tailieunhanh - Computational Fluid Dynamics Harasek Part 14

Tham khảo tài liệu 'computational fluid dynamics harasek part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 384 Computational Fluid Dynamics Tip-vortex trajectory The tip vortex trajectory was predicted and compared with the experiment measurements. An approximate approach to locate the tip vortex core location is to limit the search for a minimum pressure within the region of the known vortex indicated by a swirl parameter. The physical interpretation for this criterion is given by Jeong and Hussain Jeong Hussain 1995 . Within the vortex core pressure tends to have a local minimum on the axis of a circulatory or swirling motion when the centrifugal force is balanced by the pressure force which is strictly true only in a steady inviscid planar flow. Using this method the tipvortex trajectories were identified from computed flows at the advance ratio of J . Fig. 8 compared the predicated radial locations of the tip vortex with the experimental observation. In the experiment the tip vortex was tracked from the blade tip to an axial location of approximately one diameter downstream where x R . The current simulation conducted in this study can predict the tip vortex radial trajectory accurately up to a limited distance downstream due to the grid coarsening in the downstream of the propeller. As shown in Fig. 8 the predicted tip-vortex trajectory is tracked to the location about only one radius downstream at x R before dissipated into the flow field. The largest disagreement between the prediction and the experiment measurement occurs at the last station of x R . Beyond that point it appeared to be difficult to trace the tip vortex as it has completely smeared out in the flow field. Examination of the grid resolution of the propeller indicated a finer grid resolution only coving a limited distance in the downstream of the propeller. The grid cells became very coarser as moving beyond the shaft rear surface at station x R . Fig. 9 clearly demonstrated the tip vortex convection which is quickly dissipated due to the limited grid resolution. As discussed in

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