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  • 1.
    Ford, C. L.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Winroth, Marcus
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Development of a pressure based vortex-shedding meter: measuring unsteady mass-flow in variable density gases2016In: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 27, no 8, article id 085901Article in journal (Refereed)
    Abstract [en]

    An entirely pressure-based vortex-shedding meter has been designed for use in practical time-dependent flows. The meter is capable of measuring mass-flow rate in variable density gases in spite of the fact that fluid temperature is not directly measured. Unlike other vortex meters, a pressure based meter is incredibly robust and may be used in industrial type flows; an environment wholly unsuitable for hot-wires for example. The meter has been tested in a number of static and dynamic flow cases, across a range of mass-flow rates and pressures. The accuracy of the meter is typically better than about 3% in a static flow and resolves the fluctuating mass-flow with an accuracy that is better than or equivalent to a hot-wire method.

  • 2.
    Ford, C. L.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Winroth, P. Marcus
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Vortex-meter design: The influence of shedding-body geometry on shedding characteristics2018In: Flow Measurement and Instrumentation, ISSN 0955-5986, E-ISSN 1873-6998, Vol. 59, p. 88-102Article in journal (Refereed)
    Abstract [en]

    The periodic vortex shedding from bluff bodies may be used in flow metering applications. However, because the bluff-body is highly confined (typically in a pipe) the shed vortices may interact with the pipe wall; causing an undesirable non-linear behaviour. An experimental investigation has been conducted; examining the vortex-shedding characteristics of highly confined bluff-bodies in pipe flow, at high Reynolds number (ReD=4.4×104 to 4.4×105). The bluff-bodies were comprised of a forebody and tail; both of which affected the primary-shedding characteristics. The shedders typically produced two unsteady modes: Mode-I was associated with the vortex shedding and mode-II resulted from a separation of the pipe-wall boundary layer. The mode-I behaviour allowed two classes of shedder to be defined: long-tails and short-tails. Modes I and II interacted, particularly for long-tailed geometries. When the length-scale of mode-II exceeded 0.8κ (where κ is the physical scale of the primary shedding vortex), mode-II disrupted mode-I, as the mode-frequency ratio (fII/fI) approached an integer value. The coupling of modes I and II caused mode-I to deviate from its preferred Strouhal number. When the deviation exceeded 25–30%, mode-I locked on to the mode-II frequency. This did not happen for short-tailed geometries, as the length-scale of mode-I was always dominant. Mode-coupling for short-tails occurred only when the mode frequencies were equal. 

  • 3.
    Ford, Christopher L.
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Winroth, Per Marcus
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    On the scaling and topology of confined bluff-body flows2019In: Journal of Fluid Mechanics, ISSN 0022-1120, E-ISSN 1469-7645, Vol. 876, p. 1018-1040Article in journal (Refereed)
    Abstract [en]

    An experimental study of bluff bodies in confinement is presented. Two Reynolds matched rigs (pipe diameters: D D 40 mm and D D 194 mm) are used to derive a picture of the flow topology of the primary-shedding mode (Karman vortex, mode-I). Confined bluff bodies create an additional spectral mode (mode-II). This is caused by the close coupling of the shedder blockage and the wall and is unique to the confined bluff-body problem. Under certain conditions, modes-I and II can interact, resulting in a lock-on, wherein the modes cease to exist at independent frequencies. The topological effects of mode interaction are demonstrated using flow visualisation. Furthermore, the scaling of mode-II is explored. The two experimental facilities span Reynolds numbers (based on the shedder diameter, d) 104 < Red < 105 and bulk Mach numbers 0 : 02 < Mb < 0 : 4. Bluff bodies with a constant blockage ratio (d = D), forebody shape and various splitter-plate lengths (l) and thicknesses (t) are used. Results indicate that the flow topology changes substantially between short (l < d) and long (l > d) tailed geometries. Surface flow visualisation indicates that the primary vortex becomes anchored on the tail when l & 3h (2h D d t). This criterion prohibits the development of such a topology for short-tailed geometries. When mode interaction occurs, which it does exclusively in long-tailed cases, the tail-anchored vortex pattern is disrupted. The onset of mode-II occurs at approximately the same Reynolds number in both rigs, although the associated dimensionless frequency is principally a function of Mach number. Accordingly, mode interaction is avoided in the larger-scale rig, due to the increased separation of the modal frequencies.

  • 4.
    Winroth, Marcus
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Dynamics of Exhaust Valve Flows and Confined Bluff Body Vortex Shedding2019Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis can be divided into two interconnected topics; engine exhaust-valve flows and confined bluff-body vortex shedding. When optimising engine flow systems it is common to use low order simulation tools that require empirical inputs, for instance with respect to flow losses across the exhaust valves. These are typically obtained from experiments at low pressure ratios and for steady flow, assuming the flow to be insensitive to the pressure ratio and that it can be considered as quasi-steady. Here these two assumptions are challenged by comparing measurements of mass-flow rates under steady and dynamic conditions at realistic pressure ratios. The experiments with a static valve were carried out using a high-pressure flow bench at cylinder pressures up to 500 kPa. For the dynamic-valve experiments the transient flow rate during the blowdown phase of an initially pressurised cylinder was determined. Here a linear motor actuated the valve to obtain equivalent engine speeds in the range 800–1350 rpm. It was shown that neither of the above mentioned assumptions are valid and a new non-dimensional quantification of the steadiness of the process was formulated. Furthermore it was shown through Schlieren visualisation that the shock structures in the exhaust port differ depending on if the system dynamics are included or not. The study shows that reliable results of flow losses past exhaust valves can only be obtained in dynamic experiments at representative pressure ratios. The second topic arose from the need to monitor time-resolved mass-flow rates in conduits. A mass-flow meter based on vortex shedding from bluff bodies was designed where microphones are used to detect the shedding frequency. It consists of a forebody and a downstream mounted tail and the system was shown to be capable of measuring pulsating flow rates. Furthermore, the flow topology associated with different forebody and splitter plates has been characterised, through visualisation of the flow behind the shedder and on the splitter plate. It has been shown that for long splitter plates a “horse shoe” like vortex, which attaches to the tail, is formed. It has also been shown that another energetic mode (denoted mode-II) can interact with and disrupt the primary vortex formation. A hypothesis for the appearance of mode-II has been formulated, linking it to the periodic separation of the boundary layer at the conduit wall.

  • 5.
    Winroth, Marcus
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    On Gas Dynamics of Exhaust Valves2017Licentiate thesis, monograph (Other academic)
    Abstract [en]

    With increasing effects of global warming, efforts are made to make transportation

    in general more fuel efficient. When it comes to internal combustion engines,

    the most common way to improve fuel efficiency is through ‘downsizing’. Downsizing

    means that a smaller engine (with lower losses and less weight) performs

    the task of a larger engine. This is accomplished by fitting the smaller engine

    with a turbocharger, to recover some of the energy in the hot exhaust gases.

    Such engine systems need careful optimization and when designing an engine

    system it is common to use simplified flow models of the complex geometries

    involved. The exhaust valves and ports are usually modelled as straight pipe

    flows with a corresponding discharge or loss coefficient, typically determined

    through steady-flow experiments with a fixed valve and at low pressure ratios

    across the valve. This means that the flow is assumed to be independent of

    pressure ratio and quasi-steady.

    In the present work these two assumptions have been experimentally tested

    by comparing measurements of discharge coefficient under steady and dynamic

    conditions. The steady flow experiments were performed in a flow bench, with

    a maximum mass flow of 0.5 kg/s at pressures up to 500 kPa. The dynamic

    measurements were performed on a pressurized, 2 litre, fixed volume cylinder

    with one or two moving valves. Since the volume of the cylinder is fixed, the

    experiments were only concerned with the blowdown phase, i.e. the initial part

    of the exhaustion process. Initially in the experiments the valve was closed and

    the cylinder was pressurized. Once the desired initial pressure (typically in the

    range 300-500 kPa) was reached, the valve was opened using an electromagnetic

    linear motor, with a lift profile corresponding to different equivalent engine

    speeds (in the range 800-1350 rpm).

    The results of this investigation show that neither the quasi-steady assumption

    nor the assumption of pressure-ratio independence holds. This means

    that if simulations of the exhaustion process is made, the discharge coefficient

    needs to be determined using dynamic experiments with realistic pressure ratios.

    Also a measure of the quasi-steadiness has been defined, relating the change

    in upstream conditions to the valve motion, i.e. the change in flow restriction,

    and this measure has been used to explain why the process cannot be regarded

    as quasi-steady.

  • 6.
    Winroth, Marcus
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Ford, Christopher L.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Alfredsson, Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    On discharge from poppet valves: effects of pressure and system dynamics2018In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 59, no 2, article id 24Article in journal (Refereed)
    Abstract [en]

    Simplified flow models are commonly used to design and optimize internal combustion engine systems. The exhaust valves and ports are modelled as straight pipe flows with a corresponding discharge coefficient. The discharge coefficient is usually determined from steady-flow experiments at low pressure ratios and at fixed valve lifts. The inherent assumptions are that the flow through the valve is insensitive to the pressure ratio and may be considered as quasi-steady. The present study challenges these two assumptions through experiments at varying pressure ratios and by comparing measurements of the discharge coefficient obtained under steady and dynamic conditions. Steady flow experiments were performed in a flow bench, whereas the dynamic measurements were performed on a pressurized, 2 l, fixed volume cylinder with one or two moving valves. In the latter experiments an initial pressure (in the range 300–500 kPa) was established whereafter the valve(s) was opened with a lift profile corresponding to different equivalent engine speeds (in the range 800–1350 rpm). The experiments were only concerned with the blowdown phase, i.e. the initial part of the exhaustion process since no piston was simulated. The results show that the process is neither pressure-ratio independent nor quasi-steady. A measure of the “steadiness” has been defined, relating the relative change in the open flow area of the valve to the relative change of flow conditions in the cylinder, a measure that indicates if the process can be regarded as quasi-steady or not.

  • 7.
    Winroth, P. Marcus
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). CCGEx.
    Characterization of and correction for pressure-measurement installation2017Report (Other academic)
    Abstract [en]

    A method to experimentally determine the dynamic characteristics of pressure measurement installations has been developed and tested. The method involves pressurising a volume enclosed by a rubber membrane until the membrane burst, generating a negative pressure step. The natural frequency and damping ratio of the system can then be found through analysis of the step response of the measurement system.

    An example showing how it is possible to compensate for the dynamic characteristics of the installation, for qualitative measurements of highly dynamic processes is also given. This is done by modelling the system as an acoustic oscillator. Since the model requires that the time derivative of the signal is taken it amplifies noise in the signal, meaning that the quantitative values of the corrected measurements should be handled with care.

  • 8.
    Winroth, Per Marcus
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Ford, Christopher Luke
    KTH, School of Engineering Sciences (SCI), Mechanics.
    On the scaling and topology of confined bluff-body flowsManuscript (preprint) (Other academic)
1 - 8 of 8
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