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Fundamental Model for Compressor Cavity Heat Transfer: Theory and Validation
Get PDFThe buoyancy-driven flow inside compressor cavities is three-dimensional, unsteady and features a large range of time- and length-scales. The temperature and rotation of the fluid core of the cavity are influenced by an exchange (and recirculation) of enthalpy and momentum with an axial throughflow of cooling air at low radius. The complexity of the flow and conjugate nature of the heat transfer to the discs creates a challenge for the aero-engine designer when calculating thermal stresses, radial expansion, and blade-tip clearances.This paper presents a low-order model to predict the radial variation of disc and fluid-core temperatures, and the mass exchange (entrainment) to the rotating cavity. Fundamental physical principles and experimental data are used to create a single set of Rayleigh-Grashof correlations for heat transfer and radial mass flow of buoyant plumes. The model is applied to eleven test cases from experimental rigs at Bath, Dresden and Sussex, each with unique instrumentation, thermal boundary conditions, geometries and throughflow swirl. Empirical correlations for exchange and recirculation mass flow were determined for each rig using a common theoretical methodology. The model captures the heat and mass transfer characteristics with accuracy quantified relative to experimental data.New experimental data from the Bath Compressor Cavity Rig is used to validate the model under conditions of asymmetrical heating, demonstrating the effects associated with the axial gradient of temperature in the compressor are captured appropriately. The consistent agreement with experimental data and correlation methodology demonstrates a robust framework appropriate for application to thermo-mechanical design codes in the aero-engine
Scaling Sealing Performance Across Engine Operating Conditions
Get PDFThe Secondary Air System in an aero-engine uses relatively cool purge from the compressor to limit the ingress of hot annulus gases into vulnerable turbine cavities through rim seals. Superfluous use of purge is inefficient, while insufficient use leads to thermal degradation of highly-stressed turbine components. This study establishes a predictive design tool to fully characterise a rim seal across the performance envelope of the engine. Physically-informed low-order models are important in the engine design process. The Ingress Wave Model uses a single, empirically-correlated parameter to physically link the shear-driven unsteadiness in the cavity with the swirl in the annulus. In this paper, newly-collected and existing experimental data from three facilities and rim seal geometries demonstrated that this unsteadiness is a linear function of the annulus swirl, with the superposition of purge creating a weak, secondary effect. The novel introduction of the linear correlation enables predictions of sealing effectiveness across the entire engine operating range from just two data points. A larger set of data is shown to improve the accuracy and robustness. Here the method is validated by data collected at low technology readiness level (TRL). The methodology could be applied to data collected from a high TRL demonstrator engine or computational fluid dynamics. This will reduce the number of demonstrator experiments (and associated costs) during design iterations. This paper provides an original scaling methodology in the practical context of the engine design process, including the effects of density. Aero-engines operate with a significant purge-mainstream density ratio (DR), due to differences in the temperatures of the two streams. The methodology incorporates predictions of DR and is further validated against data collected at DR = 1 and 1.5. The model demonstrates that neglecting DR will provide significantly underpredicted rim seal performance.</p
Enhanced piezoelectric properties of additively manufactured BCZT with an oriented ceramic lamellar structure formed via vat photopolymerization
Get PDFAdvances in additive manufacturing have enabled the creation of piezoceramic materials with complex architectures. However, the lack of a clear structural design strategy limits their performance and application in high-performance piezoelectric transducer devices. This work outlines the additive manufacture of a novel sandwich architecture based on a porous (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3 (BCZT) layer containing oriented ceramic lamellae. The d33 charge coefficients and g33 voltage coefficients of the optimized porous ceramic were 1.16 times and 2.11 times higher than those of the dense counterparts respectively. After electroding the aligned lamellar ceramic with an indium tine oxide film a piezoelectric sensor was obtained which, when subject to a pressure of 7.5 MPa, produced a open circuit voltage of 173 V. This paper provides a new structural design strategy to effectively improve the performance of piezoelectric ceramics, and provides new opportunites for the design and production of additive manufactured piezoelectric sensors and energy harvesting devices.</p
The Influence of Axial Throughflow Swirl on Buoyancy-Induced Flow in a Compressor Cavity
Get PDFNext-generation aero-engine compressors will operate with overall pressure ratios exceeding 70:1. This will require shorter compressor blades, presenting a challenge to the designer when predicting tip clearance and efficiency. Buoyancy-induced flow within co-rotating compressor discs drives the heat transfer that determines rotor expansion and the resulting blade-tip clearance. This inherently unstable flow is influenced by the radial temperature distribution of the discs, rotational speed, as well as enthalpy and momentum exchange with an axial throughflow of cooled air at low radius. Due to the rotation of the engine compressor, this throughflow may become swirled, altering the temperature, mass exchange and swirl within the rotating cavity. The University of Bath Compressor Cavity Rig has been adapted to introduce pre-swirl into the axial throughflow by passing it through rotating holes. The effects of inlet swirl have been characterised in terms of Rossby and Reynolds numbers. Measurements of disc temperature, shroud heat flux and unsteady pressure in the rotating frame of reference are used to quantify the effects of ingestion (entrainment) of fluid into the cavity. The unsteady dynamics and rotation of the core relative to the disc have been measured in both the stationary and rotating frames of reference with consistent results. A single correlation between shroud Nusselt and Grashof numbers has been established, effectively capturing the impact of swirl, Rossby number and free convection
The Adverse Effect of Pre-Swirl on Ingestion in a Downstream Cavity
Get PDFGas turbine designers demand accurate predictions of metal temperature to ensure acceptable operating life of components experiencing high thermal stress. Rotor-stator cavities ingest hot mainstream gas through rim seals when inadequately purged with relatively cool air bled off the compressor. Superfluous use of purge, and any associated windage increase, creates a parasitic loss in overall efficiency. Shear interaction caused by the difference in swirl between the purge and mainstream flow is a principal driver for ingestion; pre-swirled purge flow has the potential to alter the swirl gradient. This paper presents the first assessment of purge conditioning in a downstream cavity.An experimental campaign was conducted in a new aeroengine representative 1.5-stage test facility designed to facilitate expedient changeover of modular components in the downstream stator assembly. Purge flow in the downstream cavity was supplied through a series of angled injectors contained in a single component at mid-radius. Three co-swirled injection angles were tested.Measurements of CO2 gas concentration, static pressure and swirl were taken in the cavity to examine the relationship between purge-mainstream swirl gradient and ingress downstream of a rotor blade. The aero-engine designer must balance caution when employing pre-swirl to reduce disc windage; co-swirled purge increased the purge-mainstream swirl gradient and subsequently increased shear-driven ingestion
“It’s Like All of My Senses and My Body Become More Awakened”:Autistic Adult’s Experiences of Attending Live Music
Get PDFBackground: Up to 94% of Autistic people have sensory responsivity differences, associated with experiences that can range from being distressing to highly pleasurable. Despite the importance of live music in fostering social inclusion, many venues and events are not inclusive, creating barriers for Autistic people. Given the challenges Autistic people face in accessing live music events, our study aimed to explore their experiences to improve inclusivity, using a critical realism epistemological approach. Methods: We conducted a qualitative study with 16 Autistic adults aged 21-52 through online focus groups (n = 13), individual interviews (n = 1), and email exchanges (n = 2), allowing for spoken or typed communication. Each focus group lasted 1 hour, and we analyzed the data using reflexive thematic analysis, following good practice guidelines. Results: We developed four main themes and two subthemes: (1) “This is a military operation”—Planning to manage uncertainty and overwhelm; (2) “Hating a crowd and loving a crowd at the same time”—Social connection; (3) The duality of an intense sensory environment; (3a) “The music, the vibrations bring out the colors … in my mind”—Immersive sensory joy; (3b) “My brain is screaming at me”—Sensory overload; and (4) “I think the biggest difference, always, is the staff”—Combating stigma and creating safe spaces. Conclusions: Our study highlights the positive and negative aspects of attending live music for Autistic people, offering actionable recommendations for inclusivity. Key suggestions include providing advance information, earplugs/quiet spaces, minimizing crowd exposure, and ensuring staff are trained to support Autistic attendees. These measures can help create accessible, enjoyable live music experiences, fostering social connections and reducing isolation for Autistic people.</p
Towards A New Skills Framework for the UK’s Left-behind Regions: Insights for Place-Based Policy
No full textAn Automatic HTS Flux Pump with Pulsed Voltage Drive
Get PDFFlux pumps supply current to superconducting magnets without direct electrical contact, eliminating resistive leads and reducing their associated cryogenic load. Automatic flux pumps achieve this by periodically driving a section of the superconductor into the normal state by exceeding its critical current during part of the waveform cycle. Previously reported high-temperature superconductor (HTS) automatic flux pumps rely on bulky drive electronics and nonlinear current waveforms on the primary side for operation. In this work, we present an automatic HTS flux pump that simplifies these requirements by using a pulsed voltage waveform to drive the transformer primary. The system successfully charges an HTS magnet to 120 A dc within 20 s. It utilizes a noninductive bifilar HTS bridge as the self-rectifying element and a resistive copper braid as the transformer secondary. These results demonstrate how automatic flux pumps can be powered by simple dc sources, such as batteries, thereby improving the portability and practicality of HTS magnet power systems.</p
A Generalized Approach for Recovering Time Encoded Signals with Finite Rate of Innovation
Get PDFIn this paper, we consider the problem of reconstructing a function g(t) from its direct time encoding machine (TEM) measurements in a general scenario in which the signal is represented as an infinite sum of weighted generic functions φ(t) shifted in real time points. These functions belong to the class of signals with finite rate of innovation (FRI), which is more general than shift-invariant or bandlimited spaces, for which recovery guarantees were already introduced. For an FRI signal g(t), recovery guarantees from their direct TEM samples wereintroduced for particular functions φ(t) or functions φ(t) with alias cancellation properties leading to g(t) being periodic and bandlimited. On the theoretical front, this work significantly increases the class of functions for which reconstruction is guaranteed, and provides a condition for perfect input recoverydepending on the first two local derivatives of φ(t). We extend this result with reconstruction guarantees in the case of noise corrupted FRI signals. On the practical front, we validate the proposed method via numerical simulations with filters previously used in the literature, as well as filters that are not compatible with the existing results. In cases where the filter has an unknown mathematical function and is only measured, the proposed method streamlines the recovery process by bypassing the filter modelling stage. Additionally, we validate the proposed method using a TEM hardware implementation
One exercise session a day keeps the physio away:effect of a newly designed daily exercise programme on injury prevention in youth football - A randomised controlled trial
Get PDFObjectives: To compare the effect of a newly conceived daily injury prevention programme with FIFA11+ on injury incidence and severity in academy football players. Design: Randomised controlled trial. Setting: Football academy. Participants: Ninety-three male academy football players were randomly assigned to either the control group (FIFA11+ or FIFA11+ Kids) or the intervention group (new injury prevention programme). Main outcome measures: Injury incidence rate (per 1000 hours) and severity (days lost). Results: Over 6 months, the control group recorded 45 injuries (incidence rate = 9.07/1000 hours), while the intervention group recorded 50 injuries (incidence rate = 10.10/1000 hours). The median number of days lost was 16 [95% confidence interval: 11, 27] in the control group and 15 [95% confidence interval: 7, 23] in the intervention group. No significant differences were found in injury incidence or severity between the two groups. Conclusions: The newly conceived injury prevention programme was as effective as the FIFA11+ in reducing injury incidence and severity, thus representing an easy-to-implement injury prevention programme for football academies. Trial registration: The trial was registered with the Australian New Zealand Clinical Trials Registry (ACTRN12623000359639) retrospectively, as it was initially conducted for academic purposes, negating the requirement for prospective registration.</p
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