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Flow structures and associated turbulence in the tip region of an axial waterjet pump rotor.

机译：轴向水射流泵转子尖端区域的流动结构和相关的湍流。

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摘要

The flow field and associated turbulence in the tip region of an axial waterjet pump are investigated using cavitation visualization and particle image velocimetry. These measurements provide unprecedented details of the tip flow. Mechanisms of flow structure formation and evolution, as well as turbulence generation, are clarified. Unobstructed optical access in the measurements is achieved by matching the optical refractive indices of the casing, the blade, and the working fluid.;The flow in the blade tip region is dominated by backward tip leakage flow, which is driven by the pressure difference across the blade, and the subsequently developed tip leakage vortex (TLV). It is found in the present research that backward leakage flow separates from the casing after impinging on the forward passage flow and gets engulfed into the TLV. The TLV detaches from the blade due to vortex-wall interaction, and the leakage flow penetrates deeply into the passage, generating a three dimensional shear layer at its interface with the forward passage flow and a boundary layer near the casing. Both of them are entrained into the TLV after the endwall boundary layer separation. In instantaneous pictures, the TLV core is composed of multiple vortices interlacing each other. A fraction of vortex filaments spiral the main TLV along its periphery and form coil structures. In addition, the leakage flow varies substantially with the blade loading. The TLV persists much longer near the design condition than the off-design condition.;Turbulence in the tip region is highly anisotropic and inhomogeneous. It is generated primarily by the shear production in the shear layer and the contraction associated with the leakage flow separation. Consequently, turbulence kinetic energy peaks at these regions, but it is also elevated in other areas such as the TLV center due to the mean flow convection and low local dissipation rate. The vortex bursting and the vortex-blade interaction alter the production and turbulence energy significantly. Moreover, the unsteady motion of large scale coherent structures forms a significant fraction of the turbulent kinetic energy in the TLV core.
机译：使用空化可视化和粒子图像测速技术研究了轴向喷水泵尖端区域的流场和相关湍流。这些测量提供了尖端流量的前所未有的细节。阐明了流结构形成和演化以及湍流产生的机理。通过匹配外壳，叶片和工作流体的光学折射率，可以实现测量中无障碍的光学通道;叶片尖端区域中的流动主要由反向尖端泄漏流控制，该尖端泄漏流由跨过的压差驱动叶片，以及随后形成的尖端泄漏涡（TLV）。在本研究中发现，后向泄漏流在撞击前向通道流之后与套管分离，并被吞噬到TLV中。由于涡流-壁相互作用，TLV从叶片上脱离，泄漏流深深渗透到通道中，在与前向通道流的界面处产生三维剪切层，并在壳体附近产生边界层。在端壁边界层分离之后，它们两者都被夹带到TLV中。在瞬时图像中，TLV核心由相互交织的多个涡流组成。一部分涡流丝沿着主TLV的外围螺旋缠绕并形成线圈结构。另外，泄漏流量随叶片负载而显着变化。在设计条件下，TLV的持续时间比在设计条件外的持续时间长。尖端区域的湍流高度各向异性且不均匀。它主要由剪切层中的剪切产生以及与泄漏流分离相关的收缩产生。因此，湍流动能在这些区域达到峰值，但由于平均对流和低局部耗散率，湍流动能在其他区域（例如TLV中心）也有所升高。涡旋爆发和涡旋叶片相互作用极大地改变了产生和湍流能量。而且，大规模相干结构的非定常运动构成了TLV核中湍流动能的很大一部分。

著录项

  • 作者

    Wu, Huixuan.;

  • 作者单位

    The Johns Hopkins University.;

  • 授予单位 The Johns Hopkins University.;
  • 学科 Engineering Aerospace.;Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2011
  • 页码 147 p.
  • 总页数 147
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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