Lagrangian features of circular and semi-circular jets via 3D particle tracking velocimetry

Significance Statement

Substantial research on jet flows has considered circular cross sections. However, jets from prismatic pipes and complex sections are common in many engineering applications. Evidence shows that mean flow and turbulence levels exhibit similarities in the far field irrespective of the pipe section.

Research led by Dr. Leonardo P. Chamorro from the University of Illinois aims to uncover persisting signatures of a particular configuration in the far field. In particular, they proposed a method to investigate distinctive Lagrangian statistical properties of jets from circular and semi-circular pipes sharing the same Reynolds number and hydraulic diameter. Two independent setups and particle tracking velocimetry (PTV) systems were employed at two scales. Their work is now published in the peer-reviewed journal, Experimental Thermal and Fluid Science.

Jets from semi-circular and circular pipes were investigated from two setups. Air was used as the working fluid in one of the set ups, where a real-time large scale LS-PTV was implemented to describe the flow in intermediate and far fields. Water was used as the working fluid in the second setup. Here, high-resolution flow measurements were performed with a small-scale SS-PTV. SS-PTV provided well-resolved high-density trajectories, while the other covered an extended region.

In the first setup, air was released from the pipes in an unbounded, quiescent room at a fixed rate. Jets were seeded with Helium filled soap bubbles and illuminated by four LED light panels. Six cameras with onboard image processing tracked particle image intensity. The coordinates of each particle centroid were then transferred to the computer for processing. In the second set up, water was released in a quiescent water body from fully submerged pipes, far from walls and free surface. The jets were seeded with hollow ceramic spheres. The particles were illuminated by five Lithium Ion Halogen spotlights, and images captured with a Mikrotron camera. Multiple camera angle views were captured with a four-view image splitter. Approximately 500 particles were detected in each of the four views. Data recorded was processed using the openPTV.

In the LS-PTV experiment, the background flow is not seeded. Therefore, the monotonic expansion of fluid particle trajectories is from the jets. Complementary Eulerian description of the velocity field was obtained by interpolating Lagrangian scattered data into a grid using triangulation method. The views show no relevant Eulerian differences between the two pipes, and indicate the major features of the mean flow, i.e. maximum velocity at the jet core, and the velocity decrease with axial and radial distances.

In the SS-PTV experiment, jet and background medium were seeded and about 20,000 trajectories were resolved and used to get Lagrangian statistical description of the flow. Probability density functions (PDF) of the velocity fluctuations showed departure from the Gaussian distribution away from the jet core. The acceleration PDFs exhibited heavy tails in the two jets; however the curvature PDF revealed distinctive signature of the pipe shape. This approach open possibilities to connect far-field flow perturbations with the source.

Reference

J.-T. Kim1, Z. Zhang2, A. Liberzon3, Y. Zhang2, L.P. Chamorro1,4,5. On the Lagrangian features of circular and semicircular jets via 3D particle tracking velocimetry. Experimental Thermal and Fluid Science 77 (2016) 306–316.

Show Affiliations
  1. Department of Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
  2. Department of Agricultural and Biological Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
  3. Turbulence Structure Laboratory, School of Mechanical Engineering, Tel Aviv University, 69978 Ramat Aviv, Israel
  4. Department of Aerospace Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
  5. Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA

 

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