CoHERENT STRUCTURES in Pump-intake FLOWS: A LARGE EDDY SIMULATION (LES) STUDY

The presence of unsteady intermittent meandering wall attached and free-surface vortices is a common feature of pump intake flows.  These vortices are known to induce high levels of unsteady swirl inside the pump column and negatively affect the performance of the pumps.  LES is used to predict the dynamics of the main vortical structures (phenomena such as vortex meandering and intermittency are investigated along with an analysis of the changes in the structure of these large vortices in time) in the flow as well as the mean flow statistics.  These statistics are compared to the PIV data collected by Yulin et al. (2000) on a scaled model of a pressurized (no free surface) pump sump.  For completeness results from a RANS simulation using the SST model on a fine mesh (no wall functions are used) are shown.  The dynamic Smagorinsky model is used in LES without wall functions.  The Reynolds number in the pump column is close to 200,000, while the physical Reynolds number in the pump sump region is about one fifth (~40,000) of that.  The unstructured mesh in the LES simulation contains close to 5 million cells. 

 The long time goal of the present work is to use LES as a predictive tool that can be employed in the design or redesign process of pump intakes.  As LES directly resolves the most energetic coherent structures, it has build into it much more physics compared to RANS/URANS models and thus a much better chance to accurately capture not only the unsteady dynamics of the vortices but also to more accurately predict the mean flow, in particular the mean swirl distribution inside the pipe.

  1. Figure. General view of the pump intake
  2. Figure. Sections where the comparisons with the experimental data obtained using PIV data by Yulin et al. (2000) are made.
  3. Figure. General view of the computational domain. 1) Grid at a section through the center of the pipe; 2) Grid at a section parallel to the channel bottom close to the pump bell level; 3) Grid near the pump bell.

 

VALIDATION

  1. Figure. Streamlines at representative sections in the domain; 1) x2 plane; 2) x3 plane; 3) x4 plane; 4) x5 plane; 5) x7 plane. (See Figure 2 for the positions of these planes)
  2. Figure. Streamlines at different representative sections in the domain; 1) z1 plane; 2) z3 plane; 3) z5 plane. (See Figure 2 for the positions of these planes)
  3. Figure. Validation: Contours of velocity magnitude and turbulent kinetic energy (TKE) at different sections; 1) Velocity magnitude - x7 plane; 2) TKE - x7 plane. (See Figure 2 for the positions of these planes)
  4. Figure. Contours of velocity magnitude and turbulent kinetic energy (TKE) at different sections; 1) Velocity magnitude - y1 plane; 2) TKE - y1 plane; 3) Velocity magnitude - y3 plane; 4) TKE - y3 plane. (See Figure 2 for the positions of these planes)
  5. Figure. Velocity magnitude, turbulent kinetic energy (TKE) and absolute out-of-plane vorticity contours in the z1 plane; a) Velocity magnitude - z1 plane; b) TKE - z1 plane; c) Absolute vorticity - z1 plane. (See Figure 2 for the position of this plane)
  6. Figure. Velocity magnitude, turbulent kinetic energy (TKE) and absolute out-of-plane vorticity contours in the z2 plane; 1) Velocity magnitude - z2 plane; 2) TKE - z2 plane; 3) Absolute vorticity - z2 plane. (See Figure 2 for the position of this plane)

 

COHERENT STRUCTURES

  1. Movie 1: Dynamics of coherent structures in a plane 0.6D from the channel bottom. (Streamlines)
  2. Movie 2: Dynamics of coherent structures in a plane parallel to the sidewall 2, 0.62D away from it. (Streamlines)
  3. Movie 3: Pressure contours at a section cutting through the center of the pump column showing the core of the floor attached vortex.
  4. Movie 4: Dynamics of coherent structures in a plane cutting through the center of the pump column. (Streamlines)
  5. Movie 5: Vorticity contours in a plane cutting through the center of the pipe, parallel to the backwall showing the floor attached vortex.
  6. Movie 6: Dynamics of coherent structures around the pump column showed in a plane 0.53D above the pump bell level and parallel to the channel bottom. (Streamlines)
  7. Movie 7: Vorticity contours around the pump column showed in a plane 0.53D above the pump bell level and parallel to the channel bottom.
  8. Figure. Contours of vorticity at different levels inside the vertical pipe and decay of absolute circulation inside the pipe.
  9. Figure. Time series and power spectra at selected points around the pump column 1) Pressure at a point 0.2D away from the channel bottom; 2) Pressure at a point at the pump bell level; 3) Pressure at a point inside the pipe 0.9D away from the channel bottom; 4) z-velocity at the same point.
  10. Figure. Energy spectrum of a point near sidewall 2 inside the sidewall attached vortex