bluuebunny/crossref_metadata_2025_split huggingface dataset:
Progress on Combined Optic-Acoustic Monitoring of Combustion in a Gas Turbine
Authors: Andracher Lukas , Giuliani Fabrice , Paulitsch Nina , Moosbrugger Vanessa 
Published: January 2021

Abstract
The need for better combustion monitoring in gas turbines has become more acute with the latest technical requirements, standards, and policies in terms of safety, environment, efficiency, operation flexibility and operation costs. This paper reports on a concept for gas turbine combustion monitoring using multiple probes that combine optical and acoustical measurements. The motivation of the project is twofold. On the one side, one wants to exploit the radiative feature of the flame and transform it into a piece of reliable information about the combustion status. On the other side, this information can be useful in terms of data interpretation or data reconciliation with other information coming from further sensors such as temperature probes, fast pressure probes or accelerometers. For this purpose, a set of multiple Rayleigh Criterion Probes (RCPs) combining optical and acoustical sensors is used. Detailed information about the RCP can be found in paper GT2017-63626, [1]. The focus is put on the detection of the flame, on the monitoring of the ignition process, on the quality assessment of combustion based on its spectral contents (including soot formation) and on the detection of possible combustion instabilities. The novel test rig used for validation of this advanced combustion monitoring concept is introduced, and minimal instrumentation including three probes is recommended. The split in red, green and blue (RGB) light components and their further analysis allows mapping the different types of operation. Solutions are proposed to bring the optical interface as near as possible to the flame and make it operational and reliable despite prevailing heat. The paper closes with a description of the ongoing tests on a pressurized combustion facility, and a sketch for a 3-RCPs based compact combustion monitoring system. The advantages of selected chromatic spectral bands are discussed, as well as the remaining challenges towards a full demonstration.
Topology Optimization of High Aspect Ratio Internal Cooling Channels As a Design for Additive Manufacturing
Authors: Ghosh Shinjan , Kapat Jayanta S. 
Published: January 2021

Abstract
High aspect ratio channels are a common internal cooling feature in Gas Turbine blades, mostly suitable for the trailing edge region or mid-chord regions. Traditionally such channels are fitted with rib-turbulators and/or pin-fin turbulators to augment heat transfer and prevent material failure. Highly efficient internal cooling of blades can improve the efficiency of a real Gas Turbine power cycle by tolerating higher Turbine Inlet Temperatures (TIT). Multi-physics Topology optimization (TO) has been employed in the current study to find optimized shape of these ducts, with an aim to increase heat transfer, while constraining the pressure drop across the channel. This method, commonly used in structural problems, is a novel topic of research when applied to fluid-thermal studies. Material distribution in the computational domain is varied by changing porosity value in each cell and thereby altering the fluid path and creating a conjugate heat transfer problem. Each cell has a value of Brinkmann porosity factor which either simulates a blockage, or a fluid region depending on a low or high value of this design variable. Hence the degree of freedom is high in this method, and there is no manual bias introduced, unlike in parametric shape optimization which is limited to a few design parameters. The unconventional geometries obtained as an end product of this optimization process can thus be an alternative to existing rib/pin-fin type of cooling geometries. The recent progress in additive manufacturing can now facilitate the manufacturing of complicated shapes. An in-house Open-FOAM solver has been used to carry out the process in only twice the amount of time compared to a regular RANS-CFD. 3-Dimensional rectangular channels with inlet aspect ratios of 4:1 and 8:1 have been considered as baselines with a constant inlet velocity. Resulting optimum geometries were found to have organic tree like branching arrangements of rib-like wall roughness and v-shaped structures.
Numerical Investigation of the Effect of Operating Point on the Aerodynamic Excitation in a Radial Turbine Stage
Authors: Kovachev Nikola , Vogt Damian M. 
Published: January 2021

Abstract
The effect of operating point on the aerodynamic excitation that causes forced response vibrations in turbomachinery blading is studied numerically. For this purpose, a novel method for rapid assessment of large operating point variations on the mode excitability is introduced. This method includes a surrogate modeling approach based on Kriging interpolation in combination with an adaptive sampling technique. The data for the model is predicted by means of unsteady Computational Fluid Dynamics (CFD) simulations with the Nonlinear Harmonic (NLH) method in the frequency domain. The concept of an excitation map describing the excitation as a function of rotational speed and expansion ratio is introduced. Excitation maps for the blade passing frequency are obtained for ten mode shapes and two total inlet temperatures in a radial turbine stage.
The analysis of the excitation maps has shown that the aerodynamic excitation can be reduced similarly to a performance map and used for different inlet conditions. The effect of the rotational speed appears largely mode dependent and without a clear trend. On the other hand, an increase of the expansion ratio leads to higher excitation for all mode shapes. A study of the harmonic pressure field causing the aerodynamic excitation showed that these dependencies are driven by changes in the velocity triangle and pressure at the rotor inlet. Considering the relatively short computational time to obtain multiple excitation maps, the presented approach is considered suitable to be used for optimizing turbine designs with respect to minimizing the aerodynamic excitation.
Experimental Study on Aerodynamic Loss and Heat Transfer for Various Squealer Tips
Authors: Jung Jin-sol , Kim Inkyom , Joo Jin Sung , Lee Sang Woo 
Published: January 2021

Abstract
This paper presents aerodynamic loss data for five squealer configurations of a full squealer (FS), a pressure-side squealer (PS), a suction-side squealer (SS), a camberline squealer (CS), and a full-camberline squealer (FCS) in a low speed turbine cascade. In addition, tip thermal load data are also reported for the FS, PS, and SS tips. The results show that when h/s (tip clearance-to-span ratio) ≥ 0.96%, the mass-averaged loss for the FS tip decreases, has a minimum value, and then increases, as the squealer height (hst) increases. For h/s = 0.48%, however, the loss changes with hst/s is found to be minute. For the FS tip, the loss tends to increase, as the squealer thickness increases. Adding a camberline squealer to the FS tip is not beneficial in the loss reduction. When hst/s &lt; 3.82% for h/s = 0.96%, the FS tip has the lowest mass-averaged loss, the SS tip has the second lowest loss, the PS tip has higher loss compared to the SS tip, and the CS tip loss is highest, regardless of hst/s. For h/s = 0.96%, the average tip thermal load for the FS tip is lower than the PS tip one but is higher than the SS tip one. Thus, the SS tip delivers the lowest average thermal load, irrespective of hst/s.
A Computational Model for the Analysis of the Static Forced Performance of Self-Equalizing Tilting Pad Thrust Bearings
Authors: Koosha Rasool , San Andrés Luis 
Published: January 2021

Abstract
While failure analyses in the archival literature report thrust collar misalignment as a major cause of collapse in oil lubricated thrust bearings, a self-equalizing tilting pad thrust bearing (TPTB) improves operation reliability by adjusting its pads to account for thrust collar tilt. The paper describes a kinematics model for the equalizing mechanism integrated into an existing thermo-elasto-hydrodynamic (TEHD) analysis tool to deliver load performance predictions for self-equalizing TPTBs. The analysis considers the actual leveling plates geometric model as obtained from a solids modeling commercial software and accounts for the sliding friction forces acting at the contact points of the leveling plates and the rolling friction at their pivots. Further, a Hertz contact analysis model uses the predicted forces to deliver a peak pressure and deformation over the contact area between the leveling plates. Next, the paper presents predictions for an example self-equalizing TPTB operating with a thrust collar static misalignment φ = 0.01°. The bearing 126 mm in outer diameter has six pads, operates at 4 krpm (26 m/s max. surface speed) and under a specific load/pad ranging from 0.5 to 3.5 MPa. Compared to a non-equalizing TPTB, a self-equalizing TPTB operates with up to 50% larger minimum film thickness and about ½ largest elastic deformation. Friction forces acting at the contact points of the leveling plates show a significant effect on the performance of the pad leveling system as they reduce the film clearance and increase a pad peak pressure. Predictions from the Hertz contact analysis agree with those from a commercial finite element analysis tool and show a significantly large peak pressure at the contact points of the leveling plates (&gt; 0.9 GPa) when the bearing supports a 3 MPa/pad specific load. The paper stresses the importance of conducting a comprehensive multiple-pad analysis to accurately evaluate the performance and reliable operation of self-equalizing TPTBs.
Large Eddy Simulation of a Condensing Wet Steam Turbine Cascade
Authors: Post Pascal , Winhart Benjamin , di Mare Francesca 
Published: January 2021

Abstract
The influence of turbulence modeling approach by means of (U)RANS and LES on the overall modeling of turbulent condensing wet steam flows is investigated using the example of a low-pressure steam turbine cascade. For an accurate numerical treatment of turbulence in presence of shock waves, necessary for predictive scale-resolving computations, a hybrid flux treatment switches between a baseline non-dissipative central flux in energy consistent split form and a shock-capturing upwind flux in shocked regions based on a shock sensor. Condensation is realized by a mono-dispersed Euler-Euler source term model, the equation of state by the highly efficient and accurate SBTL tabulation. The numerical treatment is validated with a decay of homogeneous isotropic turbulence test case containing eddy shocklets. The measurement results of the condensing wet steam cascade are overall much better matched by LES compared to RANS and URANS. Analysis shows that the LES is much better able to account for the inherently unsteady nature of the spontaneous condensation process and its interaction with the trailing edge shock wave structure.
Effects of Rim Seal Geometries on Aerodynamic Performance and Rotor Platform Cooling in a One-Stage Turbine
Authors: Zhao Qiang , Yang Xing , Feng Zhenping 
Published: January 2021

Abstract
Rim seals are used to prevent ingestion of hot gas into turbine rim cavities. As these cavities are not actively cooled, high-pressure air, known as purge flow, is taken from the compressor and introduced beneath the platform to prevent hot gas from penetrating through the gaps between stationary and rotating parts. Meanwhile, the purge flow impacts the aerodynamic performance and provides secondary-order cooling on the rotor platform. In this paper, the effect of four kinds of engine realistic rim seals on flow fields and rotor platform cooling is investigated with constant coolant rate of 1.0% in a one-stage highly-loaded turbine using an unsteady numerical simulation. The numerical simulation is validated by extensive aerodynamic and heat transfer experimental data. Flow fields and film cooling on the rotor platform and turbine overall aerodynamic performance are discussed and compared in detail for four different rim seal geometries at a design condition of mainstream flow. Case 1 is the conventional radial rim seal geometry and is taken as the baseline (radial injection) rim seal geometry for comparisons. Case 2 (with additional cavity) and Case 3 (incline injection) are obtained by modifying the rim seal geometries based on Case 1. In particular, Case 4 (end wall flank flow), a new structure, is proposed to improve film cooling effectiveness on the rotor hub platform. Comparisons among four rim seal geometries show that the new rim seal structure significantly alters the flow structures near the rotor platform by modifying the development and migration of the purge flow and ingestion of hot gas. The highlight is that the new rim seal geometry of Case 4 could double the film cooling effectiveness or even higher, while at the same amount of coolant. Meanwhile, the aerodynamic performance does not decrease obviously than the other rim seal structures.
Evaluation of the Rotor Temperature Distribution of an Automotive Turbocharger Under Hot Gas Conditions Including Indirect Experimental Validation
Authors: Zeh Christopher , Willers Ole , Hagemann Thomas , Schwarze Hubert , Seume Joerg R. 
Published: January 2021

Abstract
While turbocharging is a key technology for improving the performance and efficiency of internal combustion engines, the operating behavior of the turbocharger is highly dependent on the rotor temperature distribution as it directly modifies viscosity and clearances of the fluid film bearings. Since a direct experimental identification of the rotor temperature of an automotive turbocharger is not feasible at an acceptable expense, a combination of numerical analysis and experimental identification is applied to investigate its temperature characteristic and level. On the one hand, a numerical conjugate heat transfer (CHT) model of the automotive turbocharger investigated is developed using a commercial CFD-tool and a bidirectional, thermal coupling of the CFD-model with thermohydrodynamic lubrication simulation codes is implemented. On the other hand, experimental investigations of the numerically modelled turbocharger are conducted on a hot gas turbocharger test rig for selected operating points. Here, rotor speeds range from 64.000 to 168.000 rpm. The turbine inlet temperature is set to 600°C and the lubricant is supplied at a pressure of 300 kPa with 90°C to ensure practically relevant boundary conditions. Comparisons of measured and numerically predicted local temperatures of the turbocharger components indicate a good agreement between the analyses. The calorimetrically determined frictional power loss of the bearings as well as the floating ring speed are used as additional validation parameters. Evaluation of heat flow of diabatic simulations indicates a high sensitivity of local temperatures to rotor speed and load. A cooling effect of the fluid film bearings is present. Consequently, results confirm the necessity of the diabatic approach to the heat flow analysis of turbocharger rotors.
Study of Using Exhaust Gas Recirculation on a Gas Turbine for Carbon Capture
Authors: Burnes Dan , Saxena Priyank , Dunn Paul 
Published: January 2021

Abstract
The growing call of minimizing carbon dioxide and other greenhouse gases emitting from energy and transportation products will spur innovation to meet new stringent requirements while striving to preserve significant investments in the current infrastructure. This paper presents quantitative analysis of exhaust gas recirculation (EGR) on industrial gas turbines to enable carbon sequestration venturing towards emission free operation. This study will show the effect of using EGR on gas turbine performance and operation, combustion characteristics, and demonstrate potential hybrid solutions with detailed constituent accounting. Both single shaft and two shaft gas turbines for power generation and mechanically driven equipment are considered for application of this technology. One key element is assessing the combustion system operating at reduced O2 levels within the industrial gas turbine. With the gas turbine behavior operating with EGR defined at a reasonable operating state, a parametric study shows rates of CO2 sequestration along with quantifying supplemental O2 required at the inlet, if needed, to sustain combustion. With rates of capture known, a further exploration is examined reviewing potential utilities, monetizing these sequestered constituents. Ultimately, the objective is to preview a potential future of operating industrial gas turbines in a non-emissive and in some cases carbon negative manner while still using hydrocarbon fuel.
Effect of an Azimuthal Mean Flow on the Structure and Stability of Thermoacoustic Modes in an Annular Combustor Model With Electroacoustic Feedback
Authors: Humbert Sylvain C. , Moeck Jonas P. , Orchini Alessandro , Paschereit Christian Oliver 
Published: January 2021

Abstract
Thermoacoustic oscillations in axisymmetric annular combustors are generally coupled by degenerate azimuthal modes, which can be of standing or spinning nature. Symmetry breaking due to the presence of a mean azimuthal flow splits the degenerate thermoacoustic eigenvalues, resulting in pairs of counter-spinning modes with close but distinct frequencies and growth rates. In the present study, experiments have been performed using an annular system where the thermoacoustic feedback due to the flames is mimicked by twelve identical electroacoustic feedback loops. The mean azimuthal flow is generated by fans. We investigate the standing/spinning nature of the oscillations as a function of the azimuthal Mach number for two types of initial states, and how the stability of the system is affected by the mean azimuthal flow. It is found that spinning, standing or mixed modes can be encountered at very low Mach number, but increasing the mean velocity promotes one spinning direction. At sufficiently high Mach number, only spinning modes are observed in the limit cycle oscillations. In some cases, the initial conditions have a significant impact on the final state of the system. It is found that the presence of a mean azimuthal flow increases the acoustic damping. This has a beneficial effect on stability: it often reduces the amplitude of the self-sustained oscillations, and can even suppress them in some cases. However, we observe that the suppression of a mode due to the mean flow may destabilize another one. We discuss our findings in relation with an existing low-order model.
4D Measurements and Analysis of Heat Release Rate in a Model Gas Turbine Combustor
Authors: Dong Rongxiao , Lei Qingchun , Chi Yeqing , Zhang Qun , Fan Wei 
Published: January 2021

Abstract
Time-resolved volumetric measurements (4D measurements) were performed to study the heat release rate characteristics in a model gas turbine combustor at 10 kHz. For this purpose, a high-speed camera combined with an image intensifier and a set of customized fiber probes were employed to continuously capture the CH* chemiluminescence signals from nine different viewing angles. Based on the measurements, the computed tomography program was performed to reconstruct the shot-to-shot 3D distributions of the CH* signals. Specific focuses have been made to demonstrate the capabilities of the current tomographic technique in applications of a realistic combustor, in which the full optical access was usually not available for every viewing angle. The results showed that the 3D reconstruction can successfully retrieval the flame edge contours rather than the signal intensity. The flame surface area was then calculated based on the reconstructed flame edge contours and used to infer the heat release rate. The fluctuation of global/local flame surface area indicated that there existed distinct difference between the global instability and local instabilities at various locations in the non-symmetric combustor. The global instability appears to be an integration of those local instabilities.
Effects of Turning Angle and Turning Internal Radius on Channel Impingement Cooling for a Novel Internal Cooling Structure
Authors: He Wei , Deng Qinghua , Yang Guoying , Feng Zhenping 
Published: January 2021

Abstract
Leading edge multi-channel double wall design, a novel internal cooling structure, has been put forward recently to enable higher overall cooling effectiveness with less penalty of coolant mass flow and pressure loss. Our previous work has proved the advantages of the design under operating condition relative to conventional internal cooling methods including impingement cooling and swirl cooling. Channel impingement cooling structure, which is utilized at the turning region of the leading edge, is the critical factor to realize the high cooling performance of the design. Hence, the turning angle and turning internal radius of the cooling channel are two key parameters for the novel design, and this paper focuses on the effects of these two parameters on the flow and heat transfer characteristics of the channel impingement cooling structure. Nine simplified single-channel models with different turning angles (45°, 60°, and 75°) and radiuses (0.6 mm, 0.9 mm, and 1.2 mm) were adopted to conduct the study, and the jet Reynolds number ranges from 10,000 to 40,000.
The results show that the turning angle and turning internal radius affect the jet form significantly for the same mechanism. Small turning angle means large impingement, which leads to stream-wise counter-rotational vortices and high turbulence intensity, but increasing turning internal radius transfers the jet form from impingement jet to laminar layer attaching the target surface with low heat transfer. The turning internal radius has stronger effect than turning angle. With higher jet Reynolds number, both the heat transfer and total pressure loss increase dramatically, and the effects of geometrical parameters are clearer.
Scaling Considerations for Thermal and Pressure Sensitive Paint Methods Used to Determine Adiabatic Effectiveness
Authors: McNamara Luke J. , Fischer Jacob P. , Rutledge James L. , Polanka Marc D. 
Published: January 2021

Abstract
To be representative of engine conditions, a measurement of film cooling behavior on an experimental model must have certain nondimensional parameters matched, such as the freestream Reynolds number. However, the coolant flow rate must also be properly scaled between the low temperature tests and engine temperatures to accurately predict film cooling effectiveness. This process is complicated by gas property variation with temperature. Additionally, selection of the appropriate coolant flow rate parameter to scale from low to high temperatures is a topic of continued uncertainty. Furthermore, experiments are commonly conducted using thermal measurement techniques with infrared thermography (IR) but the use of pressure sensitive paints (PSPs) implementing the heat-mass transfer analogy is also common. Thus, the question arises of how the adiabatic effectiveness distributions compare between mass transfer experimental methods and thermal experimental methods and whether these two methods are sensitive to coolant flow rate parameters in different ways. In this study, a thermal technique with IR was compared to a heat-mass transfer method with a PSP on a flat plate model with a 7-7-7 film cooling hole. While adiabatic effectiveness is best scaled by accounting for specific heats with the advective capacity ratio (ACR) using thermal techniques, results revealed that PSP measurements are scaled best with the mass flux ratio (M). The difference in these methods has significant implications for engine designers that rely on PSP experimental data to predict engine thermal behavior as PSP is fundamentally not sensitive to the same highly relevant physical mechanisms to which thermal methods are sensitive.