ORCID Profile
0000-0001-9847-6004
Current Organisation
University of Adelaide
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Publisher: American Chemical Society (ACS)
Date: 24-01-2012
DOI: 10.1021/EF2014887
Publisher: Elsevier BV
Date: 06-2008
DOI: 10.1016/J.COMPBIOMED.2008.03.008
Abstract: Experimental images from particle/droplet image analyser (PDIA) and particle image velocimetry (PIV) imaging techniques of particle formation from a nasal spray device were taken to determine critical parameters for the study and design of effective nasal drug delivery devices. The critical parameters found were particle size, diameter of spray cone at a break-up length and a spray cone angle. A range of values for each of the parameters were ascertained through imaging analysis which were then transposed into initial particle boundary conditions for particle flow simulation within the nasal cavity by using Computational Fluid Dynamics software. An Eulerian-Lagrangian scheme was utilised to track mono-dispersed particles (10 and 20 microm) at a breathing rate of 10 L/min. The results from this qualitative study aim to assist the pharmaceutical industry to improve and help guide the design of nasal spray devices.
Publisher: Elsevier BV
Date: 03-2023
Publisher: SAGE Publications
Date: 28-05-2021
Abstract: This study deals with improving airfoil active flutter suppression under control-input constraints from the optimal control perspective by proposing a novel optimal neural-network control. The proposed approach uses a modified value function approximation dynamically tuned by an extended Kalman filter to solve the Hamilton–Jacobi–Bellman equality online for continuously improved optimal control to address optimality in parameter-varying nonlinear systems. Control-input constraints are integrated into the controller synthesis by introducing a generalized nonquadratic cost function for control inputs. The feasibility of using a performance index involving the nonquadratic control-input cost with the modified value function approximation is examined through the Lyapunov stability analysis. Wind tunnel experiments were conducted for controller validation, where an optimal controller synthesized offline via linear parameter-varying technique was used as a benchmark and compared. It is shown, both theoretically and experimentally, that the proposed method can effectively improve airfoil active flutter suppression under control-input constraints.
Publisher: MDPI AG
Date: 29-03-2021
DOI: 10.3390/GEOSCIENCES11040153
Abstract: Most rock masses contain natural fractures. In many engineering applications, a detailed understanding of the characteristics of fluid flow through a fractured rock mass is critically important for design, performance analysis, and uncertainty/risk assessment. In this context, rock fractures and fracture networks play a decisive role in conducting fluid through the rock mass as the permeability of fractures is in general orders of magnitudes greater than that of intact rock matrices, particularly in hard rock settings. This paper reviews the modelling methods developed over the past four decades for the generation of representative fracture networks in rock masses. It then reviews some of the authors’ recent developments in numerical modelling and experimental studies of linear and non-linear fluid flow through fractures and fracture networks, including challenging issues such as fracture wall roughness, aperture variations, flow tortuosity, fracture intersection geometry, fracture connectivity, and inertia effects at high Reynolds numbers. Finally, it provides a brief review of two applications of methods developed by the authors: the Habanero coupled hydro-thermal heat extraction model for fractured reservoirs and the Kapunda in-situ recovery of copper minerals from fractures, which is based on a coupled hydro-chemical model.
Publisher: IEEE
Date: 07-2017
Publisher: AIP Publishing
Date: 05-2018
DOI: 10.1063/1.5026719
Abstract: We present a systematic experimental study of the interaction between four rotationally symmetric jets within a cylindrical chamber, under conditions relevant to a wide range of engineering applications, including the technology of a Hybrid Solar Receiver Combustor (HSRC). The HSRC geometry is simplified here to a cylindrical cavity with four inlet jets (representing four burners) which are configured in an annular arrangement and aligned at an inclination angle to the axis with a tangential component (azimuthal angle) to generate a swirl in the chamber. In this study, the jet inclination angle (αj) was varied over the range of 25°–45°, while the jet azimuthal angle (θj) was varied from 5° to 15°. The inlet Reynolds number for each injected jet and the number of jets were fixed at ReD = 10 500 and 4, respectively. Measurements obtained with Particle Image Velocimetry were used to characterise the large-scale flow field within selected configurations. The results reveal a significant dependence of the mean and root-mean-square flow-fields on the jet azimuthal angle (θj) and the jet inclination angle (αj). Three different flow regimes with distinctive flow characteristics were identified within the configurations investigated here. It was also found that θj can significantly influence (a) the position and strength of an external recirculation zone and a central recirculation zone, (b) the extent of turbulence fluctuation, and (c) the flow unsteadiness. Importantly, the effect of αj on the flow characteristics was found to depend strongly on the value of θj.
Publisher: Elsevier BV
Date: 09-2021
Publisher: Informa UK Limited
Date: 30-06-2009
Publisher: American Chemical Society (ACS)
Date: 23-08-2010
DOI: 10.1021/EF100514V
Publisher: Elsevier BV
Date: 08-2016
Publisher: ASME International
Date: 20-04-2017
DOI: 10.1115/1.4035950
Abstract: A comprehensive study on the flow structure of an ensemble-averaged fluidic precessing jet (FPJ) flow is reported. This study is based on the concepts of critical point theory, previous experimental data, and validated simulation results. The unsteady k–ω shear stress transport (SST) turbulence model was adopted for the simulation, which provided high resolution flow details. The numerical model successfully reproduced the four main flow features of the FPJ flow. The predicted equivalent diameter and the centerline velocity of the phase-averaged FPJ flow were compared against the measured results and achieved reasonable agreement. The streamlines, velocity, and vorticity contours in a series of cross-sectional planes are presented. The calculated streamlines at the surfaces of the nozzle and the center-body (CB) are compared with previously deduced surface flow patterns. With these methods, a vortex skeleton with six main vortex cores of the FPJ flow within the nozzle is identified for the first time. This skeleton, which is illustrated diagramatically, is deduced to be responsible for the jet precession.
Publisher: AIP Publishing
Date: 12-2018
DOI: 10.1063/1.5063500
Publisher: Springer Science and Business Media LLC
Date: 13-03-2022
Publisher: Elsevier BV
Date: 03-2008
Publisher: Elsevier BV
Date: 12-2015
Publisher: Elsevier BV
Date: 03-2008
Publisher: IEEE
Date: 07-2019
Publisher: Informa UK Limited
Date: 06-04-2018
Publisher: Elsevier BV
Date: 09-2021
Publisher: AIP Publishing
Date: 2022
DOI: 10.1063/5.0081345
Publisher: Elsevier BV
Date: 2022
Publisher: Informa UK Limited
Date: 05-12-2007
Publisher: Informa UK Limited
Date: 06-01-2015
Publisher: AIP Publishing
Date: 05-2020
DOI: 10.1063/5.0004288
Abstract: In this paper, the transition to chaos for buoyant flows in a groove heated from below is analyzed using a three-dimensional numerical model. With a Prandtl number of 0.71 and an aspect ratio of 0.5, numerical simulations are performed for Rayleigh number Ra from 100 to 105. This wide range covers the transition process to chaos, the first change being the instability of the primary steady symmetric flow in the form of a symmetry-breaking pitchfork bifurcation between Ra = 1.5 × 103 and 1.6 × 103 that tilts the buoyant flow toward one or the other sidewall of the groove. A second pitchfork bifurcation to the three-dimensional flow occurs between Ra = 5.3 × 103 and 5.4 × 103. A Hopf bifurcation is observed between Ra = 5.6 × 103 and 5.7 × 103 at which the buoyant flow in the groove becomes temporally periodic this is followed by a sequence of further bifurcations including period-doubling and quasi-periodic bifurcations. Finally, the buoyant flow becomes chaotic when bulge motion appears along the groove between Ra = 6.5 × 103 and 6.6 × 103. Limit points, limit cycles, attractors, maximum Lyapunov exponents, and power spectral density are presented to analyze typical buoyant flows in the transition to chaos. Additionally, the heat and mass transfer is quantified for the different regimes.
Publisher: American Institute of Aeronautics and Astronautics (AIAA)
Date: 10-2016
DOI: 10.2514/1.J054958
Publisher: AIP Publishing
Date: 2020
DOI: 10.1063/5.0028712
Publisher: AIP Publishing
Date: 12-2018
DOI: 10.1063/1.5054847
Publisher: American Institute of Aeronautics and Astronautics
Date: 18-06-2015
DOI: 10.2514/6.2015-3210
Publisher: Springer Science and Business Media LLC
Date: 08-02-2022
DOI: 10.1007/S10237-022-01563-8
Abstract: In this paper, the effect of the turbulence and swirling of the inlet flow and the diameter of the nozzle on the flow characteristics and the particles' transport/deposition patterns in a realistic combination of the nasal cavity (NC) and the maxillary sinus (MS) were examined. A computational fluid dynamics (CFD) model was developed in ANSYS® Fluent using a hybrid Reynolds averaged Navier–Stokes–large-eddy simulation algorithm. For the validation of the CFD model, the pressure distribution in the NC was compared with the experimental data available in the literature. An Eulerian–Lagrangian approach was employed for the prediction of the particle trajectories using a discrete phase model. Different inlet flow conditions were investigated, with turbulence intensities of 0.15 and 0.3, and swirl numbers of 0.6 and 0.9 applied to the inlet flow at a flow rate of 7 L/min. Monodispersed particles with a diameter of 5 µm were released into the nostril for various nozzle diameters. The results demonstrate that the nasal valve plays a key role in nasal resistance, which d s the turbulence and swirl intensities of the inlet flow. Moreover, it was found that the effect of turbulence at the inlet of the NC on drug delivery to the MS is negligible. It was also demonstrated that increasing the flow swirl at the inlet and decreasing the nozzle diameter improves the total particle deposition more than threefold due to the generation of the centrifugal force, which acts on the particles in the nostril and vestibule. The results also suggest that the drug delivery efficiency to the MS can be increased by using a swirling flow with a moderate swirl number of 0.6. It was found that decreasing the nozzle diameter can increase drug delivery to the proximity of the ostium in the middle meatus by more than 45%, which subsequently increases the drug delivery to the MS. The results can help engineers design a nebulizer to improve the efficiency of drug delivery to the maxillary sinuses.
Publisher: Informa UK Limited
Date: 04-2005
Publisher: Inderscience Publishers
Date: 2015
Publisher: Elsevier BV
Date: 09-2007
Publisher: Frontiers Media SA
Date: 13-09-2019
Publisher: Elsevier BV
Date: 10-2007
Publisher: Springer Science and Business Media LLC
Date: 10-2020
DOI: 10.1007/S10237-019-01230-5
Abstract: Acoustically driven nebulized drug delivery (acoustic aerosol delivery) is the most efficient noninvasive technique for drug delivery to maxillary sinuses (MS). This method is based on the oscillation of the air plug inside the ostium to transport drug particles from the nasal cavity (NC) to the MS. The larger the wavelength of the air plug oscillation in the ostium, the greater the penetration of drug particles to the MS. However, using this technique, the maximum drug delivery efficiency achieved to date is 5%, which means 95% of the aerosolized drugs do not enter the MS and are wasted. Since the largest litude of the air plug oscillation occurs at its resonance frequency, to achieve an improved MS drug delivery efficiency, it is important to determine the resonance frequency of the nose-sinus combination accurately. This paper aims to investigate the impact of geometrical parameters on the resonance frequency of the nose-sinus model. Both experimental and computational acoustic models, along with the theoretical analysis, were conducted to determine the resonance frequency of an idealized nose-sinus model. The computational modeling was carried out using computational fluid dynamics (CFD) and finite element analysis (FEA), whereas in the analytical solution, the mathematical relationships developed for a conventional Helmholtz resonator were employed. A series of experiments were also conducted to measure the resonance frequency of a realistic NC-MS combination. The results demonstrated a good agreement between the experimental and CFD modeling, while the FEA and theoretical analysis showed a significant deviation from the experimental data. Also, it was shown that the resonance frequency of the idealized nose-sinus model increases by up to twofold with increasing the ostium diameter from 3 to 9 mm however, it has an inverse relationship with the ostium length and sinus volume. It was also reported that the resonance frequency of the nose-sinus model is independent of the NC width and MS shape.
Publisher: Elsevier BV
Date: 05-2022
Publisher: Elsevier BV
Date: 04-2020
Publisher: Elsevier BV
Date: 03-2008
Publisher: AIP Publishing
Date: 05-2019
DOI: 10.1063/1.5089904
Abstract: An experimental study is reported of the interaction between multiple isothermal jets within a cylindrical chamber under conditions relevant to a wide range of engineering applications, including the confined swirl combustors, industrial mixers, and concentrated solar thermal devices. The particle image velocimetry technique was used to investigate the swirling and precessing flows generated with four rotationally symmetric inlet pipes at a fixed nozzle Reynolds number of ReD = 10 500 for two configurations of swirl angle (5° and 15°) and two alternative tilt angles (25° and 45°). The measurements reveal three distinctive rotational flow patterns within the external recirculation zone (ERZ) and the central recirculation zone (CRZ) for these configurations. It was found that the mean and root-mean-square flow characteristics of the swirl within the chamber depend strongly on the relative significance of the ERZ and CRZ, with the swirling velocity being higher in the CRZ than that in the ERZ. A precessing vortex core was identified for all experimental conditions considered here, although its significance was less for the cases with a dominant CRZ.
Publisher: SAGE Publications
Date: 26-10-2016
Abstract: This paper reports the recent development and implementation of three teaching modules in order to teach and enhance the students’ critical thinking skills in a level IV undergraduate ostgraduate course ‘Computational Fluid Dynamics (CFD) for Engineering Applications’. These teaching modules include a lecture module, an online test module and a CFD project module. The lecture module introduces the importance of critical thinking skills by an ex le case, critical thinking definition and processes, and the application of critical thinking skills in formulation of CFD problems. In the online test module, seven online tests have been developed to enhance the students’ understanding of the contents of lectures and practical sessions. Meanwhile, students apply their critical thinking skills to work out some of the tests. In the project module, a student-driven CFD project is designed to help students to apply CFD techniques and critical thinking skills in engineering problems. In the project, students choose their own project topic and problems. They use CFD skills learned in the course and critical thinking skills to critically analyse their problems, identify the important parameters and review results. They apply the critical writing skills to finalise a project report. To the best knowledge of the author, this systematical integration of teaching and enhancement of critical thinking skills in computational fluid dynamics course is innovative. Feedback from students is quite positive shown by an anonymous survey in 2014.
Publisher: Elsevier BV
Date: 02-2015
Publisher: Elsevier BV
Date: 03-2020
Publisher: Elsevier BV
Date: 12-2013
Publisher: Cambridge University Press (CUP)
Date: 23-09-2022
DOI: 10.1017/JFM.2022.745
Abstract: Numerical simulations have been conducted to identify the dominant mechanism responsible for driving secondary flow motions in horizontal particle-laden pipe flows, based on an analysis of the forces acting on each phase. A four-way coupling Euler–Lagrangian approach was employed, using direct numerical simulations for the gas phase and Lagrangian particle tracking to account for the drag, gravitational and lift forces, together with the interactions that occur for both particle–wall and inter-particle collisions. The four different flow regimes, which had been identified previously as depending on various combinations of flow parameters and are characterised by the secondary flow structures of both the fluid and particle phases, were identified via varying the mass loading alone from $\\varPhi _m=0.4$ to $\\varPhi _m=1.8$ . The distribution of the ergence of Reynolds stresses was used to help characterise the classes of the secondary fluid flow. This shows that secondary fluid flows of both the first and second kinds can either exist separately or co-exist in such flows. The forces exerted on the fluid phase by the pressure gradient and fluid–particle interactions were examined qualitatively and quantitatively to identify their contribution to the secondary fluid flow motions. A similar study was also applied to the drag, lift and gravitational forces exerted on the particle phase for the secondary particle flow motions. These were found to explain the secondary flows of both the fluid and particle phases with regard to both the flow direction and magnitude, together with the interaction between the two phases.
Publisher: Elsevier BV
Date: 10-2021
Publisher: AIP Publishing
Date: 09-2022
DOI: 10.1063/5.0103760
Abstract: A transition to the chaotic state of the convective flows on a hot cone is investigated using three-dimensional numerical simulation. A wide range of the Rayleigh number from Ra = 100 to 107 for the Prandtl number of Pr = 7 and the aspect ratio of A = 0.1 is considered. Numerical results reveal a complex transition route to the chaotic state of the convective flows with a succession of Hopf, period-doubling, and quasiperiodic bifurcations the transition to a chaotic state followed by a succession of inverse quasiperiodic and inverse period-doubling bifurcations and a succession of period-doubling and quasiperiodic bifurcations and the transition to chaotic state again. Typical flows in the transition are characterized and analyzed using spectral analysis, the trajectory, the largest Lyapunov exponent, and the fractal dimension. Further, heat transfer in the transition is calculated, and the scaling relation is obtained.
Publisher: Elsevier BV
Date: 05-2020
Publisher: SAGE Publications
Date: 06-2010
Abstract: This paper describes the mathematical formulation and modelling issues of a computational fluid dynamics (CFD) model of a 375 MW utility furnace. This tangentially-fired furnace is fuelled by high moisture content brown coal from coal mines at Latrobe Valley in Victoria, Australia. The influences of different turbulence models, particle dispersion, and radiation models on the CFD prediction are investigated. Two turbulence models, standard k-e model and Shear-Stress Transport (SST) model, provide similar predictions that are in good agreement with the plant data. The effect of particle dispersion on the prediction is found to be insignificant for this high-volatile brown coal. The predicted wall incident radiation flux based on two radiation models, namely, discrete transfer (DT) model and P-1 model are compared against power plant measurements. The comparison reveals that the DT model provides good prediction of the radiation profiles, while the P-1 model considerably under-predicts the wall incident radiation flux.
Publisher: IEEE
Date: 02-2019
Publisher: Elsevier BV
Date: 10-2022
Publisher: SAGE Publications
Date: 2014
DOI: 10.7227/IJMEE.42.1.7
Abstract: This paper reports the development of a computational fluid dynamics (CFD) model of a spark ignition (SI) engine and the application of the engine model into an undergraduate internal combustion (IC) course. This two-dimensional (2D) four-stroke SI engine model simulates the combustion of the fuel, heptane, in the engine cylinder based on realistic boundary conditions. The development of the model helps engineering students better understand the combined effects of chemical reactions, species transport, flow patterns and temperature distributions in the SI engine. This model has been applied in a practical session in an undergraduate engineering course since 2012. To the best knowledge of the authors, this is the first time that CFD engine models are used as a hands-on tool in IC engine courses. Feedback from students is quite positive.
Publisher: Informa UK Limited
Date: 11-2006
Publisher: American Chemical Society (ACS)
Date: 24-08-2016
Publisher: Elsevier BV
Date: 12-2020
Publisher: Informa UK Limited
Date: 2007
DOI: 10.1080/08958370701665525
Abstract: Detailed deposition patterns of inhaled wood dust in an anatomically accurate nasal cavity were investigated using computational fluid dynamics (CFD) techniques. Three wood dusts, pine dust, heavy oak dust, and light oak dust, with a particle size distribution generated by machining (Chung et al., 2000), were simulated at an inhalation flow rate of 10 L/min. It was found that the major particle deposition sites were the nasal valve region and anterior section of the middle turbinate. Wood dust depositing in these regions is physiologically removed much more slowly than in other regions. This leads to the surrounding layer of soft tissues being damaged by the deposited particles during continuous exposure to wood dust. Additionally, it was found that pine dust had a higher deposition efficiency in the nasal cavity than the two oak dusts, due to the fact that it comprises a higher proportion of larger sized particles. Therefore, this indicates that dusts with a large amount of fine particles, such as those generated by sanding, may penetrate the nasal cavity and travel further into the lung.
Publisher: American Chemical Society (ACS)
Date: 19-07-2017
Publisher: Elsevier BV
Date: 05-2017
Publisher: Optica Publishing Group
Date: 23-03-2021
DOI: 10.1364/OE.421017
Abstract: We report an optical method for particle velocity measurement that is suitable for the measurement of particle velocities within dense particle-laden flows with high spatial resolution. The technique is based on particle shadow velocimetry with the use of a long-distance microscopic lens for images collection. The narrow depth of field of the lens allows particles within the focal plane to have much higher pattern intensities than those outside it on the collected images. Data processing was then employed to remove particles from outside the focal plane based on the gradient of the signal and a threshold. Following this, particle velocity was calculated from two successive images in the usual way. The technique was successfully demonstrated in a free-falling particle curtain with volume fractions in the four-way coupling regime of near-spherical micro-particles falling under gravity. The method was successfully employed to measure the transverse velocity profile through the curtain, which is the first time that such a measurement has been performed. Other highly-fidelity experimental data, which is also well suited to model development and validation, include the particle mass flow rate, curtain thickness and opacity.
Publisher: Elsevier BV
Date: 05-2017
Publisher: Elsevier BV
Date: 08-2018
Publisher: Elsevier BV
Date: 08-2020
Publisher: Elsevier BV
Date: 04-2017
Publisher: Wiley
Date: 02-07-2021
DOI: 10.1002/FAM.3004
Abstract: Eucalyptus is one of the most widespread genera around the world and a key element in recent wildfires. In a Eucalyptus forest, the accumulation of litter builds up a ground fuel layer that can support both flaming and smouldering wildfires. This work investigates the smouldering wildfire on leaf, bark, and twig beds (bulk density: 70‐140 kg/m 3 ) of Eucalyptus species. Two‐stage smouldering spread processes are observed. The first‐stage smouldering fire has the peak temperature of 600°C‐700°C and spread rate of 5‐9 mm/min. The measured emission factors are 1000‐1500 g/kg (CO2), 180‐450 g/kg (CO), 9‐16 g/kg (CH4), and 2‐6 g/kg (H2), respectively. The CO/CO2 ratio ranges from 0.15 (leaf) to 0.8 (bark). Laboratory experiments demonstrate that the smouldering fire spread is slower in leaf than those in bark and twig. The burning of stringy barks is less complete, compared to smooth barks. For leaf and twig beds, the influence of Eucalyptus species and heating value on smouldering fire is negligible. This is the first work to reveal smouldering fire behaviors on different Eucalyptus litter fuels and provides valuable information for understanding the effects of Eucalyptus species and plant parts on smouldering combustion.
Publisher: Elsevier BV
Date: 05-2018
Publisher: IEEE
Date: 07-2015
Publisher: Elsevier BV
Date: 2015
Publisher: Elsevier BV
Date: 06-2021
Publisher: Informa UK Limited
Date: 11-08-2021
Publisher: Elsevier BV
Date: 2020
Publisher: Elsevier BV
Date: 05-2023
Publisher: Elsevier BV
Date: 2022
Publisher: SAGE Publications
Date: 15-01-2018
Abstract: This paper proposes a novel adaptive nonlinear controller based on neural-networks (NNs) for active suppression of airfoil flutter (ASAF) from the optimal control perspective. Optimal control laws for locally nonlinear systems are synthesized in real time by solving the Hamilton–Jacobi–Bellman equation online with a proposed new form of NN-based value function approximation (VFA) and an extended Kalman filter. A systematic procedure based on linear matrix inequalities is further proposed for designing a scheduled parameter matrix that generalizes the new form of VFA to globally nonlinear systems to suit ASAF applications. Un-modeled dynamics are captured using an NN identifier. Comparisons drawn with a linear-parameter-varying optimal controller in wind-tunnel experiments confirm the effectiveness and validity of the proposed control scheme.
Publisher: Elsevier BV
Date: 03-2022
Publisher: AIP Publishing
Date: 12-2021
DOI: 10.1063/5.0075440
Abstract: Numerical simulations of the particle-laden gas–solid flow in horizontal circular pipes have been used to identify the role of particle collision coefficients in flow regimes within it. A four-way coupling Euler–Lagrangian approach was employed, using direct numerical simulations of the gas phase and Lagrangian particle tracking to account for the drag, gravitational and lift forces, together with particle–wall and inter-particle interactions. The influences on the flow of the mass loading ratio (Φm) and of the coefficients of restitution for collisions both between particles and the wall (ep−w) and between particles (ep−p) are assessed by examining the fluid and particle velocities, particle concentration distribution, turbulence kinetic energy, static pressure, inter-phase transferred momentum, and the secondary flow motions of both the fluid and particle phases. Three dominant flow regimes that include three sub-regimes based on their secondary flow patterns are identified, the transition between which depends on the combination of Φm, ep−w, and ep−p. Additionally, the quantitative dependence of these transitions on these three parameters is also reported for a series of Stokes and Froude numbers.
Publisher: Elsevier BV
Date: 11-2006
Publisher: AIP Publishing
Date: 10-2017
DOI: 10.1063/1.4986132
Abstract: We present a joint experimental and numerical study of the flow structure within a cylindrical chamber generated by planar-symmetric isothermal jets, under conditions of relevance to a wide range of practical applications, including the Hybrid Solar Receiver Combustor (HSRC) technology. The HSRC features a cavity with a coverable aperture to allow it to be operated as either a combustion chamber or a solar receiver, with multiple burners to direct a flame into the chamber and a heat exchanger that absorbs the heat from both energy sources. In this study, we assess the cases of two or four inlet jets (simulating the burners), configured in a planar-symmetric arrangement and aligned at an angle to the axis (αj) over the range of 0°–90°, at a constant inlet Reynolds number of ReD = 10 500. The jets were positioned in the same axial plane near the throat and interact with each other and the cavity walls. Measurements obtained with particle image velocimetry were used together with numerical modeling employing Reynolds-averaged Navier-Stokes methods to characterize the large-scale flow field within selected configurations of the device. The results reveal a significant dependence of the mean flow-field on αj and the number of inlet jets (Nj). Four different flow regimes with key distinctive features were identified within the range of αj and Nj considered here. It was also found that αj has a controlling influence on the extent of back-flow through the throat, the turbulence intensity, the flow stability, and the dominant recirculation zone, while Nj has a secondary influence on the turbulence intensity, the flow stability, and the transition between each flow regime.
Publisher: Elsevier BV
Date: 2009
Publisher: AIP Publishing
Date: 2021
DOI: 10.1063/5.0031104
Abstract: Natural convection in a V-shaped section cavity heated from below and cooled from above is investigated experimentally for the first time in the literature. Temperature measurements using fast-response thermistors and flow visualization using the shadowgraph technology have been performed. The natural convection development in the cavity including the conductional, the transitional, and the fully developed stages is described. It is experimentally proven that the scaling law of the thermal boundary layer thickness is δT ∼ (κt)1/2 and the scaling law of the plume velocity is vp ∼ κRa7/15/l. Furthermore, the occurrence of Hopf bifurcation in the transition to chaos and the flow structure are also identified experimentally. The power spectral density of the temperature time series reveals that the dominant frequency of the oscillations of the unsteady flow depends on the Rayleigh number, which is quantified.
Publisher: Institute of Electrical and Electronics Engineers (IEEE)
Date: 10-2016
Publisher: Elsevier BV
Date: 04-2011
Publisher: ASME International
Date: 24-04-2017
DOI: 10.1115/1.4036151
Abstract: We report the first systematic investigation of the phenomenon of “switching” between the two bistable axial jet (AJ) and precessing jet (PJ) flow modes in the fluidic precessing jet (FPJ) nozzle. While geometric configurations have been identified where the fractional time spent in the AJ mode is much less than that in the PJ mode, nevertheless, the phenomenon is undesirable and also remains of fundamental interest. This work was undertaken numerically using the unsteady shear stress transport (SST) model, the validation of which showed a good agreement with the experimental results. Three methods were employed in the current work to trigger the flow to switch from the AJ to the PJ modes. It is found that some asymmetry in either the inlet flow or the initial flow field is necessary to trigger the mode switching, with the time required to switch being dependent on the extent of the asymmetry. The direction and frequency of the precession were found to depend on the direction and intensity of the imposed inlet swirling, which will be conducive to the control of the FPJ flow for related industrial applications and academic research. The process with which the vortex skeleton changes within the chamber is also reported. Furthermore, both the rate of spreading and the maximum axial velocity decay of the jet within the nozzle are found to increase gradually during the switching process from the AJ to the PJ modes, consistent with the increased curvature within the local jet.
Publisher: ASME International
Date: 04-03-2019
DOI: 10.1115/1.4042748
Abstract: A systematic assessment of unsteady Reynolds-averaged Navier–Stokes (URANS) models in predicting the complex flow through a suddenly expanding axisymmetric chamber is reported. Five types of URANS models assessed in the study comprise the standard k–ε model, the modified k–ε (1.6) model, the modified k–ε (1.3) model, the renormalization group (RNG) k–ε model, and the shear stress transport (SST) model. To assess the strengths and limitations of these models in predicting the velocity field of this precessing flow, the numerical results are assessed against available experimental results. Good agreement with the flow features and reasonable agreement with the measured phase-averaged velocity field, energy of total fluctuation and precession frequency can be achieved with both the standard k–ε and the SST models. The degree of accuracy in predicting the rate of both spreading and velocity decay of the jet was found to greatly influence the prediction of the precession motion.
No related grants have been discovered for Zhao Tian.