bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigation of Gas Turbine Internal Cooling Using Supercritical CO2 – Effect of Surface Roughness and Channel Aspect Ratio
Authors: Roy Arnab , Searle Matthew , Ramesh Sridharan , Straub Douglas 
Published: October 2022

Abstract
In this paper, an experimental and numerical investigation of internal cooling channels with rib turbulators is presented with sCO2 as the working fluid at process conditions (pressure-20.7 MPa and temperature up to 150 °C). The effect of channel aspect ratio up to 2:1 on thermal-hydraulic performance is explored in additively manufactured rectangular channels and square channels, both with and without 60° ribs on the top and bottom sides. The Wilson-plot method is employed to experimentally measure channel averaged Nusselt number over a Reynolds number range up to 370,000. The friction factor is calculated from pressure drop and mass flow rate and additionally, the overall thermal performance factor (TPF) is reported. A companion computational fluid dynamics (CFD) simulation is performed for the rib turbulated cooling configurations reported in the experiments using the Reynolds Average Navier-Stokes (RANS)-based turbulence model. The objective of the numerical study is to gain insight into the local heat transfer augmentation in the ribbed channels as a result of varying the aspect ratio, channel configuration (square vs rectangular), operating conditions (Reynolds number) and the surface roughness, an inherent outcome of the additive manufacturing process. Surface roughness is simulated using sand grain roughness height (KS) calculated from the experimental data, and a comparison is presented with the corresponding channel configuration with varying surface roughness heights starting from smooth surfaces (KS = 0). Experimental results indicate that the heat transfer augmentation is negligible in the rectangular channels with ribs on the long side while compared to the square channel. However, it is enhanced by 60% in comparison to placing ribs on the shorter side. The TPF remains constant around 1 for the entire range of Reynolds numbers consistent with prior work at NETL. The simulation results highlight that increased surface roughness can have a favorable considerable influence on Nusselt number and overall thermal performance enhancement.
Fused Deposition Modeling Fabrication Evaluation of a Ti-6Al-4V Centrifugal Compressor
Authors: Warner Justin , Celli Dino , Scott-Emuakpor Onome , George Tommy , Tomlin Trevor 
Published: October 2022

Abstract
Centrifugal compressors have a critical impact on the performance of a jet engine and can be made out of aluminum, steel, or titanium alloy. However, if made out of Ti-6Al-4V it would be more lightweight than if steel were used and stronger than if aluminum were used. Compressors manufactured using traditional techniques can be relatively expensive to manufacture, therefore, fused deposition modeling (FDM) or fused filament fabrication (FFF) can help reduce the cost while maintaining structural integrity. FDM/FFF usually prints polylactic acid (PLA) or acrylonitrile butadiene styrene (ABS) layer-by-layer using an extruder with a spool of material feeding into the extruder. Recently, metal-polymer filaments have become commercially available using this same printing apparatus as common “hobby-class” FDM printers. Using FDM with a metal-polymer matrix allows for a lower cost of production because of the intricate designs it can accomplish with little to no machining involved. Additive printing with Ti-6Al-4V is challenging because of the health and safety concerns of the powder, but having the material in a spool eradicates these concerns of handling Ti-6Al-4V due to the Ti-6Al-4V powder being surrounded by a polymer. Even with the benefits of printing a spool of material using FDM, there has been very little research done of Ti-6Al-4V printed in a FDM format. Printing using the FDM process is known to create shrinkage of the part, it has been documented of different shrinkage percentages for steel using FDM but not Ti-6Al-4V. This document records the feasibility of using Ti-6Al-4V for a centrifugal compressor using FDM by incorporating a 3D structured blue light scanner before heat treatments while also analyzing manufacturing capabilities at the tips of blades as well as the base. This analysis is a first-stage to quantify FDM metal print characteristics and properties.
Experimental Determination of Blade Tip Rub Forces in a Multi-Blade System
Authors: Reifsnyder Robin , Keener Chris , Mathison Randall , D’Souza Kiran 
Published: October 2022

Abstract
As improved efficiency goals require ever smaller gaps between rotating turbomachinery blade tips and stationary outer casings, it becomes more important to understand the physics of what happens when a blade tip rubs against the casing. A key piece of information to be determined is the force exerted on the blade tip during the rub event. This paper presents a method of extracting the blade tip rub forces from experiments conducted at The Ohio State University Gas Turbine Laboratory. To identify the forces during the rub, three multi-axis load cells are mounted behind a segment of the casing to measure the forces exerted on the casing during the rub event. Recovering blade tip forcing from this load cell data requires creating an appropriate model that can relate the measured data at the load cells to the highspeed rotating blade loads. The continuous, repeated nature of the rubs in the experiment makes this a challenge. This paper discusses the creation and performance of a state-space realization model developed from stationary ping test data that is used to address these challenges. The model is augmented with information on the angular position of the blades from a rotary encoder and information on the angular span of the rub, which increases with rub depth. Challenges and solutions related to finding tangential frequency responses, simultaneous blade rubs, and irregularities in the experimental data are also discussed. This paper aims to summarize the process and effectiveness of this approach for finding blade tip forces, as well as lessons learned along the way.
Stall Margin Improvement in a Transonic Compressor With a Casing Treatment: Flow Mechanism
Authors: Hah Chunill 
Published: October 2022

Abstract
A compressor casing treatment with circumferential casing grooves (CCGs) is studied in detail. The primary objective of the current paper is to unearth the main driving fluid mechanism that changes the stall margin in a transonic compressor with CCGs.
Large Eddy Simulation (LES) is applied to calculate the transonic compressor flow fields with and without CCGs. Detailed comparisons between measured and computed flow fields show that changes in flow structures due to CCGs are very well represented with LES. The measured data show that flow blockage generation in the tip gap area is reduced significantly when CCGs are applied, which delays compressor stall onset. Calculated flow fields with and without CCGs are examined to understand how the blockage generation is reduced with CCGs.
Tip leakage flow typically travels upstream, opposite to the incoming main flow. When CCGs are applied on the compressor casing, part of the tip leakage flow goes into the grooves and is later reinjected into the main flow passage. Therefore, CCGs modify the collision between the incoming main passage flow and the tip leakage flow.
Two main aspects of the change of tip leakage flow due to CCGs are examined in the present study. The first aspect is whether the total mass flow through the tip gap changes substantially with CCGs. The second aspect is whether changes in the collision and mixing of the incoming main passage flow and the tip leakage flow due to CCGs substantially affect blockage generation.
The present investigation shows that CCGs reduce the mass flow through the tip gap by about 16 % near the stall-condition. Calculated flow fields show that most of this reduction of tip leakage flow occurs near the CCGs. Reinjected flow from the CCGs pushes the tip leakage flow radially inward below the casing and changes how the tip leakage flow collides with the incoming main passage flow. However, detailed examination of the calculated flow in the tip region shows that the reinjected flow does not contribute to the reduction of the overall blockage generation. The primary driver reducing blockage generation with CCGs is the reduction of overall mass flow rate through the tip gap.
It has been thought that circumferential grooves always incur small additional losses near the design condition due to mixing between the flow exiting the grooves and the main flow, in addition to an increased wetted area. In the present investigation, measurements show such a decrease in efficiency with CCGs, although the difference in efficiency is within the measurement uncertainty. Results from the LES simulation at the design condition with CCGs show that the tip leakage vortex (TLV) is pulled toward the blade suction side and double leakage flow is eliminated. The result is that the simulated efficiencies with and without CCGs are almost the same.
The Numerical and Experimental Evaluation of a Coupled Blade Dynamic Limit Response With Friction Contacts
Authors: Grant Kelly , Gastaldi Chiara , Berruti Teresa M. , Kellerer Rudolf 
Published: October 2022

Abstract
Increasing demand on turbine power and efficiency requires larger and higher loaded turbine blades, which in turn requires the consideration of aeromechanical interactions. Whilst CFD tools can reliably predict stability using aerodynamic damping as an indicator, the component of mechanical damping also needs consideration. An understanding of the mechanical damping in the system becomes key to a robust blade design. Mechanical damping for such a part comes predominantly from friction occurring at the coupling contact faces. It is well established and published that such contact forces are nonlinear in relation to the relative movement at the contact interface. Moreover, contact area, the rigidity in the contact, friction coefficient, and normal contact force must also be considered and included as parameters that influence the result. Consequently, the level of system damping is not a constant, and depends highly on the system response itself, as well as the other forementioned parameters. In the case of self-excited vibration such as flutter, the evaluation of the damped limit response is a part of the blade design process.
A tool has been developed to numerically simulate contact friction forces with the intention of parametrically evaluating the limit response and relating this to the mechanical integrity of the part. This paper presents the modelling of a coupled blade system with friction contact forces, results coming from this evaluation, and a comparison with test data.
Parametric Analysis for On-Board Thermal Regulation in a Hybrid-Electric Aircraft
Authors: Valsamis Mylonas Orestis S. , Gkoutzamanis Vasilis G. , Kalfas Anestis I. 
Published: October 2022

Abstract
The driving force behind the presented research is the need for more ecological applications in the aviation sector. Hybrid-electric propulsion systems are considered a promising alternative technology capable to provide fuel savings, reduced emissions and lower noise levels. Despite the added benefits, there are several pitfalls such as the commonly known issues of batteries’ low energy density — compared to that of jet-fuels —, as well as the need to efficiently regulate the various heat loads generated from the electrical propulsion system. The design of the Thermal Management System (TMS), for a hybrid-electric aircraft, alone constitutes of a ubiquitous task, due to its impact on the aircraft’s total weight, cooling drag and overall performance. This study focuses on investigating the possible operating media of a selected TMS, and their impact during the conceptual design phase of the system. On one hand, the air’s capability to transfer heat with increasing altitude is investigated. On the other hand, various liquid coolants are evaluated over their performance to remove heat loads but also, to not exceed their evaporation, boiling or autoignition points, while doing so. The simulations are conducted with the use of Modelon Impact, implementing the Modelica Liquid Cooling Library, and are transient to account for the dynamic effects of temperature change and thermal inertia of the various system elements. The results show that an atmospheric air mass flow of at least 0.848 kg/s is required to sufficiently dissipate the induced heat loads. Although, that is highly dependent on the flight altitude. If a liquid medium is to be selected, the best performing would be a propylene glycol water mixture with a mass flow of 0.204 kg/s, but the final selection is also subject to other factors that vary according to the priorities given.
Optimizing Internal Energy Streams in Micro Gas Turbines in Cogeneration Towards Flexible Heat-to-Power Ratio — Global Thermodynamic Performance Assessment and Specific Case Studies
Authors: De Paepe Ward , Clymans Tom 
Published: October 2022

Abstract
Although the simultaneous production of heat and power, so-called Combined Heat and Power (CHP), is from a thermo-dynamic point of view still the most efficient energy conversion method, cogeneration units have nowadays problems to position themselves in the current and future energy market. The increasing renewable energy penetration requires CHP units to become more flexible, especially on their currently fixed heat-to-power ratio. Within this framework, micro Gas Turbines (mGTs), as small-scale decentralized cogeneration units, offer opportunities. Since they use the recuperated Brayton cycle, they offer the theoretic option to adjust the internal heat streams to provide a flexible heat-to-power ratio as well as the unique feature of a tunable outlet temperature, making the unit feasible/interesting for a larger range of applications having a combined heat and power demand. Hence, in this paper, we assessed the impact of the use of a recuperator bypass for enhanced operational flexibility of mGTs. In a first step, the optimal pathway for the recuperator bypass, i.e., cold or hot side bypass, is selected for a typical mGT, the Turbec T100 (currently commercially available as the AE-T100), considering both thermodynamics as well as technological feasibility. Moreover, the potential performance impact on the electrical and total efficiency is calculated as well as on the total available thermal power. In a second step, the specific performance of the option of using a recuperator bypass is assessed for 2 specific cases: flexible heat-to-power ratio at low temperature and high temperature, i.e. steam generation, cogeneration. Thermodynamic simulations show that the impact on the electric efficiency remains rather limited (maximal 6% absolute efficiency reduction for a 40% bypass ratio), while the available thermal energy and exergy increase significantly: up to 60% increase for thermal power and even 115% increase in the exergy content of the flue gases. Moreover, there is no distinct difference between cold or hot bypass, leaving the selection of the optimal bypass route a pure technical choice. Finally, considering the specific cases studied, simulation results show that heat-to-power ratio could be increased by more than 50% for all power outputs for the low temperature CHP applications, even resulting in a global efficiency increase, while for the high temperature case, recuperator bypass allows for a significant increase in steam production, at total efficiencies comparable to the separate production (i.e. boiler and grid), clearly highlighting the benefits and potential of a recuperator bypass.
Methods and Apparatus for Real-Time Clearance Assessment Using a Pressure Measurement
Authors: Kim Taehong 
Published: October 2022

Abstract
An aircraft turbine engine is exposed to high temperatures, high pressures, and high speeds, and case structure and rotating parts have different thermal and mechanical expansion and contraction. Most of turbine engines adapts ACC (Active clearance controls) system to manage thermal contraction of casing and control tip clearance automatically during operation. For example, case structure can be cooled and radially contracted by cooling air outside of casing structure and the system is working to minimize the gap and improve turbine performance. However, the current system does not account of blades tip loss progression caused by rub and oxidation. As engine deteriorates on wing, the mismatching error between tip clearance calculation and actual hardware condition is increased and engine efficiency is being worsen.
Real time measurement of tip clearances would be a crucial way to understand tip loss and adjust the gap to maintain turbine efficiency, but current technology of measuring sensors including laser, capacitive, eddy current, and microwave is not applicable for production engines due to technical limitations such as short life, high cost, design complexity, etc. Analytical method using engine parameters is currently being developed, but it has not been validated to apply for accuracy.
This study is to review radial tip clearances and pressure measurement in engine flight test and demonstrate its linear correlation of Pressure Efficiency against clearance changes during test. As a result, it proposes new methods for tip clearances evaluation based on pressure measurement and conversion curves. New methods include one-point, two-points and three-points (or multi-) pressure measurement to assess clearance changes for different operating conditions. The conversion curves would be developed during engines tests on different power levels and be applicable for production engines with low cost, longer life, efficiency improvement and so on.
Technoeconomic Comparison of sCO2 and ORC Systems for Waste Heat Recovery
Authors: Allison Timothy C. , Wilkes Jason C. , Wygant Karl , Pelton Robert 
Published: October 2022

Abstract
Various supercritical carbon dioxide (sCO2) power cycles are an emerging bottoming cycle technology for gas turbine waste heat recovery with potential advantages relative to Organic Rankine Cycle (ORC) systems, including improved performance, compactness, improved economics, nonhazardous working fluids, and faster ramp capabilities. This work compares a waste heat recovery system based on an integrally geared compander in a sCO2 preheat cycle configuration with split recuperator with a recuperated ORC in the literature. The integrally geared system is comprised of an 1800 rpm generator with high-pressure and low-pressure pinions splitting a two-stage compressor and expander. Cycle constraints and design drivers, and optimization of the sCO2 system are described, along with current technology readiness and full-pressure full-temperature opera ting experience of the various components including compressors, expanders, heat exchangers, and other system components. Both cycles are paired with a commercial 15 MW gas turbine, and the resulting system costs, performance, and other attributes are presented. The cycles are compared with an cold-side temperature of 35 °C, showing an ORC system output of 5066 kW and an sCO2 system output of 5660 kW, i.e. an 11.7 % performance benefit for sCO2. Additionally, cost and size requirements and costs for the sCO2 and ORC-based systems are compared, indicating comparable nominal costs for both systems and a potentially lower cost for sCO2 systems, particularly when an indirect heat transfer loop is needed.
Analysis of sCO2 Waste Heat Recovery System for Application in a Cement Plant
Authors: Vesely Ladislav , Macadam Scott , Kapat Jayanta , Subbaraman Ganesan 
Published: October 2022

Abstract
The industrial sector contributes approximately 28% of global CO2 emissions. CO2 emissions from energy-intensive industries can be reduced by converting waste heat into electricity. This represents a low-cost, zero-emissions power generation option with near-term deployment opportunities. One energy-intensive industry is cement production. Two cement plant heat sources are flue gas streams from preheater and clinker cooler, with temperatures of 250–450 °C. Potential energy conversion systems include Organic Rankine (ORC), steam Rankine (SRC), and supercritical CO2 (sCO2) power cycles. ORC/SRCs have been commercially deployed in cement plants. However, sCO2 power cycles offer benefits such as high thermal stability of CO2, higher cycle efficiencies, and compact power generation equipment. The paper is focused on multi-objective optimization of four sCO2 cycle layouts (Recuperated, Re-compression, Partial recuperative, and cascade) and comparison with ORCs/SRCs. The optimization considers waste heat temperatures of &gt; 300°C. The results show that sCO2 power cycles can reach cycle efficiencies up to 30 %, which is higher than corresponding ORCs and almost similar to SRCs. However, cycle efficiency is not the only parameter to evaluate waste heat utilization. More meaningful parameters are the net power and capital costs. Results show higher power outputs from the sCO2 cycle compared to ORCs and SRC.
Optimization of the Traveling Time of Construction Crews to Minimize the Time to Operation of a Wind Farm
Authors: Ferrari Lorenzo , Frate Guido Francesco , Leanza Francesca , Giuliattini Burbui Gian Lorenzo 
Published: October 2022

Abstract
Building a wind farm is a long and critical process. Many operations have to be arranged in sequence to complete and put in operation a wind farm. Typically, a wind farm is located in an exposed site, with a reduced accessibility and a limited interconnections between machines. The number of crews operating in parallel on the plant is a crucial parameter. By increasing the number of teams, the time to operation decreases but the overall commissioning cost increases. The strategy adopted to schedule the building operations can have an impact on this balance. An optimized sequence may keep the time to operation low but still limiting the number of crews involved. In this study, an optimization procedure based on a genetic algorithm was used for the minimization of the construction time of a wind farm of 200 MW selected as a case study. The problem was solved by considering an approach inspired to the Multiple Travelling Salesman Problem. An increasing number of crews was also considered to find the tradeoff between time and cost. The comparison between the results of the optimization process and those of a more traditional approach showed the benefits of an optimized approach to the problem both in terms of time to operation and costs. In particular, in the case study analyzed, a saving of almost 24% of the erection and installation time (around 280k$) was achieved only by optimizing the routes followed by the construction crews.