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

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Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke Marine Diesel Engines Table 4.1: Axial Position of Measuring planes for different cylinder lengths. Chapter 4 Reynolds number. In the first part (marked by blue box), only first 6 positions for the aforementioned cylinder lengths are plotted. This provides a comparison of flow characteristics for measuring positions that are common in all the three cylinder lengths. The second part (marked by green box) describes the remaining positions i.e. position 7 and beyond which are common only for 6D and 8D cylinder lengths and also the positions which are only in 8D. Position No. Axial Positions ( z/D ) Cylinder Length (L/D) L1 =8 L2 =6 L3 =4 z1 0.963 z2 1.489 z3 2.016 z4 2.542 z5 3.068 z6 3.595 z7 4.116 z8 4.642 z9 5.168 z10 5.695 z11 6.226 z12 6.747 z13 7.268 Before discussing the results from stereoscopic PIV experiments on different cross-sectional planes along the cylinder length, it is necessary to study and understand the flow inside the swirl generator because the flow conditions and characteristics such as swirl angle (angle between radial and tangential velocity components), symmetric or asymmetric flow and turbulence level etc. in the swirl generator govern the resulting downstream in-cylinder swirling flow and knowing the flow inside swirl generator will help in better understanding of the PIV results at the downstream positions. Moreover, it will give an assessment of the design performance of swirl generator and also help in finding any possible manufacturing and human errors during construction, assembling and alignment of the inlet section. Proper and accurate alignment of all the guide vanes ensures a symmetric flow distribution/ swirl generation in the inlet section and any misalignment will introduce asymmetric swirl. 48 Swirling Flow in a Pipe
Experimental and Numerical Study of Swirling Flow in Scavenging Process for 2-Stroke Marine Diesel Engines Table 4.2: Radial Position of Measuring points along X-axis for LDA measurements. 4.1 LDA Measurements (Inlet Section) Chapter 4 Two components LDA measurements were conducted at different locations in the swirl generator as described in Section (3.6). The main reason for using LDA technique has been the possibility of conducting measurements at locations where PIV measurement becomes very difficult to be conducted due to guide vanes blocking the laser light (see section 3.1). The measurements are conducted at volume flow rate of 0.154 m 3 /s. Different radial positions from origin see figure 3.18, between inlet to swirl generator and contraction section, are selected and then measurements are conducted at same radial positions along each of the axes lines (Table 4.2). Axis Radial Positions from origin (mm) 275 230 215 200 185 X -X This must be mentioned here that in the real swirl generator the assumed axes lines, while crossing the blade row, do not lie on similar location between the two adjacent guide vanes e.g. the measurement at the radial position of 235 mm for negative Y axis is not possible due to the laser beam being blocked by a guide vane whereas for other axes measurements can be conducted at the same radial position. The measured radial velocity profiles for each half axis are shown in figure 4.1a (flow direction is from radial position at 275 mm to 180 mm). The halflength of each error bar is one standard deviation. It can be seen that the radial velocity distribution is not symmetric. Flow accelerates while passing through the row of guide vanes and further downstream due to the contraction section. Due to wake behind the guide vanes a decrease in the magnitude is also observed for radial positions of 200 mm along positive X. The tangential velocity profiles are shown in figure 4.1b. For both half axes, at radial position of 275 mm, a non-zero tangential velocity is observed which demonstrates either the flow feeling the presence of the guide vane being at downstream position or the blade edge facing the inlet section outlet is not perfectly aligned with the radius. Moreover, different values of tangential velocity and angle between radial and tangential velocity components along the axis lines indicate that there exists a small relative difference in alignment of guide vanes (Figure 4.1c). 49 Swirling Flow in a Pipe
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