Change search
Refine search result
1 - 21 of 21
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Kalpakli, Athanasia
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Experimental study of turbulent flows through pipe bends2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis deals with turbulent flows in 90 degree curved pipes of circular cross-section. The flow cases investigated experimentally are turbulent flow with and without an additional motion, swirling or pulsating, superposed on the primary flow. The aim is to investigate these complex flows in detail both in terms of statistical quantities as well as vortical structures that are apparent when curvature is present. Such a flow field can contain strong secondary flow in a plane normal to the main flow direction as well as reverse flow.

    The motivation of the study has mainly been the presence of highly pulsating turbulent flow through complex geometries, including sharp bends, in the gas exchange system of Internal Combustion Engines (ICE). On the other hand, the industrial relevance and importance of the other type of flows were not underestimated.

    The geometry used was curved pipes of different curvature ratios, mounted at the exit of straight pipe sections which constituted the inflow conditions. Two experimental set ups have been used. In the first one, fully developed turbulent flow with a well defined inflow condition was fed into the pipe bend. A swirling motion could be applied in order to study the interaction between the swirl and the secondary flow induced by the bend itself. In the second set up a highly pulsating flow (up to 40 Hz) was achieved by rotating a valve located at a short distance upstream from the measurement site. In this case engine-like conditions were examined, where the turbulent flow into the bend is non-developed and the pipe bend is sharp. In addition to flow measurements, the effect of non-ideal flow conditions on the performance of a turbocharger was investigated.

    Three different experimental techniques were employed to study the flow field. Time-resolved stereoscopic particle image velocimetry was used in order to visualize but also quantify the secondary motions at different downstream stations from the pipe bend while combined hot-/cold-wire anemometry was used for statistical analysis. Laser Doppler velocimetry was mainly employed for validation of the aforementioned experimental methods.

    The three-dimensional flow field depicting varying vortical patterns has been captured under turbulent steady, swirling and pulsating flow conditions, for parameter values for which experimental evidence has been missing in literature.

  • 2.
    Kalpakli, Athanasia
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    POD analysis of stereoscopic PIV data from swirling turbulent flow through a pipe bend2012Report (Other academic)
    Abstract [en]

    Coherent structures in turbulent swirling flow through a pipe bend are investigated experimentally by means of stereoscopic particle image velocimetry. Inparticular, the effect of the imposed swirling motion on the Dean vortices aswell as the very-large-scale structures is examined for a wide range of swirlnumbers. Proper orthogonal decomposition is employed to rank the spatialmodes by energy content and extract the underlying secondary swirling motionas well as the large-scale structures present in the flow field. Moreover theoriginal snapshots are reconstructed by using only a few of the most energeticmodes and ease visualization of the structures by inhomogeneously filtering theflow fields. Phenomena such as the unsteady motion of the Dean vortices, theso called swirl switching, in the non-swirling turbulent flow case and the tiltingof the very-large-scale structures in a highly swirling turbulent flow are capturedand presented. The results presented here are preliminary and furtheranalysis is planned in the future. Nevertheless, this work is believed to provideunique data as the first experimental study on swirling flows through a pipebend which is not restricted to single-point measurements.

  • 3.
    Kalpakli, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Turbulent pipe flow downstream a 90 degrees pipe bend with and without superimposed swirl2013In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 41, p. 103-111Article in journal (Refereed)
    Abstract [en]

    In the present work, the turbulent flow downstream a 90 degrees pipe bend is investigated by means of stereoscopic particle image velocimetry. In particular, the three dimensional flow field at the exit of the curved pipe is documented for non-swirling and swirling flow conditions, with the latter being generated through a unique axially rotating pipe flow facility. The non-swirling flow was examined through snapshot proper orthogonal decomposition (POD) with the aim to reveal the unsteady behaviour of the Dean vortices under turbulent flow conditions, the so-called "swirl-switching" phenomenon. In respect to the swirling turbulent pipe flow, covering a wide range of swirl strengths, POD has been employed to study the effect of varying strength of swirl on the Dean vortices as well as the interplay of swirling motion and Dean cells. Furthermore, the visualised large scale structures in turbulent swirling flows through the bend are found to incline and tear up with increasing swirl intensity. The present time-resolved, three component, experimental velocity field data will provide a unique and useful database for future studies; in particular for the CFD community.

  • 4.
    Kalpakli, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Dean vortices in turbulent flows: rocking or rolling?2012In: Journal of Visualization, ISSN 1343-8875, E-ISSN 1875-8975, Vol. 15, no 1, p. 37-38Article in journal (Refereed)
    Abstract [en]

    Flows in pipe bends have been studied extensively over the last decades due to their occurrence both in the human respiratory and blood systems as well as in many technical applications. When a fluid flows through a pipe bend an adverse pressure gradient is generated forcing high velocity fluid towards the outer wall which is then replaced by low velocity fluid moving along the wall towards the inner side of the bend. The physical effect is that the high velocity fluid is experiencing a large centrifugal force, resulting in an unstable ‘‘stratification’’ making the high velocity fluid in the centre deflect outwards along the pipe bend, thereby forming two counter-rotating roll cells, so-called Dean vortices. While their behavior in laminar flows has been nicely visualized, the picture of their unsteady behavior in turbulent flows still remains rather blurry, and in fact ‘‘the questions, for example, whether the Dean vortices stay symmetric with respect to the geometric plane of symmetry or whether the strength of the Dean vortices varies with time are hardly addressed’’ (Rütten et al 2005). In the present study, stereoscopic particle image velocimetry has been employed to seize the unsteady behavior of the Dean vortices at the exit of a 90 degree pipe bend at a Reynolds number and Dean number of 34,000 and 19,000, respectively. While the time-averaged flow field shows two symmetrical roll cells, that can be observed both in the streamwise and cross stream velocities, as well as in the streamwise vorticity, the instantaneous snapshots reveal an unsteady behavior where the roll cells are pushing one another alternatively towards the lower or upper half of the pipe, in what could be described as a ‘‘rocking’’ motion of the high speed ‘‘stem’’ in between the roll cells. Hence, the real question is not whether ‘‘to be, or not to be’’ in regards to the instantaneous existence of the Dean vortices in turbulent flows, but rather why, when and how they roll (as their time-averaged counterpart) or rock between the states caught in the presented snapshots.

  • 5.
    Kalpakli, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Tillmark, Nils
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    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).
    Experimental investigation on the effect of pulsations on exhaust manifold-related flows aiming at improved efficiency2012In: Institution of Mechanical Engineers - 10th International Conference on Turbochargers and Turbocharging, 2012, p. 377-387Conference paper (Refereed)
    Abstract [en]

    The gas flowing through the exhaust manifold of the internal combustion engine to the inlet of the turbine side of a turbocharger is highly pulsating and turbulent. The gas enters the turbine after travelling through a complex curved and branched pipe system where the effect of centrifugal (from the acute curvature), inertia and viscous forces result in a three-dimensional, non-symmetric flow field. Additionally, vortical structures are being formed and dissolved due to the co-existence of these forces that change in magnitude under a pulse period. This complex flow field, typical for the inflow condition to the turbine, is the focus of the present study. Instantaneous mass flow rate and pressure measurements that provide information on changes in the turbine map when a sharp bend is mounted at the inlet of the turbine are performed and complemented with time-resolved stereoscopic particle image velocimetry measurements of the pulsating turbulent flow downstream a 90° pipe bend. The results indicate, that the time-averaged operation point in a turbine map is only marginally affected by the inflow conditions and the pulsation frequency. The hysteresis loops, on the other hand, exhibit differences not only for different pulsation frequencies, but also for different inflow conditions as a comparison between a straight and a curved pipe section upstream the turbine shows.

  • 6.
    Kalpakli, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, Centre for Internal Cumbustion Engine Research Opus, CICERO (closed 20101231).
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, Centre for Internal Cumbustion Engine Research Opus, CICERO (closed 20101231).
    Tillmark, Nils
    KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Centre for Internal Cumbustion Engine Research Opus, CICERO (closed 20101231).
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Centres, Centre for Internal Cumbustion Engine Research Opus, CICERO (closed 20101231).
    Experimental investigation on the effect of pulsations on turbulent flow through a 90degrees pipe bend2010In: Proc. of 3rd Int. Conf. on Jets, Wakes & Separated Flows 2010, 2010Conference paper (Other academic)
    Abstract [en]

    Pulsatile turbulent flows in curved pipes at high Dean numbers are prevalent in various components of internal combustion engines, particularly the intake of exhaust manifolds. Despite their technological importance, there is a clear lack of experimental data. The present paper provides preliminary, albeit unique, data from an experimental investigation, thereby addressing this gap and depicts impressions of the phase evolution of the complex flow including a back flow region. It is also shown, that due to the scale separation of the pulsations and the turbulence, the pulsatile flow can statistically be decomposed into its large-scale pulsations and the steady case.

  • 7.
    Kalpakli, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Tillmark, Nils
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Pulsatile turbulent flow through pipe bends at high Dean and Womersley numbers2011In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 318, p. 092023-Article in journal (Refereed)
    Abstract [en]

    Turbulent pulsatile flows through pipe bends are prevalent in internal combustion engine components which consist of bent pipe sections and branching conduits. Nonetheless, most of the studies related to pulsatile flows in pipe bends focus on incompressible, low Womersley and low Dean number flows, primarily because they aim in modeling blood flow, while internal combustion engine related flows have mainly been addressed in terms of integral quantities and consist of single point measurements. The present study aims at bridging the gap between these two fields by means of time-resolved stereoscopic particle image velocimetry measurements in a pipe bend with conditions that are close to those encountered in exhaust manifolds. The time/phase-resolved three-dimensional cross-sectional flow-field 3 pipe diameters downstream the pipe bend is captured and the interplay between different secondary motions throughout a pulse cycle is discussed.

  • 8.
    Kalpakli Vester, Athanasia
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Turbulent pipe flow past a pipe bend: effects of upstream conditions and curvature ratio2014Report (Other academic)
  • 9.
    Kalpakli Vester, Athanasia
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Vortices in turbulent curved pipe flow-rocking, rolling and pulsating motions2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis is motivated by the necessity to understand the flow structure of turbulent flows in bends encountered in many technical applications such as heat exchangers, nuclear reactors and internal combustion engines. Flows in bends are characterised by strong secondary motions in terms of counter-rotating vortices (Dean cells) set up by a centrifugal instability. Specifically the thesis deals with turbulent flows in 90° curved pipes of circular cross-section with and without an additional motion, swirling or pulsatile, superposed on the primary flow.  The aim of the present thesis is to study these complex flows in detail by using time-resolved stereoscopic particle image velocimetry to obtain the three-dimensional velocity field, with complementary hot-wire anemometry and laser Doppler velocimetry measurements.

    In order to analyse the vortical flow field proper orthogonal decomposition (POD) is used. The so called ``swirl-switching'' is identified and it is shown that the vortices instantaneously, ``rock'' between three states, viz. a pair of symmetric vortices or a dominant clockwise or counter-clockwise Dean cell. The most energetic mode exhibits a single cell spanning the whole cross-section and ``rolling'' (counter-)clockwise in time. However, when a honeycomb is mounted at the inlet of the bend, the Dean vortices break down and there is strong indication that the ``swirl-switching'' is hindered.

    When a swirling motion is superimposed on the incoming flow, the Dean vortices show a tendency to merge into a single cell with increasing swirl intensity. POD analysis show vortices which closely resemble the Dean cells, indicating that these structures co-exist with the swirling motion. In highly pulsating turbulent flow at the exit of a curved pipe, the vortical pattern is diminished or even eliminated during the acceleration phase and then re-established during the deceleration.

    In order to investigate the effect of pulsations and curvature on the performance of a turbocharger turbine, highly pulsating turbulent flow through a sharp bend is fed into the turbine. Time-resolved pressure and mass-flow rate measurements show that the hysteresis loop in the pressure-ratio-mass-flow plane, may differ significantly between straight and curved inlets, however the mean operating point is only slightly affected.

  • 10.
    Kalpakli Vester, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Sattarzadeh, Sohrab Shirvan
    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, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Combined hot-wire and PIV measurements of a swirling turbulent flow at the exit of a 90° pipe bend2015In: Journal of Visualization, ISSN 1343-8875, E-ISSN 1875-8975Article in journal (Refereed)
    Abstract [en]

    Measurements of turbulent swirling flow by means of hot-wire anemometry and stereoscopic particle image velocimetry were performed, 0.67 pipe diameters downstream a 90° pipe bend. The flow for a wide range of swirl numbers up to (Formula presented.), based on the angular velocity of the pipe wall and bulk velocity, was investigated and compared to the non-swirling case. The limitations and advantages of using a single hot-wire probe in a highly complex flow field are investigated and discussed. The present paper makes available a unique database for a kind of flow that has been neglected in literature and which is believed to be useful for validation purposes for the computational fluid dynamics community.

  • 11.
    Kalpakli Vester, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    High Womersley number pulsatile turbulent flow past a straight and bent pipeManuscript (preprint) (Other academic)
  • 12.
    Kalpakli Vester, Athanasia
    et al.
    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.
    Örlü, Ramis
    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.
    POD analysis of the turbulent flow downstream a mild and sharp bend2015In: Experiments in Fluids, ISSN 0723-4864, E-ISSN 1432-1114, Vol. 56, no 3, article id 57Article in journal (Refereed)
    Abstract [en]

    Time-resolved stereoscopic particle image velocimetry measurements have been taken of the turbulent flow at the exit plane of a mild and a sharp pipe bend. Cross-sectional flow fields were obtained 1, 2 and 3 pipe diameters downstream the bend in order to capture the flow evolution. Proper orthogonal decomposition (POD) was applied in order to identify the underlying vortical patterns and revealed the existence of a single cell spanning the whole cross section as the most dominant structure, while the Dean cells appeared in the next most energetic modes. The results from these investigations, which indicate the origin of the oscillatory motion of the Dean vortices, the so-called swirl switching, were found to agree with those presented by Hell-strom et al. (J Fluid Mech 735: R7, 2013). Furthermore, the effect of a honeycomb, mounted at the bend inlet, on the flow field has been studied by means of statistical and POD analysis in order to test the hypothesis by Sakakibara and Machida (Phys Fluids 24: 041702, 2012), viz. whether the unsteady behaviour of the Dean cells is related to large-scale structures existing upstream the bend. As a consequence of the honeycomb, the Dean vortices do not appear in the mean field, nor in the most energetic modes, which opens possibilities to overcome or at least delay the problem of fatigue in piping systems which can be caused by the swirl switching.

  • 13.
    Kalpakli Vester, Athanasia
    et al.
    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.
    Örlü, Ramis
    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 Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx). KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Pulsatile Turbulent Flow in Straight and Curved Pipes - Interpretation and Decomposition of Hot-Wire Signals2015In: Flow Turbulence and Combustion, ISSN 1386-6184, E-ISSN 1573-1987, Vol. 94, no 2, p. 305-321Article in journal (Refereed)
    Abstract [en]

    Pulsatile turbulent flows in curved pipes at high Womersley and Reynolds numbers are prevalent in various components of internal combustion engines, in particular in the intake of the exhaust manifold. Despite their technological importance, there appears to be a lack of experimental data both with regard to straight and bent pipes. The present paper addresses this gap through phase-locked hot-wire anemometry measurements in a highly pulsatile turbulent flow through straight and bent pipes and compares the results with those obtained under steady flow conditions. The aim is to understand to some extent the effect of pulsations on the turbulent flow itself and for that purpose different decomposition methods are applied to the data in order to reveal the underlying turbulence from the pulsatile signal. Besides classical phase-averaging, also temporal filtering and singular value decomposition have been employed to investigate the decomposed turbulence statistics in terms of their pulsatile and turbulence contributions. Results show that-due to the large scale separation between the turbulence and pulsations-both decomposition techniques provide similar results and highlight, that the statistics from the turbulent part of the pulsatile flow resemble those of the steady one.

  • 14.
    Kalpakli Vester, Athanasia
    et al.
    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.
    Örlü, Ramis
    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.
    Vortical patterns in turbulent flow downstream a 90° curved pipe at high Womersley numbers2013In: International Journal of Heat and Fluid Flow, ISSN 0142-727X, E-ISSN 1879-2278, Vol. 44, p. 692-699Article in journal (Refereed)
    Abstract [en]

    The present experimental work focuses on highly pulsatile, i.e. inertia dominated, turbulent flow downstream a curved pipe and aims at investigating the vortical characteristics of such a flow. The flow parameters (Dean and Womersley number) investigated are of the same order as those met in the internal combustion engine environment. The technique employed is time-resolved stereoscopic particle image velocimetry at different cross-sections downstream the pipe bend. These measurements allow the large-scale structures that are formed to be analyzed by means of proper orthogonal decomposition. The flow field changes drastically during a pulsatile cycle, varying from a uniform flow direction across the pipe section from the inside to the outside of the bend to vortical patterns consisting of two counter-rotating cells. This study characterizes and describes pulsatile curved pipe flow at Womersley numbers much higher than previously reported in the literature. Furthermore, the oscillatory behaviour of the Dean cells for the steady flow - the so-called 'swirl switching' - is investigated for different downstream stations from the bend exit and it is shown that this motion does not appear in the immediate vicinity of the bend, but only further downstream.

  • 15.
    Kalpakli Vester, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Tillmark, Nils
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Some observations of pulsating, curved pipe flow and its influence on turbine maps2014Report (Other academic)
  • 16.
    Laurantzon, Fredrik
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Kalpakli, Athanasia
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Alfredsson, Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Review on the sensed temperature in cold-wire and hot-wire anemometry2010Report (Other academic)
    Abstract [en]

    Instantaneous velocity and temperature measurements by means of hot-wire and coldwires have become a standard technique used in almost every fluid dynamic research laboratory. Nonetheless, when it comes to compressible flows in applied fields, there seems to remain a need for clarification on which temperature is actually measured by a cold-wire and which temperature a hot-wire senses as its fluid temperature. The present paper reviews the view present in the literature and presents additional experimental evidence, that it is indeed the recovery temperature that is measured by a cold-wire and that this is also the temperature needed to compensate hot-wire readings in nonisothermal compressible flows

  • 17.
    Pastuhoff, Markus
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Kalpakli, Athanasia
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Alfredsson, P Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Pressure and velocity field measurements of pulsating flow in a square channel y-junction2013In: Bulletin of the American Physical Society 58, 2013Conference paper (Refereed)
    Abstract [en]

    The pressure and velocity fields in a y-junction of a square (40×40 mm²) cross-section channel were investigated during pulsating flow. One of the sides of the channel was covered with fast responding pressure sensitive paint (PSP) whereas the velocity field at the channel center parallel to the PSP surface was measured using particle image velocimetry (PIV). The flow conditions, in terms of mass flow rate and pulsation frequency, were selected to resemble the flow inside an exhaust manifold of a small internal combustion engine, although the gas was at room temperature. The mass flow was varied between 10 and 130 g/s with pulsations between 0 and 80 Hz. For both the PSP and the PIV measurements images were acquired unsynchronized to the pulses using a high-speed camera and phase averages were formed a posteriori. The use of PSP together with PIV demonstrates how the two techniques can be used to verify and complement each other, PIV excelling at the lower mass flow rates and PSP at the higher. It is shown that the signal-to-noise ratio for PSP at low velocities can be enhanced using a technique based on singular value decomposition.

  • 18.
    Sattarzadeh Shirvan, Sohrab
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW.
    Kalpakli, Athanasia
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Hot-Wire Calibration at Low Velocities: Revisiting the Vortex Shedding Method2013In: Advances in Mechanical Engineering, ISSN 1687-8132, E-ISSN 1687-8140, Vol. 2013, p. 241726-Article in journal (Refereed)
    Abstract [en]

    The necessity to calibrate hot-wire probes against a known velocity causes problems at low velocities, due to the inherent inaccuracy of pressure transducers at low differential pressures. The vortex shedding calibration method is in this respect a recommended technique to obtain calibration data at low velocities, due to its simplicity and accuracy. However, it has mainly been applied in a low and narrow Reynolds number range known as the laminar vortex shedding regime. Here, on the other hand, we propose to utilize the irregular vortex shedding regime and show where the probe needs to be placed with respect to the cylinder in order to obtain unambiguous calibration data.

  • 19.
    Vester, Athanasia Kalpakli
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Nishio, Yu
    Tohoku Univ, Grad Sch Engn, Aoba Ku, 6-6-01 Aramaki Aoba, Sendai, Miyagi 9808579, Japan..
    Alfredsson, P. Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics.
    Unravelling tumble and swirl in a unique water-analogue engine model2018In: Journal of Visualization, ISSN 1343-8875, E-ISSN 1875-8975, Vol. 21, no 4, p. 557-568Article in journal (Refereed)
    Abstract [en]

    The in-cylinder flow prior to combustion is considered to be one of the most important aspects controlling the combustion process in an engine. More specifically, the large-scale structures present in the cylinder, so-called tumble and swirl, before compression are believed to play a major role into the mixing and combustion processes. Their development during the intake stroke and their final strength depend mainly (but not only) on the inlet port design. In the present study, the turbulent large-scale structures during the intake stroke are investigated in a unique water-analogue engine where inlet ports and valve timings can easily be configured and tested. The flow field in the cylinder volume is reconstructed through multi-planar stereoscopic particle image velocimetry measurements which reveal a wealth of vortical structures during the stroke's various phases. The aim of the present paper is to present and show results from a unique setup which can serve as a test bench for optimisation of inlet port designs to obtain a desired vortical pattern in the cylinder after the intake stroke is finished. This setup can simulate the intake stroke in a much more realistic way as compared to a through-flow setup with a fixed valve lift.

  • 20.
    Vester, Athanasia
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Örlü, Ramis
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Tillmark, Nils
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    Alfredsson, Henrik
    KTH, School of Engineering Sciences (SCI), Mechanics, Fluid Physics.
    The characteristics of turbulence in curved pipes under highly pulsatile flow conditions2014In: Springer Proceedings in Physics, Springer, 2014, p. 183-187Conference paper (Refereed)
    Abstract [en]

    High speed stereoscopic particle image velocimetry has been employed to provide unique data from a steady and highly pulsatile turbulent flow at the exit of a 90 degree pipe bend. Both the unsteady behaviour of the Dean cells under steady conditions, the so called “swirl switching” phenomenon, as well as the secondary flow under pulsations have been reconstructed through proper orthogonal decomposition. The present data set constitutes – to the authors’ knowledge – the first detailed investigation of a turbulent, pulsatile flow through a pipe bend.

  • 21.
    Örlü, Ramis
    et al.
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Kalpakli Vester, Athanasia
    KTH, School of Engineering Sciences (SCI), Mechanics. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Industrial Engineering and Management (ITM), Centres, Competence Center for Gas Exchange (CCGEx).
    Flow visualization of an oblique impinging jet: vortices like it downhill, not uphill2015In: Journal of Visualization, ISSN 1343-8875, E-ISSN 1875-8975Article in journal (Refereed)
1 - 21 of 21
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf