This study has made clear the characteristics of the velocity and the mean temperature fields in mixing T-junctions with rectangular cross sections, which simulate the turbulent mixing of hot and cold air in the HVAC (heating, ventilation, air-conditioning) unit used for automobile air-conditioning system. The influences of the cross-sectional aspect ratio of the channel (AR) and the velocity ratio of hot and cold flows (VR) on the velocity and temperature distributions in the mixed flow have been examined experimentally. The main results ca be summarised as follows. (1) The flow that enters the main channel from the branch is separated at the downstream edge of the T-junction, and a large separation bubble is formed on the bottom wall of the main channel. This separation bubble has a three-dimensional shape with a trailing edge stretched further downstream at the location closer to the spanwise centreline of the channel. The scale of this separation bubble increases as VR is increased, but it is far less sensitive to AR. (2) In the cross section of the main channel, a Iongitudinal vortex appears near the lower corner at a location of X/B nearly equal 2, in which the separation bubble mostly develops in the Y-direction. This vortex is formed as it straddles the boundary between the reversed flow region and the favourable flow region outside it. In the downstream region of X/B nearly equal 4, however, the longitudinal vortex disappears together with the reattachment of the separated flow. Qualitatively similar distributions of the secondary flow appear in the channels with different AR. (3) The fluctuating velocity in the vertical direction by' that contributes directly to the turbulent transport of heat shows the local maximum in the mixing layer just after the merging of two flows. It shows a uniform distribution in the spanwise direction there. In the downstream region, ny' shows large values not in the mixing layer but in the shear layer around the separation bubble, and its values become larger in the region closer to the spanwise centreline of the channel reflecting the three-dimensional feature of the separation bubble. (4) The mean temperature distribution in the mixed flow shows two-dimensional feature, i.e., uniform in the spanwise direction, over the whole region after the flow merging, and thus the influence of the three-dimensional flow field does not appear in it. In the downstream region, the location of the maximum deltaT/deltaY does not agree with that of the maximum ny'. This suggests that the strong turbulence produced in the shear layer around the separation bubble does not contribute to the turbulent mixing of hot and cold airflows.


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    Titel :

    Experimental study on turbulent flow and thermal mixing in T-junction modeled after automobile HVAC unit


    Beteiligte:
    Asano, Hideo (Autor:in) / Hirota, Masafumi (Autor:in)


    Erscheinungsdatum :

    2005


    Format / Umfang :

    9 Seiten, 15 Bilder, 15 Quellen



    Medientyp :

    Aufsatz (Konferenz)


    Format :

    Print


    Sprache :

    Englisch




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