Performance Limits of Axial Compressor Stages

This paper presents a framework for estimating the upper limit of compressor stage efficiency. Using a compressor stage model with a representative design velocity distribution with turbulent boundary layers, losses are calculated as the sum of selected local irreversibilities, rather than from correlations based on data from existing machines. By considering only losses that cannot be eliminated and optimizing stage design variables for minimum loss, an upper bound on stage efficiency can be determined as a function of a small number of stage design parameters. The impact of the stage analysis results are evaluated in the context of gas turbine cycle performance. The implication from the results of the stage level and cycle analyses is that compressor efficiency improvements that result in substantial increases in cycle thermal efficiency are still to be realized.Fundamental Aeronautics Program (U.S.) (Agreement Number NNX08AW63A

High Fidelity Simulation of Loss Mechanisms in Compressors

Further improvements in aero-engine efficiencies require better understanding of loss mechanisms. The rise of high performance computing is unlocking the potential of scale-resolving simulations for industrially relevant cases thus allowing new levels of simulation fidelity. As a result, previously unexplored effects of unsteadiness can be simulated and their impact on loss understood. The work undertaken in this thesis aims to establish a framework for accurate loss predictions using scale-resolving simulations and inform the field with regards to the effects of unsteadiness on loss mechanisms within the multi-stage compressors. The lack of computational requirements for accurate industrial simulations lead to inconsistent loss predictions even for scale-resolving simulations depending on the chosen convergence criteria. This work studies aspects of loss generation by employing two test-cases: Taylor-Green vortex and compressor cascade subjected to freestream turbulence. The results show that both resolving local entropy generation rate and capturing the inception and growth of instabilities are critical to accuracy of loss prediction. In particular, the interaction of free-stream turbulence at the leading-edge and development of instabilities in the laminar region of the boundary layer are found to be important. These two outcomes allow for a formulation of resolution criteria that ensure accurate loss predictions for compressor flows. One of the major sources of uncertainty in the current simulation methods for compressor flows is the level of unsteadiness and its impact on loss This work makes a series of steps towards understanding the nature and the origin of unsteadiness within multi-stage machines and investiages the impact of gapping on mid-span compressor loss. It is found that freestream turbulence levels rise significantly as the size of the rotor-stator axial gap is reduced. This is because of the effect of axial gap on turbulence production mechanisms, which amplify at smaller axial gaps and drive increases in dissipation and loss. This effect is found to raise loss by between 5.5 - 9.5\% over the range of conditions tested here. This effect was found to significantly outweigh the beneficial effects of wake recovery on loss.Financial support for this work was provided by the Whittle Laboratory and the University of Cambridge through the Denton Scholarship fund and the CDT in Gas Turbine Aerodynamics, funded by the EPSRC $EP/L015943/1$

Influence of cavity flow on turbine aerodynamics

In order to deal with high temperatures faced by the components downstream of the combustion chamber, some relatively cold air is bled at the compressor. This air feeds the cavities under the turbine main annulus and cool down the rotor disks ensuring a proper and safe operation of the turbine. This thesis manuscript introduces a numerical study of the effect of the cavity flow close to the turbine hub on its aerodynamic performance. The interaction phenomena between the cavity and main annulus flow are not currently fully understood. The study of these phenomena is performed based on different numerical approaches (RANS, LES and LES-LBM) applied to two configurations for which experimental results are available. A linear cascade configuration with an upstream cavity and various rim seal geometries (interface between rotor and stator platform) and cavity flow rate available. A rotating configuration that is a two stage turbine including cavities close to realistic industrial configurations. Additional losses incurred by the cavity flow are measured and studied using a method based on exergy (energy balance in the purpose to generate work)

Impacts of Anthropogenic Noise on Litter Chemistry and Decomposition Processes in a Semi-Arid Ecosystem

Chronic anthropogenic noise in ecosystems can change avian/arthropod/plant interactions, but it is unclear how changes in herbivory pressure affects functional traits of plants. We asked how anthropogenic noise, mediated through changes in arthropod abundance, altered timing of leaf senesce, chemical composition (i.e. C/N ratios, total phenolics) and decomposition rates of leaf litter in Wyoming big sagebrush (Artemisia tridentata spp. wyo.). Additionally, we asked if changes in arthropod abundance altered secondary metabolites (i.e. monoterpenes) in foliage. We broadcasted recorded gas compressor station noise (24hrs/day) from April through October 2015 in a sagebrush steppe ecosystem of Idaho, USA. We quantified quantity, chemical composition (i.e. C/N ratios, total phenolics) and decomposition rates of leaf litter and changes to monoterpene concentrations. We found that: (1) changes to top down forces resulting from noise treatments did not impact the leaf abscission rates, the chemical composition of leaf litter or litter decomposition and (2) time of year significantly affected quantity, chemical composition (i.e. C/N ratios and phenolic concentrations) and decomposition of leaf litter. Our research indicates that increases in anthropogenic noise over one growing season does not impact litter chemistry or decomposition processes. Future research should evaluate whether prolonged noise-induced changes in herbivory lead to changes in litter chemistry and decomposition

Prédiction de la génération des pertes des écoulements compressibles anisothermes appliquée aux distributeurs hautes pressions de turbine avec les simulations aux grandes échelles

Afin d'améliorer l'efficacité des moteurs aéronautiques, une des solutions envisagées par les industriels est d'augmenter la température d'entrée de la turbine. Cependant, ces hautes températures induisent de fortes contraintes thermiques sur les pales de turbine ce qui réduit leur durée de vie. Pour surmonter ces problèmes thermiques, des systèmes de refroidissement efficaces sont nécessaires. Afin d'évaluer la performance de ces systèmes, une prédiction précise de la température de paroi des pales de turbine et des pertes générées par ces systèmes est requise. Profitant de l'opportunité de récents développements d'outils de prédiction haute-fidélité, cette thèse financée par Safran Helicopter Engines à travers le projet FUI CASCADE, a pour but de valider la prédiction de la température de paroi des pales de turbine refroidie et des pertes générées par ces systèmes avec la Simulation aux Grandes Echelles (SGE). Pour atteindre ces objectifs, différentes configurations académiques et industrielles refroidies par film de refroidissement ont été simulées et étudiées. Les résultats obtenus dans cette thèse montrent que la SGE est capable de prédire l'aérodynamique et l'environnement thermique pour de tels systèmes. Pour faciliter l'utilisation de la SGE dans l’industrie et limiter le coût CPU lié à la résolution de l'écoulement dans le système de refroidissement des pales, un modèle de jets de refroidissement a été proposé et évalué dans ce travail. Les résultats montrent que ce modèle permet de reproduire l'aérodynamique des jets de refroidissement et la température de paroi des pales sans mailler le système de refroidissement. Pour évaluer les pertes dans ce contexte, l’approche Second Law Analysis (SLA) est adoptée. Contrairement aux bilans de température et pression totales, cette approche donne directement accès aux champs de perte 3D qui sont construits à partir des termes sources de l’entropie résolus sur le maillage. Ainsi, le mécanisme de génération de perte peut être localement étudié et ne requière pas de procédure de moyenne contrairement aux modèles de perte 1D. Ces champs de perte sont décomposés en deux contributions : une contribution aérodynamique et une contribution thermique liée au mélange chaud-froid. L'étude de ces champs montre que les pertes aérodynamiques sont principalement générées dans les régions de fort cisaillement (couche limite et de mélange) alors que les pertes de mélange sont générées dans les films de refroidissement et dans le sillage des pales. Des analyses avancées des champs de perte mettent en évidence que les fluctuations turbulentes dominent la génération des pertes pour ces systèmes. Ce dernier résultat met en évidence les bénéfices de l'approche Second Law Analysis pour prédire les pertes à partir des champs obtenus avec la SGE. En effet et contrairement aux approches RANS, les contributions turbulentes des pertes sont directement résolues sur le maillage avec la SGE et ne requiert aucune stratégie de modélisation. La principale conclusion de cette thèse est que l'approche Second Law Analysis couplée avec la SGE est une méthodologie très prometteuse et pertinente pour la prédiction des écoulements et des pertes pour les futurs designs de pale de turbine industriel

Novel turbomachinery concepts for highly integrated airframe/propulsion systems

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2007.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 251-260).Two novel turbomachinery concepts are presented as enablers to advanced flight missions requiring integrated airframe/propulsion systems. The first concept is motivated by thermal management challenges in low-to-high Mach number (4+) aircraft. The idea of compressor cooling combines the compressor and heat exchanger function to stretch turbopropulsion system operational limits. Axial compressor performance with blade passage heat extraction is assessed with computational experiments and meanline modeling. A cooled multistage compressor with adiabatic design point is found to achieve higher pressure ratio, choking mass flow, and efficiency (referenced to an adiabatic, reversible process) at fixed corrected speed, with greatest benefit occurring through front-stage cooling. Heat removal equal to one percent of inlet stagnation enthalpy flux in each of the first four blade rows suggests pressure ratio, efficiency, and choked flow improvements of 23%, 12%, and 5% relative to a baseline, eight-stage compressor with pressure ratio of 5. Cooling is also found to unchoke rear stages at low corrected speed. Heat transfer estimations indicate that surface area limitations and temperature differences favor rear-stage cooling and suggest the existence of an optimal cooling distribution.(cont.) The second concept is a quiet drag device to enable slow and steep approach profiles for functionally quiet civil aircraft. Deployment of such devices in clean airframe configuration reduces aircraft source noise and noise propagation to the ground. The generation of swirling outflow from a duct, such as an aircraft engine, is conceived to have high drag and low noise. The simplest configuration is a ram pressure driven duct with non-rotating swirl vanes, a so-called swirl tube. A device aerodynamic design is performed using first principles and CFD. The swirl-drag-noise relationship is quantified through scale-model aerodynamic and aeroacoustic wind tunnel tests. The maximum measured stable flow drag coefficient is 0.83 at exit swirl angles close to 500. The acoustic signature, extrapolated to full-scale, is found to be well below the background noise of a well populated area, demonstrating swirl tube conceptual feasibility. Vortex breakdown is found to be the aerodynamically and acoustically limiting physical phenomenon, generating a white-noise signature that is [approx.] 15 dB louder than a stable swirling flow.by Parthiv Narendra Shah.Ph.D

Numerical Simulation of Air Flow in Aeroengine Compressors

The performance of an aeroengine is influenced by the performance of the compressor system. A typical compressor consists of multistage axial compressors followed by a centrifugal stage. Here, a high-speed centrifugal and an axial stage are investigated in terms of turbulence modelling, flow blockage and rotor-stator (R-S) gap using the commercial software ANSYS CFX. The curvature corrected Shear stress transport (SST-CC) model of Smirnov and Menter is investigated for the first time in a high-speed centrifugal stage in terms of curvature and rotation effects. The SST-CC predictions are compared with the standard SST, Speziale, Sarkar, and Gatski Reynolds stress model (RSM-SSG) and the experimental data in terms of the global performance as well as the velocity profiles at the impeller-diffuser interface. The comparisons show that SST-CC has the best agreement with the experiments at choke condition while SST has better performance at the stall condition. The production term shows the expected sensitivity to the convex and concave curvatures. A new method to quantify blockage for both axial and centrifugal compressors is developed. Both steady and unsteady simulations are used to examine the flow blockage in the axial transonic stage. The variation of the rotor tip blockage with respect to the blade loading shows good agreement with previous studies. The total planar blockage indicates that stall might initiate at the stator trailing edge. The differences between the steady and unsteady predictions are mainly attributed to the local differences in the total pressure profiles at the inlet guide vanes–rotor interface. It was previously argued that reducing the R-S gap improves the efficiency of axial compressors due to reduced viscous mixing of the rotor wake. However, the current simulations show that the smallest R-S gap has the highest levels of total pressure losses within the stator passage and the highest levels of unsteady stator forces at reduced mass flow rates. The unsteadiness in the stator flow field is attributed to the larger stator suction surface boundary layer separation associated with the smallest gap. The smallest R-S gap reduces the viscous mixing of the wake at the expense of the efficiency

Effects of rotor tip clearance on an embedded compressor stage performance

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 111-114).Compressor efficiency variation with rotor tip gap is assessed using numerical simulations on an embedded stage representative of that in a large industrial gas turbine with Reynolds number being approximately 2 x 106 to 7 x 106. The results reveal three distinct behaviors of efficiency variation with tip gap. For relatively small tip gap (less than 0.8% span), the change in efficiency with tip gap is non-monotonic with an optimum tip gap for maximum efficiency. The optimum tip gap is set by two competing flow processes: decreasing tip leakage mixing loss and increasing viscous shear loss at the casing with decreasing tip gap. An optimum tip gap scaling is established and shown to satisfactorily quantify the optimal gap value. For medium tip gap (0.8% - 3.4% span), the efficiency decreases approximately on a linear basis with increasing tip clearance. However, for tip gap beyond a threshold value (3.4% span for this rotor), the efficiency becomes less sensitive to tip gap as the blade tip becomes more aft-loaded thus reducing tip flow mixing loss in the rotor passage. The threshold value is set by the competing effects between increasing tip leakage flow and decreasing tip flow induced mixing loss with increasing tip gap. Thus, to desensitize compressor performance variation with blade gap, rotor should be tip aft-loaded and hub fore-loaded while stator should be tip fore-loaded and hub aft-loaded as much as feasible. This reduces the opportunity for clearance flow mixing loss and maximizes the benefits of reversible work from unsteady effects in attenuating the clearance flow through the downstream blade-row. The net effect can be an overall compressor performance enhancement in terms of efficiency, pressure rise capability, robustness to end gap variation and potentially useful operable range broadening. Preliminary assessment of a stage redesign with a 4% chord more tip aft-loaded blade design for 1.7 % span tip clearance yields 0.2 point stage efficiency benefit.by Sitanun Sakulkaew.S.M

Relative bioavailability of terbutaline to the lungs following inhalation using different methods.

The primary aim was to validate and implement a urinary pharmacokinetic method for terbutaline to determine the relative lung and systemic bioavailability following inhalation and to measure the in-vitro characteristics of the emitted dose by these inhalation methods. Two new robust, accurate and sensitive high performance liquid chromatography methods for the determination of terbutaline in aqueous and urine samples were validated in accordance with the FDA and ICH guidelines. Terbutaline was extracted using solid phase extraction with salbutamol and bamethane as internal standards. The accuracy, precision, lower limit of detection and recovery for both methods were within recognized limits. The in-vitro characteristics of terbutaline sulphate inhalers were measured according to standard compendial methodology as well as adaptation of this methodology to simulate routine patient use. The dose emission of terbutaline sulphate from a Bricanyl Turbuhaler was determined using an inhalation volume of 4 L at inhalation flows of 10-60 L min-1. The particle size distribution was measured using an Anderson Cascade Impactor (ACI) with a mixing inlet valve to allow measurement at different flows. A steady increase in total emitted dose (TED) and the fine particle dose (FPD) was observed as the inhalation flow increased thereby highlighting the flow dependent dose emission characteristics of the Turbuhaler. The in-vitro dose emission characteristics of terbutaline sulphate from Bricanyl MDIs were measured according to the standard compendial methodology at a flow of 28.3 L min-1 using a 4 L inhalation volume. The TED and particle size distribution of terbutaline sulphate from the Bricanyl MDI were determined alone and with different spacers [AeroChamber Max (AMAX), AeroChamber Plus (APLUS), Fisonair and Nebuhaler]. The TED from the MDI alone was significantly higher than all MDI+spacers (p<0.001). The MDI with APLUS resulted in the smallest mass median aerodynamic diameter (MMAD) and the highest fine particle fraction (FPF). The MDI with AMAX resulted in the highest FPD. The in-vitro characteristics of terbutaline sulphate from Bricanyl respules using the Aeroneb Pro (vibrating mesh) and Sidestream jet nebulisers were determined by the CEN methodology and the Next Generation Impactor (NGI) methodology. The Aeroneb Pro was found to have significantly better aerodynamic properties than the Sidestream. The results from the NGI method were significantly different from the CEN method suggesting further evaluation of both methods. Cooling the NGI decreased the evaporation effect. Twelve healthy volunteers (6 females) completed in-vivo urinary terbutaline pharmacokinetic studies to determine the relative bioavailability following inhalation. The differences between the amounts excreted 0.5, 1, 2, 4, 6 and 24 hour post inhalation from a Bricanyl MDI (I) and oral (O) dosing of 500 µg terbutaline sulphate and with the co-administration of oral charcoal (IC and OC, respectively) were studied. No terbutaline was found in OC samples. The amount of terbutaline excreted 30 minutes post I and IC were significantly (p<0.001) higher than post O suggesting that the amount of terbutaline excreted 30 minutes post dosing can be used as an index of the lung deposition. The amount of terbutaline excreted 24 hour post I was significantly (p<0.01) higher than post O suggesting that the amount of terbutaline excreted 24 hour post dosing can be used as an index of the relative systemic bioavailability. The dose response relationships and the low inter and intra-subject variability studies confirm the feasibility of this method. To demonstrate the application of the method the effect of inhalation technique on the lung and systemic bioavailability following inhalation from a dry powder inhaler was evaluated. The effect of different spacers on the dose emitted from the Bricanyl MDI and the effect of different nebulisers on the dose emitted were also studied using twelve healthy volunteers (6 females) for each study. A fast inhalation flow using the Bricanyl Turbuhaler resulted in significantly higher amounts of terbutaline excreted 0.5 and 24 hour post dosing (2 doses of 500µg terbutaline sulphate from Bricanyl Turbuhaler) than slow inhalation flow (p<0.001). The Bricanyl MDI alone resulted in a significantly higher amount of terbutaline excreted 24 hour post dosing (2 doses of 250µg terbutaline sulphate from Bricanyl MDI) and significantly lower amounts excreted 30 minutes post dosing than the MDI+Spacers. The AMAX provided a greater amount of urinary terbutaline excreted 30 minutes post dosing than the APLUS and Nebuhaler. The Aeroneb Pro resulted in significantly higher amounts of terbutaline excreted 0.5 and 24 hour post dosing (1 dose of 5mg/2ml terbutaline sulphate from Bricanyl respule) than a Sidestream Jet nebuliser (p<0.001). Further application of the method was demonstrated by 12 (6 female) COPD non-invasive mechanically ventilated patients. One dose of 2mg in 0.8ml terbutaline sulphate respiratory solution from Aeroneb Pro and one dose of 5mg in 2ml terbutaline sulphate respiratory solution from Sidestream jet nebuliser resulted in a similar amounts of urinary terbutaline excreted 0.5 and 24 hour post dosing. The results were consistent with the results of the ex-vivo study performed on the same patients. The thesis highlights extension of the urinary pharmacokinetic method following inhalation to terbutaline and its application in volunteer and patient studies.Egyptian Culture Office in UK, Missions Department in Egyp

The role of end-use energy conversion efficiency as a climate mitigation tool

Historically, conversion efficiency improvements have revolutionised the energy system, yet to reach climate targets, the scientific community agrees that even higher levels of energy efficiency improvement are required. When focusing on technical options there are two classes of technologies: conversion devices and passive systems. This thesis explores the role that the former can have in reducing energy demand with the aim of providing advice on the prioritisation and differentiation of policy action among these devices. The analysis is divided into three main chapters. First, issues with data quality were identified a cause for the marginalisation of end-use efficiency measures compared to supply-side ones. For the first time, the uncertainty of end-use statistics is quantified by drawing from methods developed in the field of Material Flow Analysis using the United Kingdom as a case study. The majority (85%) of the Useful energy balance uncertainties are below an acceptable (±25%) threshold. Therefore, end-use statistics are deemed sufficiently reliable for the development of policy-relevant indicators. Second, the technical efficiency limits for six widely used conversion devices are determined stochastically based on a combination of engineering models and review of the technical literature. The resulting limits are used to calculate the energy saving potential of each conversion device, and each design parameter for the United Kingdom. It is shown that 25% of the UK’s Final energy demand could be avoided if all conversion devices reached their technical limit. On the other hand, 15% savings could be achieved by applying available technology. Nonetheless, improvement margins vary substantially among devices meaning that strategies involving different balances of R&D and technology adoption incentives are required for each technology. Third, the International Energy Agency’s Energy Technology Perspective’s modelling results are used to assess the saving potential of seven conversion devices in three emission scenarios. Between 3.2% and 4.2% of cumulative energy demand between 2014 and 2060 can be saved thanks to improvements in conversion efficiency. Most savings come from improved internal combustion engines in all scenarios. Carbon emission savings from conversion efficiency are highest in the baseline scenario and lowest in the most ambitious climate scenario due to negative emissions in electricity generation nullifying the effect of improvements in electricity-using devices. No technology was found to breach the technical efficiency limit in the IEA’s assessment meaning that expected efficiency improvements technically realistic. Current innovation activity in energy conversion devices is quantified by means of patent counts and it’s compared to the distribution of saving potentials. It is found that innovation in air coolers and heat pumps is low when compared to the expected efficiency savings from these technologies. The thesis results are useful for directing policy and investment priorities for conversion devices as function of the ambition of the climate scenario. The analysis of technical efficiency limits for conversion devices, help improve energy system models. The novel uncertainty method provides a powerful tool for supporting energy planning and decision making