Control of Shroud Leakage Loss and Windage Torque in a Low-Pressure Turbine Stage

As new aeroengine architectures move to larger diameter fans and rotors, the associated increase in weight will need to be counterbalanced by lighter, more compact, and more efficient low-pressure turbines (LPT). Efficiency gains in LPTs can be achieved by reducing the losses associated with the shroud leakage flows. Flow control studies on the topic have traditionally focused on reducing the mixing loss, which constitutes a considerable proportion of the total loss. Nonetheless, increasing engine speeds are driving additional gains obtained by also targeting the reduction of windage losses. Developing a flow control solution with the dual objective of reducing over-tip cavity mixing and windage losses has not previously been attempted. This is a challenge due to conflicting flow control requirements and geometric constraints. Reducing windage loss generally requires increasing the swirl ratio of the leakage flow, while reducing mixing loss requires reducing this ratio to match that of the main gas path. The current work proposes a novel flow control solution to successfully achieve this purpose through the emerging technology of additive manufacturing. The successful flow control concept (FCC) was developed through numerical simulation, printed using an additive manufacturing process, and validated in a purpose-built rig. Experiments and computations were consistent with a cumulative reduction in cavity windage of 16%. The FCC is estimated to increase the mechanical efficiency of the turbine stage in isolation by 1%

Control of Shroud Leakage Loss and Windage Torque in a Low-Pressure Turbine Stage

As new aeroengine architectures move to larger diameter fans and rotors, the associated increase in weight will need to be counterbalanced by lighter, more compact, and more efficient low-pressure turbines (LPT). Efficiency gains in LPTs can be achieved by reducing the losses associated with the shroud leakage flows. Flow control studies on the topic have traditionally focused on reducing the mixing loss, which constitutes a considerable proportion of the total loss. Nonetheless, increasing engine speeds are driving additional gains obtained by also targeting the reduction of windage losses. Developing a flow control solution with the dual objective of reducing over-tip cavity mixing and windage losses has not previously been attempted. This is a challenge due to conflicting flow control requirements and geometric constraints. Reducing windage loss generally requires increasing the swirl ratio of the leakage flow, while reducing mixing loss requires reducing this ratio to match that of the main gas path. The current work proposes a novel flow control solution to successfully achieve this purpose through the emerging technology of additive manufacturing. The successful flow control concept (FCC) was developed through numerical simulation, printed using an additive manufacturing process, and validated in a purpose-built rig. Experiments and computations were consistent with a cumulative reduction in cavity windage of 16%. The FCC is estimated to increase the mechanical efficiency of the turbine stage in isolation by 1%

Influence of Strain Rate and Temperature on the Multiaxial Failure Stress Locus of a Polyamide Syntactic Foam

This study introduces a comprehensive experimental methodology allowing for the direct measurement of the rate dependent multiaxial response of polymer syntactic foams under combined direct-shear loading. The combined tension-torsion behaviour of a syntactic foam and its rate dependence are investigated for the first time.Dynamic tension-torsion experiments were conducted using a newly developed Tension-Torsion Hopkinson Bar (TTHB) enabling the measurement of the combined tensile-shear response of engineering materials at high rates of strain.The response and multiaxial failure envelope of a polyamide syntactic foam were experimentally measured and analysed to determine the combined influences of stress state, strain rate, and temperature. The multiaxial failure stress locus was defined in both the normal versus shear stress space and the principal stress space, providing a comprehensive characterisation of the behaviour of the material under various loading and environmental conditions.The suitability of existing pressure dependent failure criteria to represent the measured experimental data was also assessed. The Drucker-Prager pressure dependent criterion proved to be effective in capturing the measured quasi-static and dynamic multi-axial stress loci at different temperatures.The effects of temperature, loading rate and stress state on the deformation and failure modes were analysed by means of SEM micrographs of the tested samples

Electrochemical sensors for the detection of immune checkpoint related proteins and their role in cancer companion diagnostics

Cancer companion diagnostics are incredibly important in helping to determine whether a patient will benefit from immune checkpoint inhibitor (ICI) treatment. Determining the chances of treatment success helps to inform clinicians to make the best treatment decisions for a particular patient. Many immune checkpoint related proteins show potential as biomarkers for ICI success, such as the checkpoint proteins themselves, cytokines, interleukins and other immune response related proteins. The most investigated checkpoint inhibitor protein is Programmed Death Ligand 1 (PD-L1), which is used as a biomarker in clinical diagnostic tests but with some limitations. In the near future, tests for many different biomarkers will start becoming commercially available along with tests for multiple biomarkers simultaneously, giving an even better prediction of potential ICI success. Electrochemical sensors are a high sensitivity point of care diagnostic technique that can have the potential to achieve detection of multiple biomarkers at once. The main problem facing this field is improving their sensitivity to be able to detect the incredibly low concentrations of biomarkers found in liquid biopsy samples. Many methods such as enhancing an electrode surface with high conductivity materials or increasing the measured electrochemical signal via signal amplifying molecules have been investigated with promising results. This review investigates the potential biomarkers relevant to predicting ICI success, as well as the current electrochemical sensors that have been developed to determine the expression levels of these proteins

Problem formulation for theorizing at the frontier:An Oliver Williamson inspired approach

Ostensibly, the evolving science of strategic management is geared towards addressing vexing managerial problems. In practice, however, scholars in the field have a marked tendency to formulate problems to fit existing theoretical and methodological frameworks, even at the expense of committing type III errors. While the tendency to do so is often attributed to institutional pressures and the like, we submit that an equally or more compelling reason is the absence of guidance on how to engage in problem-driven inquiry and formulate problems to explore theoretical frontiers. In the strategic management field’s problem-solving spirit, we provide an approach for problem formulation and theorizing inspired by Oliver Williamson and two of his accomplished advisees. We abduce five principles and six dialectic conversations. We synthesize these principles and dialectics into five protocols to enable canonical problem formulation directed at exploring theoretical frontiers, that is, a “white space.” Using a recently rejected manuscript, we show how our Williamson inspired approach can be useful in formulating problems that are both managerially relevant and theoretically fruitful

Ingress Wave Model with Purge-Mainstream Density Ratio

Aeroengines operate with a cooling flow (purge) at a significant purge-mainstream density ratio (DR), which is principally created by the differences in temperatures of these two streams. This paper will show there is a profound influence of DR on ingress, purge flow rates, and sealing effectiveness - all crucial to the superordinate aim of achieving a high thermodynamic efficiency for the engine. A new theoretical (low-order) model is introduced to enable the engine designer to flexibly predict the required purge to prevent ingress over a range of typical operating conditions. The Ingress Wave Model is based on the physical principle that unsteadiness, in the form of large-scale rotating instabilities, forms a circumferential pressure gradient driving fluidic motion against the Coriolis force. The shear created by the difference in tangential momentum between adjacent flow streams is assumed to be the primary mechanism in the process. This allows a set of equations to be derived from dimensional analysis and the assumption that flow entrainment is a function of the relative egress momentum and ingress density. The model is validated against data collected at both DR = 1 and 1.52, with good quantitative agreement across a range of purge and annulus flow conditions. Typical engine design practice exploits information captured in experimental rigs operating in benign conditions at low technology readiness level (TRL) and DR = 1. The new model is used to scale such data collected from six experimental facilities to the density ratios expected in current state-of-the-art (DR = 1.5) and future (DR = 2) engines. The result is a requirement for significantly reduced purge, with profound practical implications for the engine designer, in particular for future engines which operate at higher purge-mainstream density ratios.</p

Electrochemical sensors for the detection of immune checkpoint related proteins and their role in cancer companion diagnostics

Cancer companion diagnostics are incredibly important in helping to determine whether a patient will benefit from immune checkpoint inhibitor (ICI) treatment. Determining the chances of treatment success helps to inform clinicians to make the best treatment decisions for a particular patient. Many immune checkpoint related proteins show potential as biomarkers for ICI success, such as the checkpoint proteins themselves, cytokines, interleukins and other immune response related proteins. The most investigated checkpoint inhibitor protein is Programmed Death Ligand 1 (PD-L1), which is used as a biomarker in clinical diagnostic tests but with some limitations. In the near future, tests for many different biomarkers will start becoming commercially available along with tests for multiple biomarkers simultaneously, giving an even better prediction of potential ICI success. Electrochemical sensors are a high sensitivity point of care diagnostic technique that can have the potential to achieve detection of multiple biomarkers at once. The main problem facing this field is improving their sensitivity to be able to detect the incredibly low concentrations of biomarkers found in liquid biopsy samples. Many methods such as enhancing an electrode surface with high conductivity materials or increasing the measured electrochemical signal via signal amplifying molecules have been investigated with promising results. This review investigates the potential biomarkers relevant to predicting ICI success, as well as the current electrochemical sensors that have been developed to determine the expression levels of these proteins

Mass and Heat Exchange in Rotating Compressor Cavities With Variable Cob Separation

Next generation aeroengines will operate at ever-increasing pressure ratios with smaller cores, where the control of blade-tip clearances across the flight cycle is an emerging design challenge. Such clearances are affected by the thermal expansion of the compressor disks that hold the blades, where acute thermal stresses govern operating life. The cavities formed by corotating disks feature a heated shroud at high radius and cooler cobs at low radius. A three-dimensional, unsteady and unstable flow structure is induced by destabilizing buoyancy forces. The radial distribution of disk temperature is driven by a conjugate heat transfer at Grashof numbers of order⁠. Such flows are further influenced by the heat and mass exchange with an axial throughflow of cooling air at low radius, where the interaction depends on the Rossby number and separation of the disk cobs. This paper is the first to study the effect of cob separation ratio on mass and heat exchange for compressor cavities. A model is developed to predict the cavity-throughflow interaction, and disk and fluid-core temperatures. The judicious use of a physics-based methodology provides reliable, reduced-order solutions to the complex conjugate problem, thereby making it appropriate for practical engine thermo-mechanical design. The model is validated by detailed experimental measurements using the Bath Compressor Cavity Rig, where variable disk cob spacings were investigated over a range of engine-representative conditions. The unsteady pressure measurements collected in the frame of reference of the rotating disks reveal new insight into the fundamentally aperiodic nature of the flow structure. This new understanding of heat transfer informs an expedient reduced-order model and enables more efficient design of future high pressure-ratio aeroengines

Tracking of Bristle Tip Deflections to Demonstrate Blow-Down in Brush Seals

Sealing in gas turbines is paramount to overall performance and efficiency. Brush seals offer superior performance compared to other sealing solutions commonplace in modern turbomachinery. When subjected to a pressure load, a ring of flexible fine wire bristles—fitted at a lay angle to the radial plane—compact to resist the oncoming flow and deflect towards the rotor in a process known as blow-down. This study employs Digital Image Correlation (DIC) to track individual bristle tips in three spatial axes throughout a large-scale brush seal test facility. This is the first-time direct measurements of blow-down throughout the bristle pack have been presented, providing a unique insight into the mechanical behavior of brush seals. Increased magnitudes of blow-down and axial bristle deflection were demonstrated in upstream bristle rows and at larger clearances. Analysis of these results in conjunction with the interrogation of the inter-bristle pressure field proved that blow-down is more prevalent for pressure relieving (PR) brush seals in comparison to conventional configurations. The reduction in the through-flow clearance area resulted in a significant enhancement in sealing performance for a clearance seal, highlighting a key advantage of the pressure relieving back plate design

Influence of Strain Rate and Temperature on the Multiaxial Failure Stress Locus of a Polyamide Syntactic Foam

This study introduces a comprehensive experimental methodology allowing for the direct measurement of the rate dependent multiaxial response of polymer syntactic foams under combined direct-shear loading. The combined tension-torsion behaviour of a syntactic foam and its rate dependence are investigated for the first time.Dynamic tension-torsion experiments were conducted using a newly developed Tension-Torsion Hopkinson Bar (TTHB) enabling the measurement of the combined tensile-shear response of engineering materials at high rates of strain.The response and multiaxial failure envelope of a polyamide syntactic foam were experimentally measured and analysed to determine the combined influences of stress state, strain rate, and temperature. The multiaxial failure stress locus was defined in both the normal versus shear stress space and the principal stress space, providing a comprehensive characterisation of the behaviour of the material under various loading and environmental conditions.The suitability of existing pressure dependent failure criteria to represent the measured experimental data was also assessed. The Drucker-Prager pressure dependent criterion proved to be effective in capturing the measured quasi-static and dynamic multi-axial stress loci at different temperatures.The effects of temperature, loading rate and stress state on the deformation and failure modes were analysed by means of SEM micrographs of the tested samples