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David F. Fletcher - One of the best experts on this subject based on the ideXlab platform.

  • Scale-adaptive simulation (SAS) modelling of a pilot-scale spray dryer
    Chemical Engineering Research and Design, 2009
    Co-Authors: David F. Fletcher, Timothy A. G. Langrish
    Abstract:

    It is now well-established that flows occurring when a jet enters a large vessel are highly transient. Such is the case in spray dryers, where the Inlet gas flow can generate transient flow patterns that affect the droplet trajectories and wall deposition behaviour in the dryer significantly. This paper applies the relatively recent scale-adaptive simulation (SAS) approach to the simulation of flow in a pilot-scale dryer. It is shown that this approach produces a much more realistic flowfield than use of URANS equations that have not been adapted to resolve problems associated with their inability to predict turbulence length-scale distributions correctly. A study of the effect of the Inlet Swirl angle is used to illustrate some features of the transient results. This work makes it clear that transient, 3D simulations of spray dryers can now be made that capture the large-scale turbulence behaviour and that the questionable practice of using unconverged steady-state simulations to provide information is no longer justified.

  • Simulation of the Effects of Inlet Swirl on Gas Flow Patterns in a Pilot-Scale Spray Dryer
    Chemical Engineering Research and Design, 2004
    Co-Authors: Timothy A. G. Langrish, J. Williams, David F. Fletcher
    Abstract:

    Simulations of the transient flow behaviour in a pilot scale spray dryer are presented in order to investigate the effect of the Inlet Swirl on the flow stability within the dryer. The simulations use the transient Reynolds-averaged Navier–Stokes equations, closed via the shear stress transport (SST) turbulence model, solved using the CFX5 commercial CFD code. The results are shown to be in good agreement with the experimental data and further highlight the importance of transient phenomena in short form spray dryers. The modelling shows significant differences between the no Swirl case, where a central air jet is seen to wobble with large-scale eddying motion outside the dryer axis, through strong precession of the central air jet at moderate Swirl to vortex breakdown with reverse flow occurring on the axis of the dryer at high Swirl.

  • simulation of turbulent Swirl flow in an axisymmetric sudden expansion
    AIAA Journal, 2001
    Co-Authors: Baoyu Guo, T A G Langrish, David F. Fletcher
    Abstract:

    The numerical simulation of the turbulent flows in axisymmetric sudden expansions with Inlet Swirl is addressed, with the focus being on the unsteady flow behavior. Numerical simulations using the Reynolds-averaged Navier-Stokes equations closed via the k-e turbulence model are presented. Results for an expansion ratio of 1.96 and a Reynolds number of 1 x 10 5 (at the Inlet) are presented for a range of Swirl numbers from 0 to 0.48. The precessing vortex core (PVC) and most of the features observed experimentally, including the precession direction, zero-frequency Swirl number, and vortex breakdown have been predicted

Timothy A. G. Langrish - One of the best experts on this subject based on the ideXlab platform.

  • Scale-adaptive simulation (SAS) modelling of a pilot-scale spray dryer
    Chemical Engineering Research and Design, 2009
    Co-Authors: David F. Fletcher, Timothy A. G. Langrish
    Abstract:

    It is now well-established that flows occurring when a jet enters a large vessel are highly transient. Such is the case in spray dryers, where the Inlet gas flow can generate transient flow patterns that affect the droplet trajectories and wall deposition behaviour in the dryer significantly. This paper applies the relatively recent scale-adaptive simulation (SAS) approach to the simulation of flow in a pilot-scale dryer. It is shown that this approach produces a much more realistic flowfield than use of URANS equations that have not been adapted to resolve problems associated with their inability to predict turbulence length-scale distributions correctly. A study of the effect of the Inlet Swirl angle is used to illustrate some features of the transient results. This work makes it clear that transient, 3D simulations of spray dryers can now be made that capture the large-scale turbulence behaviour and that the questionable practice of using unconverged steady-state simulations to provide information is no longer justified.

  • Simulation of the Effects of Inlet Swirl on Gas Flow Patterns in a Pilot-Scale Spray Dryer
    Chemical Engineering Research and Design, 2004
    Co-Authors: Timothy A. G. Langrish, J. Williams, David F. Fletcher
    Abstract:

    Simulations of the transient flow behaviour in a pilot scale spray dryer are presented in order to investigate the effect of the Inlet Swirl on the flow stability within the dryer. The simulations use the transient Reynolds-averaged Navier–Stokes equations, closed via the shear stress transport (SST) turbulence model, solved using the CFX5 commercial CFD code. The results are shown to be in good agreement with the experimental data and further highlight the importance of transient phenomena in short form spray dryers. The modelling shows significant differences between the no Swirl case, where a central air jet is seen to wobble with large-scale eddying motion outside the dryer axis, through strong precession of the central air jet at moderate Swirl to vortex breakdown with reverse flow occurring on the axis of the dryer at high Swirl.

David Fletcher - One of the best experts on this subject based on the ideXlab platform.

  • proper orthogonal decomposition pod analysis of cfd data for flow in an axisymmetric sudden expansion
    Chemical Engineering Research & Design, 2017
    Co-Authors: Clint Howard, T A G Langrish, Sushen Gupta, Ali Abbas, David Fletcher
    Abstract:

    Abstract CFD simulations of Swirling flow in a 2:1 axisymmetric sudden pipe expansion are performed and used to understand the structure of the flow. The k–e and SAS-zonal LES models available in ANSYS CFX are used to model turbulence. Comparison of these results shows that the scale-resolving simulation captures much more detail of the flow and provides much more physical results in terms of the flow structures that are resolved. As well as conventional analysis using typical CFD post-processing techniques and Fast Fourier Transforms (FFTs), Proper Orthogonal Decomposition (POD) is used to extract reduced order models of the wall pressure data. This technique is used to extract dominant structures in the spatial domain and to investigate transient behaviour. Data from a finite set of monitor points located at the pipe wall are also examined as a potential means of detecting flow behaviour for use in flow control models that utilise differential wall pressure input data. Such models are required to control, for example, Inlet Swirl to minimise wall impaction in spray dryers.

T A G Langrish - One of the best experts on this subject based on the ideXlab platform.

  • proper orthogonal decomposition pod analysis of cfd data for flow in an axisymmetric sudden expansion
    Chemical Engineering Research & Design, 2017
    Co-Authors: Clint Howard, T A G Langrish, Sushen Gupta, Ali Abbas, David Fletcher
    Abstract:

    Abstract CFD simulations of Swirling flow in a 2:1 axisymmetric sudden pipe expansion are performed and used to understand the structure of the flow. The k–e and SAS-zonal LES models available in ANSYS CFX are used to model turbulence. Comparison of these results shows that the scale-resolving simulation captures much more detail of the flow and provides much more physical results in terms of the flow structures that are resolved. As well as conventional analysis using typical CFD post-processing techniques and Fast Fourier Transforms (FFTs), Proper Orthogonal Decomposition (POD) is used to extract reduced order models of the wall pressure data. This technique is used to extract dominant structures in the spatial domain and to investigate transient behaviour. Data from a finite set of monitor points located at the pipe wall are also examined as a potential means of detecting flow behaviour for use in flow control models that utilise differential wall pressure input data. Such models are required to control, for example, Inlet Swirl to minimise wall impaction in spray dryers.

  • simulation of turbulent Swirl flow in an axisymmetric sudden expansion
    AIAA Journal, 2001
    Co-Authors: Baoyu Guo, T A G Langrish, David F. Fletcher
    Abstract:

    The numerical simulation of the turbulent flows in axisymmetric sudden expansions with Inlet Swirl is addressed, with the focus being on the unsteady flow behavior. Numerical simulations using the Reynolds-averaged Navier-Stokes equations closed via the k-e turbulence model are presented. Results for an expansion ratio of 1.96 and a Reynolds number of 1 x 10 5 (at the Inlet) are presented for a range of Swirl numbers from 0 to 0.48. The precessing vortex core (PVC) and most of the features observed experimentally, including the precession direction, zero-frequency Swirl number, and vortex breakdown have been predicted

Schiffer Heinz-peter - One of the best experts on this subject based on the ideXlab platform.

  • Experimental Investigation of Rotor Tip Film Cooling at an Axial Turbine with Swirling Inflow Using Pressure Sensitive Paint
    MDPI, 2021
    Co-Authors: Wilhelm Manuel, Schiffer Heinz-peter
    Abstract:

    Rotor tip film cooling is investigated at the Large Scale Turbine Rig, which is a 1.5-stage axial turbine rig operating at low speeds. Using pressure sensitive paint, the film cooling effectiveness η at a squealer-type blade tip with cylindrical pressure-side film cooling holes is obtained. The effect of turbine Inlet Swirl on η is examined in comparison to an axial inflow baseline case. Coolant-to-mainstream injection ratios are varied between 0.45% and 1.74% for an engine-realistic coolant-to-mainstream density ratio of 1.5. It is shown that Inlet Swirl causes a reduction in η for low injection ratios by up to 26%, with the trailing edge being especially susceptible to Swirl. For injection ratios greater than 0.93%, however, η is increased by up to 11% for Swirling inflow, while for axial inflow a further increase in coolant injection does not transfer into a gain in η

  • Experimental investigation of rotor tip film cooling at an axial turbine with Swirling inflow consditions using pressure sensitive paint
    2019
    Co-Authors: Wilhelm Manuel, Schiffer Heinz-peter
    Abstract:

    Rotor tip film cooling is investigated at the Large Scale Turbine Rig, which is a 1.5-stage axial turbine rig operating at low speeds. Using pressure sensitive paint, the film cooling effectiveness eta at a squealer-type blade tip with cylindrical pressure-side film cooling holes is obtained. The effect of turbine Inlet Swirl on eta is examined in comparison to an axial inflow baseline case. Coolant-to-mainstream injection ratios are varied between 0.45 and 1.74. for an engine-realistic coolant-to-mainstream density ratio of 1.5. It is shown that Inlet Swirl causes a reduction in eta for low injection ratios by up to 26 %, with the trailing edge being especially susceptible to Swirl. For injection ratios greater than 0.93 however, eta is increased by up to 11%for Swirling inflow, while for axial inflow a further increase in coolant injection does not transfer to a gain in eta