bluuebunny/crossref_metadata_2025 huggingface dataset:
Firing Trials of the Siemens SGT-300 Dry Low Emissions Combustion System Using High Calorific Value Fuels
Authors: Calladine Kristopher , Rogerson Jim , Hubbard Phill , Sadasivuni Suresh K. , Bulat Ghenadie
Published: January 2021

The current paper presents an extension of the fuel flexibility of the Siemens SGT-300 Dry Low Emissions combustion system to include High Calorific Value fuels, achieved using the engine’s current standard combustion hardware.

Results from high pressure rig tests show that the standard SGT-300 DLE combustor can reliably operate on High Calorific Value fuels with temperature corrected Wobbe Index up to 63MJ/m3, which corresponds to Grade A LPG (60%vol. C3H8, 40%vol. C4H10). Metal temperatures of the combustion hardware when operating on High Calorific Value fuels are within life acceptance criteria for the Siemens SGT-300 industrial gas turbine. NOx emissions throughout the load range of the engine comply with the EU Industrial Emissions Directive. At part load, a reduced requirement for piloting compared to Natural Gas yields relatively low temperatures at the burner face and low NOx emissions. NOx emissions at full load, which tend to increase with increasing heating value, are higher than for Natural Gas but lower than for diesel and heavy fuel oils.
Unsteady Analysis of Inlet Hot Streaks Clocking Effects in a 1-1/2 Turbine Stage
Authors: Jin Yejia , Ma Hongwei , Yu Xinghang
Published: January 2021

Migration of inlet hot streaks and the clocking effects are investigated by three-dimensional unsteady numerical simulations in a 1-1/2 turbine stage. Two hot streak circumferential positions with respect to first-stage stator, passage centered and vane centered, are simulated. Results indicate that hot streaks tend to accumulate on rotor blade pressure side and move towards shroud, causing hot spots on these parts. Separation of hot and cold fluid is observed in rotor, thus influence of hot streaks spreads to second-stage stator. Hot streaks are broken into fragments by rotor blade wakes and rotor-stator interactions in second-stage stator. Impinging hot streaks on first-stage stator passages results in separation of hot and cold lats longer in rotor, but area-averaged temperature at rotor outlet is relatively lower. Hot streaks keep a higher temperature through rotor, yet area-averaged temperature has a quicker drop in second-stage stator. Impinging hot streaks on first-stage stator vanes brings a more uniform temperature distribution at rotor and turbine outlet while a higher area-averaged temperature at the same time. Hot streaks adhere to the first-stage stator vane surfaces and move towards hub due to tip leakage, causing extra heating to these parts compared with passage centered hot streaks. Rortex, as a new way to identify vortexes in fluid, is employed to understand how vortexes contribute to migration and dissipation of hot streaks. Also, Proper Orthogonal Decomposition analysis is applied to identify flow features that impact migration and dissipation of hot streaks, and a few connections between the flow features and POD modes are made.
The Effect of Radial Skew Angles of Blade Angle Slots on the Stability and Performance of an Axial Flow Compressor
Authors: Zhang HaoGuang , Liu WenHao , Chu WuLi , Wang EnHao
Published: January 2021

The parametric numerical study was performed to explore the effect of radial skew angles of blade angle slot casing treatment (CT) on the stability and performance of an axial flow subsonic compressor. Five kinds of blade slot casing treatment with difference radial skew angles (0 degree, 30 degrees, 45 degrees, 60 degrees, and 75 degrees) were designed in the numerical investigations. The unsteady calculated results show that among the radial skew angles of 0 degree, 30 degrees, 45 degrees, 60 degrees, the bigger the radial skew angle of the slots is, the greater the stall margin improvement (SMI) generated by the slots is, and the slots with 60 degrees radial skew angle can generate 58.86% SMI. Moreover, the SMI for the slots with 60 degrees radial skew angle is 29.64% more than that for the slots with 75 degrees radial skew angle. Besides, the slots with radial skew angle of 75 degrees cause the least penalty in peak efficiency among five kinds of radial skew angle, and the peak efficiency for the slots with 75 degrees radial skew angle is 0.88% higher than that for smooth wall casing treatment. The slots with 0 degree radial skew angle generate the biggest peak efficiency loss of 5.94% among five kinds of radial skew angle.

The flow field analyses show that the recirculated flows formed in the slots can generate momentum transport effects on the flow field in the blade tip. Under the effects of the momentum transport, the momentum balance between the tip leakage flow (TLF) and main flow (MF) is changed, and the momentum balance determines the trajectory of the TLF and the mainstream/tip leakage flows interface. As a result, the flow condition in the tip channel is also changed. By changing the radial skew angle of slots, the slots behave different capacities of momentum transport on the tip flow field, and the momentum balance between tip leakage flow and main flow is changed differently. So, the trajectory of the TLF and the mainstream/tip leakage flows interface are deflected differently. Different improvements of the compressor stability are obtained by the slots with different radial skew angles. The slots with radial skew angle of 60 degrees can largely deflect the trajectory of TLF and the mainstream/tip leakage flows interface to the blade suction surface. It improves the flow condition of the blade tip channel, and the slots generate 58.86% SMI. However, after the slots with radial skew angle of 0 degree and 30 degrees are applied, the tip leakage vortex breakdown is occurred. So, they generate few improvements of the stall margin. Furthermore, the interaction between recirculated flows inside slots and main flows inevitably causes additional flow losses. With the increase of radial skew angle, the efficiency loss caused by slot CT decreases. Thus, the slots with 75 degrees radial skew angle generate the least peak efficiency loss among five kinds of radial skew angle.
Effects of the Large Eddy Simulation Calculation Parameters on Prediction of Profile Loss in an Axial Cascade at Off-Design Incidence
Authors: Lee Yuntae , Teramoto Susumu , Toki Takahiko , Okamoto Koji
Published: January 2021

Large Eddy Simulation (LES) has already been widely applied for unsteady flow simulations (e.g., axial cascade simulation), showing its superiority in the case of turbulent flow fields. However, there are several obstacles in the practical use of LES as a cascade design tool for gas turbine engines. Several calculation parameters such as the inlet turbulence, spanwise extents, and many other boundary conditions, affect calculation results for LES simulation and can cause reliability problems. This study concentrates on investigating the effects of LES calculation parameters on the prediction of profile loss at high air inlet angle off-design condition. The LES flow field results were found to be sensitive to four parameters (i.e., inlet turbulence, spanwise domain extent, time step size, and outlet domain). The inlet turbulence affects the size of the laminar separation bubble, while the spanwise domain extent affects the velocity fluctuations of the wake in correspondence of the large-scale vortices shedding. The time step size affects the velocity fluctuations of the wake because of the number of times that the low-pass filter is applied. Finally, the outlet domain extent affects the whole calculation domain (from the leading edge to the wake). Overall, the results show that all four calculation parameters can change the flow characteristics, affecting the prediction of profile loss at off-design condition when using LES.
Effect of Boundary Layer Suction on the Corner Separation in a Highly Loaded Axial Compressor Cascade
Authors: Liang Tian , Liu Bo , Spence Stephen
Published: January 2021

Control of corner separation in axial compressor blade rows has attracted much interest due to its potential to improve compressor efficiency and the energy utilization in turbomachinery. This paper investigates the effectiveness and mechanisms of boundary layer suction in controlling the corner separation of a highly loaded axial compressor cascade. Numerical simulations have been carried out to investigate the effect of different suction schemes on the loss downstream of the cascade and the change in incidence characteristics with the variation of the suction flow rate. The results show that the effectiveness of flow suction in controlling the flow separation depends heavily on the proportion of the blade for which it is applied. It was found that suction along part of the blade span on the suction surface could effectively remove the separation at the region of the span influenced by the suction slot. However, this resulted in a deterioration of the flow field at other parts of the span. The full span suction scheme on the suction surface not only eliminated the separation of the boundary layer in the middle of the blade, but also significantly improved the flow uniformity near the end-wall.

Despite the improvement in flow uniformity using the full-span suction scheme, a three-dimensional (3D) corner separation still existed due to the strong cross-passage pressure gradient. To improve the flow field uniformity further, two combined suction schemes with one spanwise slot on the suction surface and another slot on the end-wall were designed in order to fully remove both the separated flow on the blade suction surface and the 3D corner separation. It was found that the total pressure loss coefficient was reduced significantly by 63.8% with suction flow rates of 1.88% and 0.82% for the slots on the suction surface and the end-wall respectively. Further work showed that the behavior of the loss coefficient is different as the combination of suction flow rates is changed for different incidence. The cascade loss at high incidence operation can be more effectively reduced with suction control on the end-wall. When implementing combined suction, it is necessary to determine the best combination of suction flow rate according to the incidence level.
Multidisciplinary Design Optimization of a Low-Noise and Efficient Next-Generation Aero-Engine Fan
Authors: Jaron Robert , Moreau Antoine , Guérin Sébastien , Enghardt Lars , Lengyel-Kampmann Timea , Otten Tom , Nicke Eberhard
Published: January 2021

Due to the increasing bypass ratios of modern engines, the fan stage is increasingly becoming the dominant source of engine noise. Accordingly, it is becoming more and more important to develop not only efficient but also quiet fan stages. In this paper the noise emission of a fan for an aero-engine with a bypass ratio of 19 is reduced within a multidisciplinary design optimization (MDO) by means of an hybrid noise prediction method while at the same time optimizing the aerodynamic efficiency. The aerodynamic performance of each configuration in the optimization is evaluated by stationary Reynolds-Averaged Navier-Stokes (RANS) simulations. These stationary flow simulations are also used to extract the aerodynamic excitation sources for the analytical fan noise prediction. The resulting large database of the optimization provides new insights into which extent an MDO can contribute to the design of both quiet and efficient fan stages. In addition to that the hybrid approach of numerical flow solutions and analytical description of the noise sources enables to understand the noise reduction mechanisms. In particular, the influence of rotor blade loading on the aerodynamic efficiency and the noise sources as well as the potential of configurations with a comparatively low number of outlet guide vanes (OGV) is explored. The acoustic results of selected configurations are confirmed by unsteady RANS simulations.
Platform Film Cooling Investigation on an HP Nozzle Vane Cascade With Discrete Shaped Holes and Slot Film Cooling
Authors: Barigozzi G. , Perdichizzi A. , Abba L. , Pestelli L.
Published: January 2021

The present paper reports on an experimental investigation on the aerodynamic and heat transfer performance of different platform cooling schemes: two based on cylindrical and shaped holes and one featuring a slot located upstream of the leading edge plane simulating the combustor to stator interface gap. Tests were run on a 6-vane cascade operated at an isentropic cascade exit Mach number of 0.4 and a significant inlet turbulence intensity level of about 9%. The cooling schemes were first tested to quantify their impact on secondary flows and related losses for variable injection conditions. Heat transfer performance was then assessed through adiabatic film cooling effectiveness and heat transfer coefficient measurements. The Net Heat Flux Reduction parameter was then computed to critically assess the cooling schemes. When compared with the cylindrical hole scheme, shaped holes outperform for all tested injection rates, while the slot alone is able to thermally protect only the front of the passage. Discrete holes are required to cool the platform region along the whole pressure side and the suction side leading edge region.
A Marine Turbocharger Retrofitting Platform
Authors: Ntonas Konstantinos , Aretakis Nikolaos , Roumeliotis Ioannis , Mathioudakis Konstantinos
Published: January 2021

A turbocharger retrofitting platform utilizing 1D models for calculating turbomachinery components maps and a fully coupled process for integration with the turbomachinery components and the diesel engine, is presented. The platform has been developed with two modes of operation, allowing the retrofitting process to become fully automatic. In the first mode, available turbo-components are examined, in order to select the one that best matches the entire engine system, aiming to retain or improve the diesel engine efficiency. In the second mode, an optimization procedure is employed, in order to redesign the compressor to match the entire system in an optimum way. Dimensionless parameters are used as optimization variables, for a given compressor mass flow and power.

A retrofitting case study is presented, where three retrofitting options are analyzed (compressor retrofit, turbocharger retrofit and compressor redesign). In the first and second option, turbocharger retrofitting is carried out, using available turbo-components. It is shown that initial performance cannot be reconstituted using off-the-self solutions. In the third option, compressor designing is performed, using the optimization mode, in order to provide an improved retrofitting solution, aiming to at least reconstituting the original diesel engine performance. Finally, a CFD analysis is carried out, in order to validate the compressor optimization tool capability to capture the performance trends, based on geometry variation.
Effect of Axial Casing Groove Geometry on Rotor-Groove Interactions in the Tip Region of a Compressor
Authors: Shankha Koley Subhra , Chen Huang , Saraswat Ayush , Katz Joseph
Published: January 2021

The present experimental study expands an ongoing effort to characterize the interactions of axial casing grooves (ACGs) with the flow in the tip region of an axial turbomachine. In recent work, we have tested a series of grooves with the same inlet geometry that overlaps with the rotor blade leading edge, but with different exit directions. Two geometries have stood out: The U grooves, which have an outflow in the negative circumferential direction (opposing the blade motion) are the most effective in suppressing stall, achieving as much as 60% reduction in stall flowrate, but cause a 2% decrease in efficiency around the best efficiency point (BEP). In contrast, the S grooves, which have an outflow in the positive circumferential direction, achieve a milder improvement in stall suppression (36%) but do not degrade the performance near BEP. This paper focuses on explaining these trends by measuring the flow in the tip region and within the U and S grooves. The stereo-PIV (SPIV) measurements are performed in the JHU refractive index matched facility, which allows unobstructed observations in the entire machine. Data has been acquired in two meridional planes that intersect with the grooves at different locations, and two radial planes (z, θ), the first coinciding with the blade tip, and the second, with the tip gap. For each plane, data has been acquired at fourteen rotor orientations relative to the grooves to examine the rotor-grooves interactions. At low flow rates, the inflow into both grooves peaks periodically when the blade pressure side (PS) faces the entrance (downstream side) to the grooves. This inflow rolls up into a large vortex that remains and lingers within the groove long after the blade clears the groove. The outflow depends on the shape of the groove. For the S groove, the outflow exits at the upstream end of the groove in the positive circumferential direction, as designed. In contrast, for the U grooves, the fast radially and circumferentially negative outflow peaks at the base of the U. The resulting jet causes substantial periodic variations in the flow angle near the leading edge of the rotor blade. Close to the BEP, the chordwise location of primary blade loading moves downstream, as expected. The inflow into the grooves occurs for a small fraction of the blade passing period, and most of the tip leakage vortex remains in the main flow passage. For the S grooves, the rotor-groove interactions seem to be minimal, with little (but not zero) inflow or outflow at both ends, and minimal changes to the flow angle in the passage. In contrast, for the U groove, the inflow into and outflow from the groove reverse direction (compared to the low flowrate trends), entering at the base of the U, and exiting mostly at its downstream end, especially when the blade is not near. The resulting entrainment of secondary flows from the groove into the passage are likely contributors to the reduced efficiency at BEP for the U grooves.
Study of Heat Transfer Characteristics of a Single Jet Impinging on a Conical Surface
Authors: Su Bo , Xu Wei-jiang , Li Zhi-ping , Zhou Tian-liang , Lu Fei
Published: January 2021

In this paper, the heat transfer performance of single jet impinging conical surface is investigated based on transient liquid crystal experiments. Because of different target surface structures, impingement heat transfer will have different heat transfer characteristics. In order to better understand the heat transfer mechanism of the impinging conical target surface, this paper studies the three jet Reynolds number (Re) ranged from 25000 to 70000, three the dimensionless nozzle-to-surface distance (H/D) from 0.75 to 6 on heat transfer characteristics. The liquid crystal thermal imaging technology is used in the experiment to obtain the heat transfer efficiency of jet heat transfer on the conical target surface. The research in this paper shows that the larger the jet Reynolds number, the larger the Nusselt number at the stagnation point. It is worth noting that the maximum Nusselt number is not necessarily obtained at the stagnation point. When Re = 70000 and H/D = 0.75, the maximum value of the Nusselt number is 1.24 times the stagnation point. The larger the Reynolds number, the smaller the impingement distance, and the more obvious the secondary maxima. At the same impingement distance, when the Reynolds number is larger, the position of the secondary maxima appears earlier. When Re = 25000, H/D = 3.5, 6 and Re = 45000, H/D = 6, the local Nusselt number monotonously decreases from the maximum value at the stagnation point along the flow, and it appears secondary maxima in other experimental conditions. Within the scope of this study, the overall heat transfer performance is better when the dimensionless distance between the jet hole and the target surface is 3.5.
High-Fidelity Simulations of Multi-Jet Impingement Cooling Flows
Authors: Otero-Pérez J. Javier , Sandberg Richard D. , Mizukami Satoshi , Tanimoto Koichi
Published: January 2021

This article shows the first parametric study on turbulent multi-jet impingement cooling flows using large-eddy simulations (LES). We focus on assessing the influence of the inter-jet distance and the cross-flow conditions on the heat transfer at the impingement wall. The LES setup is thoroughly validated with both experimental and direct numerical simulation data, showing an excellent agreement. The inter-jet distance effect on the heat transfer is studied comparing three different distances, where the full Nusselt number profile decreases in amplitude when the jet distance is increased. To evaluate the cross-flow effects, we prescribe both laminar and turbulent inflow conditions at different cross-flow magnitudes ranging between 20% and 40% of the impinging jet speed. Large cross-flow intensities cause a jet deflection which reduces the maxima in the Nusselt number distribution, and it increases the heat transfer in the areas of the wall less affected by the jet impingement. Adding realistic turbulent fluctuations to the inflow enhances the cross-flow effects on the heat transfer at the impingement wall.
Development of the Functional-Gradient Turbine Wheel With Cooled Blades Without Lock Connection
Authors: Magerramova Liubov , Volkov Michael , Salnikov Anton , Kratt Eugene
Published: January 2021

Wheels of high-temperature turbines are traditionally produced in the form of detachable joints of the disk and blades made from different materials.

The blades, which are under the influence of high gas temperatures, are made with internal channels by air cooling. The disk is subject to significant centrifugal loads, but lower temperatures. The locking connection of the blades to the disk is a stress concentrator, which leads to resource limitation.

One of the solutions is the wheel of the turbine type blisk consisting of cast-cooled blades of heat-resistant alloys and a disk of granulated nickel alloys, interconnected by hot isostatic pressing.

The disk can be made of granules of different sizes in different parts. This approach is based on the fact that during operation, the disk is also subject to uneven heating and loading along the radius.

The blisk design of the wheel with cooled blades is developed on the basis of the turbine wheel with a detachable connection of the blades with the disk. The blades of the blisk are produced from casting heat-resistant nickel alloy. The disk portion is created from granulated alloy with different grain sizes along the disk radius. The system of supplying cooling air in the blades of the wheel is developed. The technology of manufacturing a disk consisting of granules of various sizes and technology of connection of a disk with cooled cast blades is developed.

To determine the mechanical characteristics of the zones of connection of dissimilar materials samples were tested. The combined samples were made of a granulated alloy with different sizes of granules. The bimetallic samples were made of a casting blade alloy and a granulated disk alloy.

Multi-parameter optimization of the blisk was carried out. The mass of the designed wheel was reduced by more than 40% compared to the original wheel with lock connection when the strength and service life conditions were satisfied.
Recuperator Transient Simulation for Supercritical Carbon Dioxide Cycle in CSP Applications
Authors: Thanganadar Dhinesh , Fornarelli Francesco , Camporeale Sergio , Asfand Faisal , Patchigolla Kumar
Published: January 2021

Supercritical carbon dioxide (sCO2) cycles are considered to provide a faster response to load change owing to their compact footprint. sCO2 cycles are generally highly recuperative, therefore the response time is mainly dictated by the heat exchanger characteristics. This study model the transient behaviour of a recuperator in 10 MWe simple recuperative Brayton cycle. The response for the variation of inlet temperature and mass flow boundary conditions were investigated using two approaches based on temperature and enthalpy. The performance of these two approaches are compared and the numerical schemes were discussed along with the challenges encountered. The simulation results were validated against the experimental data available in the literature with a fair agreement. The characteristic time of the heat exchanger for a step change of the boundary conditions is reported that supports the recuperator design process. Compact recuperator responded in less than 20 seconds for the changes in the temperature boundary condition whilst it can take upto 1.5 minutes for mass flow change. In order to reduce the computational effort, a logarithmic indexed lookup table approach is presented, reducing the simulation time by a factor of 20.
Experimental Study of the Endwall Heat Transfer of a Transonic Nozzle Guide Vane With Upstream Jet Purge Cooling: Part 2 — Effect of Combustor-NGV Misalignment
Authors: Sibold Ridge A. , Mao Shuo , Ng Wing F. , Xu Hongzhou , Fox Michael
Published: January 2021

A misalignment between the combustor exit and the nozzle guide vane (NGV) platform commonly exists due to manufacturing tolerances and thermal transience. This study experimentally investigated the effect of the combustor-turbine misalignment on the heat transfer for an axisymmetric converging endwall with a jet purge cooling scheme at transonic conditions. Tests were conducted at engine-representative freestream exit Mach number of 0.85, inlet turbulence intensity of 16%, film cooling blowing ratio of 2.5 (design condition) and 3.5, and density ratio of 1.95. Three different step misalignments, combustor exit 4.9% span higher than turbine inlet (backward-facing), no step (baseline), and combustor exit 4.9% span lower than turbine inlet (forward-facing), were tested to demonstrate the misalignment effect on endwall Nusselt number, adiabatic film cooling effectiveness, and net heat flux reduction. A supportive numerical simulation was conducted to provide insight into the flow field.

Experimental and numerical results indicated a blowing ratio of 2.5 amid a backward-facing step leads to more turbulent mixing between the coolant and mainstream due to the horseshoe vortex and step-induced cavity vortex, reducing coolant coverage and adversely affecting coolant performance. For the same blowing ratio, a forward-facing step induced more lift-off and shifted the coverage downstream and toward the pressure side, ultimately slightly enhancing the cooling performance. Nevertheless, the forward-facing step leads to a large cooling effectiveness gradient in the pitch-wise direction. At a blowing ratio of 3.5, the baseline no-step case provided superior coolant performance, however, the effect of the step was much less significant as compared to the lower blowing case. The forward-facing step amid a blowing ratio of 3.5 results in severe jet lift-off, diminishing the returns traditionally associated with increasing coolant mass flow. Based on this study, a backward-facing step should be avoided to prevent endwall burnout in the nozzle guide. Additionally, a forward-facing step should be avoided, especially amid high blowing ratios.
Detailed Study of Front Module for Low-Emission Combustor
Authors: Vasilyev A. , Zakharov V. , Chelebyan O. , Zubkova O.
Published: January 2021

At the ASME Turbo Expo 2018 conference held in Oslo (Norway) on the 11th-15th of June 2018, the paper GT2018-75419 «Experience of Low-Emission Combustion of Aviation and Bio Fuels in Individual Flames after Front Mini-Modules of a Combustion Chamber» was published. This paper continues the studies devoted to the low-emission combustion of liquid fuels in GTE combustors. The paper presents a description of more detailed studies of the front module with a staged pneumatic fuel spray. The aerodynamic computations of the front module were conducted, and the disperse characteristics of the fuel-air spray were measured. The experimental research was carried out in two directions: 1) probing of the 3-burner sector flame tube at the distance of one third of its length (temperature field and gas sampling); 2) numerical study of the model combustor with actual arrangement of the modules in the dome within a wide range of fuel-air ratio. The calculated and experimental data of velocity field behind the front module were compared. And new data about the flame structure inside the test sector were obtained. Experimental data confirm the results of preliminary studies of the 3-burner sector: combustion efficiency is higher than 99.8%, EiNOx is at the level of 2–3 g/fuel kg at the combustor inlet air temperature of 680K and fuel-air ratio of 0.0225.

The conducted research allowed to receive additional information on the influence of some design units on the pollutant emission and to estimate the different elements of computational methods for simulation of a low-emission combustor with a multi-atomizer dome.
Investigation of Rotordynamic Coefficients of Gas Labyrinth Seals Using a Steady State CFD Approach
Authors: Palanca Casey , Engeda Abraham , Cave Mike
Published: January 2021

Labyrinth seals were one of the first seal configurations used in modern turbomachinery and continue to be one of the most frequently used clearance seal configurations today. Their primary purpose is to control internal leakage between the rotating and stationary components of centrifugal compressors. However, when fulfilling this objective, labyrinth seals have been shown to be a potential source of instability within the rotor-stator system. Driving forces inside the leakage flow path of the cavities often induce destabilizing vibrations on the rotor. The forces are characterized by stiffness and damping coefficients which describe the stability behavior of the seal. Therefore, accurately predicting these rotordynamic coefficients remains an important area of interest in gas compressor design. This paper reviews the status of current methods of obtaining rotordynamic coefficients. The objective of this work is to verify the accuracy of current steady state CFD models used to predict rotordynamic coefficients in dry gas labyrinth seals. For this purpose, a full 3D eccentric CFD model is conducted for three different labyrinth seal geometries. In this approach, the rotordynamic coefficients are predicted from the regression of the radial and tangential impedances as a function of whirl frequencies. For comparison, two seals are compared with experimental data available in literature, and a third seal is compared to bulk flow and numerical CFD results also found in the literature. Furthermore, the influence of pre-swirl entering the labyrinth seal and turbulence modeling are also considered in this work.
Research on the Periodicity of Flow Field in a Compressor Sector Cascade
Authors: Xu Wenfeng , Sun Peng , Yang Guogang
Published: January 2021

Sector cascade experiments can not only be convenient to measure various aerodynamic parameters but also reveal the real flow characteristics in turbomachinery. However, the sector cascade is only a part of the whole annular cascade. The circumferential angle, the structure of the side guide plate (SGP) and the suction mode on the SGP have a great effect on the periodicity of the flow field. Therefore, the effect of structure on periodicity must be taken into consideration in order to obtain accurate data of the sector cascade experiment. In this paper, a compressor sector cascade composed of a row of adjustable guide vanes (AGVs) and a row of stators is designed. The effect of the circumferential angle, SGP structure and suction position on the periodicity is studied by numerical simulation. An optimal cascade scheme is selected for experimental research. The results show that a larger circumferential angle can weaken the effect of low-energy fluid near the SGP on the middle passages. However, given the limited experimental conditions, the circumferential angle is set at 110° which consists of 15 AGVs and 14 stators. What’s more, the SGP with the same bowed angle of AGV on both sides of the cascade can reduce the influence of the SGP on the adjacent passages and obtain a regular periodicity. The low-energy fluids still accumulate near the SGP. The suction near the stator suction side of the SGP can alleviate the blockage in the flow passage and further improve the periodicity of the cascade. Serious analysis of the experiment results have further identified that the suction near the stator suction side of SGP can make the aerodynamic parameters of the flow field uniform and lead to a good periodicity. At the same time, the feasibility of this design method is verified.
Experimental and Numerical Rotordynamic Analysis of a 1500 KW Turbocharger
Authors: Zamanian Yazdi Behzad , Tran Dung L. , Deshpande Chinmay
Published: January 2021

Hydraulic turbochargers are used in sea water reverse osmosis or acid gas removal cycles to recover wasted pressure energy, decrease operating cost, and increase the overall process efficiency. This paper presents rotordynamic analysis of a large hydraulic turbocharger developed for the acid gas removal process (1500 KW output power, shaft diameter of 101 mm, and operating speed of 8,000 rpm). The hydraulic turbocharger has significant advantages when compared to a reverse running pump such as high speed, compact hydraulics, seal-less design and process lubricated bearings. Utilizing a hydraulic turbocharger in acid gas removal cycles results in a much smaller footprint and no external lubrication oil skid and support system for mechanical seals. The turbocharger rotor consists of a hydraulic turbine runner directly coupled to a pump impeller in a back-to-back arrangement. The shaft is supported in the middle by a set of rigid-walled process-lubricated journal bearings resulting in an overhung configuration (bearing span = 180 mm, rotor mass = 50 kg). For a large high-speed rotor-bearing system, the bearing load-carrying capacity and rotordynamic stability are crucial to ensure a stable performance and to avoid catastrophic failure.

In the presented study, rotordynamic performance of a rotor-bearing system is evaluated analytically and experimentally. An analytical model is developed to simulate the rotordynamic performance of a shaft supported by a set of journal bearings. The analytical model simulates the rotor’s orbit in the time domain by solving the rotor’s equation of motion, and solving the transient Reynold equation for each bearing simultaneously. In addition, the model considers the effect of turbulence. An in-house test loop is developed and used to evaluate the turbocharger’s hydraulic and mechanical performance. The test loop runs on a LabView-based control system. The rotor vibration is measured by a set of eddy-current probes, oriented perpendicular to each other. The simulation results from the analytical model are compared against measured experimental data. Comparison of the simulated waterfall and bode plots with experimental data shows that the simulation results agree with the measured data for the frequency and amplitude of vibration. Moreover, the effect of turbulence on the rotordynamic performance of the hydraulic turbocharger is investigated, and it is shown that the turbulence significantly changes the rotordynamic behavior of the system.
A Statistical Study on HCF Validation Data for Axial Gas Turbine Compressor Blades
Authors: Schuchard Lukas C. , Cerutti Stefano , Voigt Matthias , Mailach Ronald
Published: January 2021

An enhanced process to Ansaldo Energia Switzerland’s validation approach for vibrational behaviour of gas turbine compressor blading is investigated. The opportunity of relying on less and early-stage measurements is assessed as a driver for cost and time optimisation. Accordingly, an analysis of possible variations of measurement data available during all validation phases is performed in order to confirm observed and expected correlations on a large scale, facilitating measurement chain improvement and simplification.

Profile deviation and frequency distribution analysis finds the present coordinate-measuring machine (CMM) data and statically measured eigenfrequencies to be normally distributed. Correlation analysis exposes strong autocorrelations of CMM and static frequency data and distinct linear correlations between them. Consistent correlations with and within rotating machinery cannot be established with the limited data basis at hand as clamping conditions of blades with hammer foot roots introduce an additional degree of variation.

CMM data are employed for meta-models translating geometry deviations into static-test-alike frequency information. Average aerofoil thickness deviation is identified as the decisive parameter for eigenfrequency uncertainties founded in geometry deviations.

A stage statistics based approach for frequency forecasting in rotating machinery is proposed, allowing the calculation of expected eigenfrequency bands with corresponding confidence levels. Brought up to operational levels it would allow more efficient forecasting of in-engine conditions and constitute a valuable means for exploring compressor blading design space.
Experimental Investigations on the Effect of Slot-Type Casing Treatments With the Aim of Improvement the Aerodynamic and Acoustic Characteristics of Advanced Fans
Authors: Mileshin Victor , Markov Sergey , Korzhnev Vladimir , Khaletskii Iurii
Published: January 2021

This paper presents experimental investigations of aerodynamic and acoustic characteristics for the C179-2 bypass fan model with different versions of a slot-type casing treatment (CT).

This work aims at optimization the CT configuration for a simultaneously improvement of aerodynamic parameters (efficiency and stall margin), as well as the use of this CT as a reactive type silencer to reduce fan noise.

All versions of the slot-type CTs under study are designed on the basis of a semi-empirical procedure developed by CIAM.

Three versions of a slot-type CT are designed and tested as applied to the C179-2 fan model. Based on the analysis of experimental data found by aerodynamic tests to study the effect of the number of CT rows, the geometry of CT slots, their relative positions and the height of its annular cavity on key aerodynamic characteristics of the C179-2 fan model, it is found that:

- all CTs under study considerably increase stall margins (by 8%–16%) of the fan in moderate and high modes determined by n-corrected rotational speed (n = 75–100 %). The stall margin at n = 54 % increases by approx. 30 %.

- relative position of slots in the three CTs with identical number of slots in both rows has a noticeable effect on the CT gas-dynamic efficiency. A half-step shift of axes of the slots relative to each other leads to a slight increase (by max. 1.6%) in stall margins in moderate and high modes and a considerable increase in efficiency (by avg. 2 %) in the same modes, except for n = 100 %.

The beneficial effect of the CT on an increase in stall margins ASM and efficiency (along the operating line) is found for the C179-2 single-row bypass fan model stage with total pressure ratio 1.56 in the bypass duct and corrected tip speed 404 m/s.

A series of experimental studies of acoustic characteristics of the C179-2 fan model stage with three versions of the slot-type casing treatment is completed in conditions of the C-3A acoustic test facility with an anechoic chamber. The acoustic tests of the fan model are carried out within n = 40–100 % corrected rotational speeds (as compared with the nominal speed). The specified speed range covers takeoff (n = 90.7 %), climb (n = 85.2 %), cruise (n = 100 %), and approach (n = 58.2 %) modes.

For all fan operating modes, narrow-band noise spectra and radiation patterns are compared for the C179-2 model configurations with a smooth flow passage and with the CT.

In addition to a substantial improvement in gas-dynamic characteristics, the use of the slot-type CT for the C179-2 bypass fan model stage results in a considerable improvement in its acoustic characteristics. In total, the sound power of the C179-2 single-row by-pass fan model decreases by 3 dB for three certification modes.
Multi-Fidelity Surrogate-Based Optimization of Transonic and Supersonic Axial Turbine Profiles
Authors: Razaaly Nassim , Persico Giacomo , Congedo Pietro Marco
Published: January 2021

Automated Fluid-dynamic Shape Optimization plays a key role in the design of turbomachinery and typically combines Computational Fluid Dynamics (CFD) solvers, parametrization techniques and numerical optimization methods, generally categorized as either direct or surrogate-based (SBO) ones. Here, a particular focus is given to SBO exploiting surrogate models constructed from low-fidelity models, often referred to as variable or multi-fidelity optimization. This study presents a multi-fidelity SBO approach for the optimization of a supersonic turbine cascade operating with an organic fluid and of the transonic LS89 high-pressure turbine vane. A cokriging method is used to simultaneously take into account quantities of interest (QoI) coming from models of different fidelities providing a global surrogate model. A classic Bayesian global optimization method permits to iteratively select promising designs. It relies on the maximization of the so-called Expected Improvement criterion. A geometrical parametrization technique based on B-splines is considered to describe the profile geometry. The total pressure loss coefficient is minimized while the mass flow rate is constrained. For both the application cases, the optimization study reveals a speed-up of 3 to 5 times in the convergence process with respect to classic optimization frameworks based on a single fidelity, while providing similar improvements in terms of fitness functions.
Detailed Description of the Fluidized Bed Mixing and Heat Transfer by Means of Eulerian Multi-Fluid Numerical Simulations
Authors: Ali Uzair Muhammad , Fornarelli Francesco , Camporeale Sergio Mario , Torresi Marco
Published: January 2021

The hydrodynamics and heat transfer of a binary mixture of sand and biomass in a fluidized bed have been numerically investigated. The Eulerian multi-fluid model MFM incorporating kinetic theory of granular flow was used to numerically investigate fluidized bed. A commercial code has been used together with user-defined functions to correctly predict the hydrodynamics and the heat transfer. Numerical results were validated against the experiment in terms of pressure drop across the bed and concentration of biomass at different heights of the bed. Influence of additional parameters, such as superficial gas velocity and sand sizes on hydrodynamics were investigated. Additionally, heat transfer in the fluidized bed was also studied highlighting the influence of the temperature dependent properties of air on the results. The present results reveal that better mixing is achieved for smallest sand size, also promoting more uniform temperature of biomass.
Investigation of Turbulence Modeling and Harmonic Balance Methods Towards Accurately Predicting Compressor Flow Fields
Authors: McManus Liam , Hodges Justin , Beary Ilyas
Published: January 2021

Numerical investigations of the NASA stage 37 compressor case are presented. Simcenter STAR-CCM+ is used for RANS based aerodynamic quantifications of the transonic compressor, with specific attention to the near stall and the peak efficiency operating points. In these axial turbomachines, the unsteady effects are non-trivial, and need to be accounted for in the design methods. Typically, transient simulation of fully realistic engine hardware is unrealistic in terms of the computational expense. However, using a harmonic balance approach in computational fluid dynamic (CFD) simulation has been shown to have a proficiency in capturing the dominant unsteady behaviors at a relatively lower computational cost. As such, the performance of the NASA stage 37 compressor is characterized with both steady and harmonic balance approaches. Furthermore, a thorough exploration and sensitivity study on the turbulence modeling is conducted. The lag elliptic blending k-ε turbulence model is considered, due to its capability for improved predictions in highly separated turbomachinery flows, as compared to the k-O SST and k-O BSL model results.
Experimental Evaluation of 200mm Hybrid Air Foil Bearing Aimed for MW Scale Turbomachinery
Authors: Kim Daejong , LaTray Nguyen , Honavara-Prasad Srikanth
Published: January 2021

The nonlinear characteristics of foil bearings often add complexities to analysis and design of foil bearings over wide size ranges. Previously, scaling laws for bearing clearance and areal stiffness of supporting foil structure for differently sized foil bearings were proposed to address these challenges. The scaling laws enable to design large foil bearing by scaling up existing small foil bearing. To verify the proposed scaling law and demonstrate the feasibility of a large foil bearing, a 200mm (in diameter) hybrid air foil bearing with potential use for 2MW generator was designed and manufactured by scaling up an existing 50mm foil bearing following the scaling laws. The 200mm hybrid foil bearing was tested for its static performance. The bearing features a three-pad offset preload with total six hydrostatic injection ports to improve the load carrying capacity at low speed. A great effort was put into designing a test rig to demonstrate the bearing static performance. The test rig is configured with a series of ball bearings-supported test rotor and the hybrid foil bearing is floating on the rotor. A pneumatic actuator is used to apply external load to the foil bearing and a torque rod measures the friction torque of the foil bearing. The test rig was designed with maximum allowable speed of 18,000rpm and the rotordynamics of the test rig was analyzed to ensure its integrity under the testing conditions. Two hybrid modes, i.e., with all injection ports open and only bottom injection ports open, were compared. The hybrid foil bearing can withstand up to 2000N at zero speed under 5 bar absolute supply pressure for both hybrid modes. Twenty start/stop cycles test at 1000rpm over extended period under 2000N in hybrid modes show the bearing temperature changes very little, demonstrating very robust bearing function. The hybrid foil bearing was also tested in hydrodynamic mode at 4400rpm under 2000N, verifying the full functionality of the bearing in hydrodynamic mode. A preview of a 2MW permanent magnet generator featuring the 200mm hybrid foil bearing is also presented as one of the potential applications.