http://bura.brunel.ac.uk/handle/2438/8626 Thu, 18 Jun 2026 23:15:40 GMT 2026-06-18T23:15:40Z http://bura.brunel.ac.uk/handle/2438/33464 Title: Leading edge blowing: A targeted approach to reduce aerofoil noise Authors: Bakrania, Yash Abstract: This thesis investigates steady leading-edge blowing as an active flow-control strategy for reducing aerofoil self-noise from a NACA 65(12)-10 aerofoil. The work considers three noise mechanisms: trailing-edge tonal noise, leading-edge broadband turbulence-interaction noise, and separation-stall noise. Far-field acoustic measurements are combined with hot-wire anemometry, surface-pressure measurements, and aerodynamic force measurements so that the acoustic response can be interpreted alongside the underlying flow physics. The first part of the study examines trailing-edge tonal noise. The results show that leading-edge blowing can strongly suppress the discrete tonal radiation associated with a suction-side laminar separation bubble and the aeroacoustic feedback loop it supports. Under the most effec-tive conditions, tonal levels are reduced by up to 20–25 dB. The main effect is not a large shift in tonal frequency, but a weakening of the organised instability and of the flow-acoustic coupling that sustains the tone. The second part addresses leading-edge broadband noise under both isotropic and anisotropic turbulent inflow conditions. Here, the effectiveness of the control is found to depend strongly on the incoming turbulence, particularly its length scale, anisotropy, and spatial coherence. When the actuation is suitably matched to the inflow, measurable broadband reductions are achieved. These reductions are linked to a weakening of spanwise coherence and to a shortening of the effective interaction length at the leading edge, showing that the control acts by modifying the structure of the incoming disturbances before they are scattered into sound. The final part of the thesis considers separation-stall noise at high incidence. In this regime, leading-edge blowing delays the onset of stall-related separation by up to about 3.7◦ and reduces the associated low-frequency acoustic radiation by up to 5 dB. The measurements show that the blowing modifies the separated-flow topology and weakens the large-scale unsteady structures that dominate the noise generation process. Overall, the thesis shows that steady leading-edge blowing is more than a case-specific method of reducing noise. It acts as a targeted control strategy that can influence several aerofoil self-noise mechanisms through changes to the near-field flow structure. The central finding is that noise reduction is achieved by weakening the coherence and organisation of the source regions that radiate most efficiently. This provides a basis for the future design of quieter aerofoils and blade sections using tunable leading-edge actuation in applications such as aircraft, turbomachinery, propellers, and wind turbines. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London Thu, 01 Jan 2026 00:00:00 GMT http://bura.brunel.ac.uk/handle/2438/33464 2026-01-01T00:00:00Z http://bura.brunel.ac.uk/handle/2438/33462 Title: Microgrid techno-economic optimisation for benchmarking operational net-zero metrics in a hotel typology Authors: Shinku, Benedict Tertsea Abstract: Hotels account for about 1.5% of global energy-related emissions and an estimated 0.6% of UK energy demand in the operational phase. Hence, they have significant potential to contribute to sustainability and Net Zero through reduction in energy and carbon intensity. In the UK, the ongoing reform of the Energy Certificate System to include headline metrics suitable for monitoring energy efficiency, and the introduction of the UK Net Zero Carbon Buildings Standard (UKNZCBS) are beneficial initiatives for the achievement of net zero in hotels. This work applied a quantitative case study research design framed on a three-pronged methodology to evaluate feasibility of operational net zero for a mid-range (3-star) non-resort hotel located in London, UK over a 28-year lifetime. A baseline dynamic simulation model of the hotel (with 2022 as base year) was developed in IESVE™ and calibrated against the measured power consumption, using ASHRAE-14 Guidelines. The calibration confirmed the model within the verification acceptance range (NMBE= 4.75%, CvRMSE = 12.6%). Additional models were developed from the calibrated model by application of 30 energy efficiency measures and future weather files under SSP2-4.5 scenarios. Evaluation of the energy and carbon performance of the models between the baseline year and 2050 showed that climate change resulted in a 15% and 230% reduction in EUI and emissions, respectively. The highest reduction in EUI (40%) over the corresponding period occurred from reduction of envelope U-values to conform with the “2025 UK Future Buildings Standard” (UKFBS), lighting retrofit from fluorescent to LED, and application of Adaptive Ventilation (AV) strategy, translated to 236% emissions reduction. The second part of the methodology entailed creation of a solar- PV generation model in HelioScope™ and in the third part, electrical and thermal loads from IESVE™ and the solar-PV generation HelioScope™ were coupled to a microgrid model in HOMER Pro™, with random day-to-day and timestep variability of 10% and 20%, respectively. The variabilities accounted for the sensitivities of the energy profile to uncertainties in weather, occupancy and operational schedule, service levels, and occupant energy behaviour. The microgrid model was simulated under existing and projected macroeconomic (medium GDP growth) conditions, reference energy and emissions forecasts, and sensitivity variables (expected inflation rate, grid carbon intensity and minimum renewable fraction). The least cost microgrid yielded an IRR (6.2%), ROI (4.1%), discounted payback (12 years) and energy cost savings of £109,698. The benchmark values of operational net zero metrics calculated from the least-cost microgrid model were: EUI of 256 kWh/m2 (EUIel = 105 kWh/m2, EUIth = 406 kWh/ m2), CEI (87 CO2/m2), ECI (29.48 £/m2). The solar-PV generation model for the case study gave: (40.1 kW capacity, 43.8 MWh annual production, 75.5% Performance Ratio, and 906 kWh/kWp specific yield). Comparison of the results to the limits and targets of operational net zero metrics in the UK Green Building Council (UKGBC) Paris Proof Methodology (PPM), UKNZCBS and Cornell Hotel Sustainability Benchmark Index (CHSBI) for fifty 3-star non-resort hotels located in London, UK. The computed EUI, CEI and ECI values were significantly-above the CHSBI benchmarks due to disproportionate thermal and electrical energy demand. The retrofit pathway with the highest EUI reduction did not lead to operational net zero in 2050 under the UKGBC-PPM, nor the UKNZCBS frameworks. In addition, the target 40 kWh/m2 of Gross Internal Area (GIA) for onsite renewable energy generation specified in the UKNZCBS was not met. Unlike the hotelspecific room-night normalised energy, carbon, and cost metrics such as kWh/roomnight, kgCO2e/room-night and RevPAR (Revenue per Available Room, the metrics in this study were floor-area normalised to align with the UK Building Regulations thereby easing regulatory oversight of hotel energy efficiency and decarbonisation. The methodology of this work is a novel contribution to the planning of energy efficiency and net zero projects, applicable to any building typology and the benchmark values of EUI, CEI and ECI are a useful addition to the body of evidence for operationalisation of the UKNZCBS. Regardless, the generalisability of the results is limited by the purposive sampling technique adopted to select the case study, and the application of deterministic safety margins to electrical and thermal loads in the microgrid model to account for uncertainties in weather, occupancy, and operational schedules. Hence, statistical sampling and detailed sensitivity and uncertainty analysis should be incorporated in future research to enhance the application of the results to energy efficiency and decarbonisation policy and project planning. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London Thu, 01 Jan 2026 00:00:00 GMT http://bura.brunel.ac.uk/handle/2438/33462 2026-01-01T00:00:00Z http://bura.brunel.ac.uk/handle/2438/33396 Title: Molecular dynamics investigation of nanobubble formation and their role in thermophysical and thermochemical behaviour of polar and nonpolar liquids Authors: Hassanloo, Hamidreza Abstract: The rapid increase in atmospheric greenhouse gas concentrations, particularly CO₂ emissions from anthropogenic activities, poses a significant global challenge requiring urgent mitigation. Key strategies include improving energy efficiency through advanced thermal management and heat-transfer technologies, developing engineered working fluids, and deploying next-generation fuels alongside carbon capture and storage (CCS) technologies. Growing attention is being directed toward nanoparticle incorporation and nanoscale mechanisms to advance these strategies by enhancing fluid and fuel properties, accelerating hydrate formation, and improving overall process efficiency. Nanobubbles (NBs), defined as gaseous cavities smaller than 1 μm, exhibit exceptional stability, high surface-to-volume ratios, and the capacity for free radical generation, highlighting their potential in energy, power, and environmental applications. A fundamental understanding of NB nucleation and behaviour is essential to elucidate their effects on the thermophysical properties of host liquids and on key processes such as CO₂ hydrate formation and combustion, which are difficult to capture experimentally. Classical and reactive molecular simulation techniques provide a rigorous approach for probing the influence of NBs on intrinsic material behaviour, process kinetics, and reaction pathways at the molecular scale. Integrating data-driven approaches with molecular dynamics (MD) simulations enables systematic characterization of NB dynamic behaviour and properties. This study investigates the possible formation and effects of NBs generated by nitrogen (N₂), oxygen (O₂), carbon dioxide (CO₂), and hydrogen (H₂) on the thermophysical properties of four host liquids, including dodecane, isooctane, water, and methanol, examines solid–liquid–gas interactions in graphene-enhanced water and methanol nanofluids (NFs), explores the phase transition and thermal behaviour of NB-enhanced dodecane and its combustion processes, and evaluates their potential impact on CO₂ hydrate formation using classical and reactive MD simulations. Furthermore, the DBSCA (density-based spatial clustering of applications with noise) algorithm was utilised to analyse the formed NB clusters, assessing their size, density, and motion over time in water and methanol as polar and alcoholic host liquids. The findings reveal that the formation of NBs reduces the density of polar and alcoholic liquids due to the establishment of a nanolayer. The presence of NBs and dispersed graphene increases the viscosity of water-based NFs but decreases viscosity in graphene-methanol NFs containing two-atom gases. Under optimal thermodynamic conditions, NBs markedly enhance hydrate formation by providing hydrophobic nucleation sites, generating local concentration gradients, and accelerating clathrate kinetics, with hydrogen and nitrogen NBs further promoting growth through rapid core-to-solution diffusion. Low temperatures suppress molecular mobility and hinder these effects. At elevated pressures, NBs exhibit a dual role, with a pressure-dependent shift from NB-induced interfacial ordering to bulk-phase interactions. In organic host liquids, NB formation and coalescence are governed by molecular interactions between the host liquid and the dispersed gas, as demonstrated by oxygen forming NB in dodecane but not in isooctane. The presence of NBs, particularly hydrogen NB, depresses the liquid-to-solid transition temperature of dodecane and enhances both thermal conductivity and specific heat capacity, with nitrogen NB yielding the highest thermal conductivity increase of approximately 14%. Nitrogen and hydrogen NBs also exhibit excellent stability over a wide temperature range, making them promising candidates for high-temperature applications. Furthermore, nitrogen NB reduce the activation energy to 52.89 kcal/mol in samples with a density of 0.17 g/mL by promoting the formation of intermediates and radicals, thereby accelerating dodecane consumption, whereas oxygen NB increase the activation energy to 66.93 kcal/mol under the same conditions. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London Thu, 01 Jan 2026 00:00:00 GMT http://bura.brunel.ac.uk/handle/2438/33396 2026-01-01T00:00:00Z http://bura.brunel.ac.uk/handle/2438/33217 Title: Development and investigation of CO₂ heat pump for domestic buildings Authors: Qayyum, Usman Abstract: The residential building sector in the UK, is responsible for 25% of energy consumption and 17% of CO2 emissions, with space heating accounting for 65% of this. More than 80% of existing dwellings use gas boilers for space heating and domestic hot water and to decarbonise this energy input, heat pumps are considered to be a key technology. Despite this potential, heat pumps have so far failed to gain wide market penetration in the UK due to high capital and installation costs, inability to provide high enough temperatures to be used with existing radiators in retrofit applications and requirement for thermal energy storage. This project makes a contribution to addressing this challenge by investigating the development of a CO2 high-temperature heat pump and its integration with thermal energy storage. to satisfy space heating requirements for existing and new dwellings, facilitate the use of low tariff electricity and provide demand services to the grid. The investigations involved: i) dynamic simulations of 2 and 3 bedroom semi-detached dwellings to establish space and domestic hot water energy demand; ii) extensive experimental investigations on a CO2 heat pump developed at Brunel to establish operating characteristics; iii) simulation of the heat pump to enable design optimisation; iv) investigations on the performance and integration of the heat pump with a Phase Change Material (PCM) thermal energy storage system. The work has demonstrated that: i) The CO2 heat pump can provide significant flexibility in the provision of different water delivery temperatures from 40 oC to 80 oC to satisfy both domestic hot water and space heating demand and the requirement of different types of heat emitter in existing and new dwellings; ii) Using the performance characteristics of the heat pump, the optimum hot water storage tank size for the 4 bedroom domestic dwelling was determined to be between 200 and 300 litres: iii) Using current domestic electricity and gas prices and CO2 emission factors, the annual running cost of the heat pump was found to be approximately double that of the gas boiler due to the large difference between gas and electricity prices, but offering 40% reduction in CO2 emissions; iv) Heat pump design and optimisation work using a simulation model developed for this purpose is expected to lead to an increase in increase the seasonal COP of the heat pump and its cost effectiveness over gas boilers; v) Integration of the heat pump with a PCM storage tank designed and using Rubitherm RT70HC PCM has shown that the heat pump can charge the storage tank effectively, leading to a 50% reduction in the storage volume required for the same thermal energy storage capacity compared to hot water storage. Description: This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London Wed, 01 Jan 2025 00:00:00 GMT http://bura.brunel.ac.uk/handle/2438/33217 2025-01-01T00:00:00Z