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  • 1.
    Rabault, Jean
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Vernet, Julie A
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Lindgren, Björn
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    A study using PIV of the intake flow in a diesel engine cylinder2016In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 62, p. 56-67Article in journal (Refereed)
    Abstract [en]

    The admission flow generated by a parallel valve diesel engine cylinder head was investigated by planar and stereoscopic Particle Image Velocimetry in a steady flow test bench through measurements in the swirl and tumble planes. By combining several sets of measurements a full three-dimensional, three component reconstruction of the flow was made. The flow out of the valves forms a jet which collides with the cylinder wall before flowing down along the wall. Despite the fact that there is no piston a recirculation bubble is formed in the tumble plane. This is due to the entrainment of gas into the jet which needs to be replaced and thereby sets up a counter flow. In the swirl plane complex jet-dominated vortex structures are detected close to the cylinder top. Moving away from the cylinder top, a counter-rotating vortex-pair structure is observed from which a single coherent swirling structure develops further down the cylinder. Some clear differences are observed between the flow at high and moderate valve lifts, which correspond to a distinct change in the swirl intensity. By introducing a strong swirling motion the flow is stabilized which can be seen by tracking the instantaneous position of the swirl centre. For high swirl the variation of the position of the swirl centre decreases substantially. (C) 2016 Elsevier Inc. All rights reserved.

  • 2.
    Söder, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Vernet, Julie
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Lindgren, Björn
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    A Coupled PIV-LES Approach to Understand PortGenerated StructuresManuscript (preprint) (Other academic)
    Abstract [en]

    Inside an engine cylinder the flow field is very complex due to high gas velocities, flowseparation and pressure pulses at the ports. Historically, simple characteristic numbers such as swirland tumble have been used in order to quantify the flow in the cylinder. These integral quantities are likely to be insucient for optimization of the mixing process and combustion in IC engines. Instead,there is a need for detailed data with adequate temporal and spatial resolution. We simulate the flowpast the valves and validate these simulations using PIV measurements. By using LES data upstreamof the measurement plane an explanation to the structures seen in the PIV measurement plane can begiven.Here we show that at low valve lifts, the flow was blocked in such a way that the inertia created at theports were counteracted leading to the formation of two unstable counter rotating vortices. We alsodetected that the fluctuations in swirl number was one order of magnitude larger at the lower valvelifts. Furthermore, the small scale turbulence created at lower lifts was more anisotropic than for thehigher valve lifts. This work has thus increased the confidence in the CFD simulations in addition toproviding an explanation to the structures identified in PIV data.

  • 3.
    Söder, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. Scania CV, Sweden.
    Vernet, Julie
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Lindgren, Björn
    Scania CV, Sweden.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Study of flow generated by the port in a heavy-duty diesel engine at different valve lifts using PIVManuscript (preprint) (Other academic)
    Abstract [en]

    In-cylinder flow structures, also prior to ignition, have a large effect on combustion efficiency and emissions. Therefore, understanding the mechanism of formation and changes in such structures is of great importance in the work of reducing fuel consumption and emissions. Here, the flow entering the cylinder was studied using stereoscopic Particle Image Velocimetry (PIV). The measurements were carried out on a steady swirl test rig, commonly used to measure engine characteristics such as the swirl number. In this study, fluctuations in swirl coefficient were found to be greater than the mean swirl at low valve lifts, the flow was found to be Reynolds number independent and the turbulent fluctuations were observed to be axisymmetric.

  • 4.
    Söder, Martin
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Vernet, Julie
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Prahl Wittberg, Lisa
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Fuchs, Laszlo
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Study of in-cylinder ow structures using PIV and LESManuscript (preprint) (Other academic)
    Abstract [en]

    In-cylinder ow structures have a large eect on combustion eciency and emissions. Thus, understanding these structures is of great importance in the work of reducing fuel consumption and emissions. In this paper, the in-cylinder flow is studied using stereoscopic Particle Image Velocimetry (PIV) measurements and Large Eddy Simulations (LES). The measurements and simulations have been carried out on a steady swirl test rig, commonly used to measureengine characteristics such as the swirl number. In this study, the cause of the fluctuation in swirl is explained, showing that the fluctuation can be of greater importance as compared to the mean value of the swirl number. Moreover, we show how the flow from the inlet ports are distributed.

  • 5.
    Vernet, Julie
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Plasma actuators for separation control - design and application2014Licentiate thesis, comprehensive summary (Other academic)
  • 6.
    Vernet, Julie A.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Plasma actuators for separation control on bluff bodies2017Doctoral thesis, comprehensive summary (Other academic)
  • 7.
    Vernet, Julie A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Örlu, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Measurements of the electric wind induced by a Single Dielectric Barrier Discharge plasma actuatorManuscript (preprint) (Other academic)
  • 8.
    Vernet, Julie A
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    A turbulent boundary layer with pressure gradient, curvature and separation: results from hot-wire measurementsManuscript (preprint) (Other academic)
  • 9.
    Vernet, Julie A
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Scania CV AB, Sweden.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Flow separation control behind a cylindrical bump using dielectric-barrier-discharge vortex generator plasma actuators2017In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 835, p. 852-879Article in journal (Refereed)
    Abstract [en]

    Dielectric-barrier-discharge plasma actuators are arranged to produce counter-rotating streamwise vortices to control flow separation on a cylindrical bump on a flat plate that is approached by a turbulent boundary layer. The control was tested for different free-stream velocities and actuation driving voltages. The recirculation area downstream of the bump was reduced by the actuation for velocities up to 15 m s(-1) at the highest voltage achievable of the present set-up. However, the flow shows a bi-modality, the nominal two-dimensional wake flow is shown to consist of large-scale streamwise vortices, which are energised by the actuation until a phenomenon of lock-on of these vortices occurs at sufficiently high driving voltages. The wavelength of the actuation is half that of the large-scale vortices. The lock-on shifts sometimes, i.e. the large streamwise vortices centre switch spanwise location, explaining the bi-modality in the flow. The details of the bi-modality are further investigated by conditional averaging and proper orthogonal decomposition.

  • 10.
    Vernet, Julie A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Flow separation control by DBD plasma actuation: Part A: Steady and pulsed momentum injectionManuscript (preprint) (Other academic)
  • 11.
    Vernet, Julie A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Flow separation control by DBD plasma actuation: Part B: Steamwise vortex generatorsManuscript (preprint) (Other academic)
  • 12.
    Vernet, Julie A
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. Scania CV AB, Sodertalje, Sweden..
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Flow separation control by dielectric barrier discharge plasma actuation via pulsed momentum injection2018In: AIP Advances, ISSN 2158-3226, E-ISSN 2158-3226, Vol. 8, no 7, article id 075229Article in journal (Refereed)
    Abstract [en]

    Control of a turbulent boundary layer separating on a half-cylinder mounted on a flat plate has been investigated using a Dielectric Barrier Discharge (DBD) plasma actuator placed along the apex of a cylinder. The main focus of the study has been to evaluate if the control ability of the actuator can be improved through pulsed actuation compared to its steady counterpart. Investigations of the electric wind induced by the DBD plasma actuator in still air, when mounted on the flat plate, revealed that while the steady actuation produces an electric wind similar to a wall jet, the pulsed actuation creates a train of co-rotating vortices. The vortices are the result of a starting vortex produced by the actuator at each actuation pulse. A parametric study showed a dependence of the size, shape and propagation velocity of the vortices on the pulse frequency and duty cycle. With the actuator mounted along the apex of the cylinder, Particle Image Velocimetry measurements of the uncontrolled and controlled flow with a free-stream velocity of 5 m/s showed a clear reduction of the recirculation region downstream the cylinder when using plasma actuation. An even higher control effect could be achieved with pulsed actuation compared to the steady actuation. Phase-locked measurements of the unsteady actuation showed that pulsed actuation periodically shifted the flow separation location resulting in the propagation of vortical structures in the recirculation region. The size of the vortical structures showed a dependence on the pulsed actuation timing parameters.

  • 13.
    Vernet, Julie A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Proof-of-concept experiment with plasma streamwise vortex generators for flow separation control on trucksManuscript (preprint) (Other academic)
  • 14.
    Vernet, Julie A
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Turbulent boundary layer upstream, over and downstream a cylindrical 2D bump2016In: Springer Proceedings in Physics, Springer, 2016, p. 279-283Conference paper (Refereed)
  • 15.
    Vernet, Julie A.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH Mech, Linne FLOW Ctr, SE-10044 Stockholm, Sweden..
    Söderblom, David
    Scania CV AB, SE-15187 Sodertalje, Sweden..
    Elofsson, Per
    Scania CV AB, SE-15187 Sodertalje, Sweden..
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Plasma Streamwise Vortex Generators for Flow Separation Control on Trucks A Proof-of-concept Experiment2018In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 100, no 4, p. 1101-1109Article in journal (Refereed)
    Abstract [en]

    An experimental study of the effect of Dielectric Barrier Discharge plasma actuators on the flow separation on the A-pillar of a modern truck under cross-wind conditions has been carried out. The experiments were done in a wind tunnel with a 1:6 scale model of a tractor-trailer combination. The actuators were used as vortex generators positioned on the A-pillar on the leeward side of the tractor and the drag force was measured with a wind-tunnel balance. The results show that the effect at the largest yaw angle (9 degrees) can give a drag reduction of about 20% and that it results in a net power reduction. At lower yaw angles the reduction was smaller. The present results were obtained at a lower Reynolds number and a lower speed than for real driving conditions so it is still not yet confirmed if a similar positive result can be obtained in full scale.

  • 16.
    Vernet, Julie
    et al.
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics.
    Ramis, Örlü
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Separation control by means of plasma actuation on a half cylinder approached by a turbulent boundary layer.2015In: Journal of Wind Engineering and Industrial Aerodynamics, ISSN 0167-6105, E-ISSN 1872-8197, Vol. 145, p. 318-326Article in journal (Refereed)
    Abstract [en]

    The flow around a half cylinder (i.e. an immersed cylinder in a flat plate) approached by a turbulent boundary layer is studied, with the aim to control separation via steady Dielectric Barrier Discharge (DBD) plasma actuation. The electric wind induced by a single DBD plasma actuator is studied in quiescent air to understand the role of the different driving parameters and how the cylindrical shape influences the downstream development of the induced electric wind. A double DBD plasma actuator is then placed on the cylinder and the influence of the position of the actuator is studied in order to find the best achievable control. Comparison of the controlled and uncontrolled cases, using both hot-wire anemometry and pressure measurements, shows that a reduction of the separation bubble is possible. By optimizing the position of the double actuator, a reduction of up to 30% of the drag is achieved. The present geometry is chosen as a generic model of the flow around the front corners (A-pillars) of a truck cabin and the work is performed with the long-term vision to be able to reduce drag on trucks.

  • 17.
    Vernet, Julie
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Alfredsson, Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    A turbulent boundary layer with pressure gradient, curvature and separation – results from hot-wire measurements2014Report (Other academic)
  • 18.
    Vernet, Julie
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Alfredsson, Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Flow separation delay on trucks A-pillars by means of Dielectric  Barrier Discharge plasma actuation2014Article in journal (Other academic)
  • 19.
    Vernet, Julie
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Alfredsson, Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Phase-averaged measurements of the electric wind induced by a single Dielectric Barrier Discharge plasma actuator2014Article in journal (Other academic)
1 - 19 of 19
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