• Neutral thermal sensation or dynamic thermal comfort? Numerical and field test analysis of a thermal chair.

      Shahzad, Sally; Calautit, John Kaiser; Aquino, Angelo I.; Nasir, Diana S. N. M.; Hughes, Ben; University of Derby; University of Nottingham; University of Sheffield (Elsevier, 2018-01-31)
      Neutral thermal sensation is considered as the measure of thermal comfort in research, as when participants report feeling neutral regarding the thermal environment, they are considered as thermally comfortable. This is taken for granted, and although a few researchers have criticised the matter, still researchers use thermal sensation and the neutral point to assess the thermal conditions in their studies. This study questions the application of thermal neutrality and consequently poses a question on the findings of all the studies that only rely on it. Field studies of thermal comfort were applied in an open plan office in the UK in the winter of 2014. Participants were provided with a thermal chair and before and after using the chair, their views of comfort were recorded, including the ASHRAE seven point scale of thermal sensation, thermal preference, comfort, and satisfaction. The thermal environment was measured and compared against the ASHRAE Standard 55-2013. In addition, numerical modelling was also conducted to investigated the airflow and thermal distribution around the proposed thermal chair with a seated occupant. The results indicated that overall, 72% of the respondents, who did not feel neutral (thermal sensation) before or after using the thermal chair reported to feel comfortable and 65% reported to be satisfied. The results indicated that a neutral thermal sensation does not guarantee thermal comfort of the occupants and that thermal comfort is dynamic and other thermal sensations need to be considered. This study recommends the use of multiple methods (e.g. thermal, preference, decision, comfort, and satisfaction) to assess thermal comfort more accurately. Also, it questions the findings of any research that solely relies on thermal sensation and particularly on the neutral thermal sensation to assess thermal comfort of the occupants. The results also emphasised the importance of the application of numerical modelling in evaluating the thermal performance of the chair.
    • Non-Cyanide Electrodeposited Ag–PTFE Composite Coating Using Direct or Pulsed Current Deposition

      Sieh, Raymond; Le, Huirong; Plymouth University; University of Derby (MDPI, 2016-07-16)
    • A novel application of sustainable material sourcing and building performance monitoring: case study based approach.

      Ceranic, Boris; Rajpurohit, Jaideep Singh; Latham, Derek; University of Derby (2018-06)
      In this research, a novel use of building materials and their impact on the building performance and its climatic adaptability is explored, based on a complex real word case study of a unique low energy sustainable building project. In particular, an innovative use of sycamore and its suitability as a structural and constructional timber has been investigated and reported, considering that is deemed not appropriate for structural applications by current standards. A research method of in-situ longitudinal study has been adopted, concentrating on the performance monitoring and assessment of its structural performance and conditions in which it might deteriorate. On the system level, the climatic adaptability of the building as a whole has been analysed via dynamic performance simulation and compared to the in-situ measurements. This was important in order to develop a holistic building performance monitoring strategy, but in particular, to understand the impact of building microclimate on the sycamore frame and hempcrete components of the external load-bearing wall. So far research has concluded that sycamore can be used as structural and constructional material in building design, but due attention has to be paid to construction detailing and provision of a breathable, low humidity environment with an effective resistance to decay and insect attack. This includes measures that ensure a low equilibrium moisture content conditions, effective ventilation provision and appropriate service class uses.
    • A novel modular design approach to “thermal capacity on demand” in a rapid deployment building solutions: Case study of Smart-POD

      Ceranic, Boris; Beardmore, John; Cox, Adrian; University of Derby; T4 Sustainability; Green 4 Architects (Elsevier, 2017-10-23)
      Designed to address the challenges of a sustainable future and the financial difficulties facing schools, Smart-POD is a unique and innovative research project which provides an alternative to traditional classroom planning. It proposes a rapid deployment building solution, transitory or permanent in its use, modular in design, flexible in set-up and self-sustaining in use, requiring nominal site works and providing for all of its energy demands from renewable energy sources. Its feasibility was tested via a design case study which investigated potential of its novel “thermal capacity on demand” energy performance approach. It combines a modular thermal storage solution capable of balancing heating demand and supply for a low rise, low mass superstructure with renewable technologies and the level of back-up power/services needed. The project team has formed a consortium of stakeholders and consulted on design methodology, performance specification and viability of other markets, the results of which are reported in this paper. The research has, in its final output, established a commercial model based on its design, procurement, financing, supply chain and the manufacturing strategy and is currently negotiating funding for the prototype.
    • A novel one variable first-order shear deformation theory for biaxial buckling of a size-dependent plate based on the Eringen's nonlocal differential law.

      Malikan, Mohammad; Nguyen, Van Bac; Islamic Azad University; University of Derby; Islamic Azad University Mashhad Branch Mashhad Iran (the Islamic Republic of); University of Derby Derbyshire United Kingdom of Great Britain and Northern Ireland (Emerald Group Publishing Limited, 2018-10-04)
      Purpose – This paper aims to present a new one-variable first-order shear deformation theory (OVFSDT) using nonlocal elasticity concepts for buckling of graphene sheets. Design/methodology/approach – The FSDT had errors in its assumptions owing to the assumption of constant shear stress distribution along the thickness of the plate, even though by using the shear correction factor (SCF), it has been slightly corrected, the errors have been remained owing to the fact that the exact value of SCF has not already been accurately identified. By using two-variable first-order shear deformation theories, these errors decreased further by removing the SCF. To consider nanoscale effects on the plate, Eringen’s nonlocal elasticity theory was adopted. The critical buckling loads were computed by Navier’s approach. The obtained numerical resultswere then compared with previous studies’ results using molecular dynamics simulations and other plate theories for validation which also showed the accuracy and simplicity of the proposed theory. Findings – In comparing the biaxial buckling results of the proposed theory with the two-variable shear deformation theories and exact results, it revealed that the two-variable plate theories were not appropriate for the investigation of a symmetrical analyses. Originality/value – A formulation for FSDT was innovated by reconsidering its errors to improve the FSDT for investigation of mechanical behavior of nanoplates.
    • Numerical Analysis of a Wind Catcher Assisted Passive Cooling Technology

      Calautit, John Kaiser; Hughes, Ben; Shahzad, Sally; Nasir, Diana S. N. M.; University of Sheffield; University of Derby (USES 2015 - The University of Sheffield Engineering Symposium, 2015)
      Buildings are responsible for almost 40% of the world energy usage. Heating Ventilation and Air-Conditioning (HVAC) systems consume more than 60% of the total energy use of buildings. Clearly any technology that reduces HVAC consumption will have a dramatic effect on the energy performance of the building. Natural ventilation offers the opportunity to eliminate the mechanical requirements of HVAC systems by using the natural driving forces of external wind and buoyancy effect. One technology, which incorporates both wind and buoyancy driven forces, is the wind catcher. Wind catchers are natural ventilation systems based on the design of traditional architecture. Though the movement of air caused by the wind catcher will lead to a cooling sensation for occupants, the high air temperature in hot climates will result in little cooling to occupants. In order to maximise the properties of cooling by wind catchers, heat transfer devices were incorporated into the design to reduce the supply air temperature. The aim of this work was to investigate the performance of a wind catcher integrated with heat transfer devices using numerical modelling and wind tunnel experiment. The wind catcher model was incorporated to a building, representing a small room of 15 people. Care was taken to generate a high-quality CFD grid and specify consistent boundary conditions. An experimental model was created using 3D printing and tested in a wind tunnel. Qualitative and quantitative wind tunnel measurements were compared with the CFD data and good correlation was observed. The study highlighted the potential of the proposed wind catcher in reducing the air temperature by up to 12 K and supplying the required fresh air rates.
    • Numerical Analysis of a Wind Catcher Assisted Passive Cooling Technology.

      Calautit, John Kaiser; Hughes, Ben; Shahzad, Sally; Nasir, Diana S. N. M.; University of Sheffield; University of Derby (USES 2015 - The University of Sheffield Engineering Symposium, 2015)
      Buildings are responsible for almost 40% of the world energy usage. Heating Ventilation and Air-Conditioning (HVAC) systems consume more than 60% of the total energy use of buildings. Clearly any technology that reduces HVAC consumption will have a dramatic effect on the energy performance of the building. Natural ventilation offers the opportunity to eliminate the mechanical requirements of HVAC systems by using the natural driving forces of external wind and buoyancy effect. One technology, which incorporates both wind and buoyancy driven forces, is the wind catcher. Wind catchers are natural ventilation systems based on the design of traditional architecture. Though the movement of air caused by the wind catcher will lead to a cooling sensation for occupants, the high air temperature in hot climates will result in little cooling to occupants. In order to maximise the properties of cooling by wind catchers, heat transfer devices were incorporated into the design to reduce the supply air temperature. The aim of this work was to investigate the performance of a wind catcher integrated with heat transfer devices using numerical modelling and wind tunnel experiment. The wind catcher model was incorporated to a building, representing a small room of 15 people. Care was taken to generate a high-quality CFD grid and specify consistent boundary conditions. An experimental model was created using 3D printing and tested in a wind tunnel. Qualitative and quantitative wind tunnel measurements were compared with the CFD data and good correlation was observed. The study highlighted the potential of the proposed wind catcher in reducing the air temperature by up to 12 K and supplying the required fresh air rates.
    • Numerical and Experimental Analysis of a Multi-Directional Wind Tower Integrated with Vertically-Arranged Heat Transfer Devices (VHTD).

      Calautit, John Kaiser; Hughes, Ben; O'Connor, Dominic; Shahzad, Sally; University of Sheffield; University of Derby (2016)
      The aim of this work was to investigate the performance of a multi-directional wind tower integrated with vertically-arranged heat transfer devices (VHTD) using Computational Fluid Dynamics (CFD) and wind tunnel analysis. An experimental scale model was created using 3D printing. The scale model was tested in a uniform flow closed-loop wind tunnel to validate the CFD data. Numerical results of the supply airflow were compared with experimental data. Good agreement was observed between both methods of analysis. The Grid Convergence Method (GCI) method was used to estimate the uncertainty due to discretisation. Results have indicated that the achieved indoor air speed was reduced by 8–17% following the integration of the VHTD. The integration of VHTD had a positive effect on cooling performance of the wind tower, it reduced the incoming fresh air by up to 12 K. The effect of varying the number of VHTD rows (1–3 rows) on the system’s performance were also investigated. Additional simulations were also conducted to investigate the effect of atmospheric boundary layer (ABL) flows on the wind tower ventilation performance and also compare it with the results of uniform flow wind tunnel study.
    • Numerical simulation of spray combustion of conventional fuels and Biofuels

      Alajmi, Ayedh; Abdalla, Ibrahim E.; Bengherbia, T.; Yang, Zhiyin; De Montfort University, UK; University of Derby, UK; Faculty of Technology, De Montfort University, UK; Faculty of Technology, De Montfort University, UK; Faculty of Technology, De Montfort University, UK; Department of Engineering and Design, University of Sussex, UK (WIT Press, 2014-07-01)
      Numerical studies based on steady Computational Fluid Dynamics (CFD) for reactive flows were performed with the objective of validating advanced reaction mechanisms used to study spray combustion for both conventional and Biofuels. The SST-4 equation model was used to model turbulence, while more than one (comprehensive) reaction mechanisms were used to model the combustion of methanol, diesel and biodiesel using CHEMKIN-CFD and Fluent CFD code. Some of the reaction mechanisms used in modelling the current reactive flow simulation was already tested while others were developed during the course of this work. The computational results have shown good agreement with the available experimental data ofWidmann and Presser (Combustion and Flame, 129, 47–86, 2002) with the developed reaction mechanism slightly over predicting the temperature range. The CFD results have also shown that most of the harmful emission of the combustion of liquid fuels is less for Biodiesel compared to conventional diesel with the exception of CO2. This is in line with the finding of many experimental data. Keywords: combustion, biofuels, emissions.
    • Numerical simulations of wake characteristics of a horizontal axis tidal stream turbine using actuator line model.

      Baba-Ahmadi, Mohammad H.; Dong, Ping; University of Dundee; University of Liverpool (Elsevier, 2017-06-10)
      The wake of a laboratory scale tidal stream turbine in a shallow water channel with a turbulent inflow is simulated using the hybrid LES/ALM technique, which combines large eddy simulation with the actuator line method. The turbulent inlet conditions are generated using the mapping method to avoid a precursor running and large space for saving data. The numerical results demonstrated the usefulness of the mapping technique as well as some shortcomings that still remain to be addressed. Good agreement between numerical predictions and experimental data is achieved for both the mean and turbulent characteristics of the flow behind the turbine. The examination of changes in turbulence intensity and turbulent kinetic energy in the streamwise direction confirms the existence of a peak and transition to a highly turbulent flow about three diameters downstream of the turbine, which means that the distinct characteristics of the streamwise changes of turbulence intensity or turbulent kinetic energy may serve as an effective indicator for the flow regime transition and wake behaviour.
    • A numerical study of active flow control for low pressure turbine blades

      Rohr, Christian; Yang, Zhiyin; University of Derby (2012-09)
      Expansion of the slow, recirculating separated region of flow inside a separation bubble on the suction surface of Low Pressure Turbine (LPT) blades is the main source of loss generation as the Reynolds number is reduced. At axial chord Reynolds numbers as low as 30,000, typical of small or high altitude jet engines, the separation bubble expands all the way to the trailing edge of the blade, with a large increase in losses caused by the fully separated flow field. Active Flow Control (AFC) is a promising tool for reducing these losses without altering blade geometry, in order to make smaller, higher flying engines more cost-effective. Alternatively, AFC allows an increase in blade loading such that the number of turbine blades required can be reduced for a given operating point. Jet Flap (JF) is one such control device, and consists of a small opening on the pressure surface of the LPT blade near its trailing edge. By injecting fluid into the free stream normal to the pressure surface, the passage between blades is effectively contracted causing increased acceleration through the throat formed by adjacent blades. This induces a more favourable pressure gradient over the aft portion of the blade below, potentially suppressing the separation bubble altogether, while increasing the suction peak and moving it rearwards. In the current study the Pak-B LPT blade was used to evaluate the suitability of the JF concept as an AFC device for LPT blades. A numerical model was developed in STAR-CCM+ and validated against experimental data
    • Numerical study of effusion cooling flow and heat transfer

      Walton, Matthew; Yang, Zhiyin; University of Derby (WIT Press, 2014)
      An isothermal and non-isothermal numerical study of effusion cooling flow and heat transfer is conducted using a Reynolds-averaged Navier–Stokes (RANS) approach. A Reynolds stress transport (RST) turbulence model is used to predict the flow field of a staggered array of 12 rows of effusion holes, each hole inclined at 30° to the flat plate. The Reynolds number based on the hole diameter and jet exit velocity is 3800. The blowing ratio in both studies is 5. A conjugate heat transfer approach is adopted in the non-isothermal simulation. For the isothermal case, the RST model is shown to be capable of predicting the injection, penetration, downstream decay and lateral mixing of the effusion jets reasonably well. In addition, the numerical model captures the existence of two counter-rotating vortices emanating from each hole, which causes the entrainment of combustor flow towards the surface of the plate at the leading edge and downstream, influences the mixing of accumulated coolant flow, providing a more uniform surface temperature across the plate. The presence and characteristics of these vortices are in good agreement with previously published research. In the non-isothermal case, the laterally averaged cooling effectiveness across the plate is under-predicted but the trend conforms to that exhibited during experimentation.
    • Numerical study of flow over a bluff body with drag reduction devices.

      Abikan, Adam; Lu, Yiling; Yang, Zhiyin; University of Derby (2018-04-17)
      A numerical study of flow over a bluff body with drag devices has been carried out using the Reynolds-Averaged-Navier-Stokes (RANS) approach and the per-formance of three turbulence models, the realizable k-, the SST k- and a Reynolds Stress Model (RSM), has been assessed. The predictions of both the mean and turbulent quantities agree reasonably well with the experimental data and the RSM gives the best overall predictions. A qualitative comparison between the pre-dicted flow field and the measurements in the near wake region has also been presented and a reasonably good agreement is obtained. It is demonstrated that the RANS approach is capable of producing reasonably good results for this kind of flow although it is inherently unsteady due to vortex shedding in the wake region.
    • Numerical study of instabilities in separated–reattached flows

      Yang, Zhiyin; University of Derby (WIT Press, 2013-01-31)
      Transition process in separated–reattached flows plays a key role in many practical engineering applications. Hence, accurately predicting transition is crucial since the transition location has a significant impact on the aerodynamic performance and a fundamental understanding of the instability mechanisms involved in transition process is required in order to make significant advances in engineering design and transition control, for example, to delay the turbulent phase where laminar flow characteristics are desirable (low friction drag) or to accelerate it where high mixing of turbulent flow are of interest (in a combustor). The current understanding of instabilities involved in the transition process in separated–reattached flows is far from complete and it is usually very difficult to theoretically and experimentally study the transition process since theoretical studies suffer from the limitation imposed by nonlinearity of the transition process at later stages and experimental studies are limited by temporal and spatial resolution; hence, a thorough description of the transition process is lacking. Nevertheless, significant progress has been made with the simulation tools, such as large eddy simulation (LES), which has shown improved predictive capabilities and can predict transition process accurately. This paper will first briefly present LES formalism followed by its applications to study the transition process in separated–reattached flows, reviewing our current understanding of several important phenomena associated with the transition process and focusing on the instabilities in particular.
    • Numerical study of separated boundary layer transition under pressure gradient

      Li, Huajun; Yang, Zhiyin; University of Sussex, Brighton, UK; University of Derby, Derby, UK (2016-07-13)
      Large-eddy simulation (LES) is conducted to study the transition process of a separated boundary layer on a flat plate with an elliptical leading edge. A streamwise pressure distribution is imposed and the free stream turbulence intensity is 3% to mimic the suction surface of a low-pressure turbine (LPT) blade. A dynamic sub-grid scale model is employed in the study and the current LES results compare well with available experimental data and previous LES results. The transition process has been analysed with a particular focus on primary instabilities at work. Streaky structures further upstream of the separation, known as the Klebanoff Streaks, have been observed. Typical two-dimensional Kelvin-Helmholtz (K-H) rolls are distorted in the separated region. When Klebanoff streaks passing over a full-span K-H roll, portion of the two-dimensional roll merges with the Klebanoff streaks and develop into chaotic three-dimensional structures, whereas the remaining undisrupted two-dimensional K-H rolls develop into Λ-vortex indicating that despite the disturbances before separation, the K-H instability may still be the main instability at work.
    • Numerical study of the combustion of conventional and biofuels using reduced and advanced reaction mechanisms

      Abdalla, Ibrahim E.; Alajmi, Ayedh; Yang, Zhiyin; University of Derby (Vinča Institute of Nuclear Sciences, Belgrade, 2015-04-04)
      Combustion process of conventional liquid fuels and BioFuels depend on many factors including thermo - physicochemical properties associated with such fuels, their chemical structure and the combustion infrastructure used. This manuscript summarises the computational results of a steady cfd simulation for reactive flows performed to validate advanced reaction mechanisms for both conventional and BioFuels. The computational results have shown good agreement with the available experimental data with the differences thoroughly discussed and explained. An important observations and findings reported in this work was that when comprehensive reaction models were used, the injected fuels burned at a slower rate compared to the situation when reduced models were employed. While such comprehensive models predicted better flame structure and far better biproducts compared to the existing experimental results, it has also led to over-predicting the temperature field. The computational results have also shown that BioDiesel produces a marginally higher rate of CO2 compared to Diesel. Such results are thought to be due to the Oxygenated nature of the fuel and how such feature influences the development of a comprehensive reaction mechanism for such fuels.
    • Numerical study of the primary instability in a separated boundary layer transition under elevated free-stream turbulence

      Langari, Mostafa; Yang, Zhiyin; University of Sussex, Brighton, UK; University of Derby, UK (AIP Publishing, 2013-07-25)
      Numerical studies of laminar-to-turbulent transition in a separation bubble subjected to two free-stream turbulence levels (FST) have been performed using Large-Eddy Simulation (LES). Separation of the laminar boundary layer occurs at a curvature change over a plate with a semi-circular leading edge at Re = 3450 based on the plate thickness and the uniform inlet velocity. A numerical trip is used to produce the targeted free-stream turbulence levels and the decay of free-stream turbulence is well predicted. A dynamic sub-grid-scale model is employed in the current study and a good agreement has been obtained between the LES results and the experimental data. Detailed analysis of the LES data has been carried out to investigate the primary instability mechanism. The flow visualisations and spectral analysis of the separated shear layer reveal that the 2D Kelvin-Helmholtz instability mode, well known to occur at low FST levels, is bypassed at higher levels leading to earlier breakdown to turbulence.
    • Numerical study of transition process in a separated boundary layer on a flat plate with two different leading edges

      Yang, Zhiyin; University of Derby (World Scientific and Engineering Academy and Society, 2012-01)
      Transition from laminar flow to turbulent flow occurs very often and plays a crucial role in many practical engineering flows. There are many different kinds of transition and broadly speaking they can be classified into three categories: classical transition in attached boundary; bypass transition in attached boundary layer and separated boundary layer transition. This paper presents a comparative study of separated boundary layer transition on a flat plate with a blunt/semi-circular leading edge. Boundary layer may separate due to an adverse pressure gradient or due to flow geometry. In the current study the geometry is a flat plate with two different leading edges: a blunt one and a semi-circular one. The main purpose of the study is to identify how similar or how different the transition process is with two different leading edges. This study shows that for both cases (blunt and semi-circular leading edges) the primary two-dimensional instability originates from the free shear layer of the separation bubble via the Kelvin-Helmholtz mechanism. Three-dimensional motions develop under any small spanwise disturbances and similar coherent structures have been observed from flow visualization in both cases, strongly indicating that the transition process is very similar.
    • On bypass transition in separation bubbles: a review

      Yang, Zhiyin; School of Mechanical Engineering and the Built Environment, College of Engineering and Technology, University of Derby (Elsevier, 2019-01-14)
      Transition from laminar flow to turbulent flow is of great practical interest as it occurs in many engineering flows and often plays a critical role in aerodynamics and heat transfer performance of those flow devices. There could be many routes through transition, depending on flow configuration, geometry and the way in which transition is initiated by a wide range of possible background disturbances such as free-stream turbulence, pressure gradient, acoustic noise, wall roughness and obstructions, periodic unsteady disturbance and so on. This paper presents a brief overview of wall bounded flow transition in general and focuses more on the transition process in the free shear layer of separation bubbles, demonstrating that at elevated free-stream turbulent intensity the so called bypass transition could occur in geometrically induced separation bubbles where the separation point is fixed.
    • On secondary instability of a transitional separation bubble.

      Yang, Zhiyin; Abdalla, Ibrahim E.; University of Derby; Jubail University College (Elsevier, 2018-12-01)
      It is well established in the natural transition of an attached boundary layer that the transition process starts with a two–dimensional primary instability (Tollmien–Schlichting wave, denoted as TS wave), followed by usually a three-dimensional secondary instability (fundamental mode or subharmonic mode) leading to the breakdown to turbulence. However, the transition process of a separation bubble (laminar flow or laminar boundary layer at separation and transition occurs downstream of the separation, leading to turbulence at reattachment) is less well understood, especially on the nature of secondary instability. The focus of this paper is on trying to advance our understanding of secondary instability of a transitional separation bubble on a flat plate with a blunt leading edge (separation is induced geometrically at the leading edge) under a very low free-stream turbulence level (< 0.1%). Large-Eddy Simulation (LES) is employed in the current study with a dynamic sub-grid-scale model. The numerical flow visualisation together with the spectral analysis has indicated that a three dimensional secondary instability, the elliptical instability, which occurs for fundamental frequency is the main mechanism at work whereas the subharmonic mode in the form of vortex-pairing is hardly active. There is no evidence for the existence of hyperbolic instability in the braid region either.