The Experts below are selected from a list of 1956 Experts worldwide ranked by ideXlab platform

Maciej Balajewicz - One of the best experts on this subject based on the ideXlab platform.

  • transported snapshot model order reduction approach for parametric steady state fluid flows containing parameter dependent shocks
    International Journal for Numerical Methods in Engineering, 2019
    Co-Authors: Nirmal J Nair, Maciej Balajewicz
    Abstract:

    A new model order reduction approach is proposed for parametric steady-state nonlinear fluid flows characterized by shocks and discontinuities whose spatial locations and orientations are strongly parameter dependent. In this method, solutions in the predictive regime are approximated using a linear superposition of parameter dependent basis. The sought after parametric reduced-basis are obtained by transporting the snapshots in a spatially and parametrically dependent transport field. Key to the proposed approach is the observation that the transport fields are typically smooth and continuous, despite the solution themselves not being so. As a result, the transport fields can be accurately expressed using a low-order polynomial expansion. Similar to traditional projection-based model order reduction approaches, the proposed method is formulated mathematically as a residual minimization problem for the generalized coordinates. The proposed approach is also integrated with well-known hyper-reduction strategies to obtain significant computational speed-ups. The method is successfully applied to the reduction of a parametric 1-D flow in a converging-Diverging Nozzle, a parametric 2-D supersonic flow over a forward facing step and a parametric 2-D jet diffusion flame in a combustor.

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

  • transported snapshot model order reduction approach for parametric steady state fluid flows containing parameter dependent shocks
    International Journal for Numerical Methods in Engineering, 2019
    Co-Authors: Nirmal J Nair, Maciej Balajewicz
    Abstract:

    A new model order reduction approach is proposed for parametric steady-state nonlinear fluid flows characterized by shocks and discontinuities whose spatial locations and orientations are strongly parameter dependent. In this method, solutions in the predictive regime are approximated using a linear superposition of parameter dependent basis. The sought after parametric reduced-basis are obtained by transporting the snapshots in a spatially and parametrically dependent transport field. Key to the proposed approach is the observation that the transport fields are typically smooth and continuous, despite the solution themselves not being so. As a result, the transport fields can be accurately expressed using a low-order polynomial expansion. Similar to traditional projection-based model order reduction approaches, the proposed method is formulated mathematically as a residual minimization problem for the generalized coordinates. The proposed approach is also integrated with well-known hyper-reduction strategies to obtain significant computational speed-ups. The method is successfully applied to the reduction of a parametric 1-D flow in a converging-Diverging Nozzle, a parametric 2-D supersonic flow over a forward facing step and a parametric 2-D jet diffusion flame in a combustor.

Poelma C. - One of the best experts on this subject based on the ideXlab platform.

  • Void fraction measurements in partial cavitation regimes by X-ray computed tomography
    'Elsevier BV', 2019
    Co-Authors: Jahangir S., Wagner E.c., Mudde R.f., Poelma C.
    Abstract:

    Cavitation is a complicated multiphase phenomenon, where the production of vapor cavities leads to an opaque flow. Exploring the internal structures of the cavitating flows is one of the most significant challenges in this field of study. While it is not possible to visualize the interior of the cavity with visible light, we use X-ray computed tomography to obtain the time-averaged void fraction distribution in an axisymmetric converging-Diverging Nozzle (’venturi’). This technique is based on the amount of energy absorbed by the material, which in turn depends on its density and thickness. Using this technique, two different partial cavitation mechanisms are examined: the re-entrant jet mechanism and the bubbly shock mechanism. 3D reconstruction of the X-ray images is used (i) to differentiate between vapor and liquid phase, (ii) to obtain radial geometric features of the flow, and (iii) to quantify the local void fraction. The void fraction downstream of the venturi in the bubbly shock mechanism is found to be more than twice compared to the re-entrant jet mechanism. The results show the presence of intense cavitation at the walls of the venturi. Moreover, the vapor phase mixes with the liquid phase downstream of the venturi, resulting in cloud-like cavitation.

  • Dynamics of partial cavitation in an axisymmetric converging-Diverging Nozzle
    'Elsevier BV', 2018
    Co-Authors: Jahangir S., Hogendoorn W.j., Poelma C.
    Abstract:

    Partial cavitation dynamics in an axisymmetric converging-Diverging Nozzle are investigated experimentally. Shadowgraphy is used to visualize and analyze different cavitation regimes. These regimes are generated by changing the global static pressure and flow velocity independently. Cloud cavitation is the most interesting and complex regime, because the shedding of vapor clouds is caused by two different mechanisms: the re-entrant jet mechanism and the bubbly shock mechanism. The dynamics are investigated using a position-time diagram. Using such a diagram we show that for cavitation number σ > 0.95 the cavity shedding is caused by the re-entrant jet mechanism, and for σ < 0.75 the mechanism responsible for periodic cavity shedding is the bubbly shock mechanism. Both mechanisms are observed in the transition region, 0.75 < σ < 0.95. The shedding frequencies, expressed as Strouhal numbers, collapse on a single curve when plotted against the cavitation number, except for the transition region. The re-entrant jet mechanism is a pressure gradient driven phenomenon, which is caused by a temporary stagnation point at the cavity front. This leads to stick-slip behavior of the cavity. In the bubbly shock regime, a shock wave is induced by a collapse of the previously shedded vapor bubbles downstream of the venturi, which triggers the initiation of the detachment of the growing cavity. The propagation velocity of the shock wave is quantified both in the liquid and the mixture phase by means of the position-time diagram.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Fluid MechanicsMulti Phase System

  • X-ray computed tomography of cavitating flow in a converging-Diverging Nozzle
    'ASME International', 2018
    Co-Authors: Jahangir S., Wagner E.c., Mudde R.f., Poelma C.
    Abstract:

    Cavitation is a complex multiphase phenomenon, where the production of vapor bubbles leads to opaqueness of the flow. While it is nearly impossible to visualize the interior of the cavitation region with visible light, we show that with X-ray computed tomography it is possible to obtain the time-averaged void fraction distribution in an axisymmetric converging-Diverging Nozzle (venturi). This technique is based on the amount of energy absorbed by the material, based on its density and thickness. Time-averaged 3D reconstruction of the X-ray images is used (i) to distinguish between vapor and liquid phase, (ii) to get radial geometric features of the flow, and (iii) to quantify the local void fraction. The results show the presence of intense cavitation at the walls of the venturi, and the vapor fraction decreases downstream of the venturi with the vapor cloud.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Fluid MechanicsChemE/AfdelingsbureauExecutive boardImPhys/Imaging PhysicsMulti Phase System

  • Complete dataset for Converging-Diverging Nozzle
    4TU.Centre for Research Data, 2018
    Co-Authors: Jahangir S., Hogendoorn W., Poelma C.
    Abstract:

    Cavitation dynamics in a converging-Diverging Nozzle are investigated experimentally. Shadowgraphy is used to visualize and analyze different cavitation regimes and the corresponding complete dataset is provided. This dataset will help researchers for validation of their numerical models. The related publications describe the mechanisms which are responsible for partial/ periodic cavitation

  • X-ray computed tomography of cavitating flow in a converging-Diverging Nozzle
    'ASME International', 2018
    Co-Authors: Jahangir S., Poelma C., Wagner E.c., Mudde R.f., Katz Joseph
    Abstract:

    Cavitation is a complex multiphase phenomenon, where the production of vapor bubbles leads to opaqueness of the flow. While it is nearly impossible to visualize the interior of the cavitation region with visible light, we show that with X-ray computed tomography it is possible to obtain the time-averaged void fraction distribution in an axisymmetric converging-Diverging Nozzle (venturi). This technique is based on the amount of energy absorbed by the material, based on its density and thickness. Time-averaged 3D reconstruction of the X-ray images is used (i) to distinguish between vapor and liquid phase, (ii) to get radial geometric features of the flow, and (iii) to quantify the local void fraction. The results show the presence of intense cavitation at the walls of the venturi, and the vapor fraction decreases downstream of the venturi with the vapor cloud

Rocco Lupoi - One of the best experts on this subject based on the ideXlab platform.

  • an analysis of the particulate flow in cold spray Nozzles
    Mechanical Sciences, 2015
    Co-Authors: Mortenc Meyer, Rocco Lupoi
    Abstract:

    Abstract. Cold Spray is a novel technology for the application of coatings onto a variety of substrate materials. In this method, melting temperatures are not crossed and the bonding is realized by the acceleration of powder particles through a carrier gas in a converging-Diverging Nozzle and their high energy impact over a substrate material. The critical aspect of this technology is the acceleration process and the multiphase nature of it. Three different Nozzle designs were experimented under constant conditions and their performance simulated using Computational Fluid Dynamics tools. The Deposition Efficiency was measured using titanium as feedstock material and it was shown that it decreases with the cross-sectional throat area of the Nozzle. Computational results based on a one-way coupled multiphase approach did not agree with this observation, while more sophisticated modelling techniques with two-way couplings can partially provide high-quality outcomes, in agreement with experimental data.

  • deposition of metallic coatings on polymer surfaces using cold spray
    Surface & Coatings Technology, 2010
    Co-Authors: Rocco Lupoi, W Oneill
    Abstract:

    Abstract Current coating technologies such as plasma spray, High Velocity Oxygen Fuel (HVOF) or laser cladding involve the delivery of molten materials during the deposition process. However, such techniques are not well suited to the deposition of metallic coatings on polymers and composites. Cold spray (CS) has attracted much industrial interest over the past two decades. In this method, a material in powder form is accelerated on passage through a converging–Diverging Nozzle to high speeds via a high pressure coaxial carrier gas jet. The high impact kinetic energy deforms the particles, which creates effective bonding to the substrate. This paper presents the results of an initial study on the potential of the CS process to produce metallic coatings on non-metallic surfaces such as polymers and composites for engineering applications. Experimental and Computational Fluid Dynamics (CFD) results when spraying copper, aluminium and tin powder on a range of substrates such as PC/ABS, polyamide-6, polypropylene, polystyrene and a glass-fibre composite material are presented and analyzed.

Jahangir S. - One of the best experts on this subject based on the ideXlab platform.

  • Experimental Investigation of Partial Cavitation
    2020
    Co-Authors: Jahangir S.
    Abstract:

    Cavitation is a well-known phenomenon, occurring in a wide range of applications. In most applications, cavitation is undesirable, such as turbines, pumps, ship propellers and diesel injector Nozzles. Cavitation can cause material erosion, flow blockage, noise and degradation of equipment over time. The ability to predict the behavior of this type of flow will be beneficial to a wide range of systems. One complex form of cavitation is the periodic shedding of cavitation clouds. This thesis experimentally describes the mechanisms which are responsible for the periodic shedding of vapor clouds. A converging-Diverging Nozzle (venturi) is selected as a canonical geometry for this project. The venturi has the highest contraction ratio, due to its shape, which results in a broader dynamic cavitation range. The venturi gives us the ability to precisely differentiate between different cavitation mechanisms due to their more intense nature

  • Void fraction measurements in partial cavitation regimes by X-ray computed tomography
    'Elsevier BV', 2019
    Co-Authors: Jahangir S., Wagner E.c., Mudde R.f., Poelma C.
    Abstract:

    Cavitation is a complicated multiphase phenomenon, where the production of vapor cavities leads to an opaque flow. Exploring the internal structures of the cavitating flows is one of the most significant challenges in this field of study. While it is not possible to visualize the interior of the cavity with visible light, we use X-ray computed tomography to obtain the time-averaged void fraction distribution in an axisymmetric converging-Diverging Nozzle (’venturi’). This technique is based on the amount of energy absorbed by the material, which in turn depends on its density and thickness. Using this technique, two different partial cavitation mechanisms are examined: the re-entrant jet mechanism and the bubbly shock mechanism. 3D reconstruction of the X-ray images is used (i) to differentiate between vapor and liquid phase, (ii) to obtain radial geometric features of the flow, and (iii) to quantify the local void fraction. The void fraction downstream of the venturi in the bubbly shock mechanism is found to be more than twice compared to the re-entrant jet mechanism. The results show the presence of intense cavitation at the walls of the venturi. Moreover, the vapor phase mixes with the liquid phase downstream of the venturi, resulting in cloud-like cavitation.

  • Dynamics of partial cavitation in an axisymmetric converging-Diverging Nozzle
    'Elsevier BV', 2018
    Co-Authors: Jahangir S., Hogendoorn W.j., Poelma C.
    Abstract:

    Partial cavitation dynamics in an axisymmetric converging-Diverging Nozzle are investigated experimentally. Shadowgraphy is used to visualize and analyze different cavitation regimes. These regimes are generated by changing the global static pressure and flow velocity independently. Cloud cavitation is the most interesting and complex regime, because the shedding of vapor clouds is caused by two different mechanisms: the re-entrant jet mechanism and the bubbly shock mechanism. The dynamics are investigated using a position-time diagram. Using such a diagram we show that for cavitation number σ > 0.95 the cavity shedding is caused by the re-entrant jet mechanism, and for σ < 0.75 the mechanism responsible for periodic cavity shedding is the bubbly shock mechanism. Both mechanisms are observed in the transition region, 0.75 < σ < 0.95. The shedding frequencies, expressed as Strouhal numbers, collapse on a single curve when plotted against the cavitation number, except for the transition region. The re-entrant jet mechanism is a pressure gradient driven phenomenon, which is caused by a temporary stagnation point at the cavity front. This leads to stick-slip behavior of the cavity. In the bubbly shock regime, a shock wave is induced by a collapse of the previously shedded vapor bubbles downstream of the venturi, which triggers the initiation of the detachment of the growing cavity. The propagation velocity of the shock wave is quantified both in the liquid and the mixture phase by means of the position-time diagram.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Fluid MechanicsMulti Phase System

  • X-ray computed tomography of cavitating flow in a converging-Diverging Nozzle
    'ASME International', 2018
    Co-Authors: Jahangir S., Wagner E.c., Mudde R.f., Poelma C.
    Abstract:

    Cavitation is a complex multiphase phenomenon, where the production of vapor bubbles leads to opaqueness of the flow. While it is nearly impossible to visualize the interior of the cavitation region with visible light, we show that with X-ray computed tomography it is possible to obtain the time-averaged void fraction distribution in an axisymmetric converging-Diverging Nozzle (venturi). This technique is based on the amount of energy absorbed by the material, based on its density and thickness. Time-averaged 3D reconstruction of the X-ray images is used (i) to distinguish between vapor and liquid phase, (ii) to get radial geometric features of the flow, and (iii) to quantify the local void fraction. The results show the presence of intense cavitation at the walls of the venturi, and the vapor fraction decreases downstream of the venturi with the vapor cloud.Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Fluid MechanicsChemE/AfdelingsbureauExecutive boardImPhys/Imaging PhysicsMulti Phase System

  • Complete dataset for Converging-Diverging Nozzle
    4TU.Centre for Research Data, 2018
    Co-Authors: Jahangir S., Hogendoorn W., Poelma C.
    Abstract:

    Cavitation dynamics in a converging-Diverging Nozzle are investigated experimentally. Shadowgraphy is used to visualize and analyze different cavitation regimes and the corresponding complete dataset is provided. This dataset will help researchers for validation of their numerical models. The related publications describe the mechanisms which are responsible for partial/ periodic cavitation