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J. T. Tough - One of the best experts on this subject based on the ideXlab platform.

  • Multiple discrete TI states of superfluid turbulence
    Journal of Low Temperature Physics, 1996
    Co-Authors: J. Castiglione, J. T. Tough
    Abstract:

    We report a most unusual new observation in thermal counterflow of liquid helium II in a weakly nonuniform Circular Channel: the appearance of multiple discrete states of superfluid turbulence. These states are in the TI regime of heat currents but exhibit a lower level of dissipation than the ordinary TI state present in both uniform and nonuniform Channels. Interestingly, these new states are only observed for diverging heat flow and are completely suppressed in converging flow. In contrast to the ordinary stable TI state, these new states are metastable. Transitions between the metastable states and to the TI state can be induced by weak mechanical perturbation. We have observed as many as five discrete metastable states at 1.75 K, but the number of states decreases markedly with temperature. Confirmatory data were obtained with a second Channel of different size and shape. Although current theories of superfluid turbulence do not provide any obvious explanations for these new states, we offer some speculations based upon competing normal fluid flow profiles and a quantized vortex mill.

  • Superfluid turbulence in a nonuniform Circular Channel
    Journal of Low Temperature Physics, 1993
    Co-Authors: P. J. Murphy, J. Castiglione, J. T. Tough
    Abstract:

    We have measured the dissipation associated with superfluid turbulence in a nonuniform Channel of Circular cross section in order to further explore the discrepancies with theory discovered previously in a nonuniform rectangular Channels. Our data show that the two turbulent states supported in uniform Circular Channels ( TI and TII ) are also present in our experiments for either diverging or converging flow, indicating that this two-state structure is quite robust. The transition from laminar flow to the TI state and the transition from the TI to the TII state each occur at stationary turbulent fronts in the Channel. One consequence of this phenomenon is that the TI/TII transition is substantially broadened. Our data for the TI state, when analysed assuming local uniformity, are in excellent agreement with previous results from uniform Channels. The broadened TI/TII transition severely restricts our experimental access to the TII state. Nevertheless, our data are consistent with the same kind of modification to the vortex line density found for the nonuniform rectangular Channels.

  • Superfluid turbulence in diverging and converging Circular Channels
    Bulletin of the American Physical Society, 1993
    Co-Authors: J. Castiglione, P. J. Murphy, J. T. Tough
    Abstract:

    Superfluid turbulence driven by thermal counterflow in a uniform Circular Channel evolves from a low vortex line density state (TI) to a homogeneous high density state (TII) as the heat current is increased. The authors have studied the effects on these states for diverging or converging flow in a weakly non-uniform Circular Channel. The TI and TII states in the non-uniform Channels are quantitatively the same for diverging and converging flow. The TI state is described by the same parameters as the TI state observed in uniform Channels, but the TII state is altered significantly in the non-uniform Channels. Their data for the transition from superfluid turbulence (TI) to laminar flow reveal important differences between converging, diverging and uniform Channels. These results will be discussed in terms of superfluid turbulent fronts and the {open_quotes}vortex mill{close_quotes} mechanism.

Hamed Azimi - One of the best experts on this subject based on the ideXlab platform.

  • Numerical study of bed slope change effect of Circular Channel with side weir in supercritical flow conditions
    Applied Water Science, 2018
    Co-Authors: Hamed Azimi, Saeid Shabanlou
    Abstract:

    In this numerical study, the pattern and the field of the passing flow through Circular Channels with the side weir in supercritical flow conditions are simulated using the FLOW-3D model. First, the numerical model results are validated with the experimental data and a good agreement between the results is obtained from the numerical simulation and the experimental data. Then, the effects of the slope change of the Circular Channel bed on the flow free surface, the discharge of the side weir, the Froude number at the end of the side weir upstream, the discharge coefficient of the side weir, the specific energy and the slope of the S3 profile are investigated. In this study, the flow field turbulence and variations of the free surface computational field are simulated using the RNG $$k - \varepsilon$$ turbulence model and the volume of fluid (VOF) method, respectively. In practice, transmission Channels used in irrigation networks and urban sewage disposal systems are steep. Therefore, the main purpose of this computational fluid dynamics (CFD) study is investigating the effect of the bed slope change of Circular Channels with side weir in supercritical flow conditions on the pattern and the structure of these types of flows.

  • Numerical Simulation of Free Surface and Flow Field Turbulence in a Circular Channel with the Side Weir in Subcritical Flow
    International Journal of Nonlinear Sciences and Numerical Simulation, 2017
    Co-Authors: Hamed Azimi, Saeid Shabanlou
    Abstract:

    AbstractWhen flow surface is higher than of a side weir crest, the overflow spilt over the crest and divert into a side Channel. These structures are extensively used in urban sewage disposal networks, water supply systems, and drainage and flood diversion networks. This study simulates stream free surface, discharge over a sharp-crest side weir, and discharge coefficient of a side weir in a Circular Channel using FLOW-3D software. Numerical model results were compared with the experimental ones and the comparison proved an acceptable consistency between the numerical and experimental results. RNG k-ε turbulence model was used for simulating flow turbulence. The volume of fluid (VOF) method was used in this CFD analysis for predicting changes of flow free surface. Then, the numerical simulation results were examined for discharge coefficient of the side weir and flow free surface for different discharge passing through the main Channel. The changes of dividing stream surface from main Channel bed toward stream free surface were examined. The concluding section assessed the effect of shape of a Circular Channel on the pattern and intensity of a secondary flow in the main Channel and the impacts of the discharge passing through the Circular Channel on height of stagnation point and shear stress pattern in the main Channel bed.

  • Discharge Coefficient of Rectangular Side Weirs on Circular Channels
    International Journal of Nonlinear Sciences and Numerical Simulation, 2016
    Co-Authors: Hamed Azimi, Saeid Shabanlou, Isa Ebtehaj, Hossein Bonakdari
    Abstract:

    AbstractIn this study, the flow turbulence and variations of the supercritical free surface flow in a Circular Channel along a side weir are simulated as three dimensional using the RNG k-ε turbulence model and volume of fluid (VOF) scheme. Comparison between the numerical model and experimental measurements shows that the numerical model simulates the free surface flow with good accuracy. According to the numerical model results, the specific energy variations along the side weir for the supercritical flow regime are almost constant and the energy drop is not significant but by increasing the side weir length the energy difference between the side weir upstream and downstream increases. Next, using the nonlinear regression (NLR) and analysis of the simulation results, some relationships for calculating the discharge coefficient of side weir on Circular Channels in supercritical flow regime are provided.

  • Discharge and flow field of the Circular Channel along the side weir
    Canadian Journal of Civil Engineering, 2015
    Co-Authors: Hamed Azimi, Hazhar Hadad, Zakarya Shokati, Mohammad Sajad Salimi
    Abstract:

    The side weir is one of the most important hydraulic structures that is used by hydraulic engineers for adjusting and controlling flow in urban waste collection systems, irrigation and drainage networks. In this study, an equation is proposed for computing side weir discharge located on Circular Channels. The equation computes the side weir discharge with sufficient accuracy. Then, the RNG k–e turbulence model is used for simulating the turbulence of the flow field and the free surface flow variations are modeled using volume of fluid scheme. Comparing experimental results with numerical simulations indicates acceptable accuracy of the numerical model. Also, the side weir discharge coefficients, flow free surface variation, behavior of dividing stream surface and variations of stagnation point height for different discharges within a Circular Channel along a side weir were examined.

  • Numerical Simulation of Flow Free Surface and Field in Circular Channel along the Side Weir in Subcritical Flow Conditions
    2015
    Co-Authors: Hamed Azimi
    Abstract:

    A side weir is being installed as a flow control structure on the side of the main Channel. When the water level exceeds the crest level of the side weir, the additional flow will spill over the weir crest and divert into the side Channel. This type of structures has wide application in urban sewage disposal, water supply systems, drainage and flood diversion networks. In this study, the free surface of flow and the side weir discharge were simulated using FLOW-3D software. The RNG k- e turbulence model was used for simulation of the flow field turbulence. Also the volume of fluid (VOF) scheme was applied to predict the variations of flow free surface. Comparing numerical simulations with experimental results showed the acceptable accuracy of numerical model. Next, the discharge coefficient of side weir and the free surface of flow variations were evaluated for different discharges of the main Channel. Then the variation of the width of the separating stream surface from bed of the main Channel toward the free surface of flow was investigated. Also, the Circular Channel effects on the pattern and strength of the secondary flow were studied. The effects of the main Channel discharge on the stagnation point height and bed shear stress pattern were investigated. According to the subcritical flows pattern, the flow depth was increased from the side weir upstream end towards its downstream end. For all longitudinal profiles with increasing discharges within Circular Channel, the flow depth was increased along the side weir.

J. Castiglione - One of the best experts on this subject based on the ideXlab platform.

  • Multiple discrete TI states of superfluid turbulence
    Journal of Low Temperature Physics, 1996
    Co-Authors: J. Castiglione, J. T. Tough
    Abstract:

    We report a most unusual new observation in thermal counterflow of liquid helium II in a weakly nonuniform Circular Channel: the appearance of multiple discrete states of superfluid turbulence. These states are in the TI regime of heat currents but exhibit a lower level of dissipation than the ordinary TI state present in both uniform and nonuniform Channels. Interestingly, these new states are only observed for diverging heat flow and are completely suppressed in converging flow. In contrast to the ordinary stable TI state, these new states are metastable. Transitions between the metastable states and to the TI state can be induced by weak mechanical perturbation. We have observed as many as five discrete metastable states at 1.75 K, but the number of states decreases markedly with temperature. Confirmatory data were obtained with a second Channel of different size and shape. Although current theories of superfluid turbulence do not provide any obvious explanations for these new states, we offer some speculations based upon competing normal fluid flow profiles and a quantized vortex mill.

  • Superfluid turbulence in a nonuniform Circular Channel
    Journal of Low Temperature Physics, 1993
    Co-Authors: P. J. Murphy, J. Castiglione, J. T. Tough
    Abstract:

    We have measured the dissipation associated with superfluid turbulence in a nonuniform Channel of Circular cross section in order to further explore the discrepancies with theory discovered previously in a nonuniform rectangular Channels. Our data show that the two turbulent states supported in uniform Circular Channels ( TI and TII ) are also present in our experiments for either diverging or converging flow, indicating that this two-state structure is quite robust. The transition from laminar flow to the TI state and the transition from the TI to the TII state each occur at stationary turbulent fronts in the Channel. One consequence of this phenomenon is that the TI/TII transition is substantially broadened. Our data for the TI state, when analysed assuming local uniformity, are in excellent agreement with previous results from uniform Channels. The broadened TI/TII transition severely restricts our experimental access to the TII state. Nevertheless, our data are consistent with the same kind of modification to the vortex line density found for the nonuniform rectangular Channels.

  • Superfluid turbulence in diverging and converging Circular Channels
    Bulletin of the American Physical Society, 1993
    Co-Authors: J. Castiglione, P. J. Murphy, J. T. Tough
    Abstract:

    Superfluid turbulence driven by thermal counterflow in a uniform Circular Channel evolves from a low vortex line density state (TI) to a homogeneous high density state (TII) as the heat current is increased. The authors have studied the effects on these states for diverging or converging flow in a weakly non-uniform Circular Channel. The TI and TII states in the non-uniform Channels are quantitatively the same for diverging and converging flow. The TI state is described by the same parameters as the TI state observed in uniform Channels, but the TII state is altered significantly in the non-uniform Channels. Their data for the transition from superfluid turbulence (TI) to laminar flow reveal important differences between converging, diverging and uniform Channels. These results will be discussed in terms of superfluid turbulent fronts and the {open_quotes}vortex mill{close_quotes} mechanism.

Saeid Shabanlou - One of the best experts on this subject based on the ideXlab platform.

  • Numerical study of bed slope change effect of Circular Channel with side weir in supercritical flow conditions
    Applied Water Science, 2018
    Co-Authors: Hamed Azimi, Saeid Shabanlou
    Abstract:

    In this numerical study, the pattern and the field of the passing flow through Circular Channels with the side weir in supercritical flow conditions are simulated using the FLOW-3D model. First, the numerical model results are validated with the experimental data and a good agreement between the results is obtained from the numerical simulation and the experimental data. Then, the effects of the slope change of the Circular Channel bed on the flow free surface, the discharge of the side weir, the Froude number at the end of the side weir upstream, the discharge coefficient of the side weir, the specific energy and the slope of the S3 profile are investigated. In this study, the flow field turbulence and variations of the free surface computational field are simulated using the RNG $$k - \varepsilon$$ turbulence model and the volume of fluid (VOF) method, respectively. In practice, transmission Channels used in irrigation networks and urban sewage disposal systems are steep. Therefore, the main purpose of this computational fluid dynamics (CFD) study is investigating the effect of the bed slope change of Circular Channels with side weir in supercritical flow conditions on the pattern and the structure of these types of flows.

  • Numerical Simulation of Free Surface and Flow Field Turbulence in a Circular Channel with the Side Weir in Subcritical Flow
    International Journal of Nonlinear Sciences and Numerical Simulation, 2017
    Co-Authors: Hamed Azimi, Saeid Shabanlou
    Abstract:

    AbstractWhen flow surface is higher than of a side weir crest, the overflow spilt over the crest and divert into a side Channel. These structures are extensively used in urban sewage disposal networks, water supply systems, and drainage and flood diversion networks. This study simulates stream free surface, discharge over a sharp-crest side weir, and discharge coefficient of a side weir in a Circular Channel using FLOW-3D software. Numerical model results were compared with the experimental ones and the comparison proved an acceptable consistency between the numerical and experimental results. RNG k-ε turbulence model was used for simulating flow turbulence. The volume of fluid (VOF) method was used in this CFD analysis for predicting changes of flow free surface. Then, the numerical simulation results were examined for discharge coefficient of the side weir and flow free surface for different discharge passing through the main Channel. The changes of dividing stream surface from main Channel bed toward stream free surface were examined. The concluding section assessed the effect of shape of a Circular Channel on the pattern and intensity of a secondary flow in the main Channel and the impacts of the discharge passing through the Circular Channel on height of stagnation point and shear stress pattern in the main Channel bed.

  • Discharge Coefficient of Rectangular Side Weirs on Circular Channels
    International Journal of Nonlinear Sciences and Numerical Simulation, 2016
    Co-Authors: Hamed Azimi, Saeid Shabanlou, Isa Ebtehaj, Hossein Bonakdari
    Abstract:

    AbstractIn this study, the flow turbulence and variations of the supercritical free surface flow in a Circular Channel along a side weir are simulated as three dimensional using the RNG k-ε turbulence model and volume of fluid (VOF) scheme. Comparison between the numerical model and experimental measurements shows that the numerical model simulates the free surface flow with good accuracy. According to the numerical model results, the specific energy variations along the side weir for the supercritical flow regime are almost constant and the energy drop is not significant but by increasing the side weir length the energy difference between the side weir upstream and downstream increases. Next, using the nonlinear regression (NLR) and analysis of the simulation results, some relationships for calculating the discharge coefficient of side weir on Circular Channels in supercritical flow regime are provided.

  • Free surface and velocity field in a Circular Channel along the side weir in supercritical flow conditions
    Flow Measurement and Instrumentation, 2014
    Co-Authors: Hamed Azimi, Saeid Shabanlou, Mohammad Sajad Salimi
    Abstract:

    A side weir is a kind of flow regulator hydraulic structure which is used in drainage systems, irrigation and sewage disposal network. The passing flow over side weir is a spatial variability flow with discharge reduction. Circular Channels with side weir have been used widely for regulating runoff and flood. In this research the flow free surface and the passing flow field through a Circular Channel with side weir is simulated by commercial software. In this CFD analysis, the RNG k–e turbulence model is used for simulating the turbulence of the flow field and the free surface changes are modeled using VOF model. Comparison between changes in the free surface, the passing discharge over the weir, the discharge coefficient and the specific energy at the beginning section of side weir obtained from the numerical simulation and experimental results indicates acceptable accuracy of the CFD model in the supercritical regime. Given that most previous numerical studies have been focused on the rectangular Channel with side weir and in the subcritical flow condition, the main purpose of this simulation is study of the free surface changes and the velocity field along a side weir located on a Circular Channel in the supercritical regime.

Ali Ijam - One of the best experts on this subject based on the ideXlab platform.

  • investigating the heat transfer performance and thermophysical properties of nanofluids in a Circular micro Channel
    International Communications in Heat and Mass Transfer, 2013
    Co-Authors: M R Sohel, R Saidur, Mohd Faizul Mohd Sabri, M Kamalisarvestani, Mohamad Fathi Mohamad Elias, Ali Ijam
    Abstract:

    Abstract In this paper, the thermal performance of a Circular shaped copper microChannel heat sink using three types of nanofluids is discussed analytically. Al2O3–Water, TiO2–water and CuO–water nanofluids were used in this analysis and the comparative thermal performance of these three nanofluids is also discussed. The hydraulic diameter of the Circular Channel is 400 μm and the total block dimension is 10 mm × 10 mm × 4 mm. A steady, laminar and incompressible flow with constant heat flux is assumed in the Circular Channel. The analyses are done at various volume fractions ranging from 0.5 vol.% to 4 vol.% and at a constant inlet velocity of 1.5 m/s. The results showed that the thermal performance can be increased significantly by using CuO–water nanofluid as a coolant for cooling of electronic heat sink when Al2O3–water and TiO2–water nanofluids showed less improvement. Compared to pure water, the highest improvement (13.15%) in the heat flux occurred for 4 vol.% CuO–water nanofluid when Al2O3–water and TiO2–water nanofluids showed 6.80% and 6.20% improvements respectively. This improvement in heat flux is calculated without considering the additional required pumping power due to the increased viscosity of nanofluids. Therefore, CuO–water nanofluid can be recommended to obtain maximum heat transfer performance in a Circular microChannel heat sink.