockage was initiated near the cutoff by the strong adverse pressure gradient in the diffuser throat area. Therefore, the key factor in the diffuser stall evolution was the development of a throat blockage near the cutoff, obtained from both experimental and computational fluid dynamics results. Furthermore, the transient stall cell blocked the impeller passages and induced a hub side blockage at the throat of the impeller passages and the impeller leading edge separation. The pressure surface separation of the impeller at the trailing edge had a great impact on the development of the stall cell within impeller passages.
Rotordynamic Characteristics Prediction for Hole-Pattern Seals Using CFD
Authors: Thorat Manish R. , Hardin James R.
Published: November 2019

The experimental set-up for a hole-pattern seal is modeled using CFD and results compared with measured test data and bulk flow model (ISOTSEAL) predictions. The inlet swirl boundary condition for prior CFD analyses of this test case have either been assumed or based on pitot-tube measurements. In this paper, the validity of each is investigated by including radial inlet nozzles with the inlet plenum in the model geometry.

A transient mesh deformation technique with multiple frequency journal excitations is used to determine frequency dependent rotordynamic coefficients. This multi-frequency excitation method is validated against single frequency sinusoidal journal excitation. An empirical limit on the number of frequencies that can be packed in a multi-frequency excitation signal to provide a reasonable estimate of rotordynamic coefficients is provided.

Rotordynamic coefficients estimated using CFD compare well with measured rotordynamic coefficients. For the given test data, the ISOTSEAL bulk flow model does not provide good correlation for cross-coupled stiffness if the measured swirl ratio at the inlet of the seal is used in the prediction. However, improvement in correlation for cross-coupled stiffness is obtained if the swirl ratio found from CFD analysis is used in the bulk flow model, indicating that pitot-tube measurements of swirl may not be accurate.
Numerical Investigation on Sand Particles Deposition in a U-Bend Ribbed Internal Cooling Passage of Turbine Blade
Authors: Li Lin , Liu Cun-liang , Shi Xiao-Yu , Zhu Hui-ren , Li Bing-ran
Published: November 2019

Sand particles impinge the internal cooling passage of the turbine blade and easily deposit, which lead to the decrease of cooling efficiency of the turbine blade and the increase of turbine blade temperature. In order to explore sand particles deposition mechanism in the internal cooling passage of turbine blades, the numerical simulation was performed in a U-bend passage with rib turbulators by means of a commercial CFD code. The fluid phase was modelled employing Reynolds-averaged Navier-Stokes approach. The discrete phase was solved using Lagrangian particle tracking method and a continuous random walk model. A particle deposition model was implemented using user-defined functions. The Reynolds numbers of 30000, 23000 and 15500 are considered. Particles sizes in the range 1–20 microns are considered. Results show that the particles deposition flux decreases gradually along the flow direction. The particles significantly deposit on the rib wall and the bend wall, especially on the windward rib wall and the upstream wall of the bend, with less deposition on the leeward rib wall. This is because the rib wall hinders the movement of fluid and sand particles impact the wall due to inertia, which lead to the energy loss. The particles deposition flux on the windward rib wall increases with the increase of Reynolds number and particles diameter, while the deposition flux on the leeward rib wall decreases. With the increase of the particles diameter, the particles deposition flux increases. The deposition rate increases with the increase of Reynolds number and particles diameter.
Performance of Public Film Cooling Geometries Produced Through Additive Manufacturing
Authors: Snyder Jacob C. , Thole Karen A.
Published: November 2019

Film cooling is an essential cooling technology to allow modern gas turbines to operate at high temperatures. For years, researchers in this community have worked to improve the effectiveness of film cooling configurations by maximizing the coolant coverage and minimizing the heat flux from the hot gas into the part. Working towards this goal has generated many promising film cooling concepts with unique shapes and configurations. However, until recently, many of these designs were challenging to manufacture in actual turbine hardware due to limitations with legacy manufacturing methods. Now, with the advances in additive manufacturing, it is possible to create turbine parts using high temperature nickel alloys that feature detailed and unique geometry features. Armed with this new manufacturing power, this study aims to build and test the promising designs from the public literature that were previously difficult or impossible to implement.

In this study, different cooling hole designs were manufactured in test coupons using a laser powder bed fusion process. Each nickel alloy coupon featured a single row of engine scale cooling holes, fed by a micro-channel. To evaluate performance, the overall cooling effectiveness of each coupon was measured using a matched Biot test at engine relevant conditions. The results showed that certain hole shapes are better suited for additive manufacturing than others, and that the manufacturing process can cause significant deviations from the performance reported in literature.
Experimental Comparison of Two Integer Valued Iterative Learning Control Approaches at a Stator Cascade
Authors: Arnold Florian , Neuhäuser Karl , King Rudibert
Published: November 2019

Experimental and simulative investigations have shown that Active Flow Control is an effective method to influence flow conditions within a compressor. This can be used for different cases like mitigating flow separation or to ensure a uniform flow throughout a compressor stage. Control performance can be improved by making use of a cyclic character found in the rotor/stator interaction or found in new gas turbine setups exploiting cycling combustion. To this end, Iterative Learning Control (ILC) is applied.

To achieve a fast actuation, irrespective of the implemented control method, solenoid valves should be installed instead of proportional valves. Unfortunately, the binary character of these valves does not allow the application of a conventional control methods, e.g., real-valued ILC.

This contribution presents two options to handle the binary control domain in the context of an ILC. Both approaches are tested in a simulation study first to analyze the behavior. Then they are applied to a real test rig featuring a linear stator cascade.
Validation of Lifetime Models for Recuperator Foils Through Long-Term Laboratory and Engine Testing
Authors: Dryepondt Sebastien , Pint Bruce A.
Published: November 2019

For the next-generation of turbine-based combined heat & power (CHP) systems, materials development can enable lower costs and higher efficiency, particularly for alloy foils used in the recuperator. To quantify the potential benefits, lifetime models are being developed for current chromia-forming alloys such as 625, 120, 310 and 709 (also called 2025Nb) as well as new alumina-forming austenitic (AFA) steels, which are much more oxidation resistant in exhaust gas. A combination of long-term laboratory (up to 30 kh) and field exposure data (up to 100 kh) are being used to develop and validate the model for operation at 650°–800°C.
Research on the Heat Insulation Performance of Advanced Thermal Barrier Coatings Based on Dense Vertical Cracked Structure
Authors: Long Yun , Wang Yuzhang , Zhao Mengtian , Weng Yiwu
Published: November 2019

The Thermal barrier coatings (TBCs) applied to gas turbine can effectively protect the metallic components from overheating. It makes contribution to raising turbine entry temperatures, which can improve the cycle thermal efficiency of turbine and prolong its service life. To understand the failure mechanism of TBCs and extend its lifetime, it is vital to prepare TBCs with excellent heat insulating performance. TBCs with dense vertical cracked structure is an essential kind of advanced thermal barrier coatings and has received great attention recently. However, most studies are based on laboratory-scale, since the complex coating preparation process makes it challenging to obtain the controllable microstructure distribution of the coating. Moreover, the thin slices of TBCs are difficult to get during the reconstruction process of the coating microstructure. Therefore, in this work, an optimized numerical reconstruction method of TBCs was applied to obtaining the TBCs with dense vertical cracked structure. The influences of the microstructural TBCs with different numbers of vertical cracks as well as different length and width of vertical cracks were herein discussed, together with the analysis by the developed numerical calculation program based on the lattice Boltzmann method (LBM). The results showed that the performance of heat insulation in dense vertical cracked coatings was improved as the characteristic network structure. Meanwhile, it indicated that the optimal heat insulation performance can get when the length and width of vertical cracks were around 125μm, 15μm respectively. The results can play a guiding role in choosing and designing the turbine blades for further development of gas turbines.
Test Rig Commissioning for Advanced Rotor-Stator Seals
Authors: Trivedi Deepak , Ruggiero Eric , Wolfe Christopher , Kirk Joel , Williams John , Graham James
Published: November 2019

Test facilities capable of simulating relevant operational environments for validating novel concepts are indispensable for advancing the state-of-the-art in turbomachinery sealing technology. A test rig suitable for demonstrating full-scale rotor-stator sealing concepts under operational environments relevant for a variety of turbomachinery gas paths was designed and commissioned at GE’s Seals Test Facility. The test rig, called the Advanced Seals Test Rig (or ASTR), can simulate conditions that include a range of rotor speeds, fluid pressures and temperatures, from steady state operating conditions of high pressure turbines of aircraft engines to sections of steam turbines.

The present paper provides a system level description of the test rig. The main test section of the rig is housed within the centerpiece of a stamped pressure vessel. A drive train penetrates the pressure vessel and consists of an integral saddle mounted rotor. A motor connected to a high-speed gearbox through couplings on each end permits rotation of the test rotor. The test rotor is supported by two bearing pedestals. The paper describes these rig subsystems with focus on novel features for ease of operation. Key instrumentation and operating procedures that enable the rig to operate safely are also described. Key drivers of the rig design, such as test requirements, rotordynamics, mechanical design, ergonomics, safety and test productivity are outlined. Mechanical design considerations include strict requirements for thermal and pressure deformation under demanding conditions of pressure and temperature. Commissioning of the rig included phases of fabrication, installation, shakeout, calibration and benchmarking. Key learnings from the rig design and commissioning process, as well as operations, are summarized.
High Fidelity Simulation of Fluid-Structure Interaction in a 1½ Stage Axial Turbine
Authors: Zorn Joshua , Davis Roger , Clark John
Published: November 2019

A high fidelity, fully coupled numerical technique for the simulation of airfoil and turbomachinery aeroelasticity configurations is presented. The unsteady structural and fluid dynamics equations are discretized by a control volume technique which is second order accurate in space along with a dual time-step scheme that is second order accurate in time. The momentum conservation equation for the solid is written in terms of the Piola-Kirchoff stresses and the displacement velocity components. The stress tensor is related to the Lagrangian strain and displacement tensors using the St. Venant-Kirchoff constitutive relationship. Source terms at the surface of the solid are included to account for surface pressure and body forces. Previous fluid-structure interaction studies of Turek’s cylinder flag and the AGARD 445.6 airfoil have provided confidence needed to accurately perform fluid structure interaction simulations in turbomachinery. In this study, a 1½ stage axial transonic turbine is simulated and results are validated with experimental data. Simulation results indicate that the inclusion of airfoil vibration leads to improved agreement with experimental unsteady surface pressures compared to simulations with fixed airfoils.
Design of High Specific Speed Mixed Flow Micro-Compressor for Co-Flow Jet Actuators
Authors: Xu Kewei , Zha Gecheng
Published: November 2019

This paper conducts aerodynamic design of a high specific speed mixed flow micro-compressor used as an actuator for Co-flow Jet (CFJ) Active Flow Control (AFC) airfoil. The aerodynamic design poses several challenges, including: 1) Small size with very low Reynolds number; 2) High specific speed for mixed-flow compressor due to high mass flow rate and low total pressure ratio; 3) Static pressure ratio lower than 1 to match the low pressure of CFJ airfoil leading edge (LE) suction peak.

The numerical design approach is validated with a mixed flow micro-compressor with very good agreement between the predicted performance and the measured data. Front loaded rotor blade work distribution is adopted to decrease boundary layer loss at the blade surface. Free vortex work distribution is applied for the rotor span to reduce spanwise mixing loss. The rotor efficiency achieved by the numerical prediction is 91.7%. Significant loss is observed downstream of the rotor when the flow reaches the stator and the outlet guide vane (OGV). For the stator, it is found that an inlet and outlet flow path area ratio of 1.05 achieves a very high total pressure recovery of 99.29%. A very good stage isentropic efficiency of 84.3% is achieved. The final design of micro-compressor achieves a flow coefficient of 0.3 at the design point with a total pressure ratio of 1.117 and a static pressure ratio of 0.987. A structure FEM analysis indicates that the rotor blades satisfy the structure strength and modal frequency requirement.
Effects of Varying Liquid Fuel and Air Co-Flow Rates on Spray Characterisation of an Annular Co-Flow Spray Burner
Authors: Alsulami R. A. , Nates S. , Wang W. , Won S. H. , Windom Bret
Published: November 2019

Development of efficient and clean combustion systems requires the understanding of all the processes experienced by a complex liquid fuel in IC engines, such as atomization, vaporization, turbulent mixing, and combustion. Many of these processes are interconnected; the atomization process, which leads to various droplet sizes can enhance or diminish the vaporization rate of the liquid fuel and consequently impact the energy conversion process. Furthermore, the combustion/flame stability of liquid-fueled gas turbine can be influenced by the fuel and the air co-flow rates delivered in the engine. Increasing the fuel and/or air flow rates can enhance droplet breakup and the turbulence of the flow, and as a result sway the droplet size distribution of the spray. This work focuses on investigating the impact of varying the fuel and air flow rates on the spray atomization (e.g. droplet size distribution) of an Annular Co-Flow Spray Burner. This was explored by measuring droplet sizes and velocities of the spray at different radial and axial positions of n-heptane fuel under nonreacting conditions. In addition, the turbulence intensity and the liquid spray droplet distribution were quantified for different fuel and air flow rate conditions. The measurements were obtained by using a Phase Doppler Particle Analyzer/Laser Doppler Velocimeter (PDPA/LDV) at P = 1 atm and T = 298 K. Moreover, the Sauter Mean Diameters for different flow conditions are predicted, using an established correlations, and compared to PDPA/LDV measurements. The results provided a fair understanding of the influence of varying the fuel and air flow rates on the droplet sizes, velocity, and turbulent intensity. Furthermore, the results presented here will support future work that will focus on unraveling the role of phase change on flame stability.
Automatic Gas Turbine Matching Scheme Adaptation for Robust GPA Diagnostics
Authors: Stenfelt Mikael , Zaccaria Valentina , Kyprianidis Konstantinos G.
Published: November 2019

When performing gas turbine diagnostics using Gas Path Analysis (GPA), a convenient way of extracting the degradations is by feeding the measured data from a gas turbine to a well-tuned gas turbine performance code, which in turn calculates the deltas on the chosen health parameters matching the measured inputs. For this, a set of measured parameters must be matched with suitable health parameters, such as deltas on compressor and turbine efficiency and flow capacity.

In aero engines, the number of sensors are in general limited due to cost and weight constraints and only the necessary sensors for safe engine operation are available. Some important sensors may have redundancy in case of a sensor loss but it is far from certain that this applies to all sensors available.

If a sensor malfunctions by giving false or no values, the functions using the sensor will be negatively affected in some way causing them to either synthesize a fictive measurement, changing operating scheme, going into a degraded operating mode or shutting down parts or the whole process. If an onboard diagnostic algorithm fails due to sensor faults it will lead to a decrease in flight safety, thus there is a need for a robust system.

This paper presents a strategy for automatic modifications of the gas turbine diagnostic matching scheme when sensors malfunction to ensure a robust function. When a sensor fault is detected and classified as malfunctioning, the gas turbine matching scheme is modified according to predefined rules. If possible, a redundant measurement replaces the faulty measurement. If not, the matching scheme will be modified by determining if any health parameters cannot be derived by the functional set of measurements and remove the least valuable health parameter while maintaining a working matching scheme for the remaining health parameters.
High-Frequency Acoustic Mode Identification of Unstable Combustors
Authors: Kim J. , Lieuwen T. , Emerson B. , Acharya V. , Wu D. , Mckinney R. , Wang X. , Isono M.
Published: November 2019

High frequency thermoacoustic instabilities are becoming increasingly problematic in modern combustion systems. Understanding which acoustic mode is being excited is important for understanding potential mechanisms and control approaches — for example, influence of a helical shear layer mode on the flame has profoundly different effects on the first tangential acoustic mode, than a higher order axial mode of similar frequency. Nonetheless, the modal density increases with frequency and it becomes increasingly difficult to determine which acoustic mode is self-excited, based upon frequency calculations alone. Moreover, access issues and cost usually limit the number of pressure probes that can be distributed axially and azimuthally in the combustor. This paper presents a methodology for identifying the acoustic mode by using high temperature pressure transducers flush mounted in a combustion chamber. Modal identification is demonstrated with a siren under non-reacting conditions. The siren is mounted on the chamber to excite longitudinal and azimuthal waves. Five acoustic sensors at different axial and azimuthal locations measure the pressure fluctuations simultaneously. Given the forcing frequency and the speed of sound, the pressure distribution in the combustor is reconstructed in the time domain from the measured data by using a least squares method to determine its mode shapes. In addition, the finite element method (FEM) solver is used to provide the eigenfrequencies and corresponding mode shapes. The test results demonstrate that the mode shapes from the reconstructed data and corresponding frequencies are consistent with those predicted from the FEM, which validates the methodology in this study. In addition, the methodology is extended to practical reacting cases without the siren to determine the acoustic mode shapes of naturally occurring instabilities. In these cases, the modal features have strong stochastic features, such as what appear to be stochastic variations in overall amplitude and relative amplitudes of clockwise and counterclockwise waves.
Transonic Turbine Vane Endwall Film Cooling Using PSP Measurement Technique
Authors: Shiau Chao-Cheng , Sahin Izzet , Ullah Izhar , Han Je-Chin , Mirzamoghadam Alexander V. , Riahi Ardeshir , Stimpson Curtis
Published: November 2019

This work focuses on the parametric study of film cooling effectiveness on turbine vane endwall under various flow conditions. The experiments were performed in a five-vane annular sector cascade facility in a blowdown wind tunnel. The controlled exit isentropic Mach numbers were 0.7, 0.9, and 1.0, from high subsonic to transonic conditions. The freestream turbulence intensity is estimated to be 12%. Three coolant-to-mainstream mass flow ratios (MFR) in the range 0.75%, 1.0%, and 1.25% are studied. N2, CO2, and Argon/SF6 mixture were used to investigate the effects of density ratio (DR), ranging from 1.0, 1.5 to 2.0. There are 8 cylindrical holes on the endwall inside the passage. Pressure-sensitive paint (PSP) technique was used to capture the endwall pressure distribution for shock wave visualization and obtain the detailed film cooling effectiveness distributions. Both the high-fidelity effectiveness contour and the laterally (spanwise) averaged effectiveness were measured to quantify the parametric effect. This study will provide the gas turbine designer more insight on how the endwall film cooling effectiveness varies with different cooling flow conditions including shock wave through the endwall cross-flow passage.
The Effect of Blade Deflections on the Torsional Dynamic of a Wind Turbine
Authors: Jauregui Juan , Cárdenas Diego , Morales Luis , Martinez Miguel , Basaldua Jovan
Published: November 2019

The dynamic behavior of a wind turbine comprises three major parts: the external torque produced by the wind, the mechanical elements and the grid. For the aerodynamic response, there is three type of models: constant aerodynamic torque for Type I and Type IV turbines, a pseudo aerodynamic model for Type I and II, and linearized aerodynamic model for Type III. The drivetrain has been model either as a single-mass shaft model or as a double-mass shaft model. Most of the dynamic models of wind turbines consider the wind torque only as a function of the wind velocity, and they neglect the vibrations of the blades as an excitation torque. Therefore, a dynamic model that includes the aerodynamic power, the torque produced by the deflection of the blades, the vortex-induced vibrations of the blades and the torque caused by the eccentricity of the center of mass represents the excitation torque. The dynamic model of the wind turbine is a multibody dynamic model with six degrees of freedom. The blades are represented as a two lumped-masses, the torsional response of the main rotor is described as a single torsional mass, which is connected to the electric generator by a gearbox. The gearbox is represented as a double-shaft model, and the gear mesh is simulated with a nonlinear torsional stiffness. The generator is described as another torsional mass. The torque produced by the wind is calculated using QBlade for different pitch angles. The dynamic parameters of the blade were determined experimentally, and it was found that the blade has only two dominant vibration modes. For this reason, the blades were modeled as two lumped-masses. It was found that the vortex-induced vibrations modify the torsional vibrations of the generator and they are an extra source of perturbations for the electric generation, and they depend on the wind velocity and the pitch angle.
Design and Experimental Assessment of Bladeless Turbines for Axial Inlet Supersonic Flows
Authors: Braun James , Paniagua Guillermo , Falempin Francois , Le Naour Bruno
Published: November 2019

Supersonic inlet flow is usually considered to be detrimental to the performance of turbine systems. This paper demonstrates an effective manner to harness power from supersonic axial inflow without swirl. The bladeless axial turbine allows for power extraction from harsh environments with minimal maintenance costs. In a first step, a baseline bladeless turbine is designed and the power extraction is analyzed. The bladeless turbine surface is parametrized in Matlab and subsequently imported into Hexpress (Numeca) to mesh an unstructured grid. The first layer thickness is kept below one for all the simulations. The unstructured mesh is loaded into CFD++ (Metacomp) to solve the three dimensional steady Reynolds Averaged Navier Stokes equations. Second, the work extraction principle is broken down from a three-dimensional unsteady problem into a two-dimensional steady phenomenon. An experimental campaign is outlined and test details are discussed. Finally, after the experimental characterization, the operational envelope and scaling of the bladeless turbine is described for several reduced mass flows, reduced speeds and geometrical features of the turbine (amplitude of the wavy surface, helix angle, hub radius and length of the axial turbine).
Topology Optimization of Serpentine Channels for Minimization of Pressure Loss and Maximization of Heat Transfer Performance As Applied for Additive Manufacturing
Authors: Ghosh Shinjan , Kapat Jayanta S.
Published: November 2019

Gas Turbine blade cooling is an important topic of research, as a high turbine inlet temperature (TIT) essentially means an increase in efficiency of gas turbine cycles. Internal cooling channels in gas turbine blades are key to the cooling and prevention of thermal failure of the material. Serpentine channels are a common feature in internal blade cooling. Optimization methods are often employed in the design of blade internal cooling channels to improve heat-transfer and reduce pressure drop. Topology optimization uses a variable porosity approach to manipulate flow geometries by adding or removing material. Such a method has been employed in the current work to modify the geometric configuration of a serpentine channel to improve total heat transferred and reduce the pressure drop. An in-house OpenFOAM solver has been used to create non-traditional geometries from two generic designs. Geometry-1 is a 2-D serpentine passage with an inlet and 4 bleeding holes as outlets for ejection into the trailing edge. Geometry-2 is a 3-D serpentine passage with an aspect ratio of 3:1 and consists of two 180-degree bends. The inlet velocity for both the geometries was used as 20 m/s. The governing equations employ a “Brinkman porosity parameter” to account for the porous cells in the flow domain. Results have shown a change in shape of the channel walls to enhance heat-transfer in the passage. Additive manufacturing can be employed to make such unconventional shapes.
Transcritical / Supercritical CO2 Recompression Brayton Cycle Using a Novel Rotary Liquid Piston Compressor
Authors: Thatte Azam
Published: November 2019

This paper presents a transcritical / supercritical CO2 (sCO2) recompression Brayton cycle using a novel rotary liquid piston compressor (LPC). This new type of multi-phase compressor utilizes a pumped motive fluid that interfaces with sCO2 in a rotating ducted cylinder for efficient CO2 compression at lower hardware costs. The energy required to pump the motive fluid can be significantly lower than that required to compress CO2 in a traditional compressor. The compressor utilizes a low compressibility, low diffusivity, low solubility liquid as the motive fluid to pressurize process fluid (sCO2) stream. Its use as a replacement for the main compressor in a recompression sCO2 Brayton cycle is expected to reduce compression power by more than 10% while maintaining robust operation over a wide range of ambient temperatures and CO2 densities that are typical for dry-cooled sCO2 cycles in arid climates. The new rotary liquid piston compressor also eliminates the need for gas lubricated bearings & dry gas seals, thus providing added advantage of rotordynamic stability, mechanical robustness & life over traditional compressors. Thermodynamic cycle analyses and 1D compressible flow analysis of multi-phase compression inside the rotary LPC is presented. An advanced 3D multi-phase flow model is developed to study fundamental physics of multi-species transport, diffusion & mixing of species and liquid-supercritical interface compression & decompression. This 3D model is used to validate some of the assumptions made in the 1D model. Various performance curves are developed to study the effect of lead flow, rotational speed and compressor inlet temperature on CO2 exit mass flow rate, % mixing of the two species, compression power requirements and overall compression efficiency. Optimization study on above system variables is carried out and a set of guidelines for use of rotary LPC in sCO2 compression is established.
Evaluation of Film Cooling Superposition Predictions Using Shaped Holes on the Suction Side of a Blade Model
Authors: Yoon Christopher , Moore Jacob , Bogard David
Published: November 2019

Film cooling is often used for turbine airfoil cooling, and there are numerous studies of the performance of a single row of holes. In actual application there will typically be multiple rows of holes which interact. Consequently there is a need to develop techniques to predict film cooling performance with multiple rows of coolant holes using superposition of single row cooling effectiveness. Although there have been many studies of superposition techniques for predicting film cooling effectiveness with multiple rows of cylindrical holes, there have been very few in which shaped holes were used with a typical turbine airfoil model. In this study, film effectiveness was measured on the suction side of a turbine blade model using two rows of shaped coolant holes. Measurements were made with each row independently and with both rows combined. This provided the experimental data for superposition predictions and to evaluate these predictions. Each row had 7-7-7 shaped holes with pitch to diameter ratio of 6, and the two rows were more than 40 diameters apart. The experiments were run using two different upstream blowing ratios, and a wide range of downstream blowing ratios. The superposition predictions of film effectiveness were reasonably accurate when the upstream row of holes were operated at a high blowing ratio with a corresponding smaller film effectiveness (due to jet separation). However, when the upstream coolant holes were operated at the optimum blowing ratio, and hence maximum film effectiveness downstream, the superposition analysis predicted film effectiveness levels slightly lower than actual levels. These results show that there was an interaction between jets that resulted in higher film effectiveness than was accounted for with a superposition prediction.
Secondary Flows in the Return System of a Centrifugal Compressor Stage
Authors: Rossbach T. , Bisping J. , Grates D. R. , Jeschke P. , Hildebrandt A. , Franz H.
Published: November 2019

This Paper presents an analysis of the flow in the return system of a centrifugal compressor with a flow coefficient of 0.15. Based on detailed experimental and numerical data, the areas of high losses and potentials for improving the return system geometry are revealed. Special emphasis is placed on the interaction of the flow in the return system components, including the U-bend, the vaned return channel and the final L-bend. Strong flow redistribution occurs due to the sharp curvature of the U-bend, forming a blockage area at the hub near the vane leading edge. This causes a strong passage vortex, which is further intensified by the pressure gradient induced by the L-bend. Additionally, the flow near the shroud accelerates due to the large blockage area near the hub at the exit of the U-bend, resulting in high friction losses. To identify the main causes of loss, a method was evolved. It was validated and supplied by pneumatic measurement data. On this basis analytical approaches were taken to quantify the total pressure losses due to friction, secondary flows, incidence and trailing edge flow. As a result, approximately 60 % of the return system losses arise due to friction. Another 30–40% are caused by secondary flows. It can be concluded that the results of the investigation contribute to the understanding of the secondary flow structures inside a centrifugal compressor return system of high mass flow rates. By combining the knowledge acquired in respect to the sources of highest losses with the experimental data, a well-founded basis for future optimization and the validation of numerical approaches is possible.
Identification of Poorly Ventilated Zones in Gas-Turbine Enclosures With Machine Learning
Authors: Corsini Alessandro , Delibra Giovanni , Giovannelli Marco , Lucherini Gabriele , Minotti Stefano , Rossin Stefano , Tieghi Lorenzo
Published: November 2019

Ventilation systems are used in gas turbine packages to control the air temperature, to protect electrical instrumentation and auxiliary items installed inside the enclosure and to ensure a proper dilution of potentially dangerous gas leakages. These objectives are reached only if the ventilation flow is uniformly distributed in the whole volume of the package, providing a good air flow quality as prescribed by international codes such as ISO 21789. To evaluate the effectiveness of the ventilation design, numerical computations are performed for several purposes, one of which is the identification of poorly ventilated portions of the enclosure. In fact, it is essential to accurately detect the regions which are less ventilated, since they could be prone to the accumulation of an accidental fuel gas leak. There are different approaches to identify these portions, such as decay regression or inlet source analysis, that require unsteady simulations of the flow field inside the package. The present work discusses the implementation of a new methodology using machine learning and artificial neural networks (ANN) to detect the poorly ventilated regions where a gas cloud can accumulate. The concentration of fuel gas is estimated starting from a steady-state computation without running a more expensive unsteady computation. The entire process is built around an accurate training of the ANN using a proper set of simpler test-cases that have been identified to match the characteristics of the gas turbine enclosure. During the training phase accuracy and overfitting of the ANN were monitored to ensure robustness of the method. The procedure is then applied to a real case scenario and the results are presented in this paper highlighting the main advantages of this approach respect to a conventional use of CFD analysis. Computations of the flow fields are carried out using OpenFOAM with RANS and U-RANS approaches, while the ANN is developed and trained in Python.
Modelling of Sonic Jets for Gas Leak Applications
Authors: Minotti Stefano , Corsini Alessandro , Delibra Giovanni , Lucherini Gabriele , Rossin Stefano , Tieghi Lorenzo , Traldi Stefania
Published: November 2019

Design of gas turbine packages is subjected to safety issues and the related guidelines are provided by ISO-21789. According to this code, the ventilation system shall guarantee a good and safe dilution in case of an unexpected gas leakage from components of the fuel gas system inside the enclosure. The evaluation of the dilution is commonly carried out by CFD simulations and the ISO-21789 indicates the criteria to evaluate the danger of a gas leak by estimating the cloud volume of the explosive mixture. To follow this prescription and to properly calculate the exact volume cloud, it is fundamental to accurately reproduce the fuel gas leak, which is always a supersonic jet of fuel gas into an air-ventilated domain. The main criticality is to simulate a supersonic jet into a complex domain such as the gas turbine package, considering the industrial goals in terms of accuracy and time constraints. The complexity is due to the geometry of the package and to the multiple locations where the leakage could occur. In such context, it is preferable to develop an advanced modeling of the phenomenon rather than simply improve the detail of the CFD, that could turn out to be unfeasible for industrial goals.

For this reason, the authors present a series of simulations of under-expanded jets at high pressure ratios carried out to investigate the applicability of the sonic source approach to not-round jets.
Turbine Cascade Profile Loss Sensitivity to Incoming Wake Parameters: Effects of Reduced Frequency, Wake Momentum Defect and Axial Gap
Authors: Simoni D. , Yepmo V. , Zunino P. , Ubaldi M. , Lengani D. , Bertini F.
Published: November 2019

In the present work the profile losses of a highly loaded low pressure turbine cascade, operating under realistic unsteady conditions, have been measured for different incoming wake parameters. A moving bar system has been used for wake generation, allowing the variation of bar diameter, bar count and axial gap between the bars and the cascade leading edge. The overall test matrix spans three different bar diameters, three different reduced frequencies and two axial gaps, for a total of 18 different conditions tested. For each of them, the time-dependent cascade inflow has been characterized by means of phase-locked hot-wire measurements in order to determine the effects of the wake parameter modification on the turbulence intensity peak and on the incoming wake momentum deficit, that are well known to affect the generation of losses in the downstream cascade. The procedure recently developed by the authors based on the simultaneous acquisition of the signals of two kiel probes, located upstream and downstream of the cascade, has been used to accurately quantify the profile losses for each condition, identifying the contribution due to the wake bowing, tilting and dilation process into the cascade channel and that due to the wake-boundary layer interaction. Additionally, Proper Orthogonal Decomposition (POD) has been applied to the ensemble data matrix constructed from the loss coefficient distributions in the pitchwise direction, measured for the different conditions, with the aim of highlighting the loss trend vs the design space parameter variation. The POD modes obtained from the cross-correlation matrix provide a direct information on the flow region where losses are prevalently produced, while the corresponding POD coefficients give the weight of each parameter in the loss generation. The paper shows the potentiality of this procedure in providing a rapid identification of the main causes of losses, and the dominant parameter affecting the process of loss generation.
Evaluation of Turbulent Spot Production Rate in Boundary Layers Under Variable Pressure Gradients for Gas Turbine Applications
Authors: Dellacasagrande M. , Lengani D. , Simoni D. , Ubaldi M. , Zunino P.
Published: November 2019

The paper presents an experimental data base on transitional boundary layers developing on a flat plate installed within a variable area opening endwall channel. Measurements have been carried out by means of time-resolved PIV. The overall test matrix spans 3 Reynolds numbers, 4 free-stream turbulence intensity levels and 4 different flow adverse pressure gradients. For each condition, 16000 instantaneous flow fields have been acquired in order to obtain high statistical accuracy. The flow parameters have been varied in order to provide a gradual shift of the mode of transition from a bypass process occurring with mild adverse pressure gradients at high free-stream turbulence, to separated flow transition, occurring with low Reynolds number, low free-stream turbulence intensity and elevated adverse pressure gradient. In order to quantify the influence of the flow parameter variation on the boundary layer transition process, the transition onset and end positions, and the turbulent spot production rate have been evaluated with a wavelet based intermittency detection technique. This post-processing technique is in fact able to identify the vortical structures developing within the boundary layer, the intermittency function is then automatically evaluated for each tested condition counting the number of such structures and defining the cumulative probability function.

The by-pass transition mode has the longest transition length that decreases with increasing the Reynolds number. The transition length of the separated flow case is smaller than the by-pass one, and the variation of the flow parameters has a similar impact. Similarly, the dimensionless turbulent spot production rate reduces when the Reynolds number is increasing. The variation of the inlet turbulence intensity has a small influence on this parameter except for the condition at the highest turbulence intensity, that always shows the lowest turbulent spot production rate because a by-pass type transition occurs. This large amount of data has been used to develop new correlations used to predict the spot production rate and the transition length in attached and separated flows.
Bayesian Analysis of In-Situ High-Resolution X-Ray Diffraction Synchrotron Experiments of Ti-6Al-4V Specimens Undergoing Tensile Loading
Authors: Armstrong Nicholas , Lynch Peter A. , Kada Sitarama R. , Cizek Pavel , Kimpton Justin A. , Antoniou Ross A.
Published: November 2019

Linking the accumulation of microstructural damage prior to crack initiation to the lifing of aero-engines components would help to better predict the time that a component spends in this crack initiation stage.

We present the results and analysis of in-situ high-resolution X-ray diffraction (XRD) experiments of a Ti-6Al-4V specimen that experienced tensile loading using medium energy synchrotron X-rays (≤ 21 keV) carried out at the Australian Synchrotron. The XRD analysis characterised XRD line-broadening due to the build-up of dislocations and the formation of crystallites in α- and β-Ti-6Al-4V specimens. Using Bayesian XRD analysis methods, the density, spatial arrangement of dislocations, and crystallite size information for α- and β-phases of the Ti-6Al-4V was extracted from the XRD line-profiles, as a function of applied load. The XRD analysis was then compared and validated with transmission electron microscopy (TEM) analysis of the specimen before and after the loading. Comparison of the TEM and XRD analysis reveals broad agreement in terms of the microstructural damage of Ti-6Al-4V specimens.
Turning Dynamic Sensor Measurements From Gas Turbines Into Insights: A Big Data Approach
Authors: Karlstetter Roman , Widhopf-Fenk Robert , Hermann Jakob , Rouwenhorst Driek , Raoofy Amir , Trinitis Carsten , Schulz Martin
Published: November 2019

Gas turbine power plants generate an ever growing amount of high frequency dynamic sensor data. One of the applications of this data is the protection against problems induced by combustion dynamics, as, e.g., with the ArgusOMDS system developed by IfTA. In the light of digitalization, this data has the potential to also be used in other areas and ultimately transform maintenance, repair and overhaul approaches. However, current solutions are not designed to cope with the large time windows needed for a general analysis and this can hinder development of advanced machine analysis algorithms. In this work, we present an end-to-end approach for large scale sensor measurement analysis, employing data mining techniques and enabling machine learning algorithms. Our approach covers the complete data pipeline from sensor measurement acquisition to analysis and visualization. We demonstrate the feasibility of our approach by presenting several case studies that prove the benefits over existing solutions.
Numerical Investigations on the Power Generation of Turbo-Expander During the Propane De-Hydrogenation Process
Authors: Kwon Hwabhin , Park Heesung
Published: November 2019

A turboexpander for the propane de-hydrogenation process with blade and splitter has been numerically investigated. Since the turboexpander expands fluid from higher inlet pressure to lower discharge pressure, the kinetic energy of fluid is converted into useful mechanical energy. The efficiency and power generation with the designed turboexpander have been simulated with different operating conditions. The pressure ratio between inlet and outlet and rotational speed are varied to characterize the performance of the turboexpander as an electrical power generator. The numerical simulations have shown the vortex at the trailing edges of blade and splitter which decreases the efficiency. The rotational speed and the pressure ratio are parameterized to obtain operation conditions which achieve high power generation and efficiency. Consequently, the generated power from 614.12 kW to 693.45kW is obtained at the normal rotational speed and the pressure ratio between 1.75 to 2.22.