Experimental and Numerical Study of Swirling ... - Solid Mechanics

Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke
Marine Diesel Engines
Chapter 2
There have been a lot of experimental studies on characteristics of turbulent
swirling flows in straight pipe/ vortex chamber where swirl is generated
using propeller (Algifri et al., 1988) (Parchen et al., 1998), tangential
injection (nozzle or holes drilled in tangential direction) (Martemianov et al.,
2004) and (Zhang et al. 2006), twisted tape (young et al. 1978) (Islek A. A.,
2004) and (Cazan et al., 2009), rotating tube bundle or honeycomb (Marliani
et al., 2003 and Pashtrapanska et al, 2006) and fixed vanes (Kitoh, 1991)
(Sarpkaya, 1971) (Leibovich et al, 1978) etc. The aforementioned works are
very few in a very large amount of experimental measurements available in
the scientific literature and a detailed account is beyond the scope of this
thesis.
The measurement techniques used also vary and include swirl vortex meters,
pitot tubes, hot wire anemometry, Laser Doppler Velocimetry and Particle
Image Velocimetry etc. For example Kreith et al. (1965) etc. used swirl vortex
meters, (Lam H. C., 1993) etc. used five hole pitot tube, Algifri et al. (1988)
and Kitoh (1991) etc. conducted measurements using hot wire anemometry,
laser Doppler Velocimetry (LDV) (Parchen et al., 1998) (Marliani et al., 2003)
etc. and particle image Velocimetry (PIV) (Zhang et al. 2006) etc.
2.3 Some Aspects of Swirling Flows
Swirling flows have different distinct aspects compared to non-swirling
flows. In this section only some of the aspects are briefly discussed and for a
detailed account see (Alekseenko et al. 2007, Gupta et al. 1984, Saffman 1995,
Greitzer et al. 2004, Wu et al., 2006) etc. Effects of Coriolis forces are beyond
the scope of this thesis and thus are not discussed.
2.3.1 Stream line Curvature
In swirling flows with pure rotation i.e. no bulk flow in axial direction, the
streamlines are curved as shown in figure 2.6a. With the addition of axial
velocity, the streamline pattern resembles to a spring/ axially stretched spiral
object (Figure 2.6b). The spiral shape of the streamlines depends on the type
of the swirling flow, axial velocity profile, swirl decay, symmetric or
asymmetric swirl, wall curvature in case of cylindrical vortex chamber etc.
Figure 2.6c gives a sketch of the streamlines in idealized case of decaying
solid-body rotation with uniform axial velocity.
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Swirling Flows