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Marcus Hultmark wins Jacobus Fellowship, top graduate student honor

Princeton University graduate students Giada Damen, Marcus Hultmark, Noam Lupu and Silviu Pufu have been named as co-winners of the Porter Ogden Jacobus Fellowship, Princeton’s top honor for graduate students. The fellowship supports the final year of study and is awarded to students whose work has exhibited the highest scholarly excellence.

The Jacobus Fellows will be honored at Alumni Day ceremonies Saturday, Feb. 26, at Jadwin Gymnasium

Hultmark, a doctoral student in the Department of Mechanical and Aerospace Engineering, first came to Princeton as a visiting student from the Chalmers University of Technology in Sweden, where he earned a master’s degree in thermo and fluid dynamics.

Hultmark’s dissertation focuses on turbulence in cases of a high Reynolds number — the ratio between inertial forces to viscous forces. High Reynolds numbers can be found in the flow of the Earth’s atmosphere and in the flow of aircraft, submarines and other vessels. In order to measure turbulence and to create circumstances with high Reynolds numbers, Hultmark and his collaborators have developed nanoscale velocity probes that have enabled turbulence measurement at higher Reynolds numbers than ever before. Hultmark also set a world record for the highest Reynolds number wake flow ever measured in a laboratory.

“I hope to make an important contribution to the basic understanding of turbulence and to the design of energy-efficient vehicles and improved climate- and weather-prediction methods,” Hultmark said.

Alexander Smits, Princeton’s Eugene Higgins Professor of Mechanical and Aerospace Engineering and Hultmark’s thesis adviser, noted that Hultmark has amassed a “remarkable record of achievement for a graduate student.” Smits added, “He is a superb experimentalist, but what makes him special is that he asks the right questions. … I am confident that Marcus has a remarkable future ahead of him as a scientist, engineer and teacher.”

Secondary Motions in Fully Developed Pipe Flow

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Secondary Motions in Fully Developed Pipe Flow

Secondary motions downstream of pipe curvatures are widely studied for low and moderate Reynolds numbers, where the secondary flows are driven by the centrifugal pressure gradient. For these Reynolds numbers, there exists two cell vortex that is symmetric around the center plane of the pipe known as the Dean motion. However, when the Reynolds number is increased the flow becomes turbulent, and instabilities are introduced to the two-cell structure. These instabilities cause the flow to alternate between a dominating upper cell and lower cell. The two cells coexist in the transition between the modes, Figure 1.

Figure 1The figure shows the instantaneous azimuthal velocity component for Re 18000 at three distinct times. The secondary motion is alternating between a dominant lower and upper cell. The ratio between the curvature of the bend and the radius of the pipe is 1.

Figure 2,The instantaneous vorticity field (left) is compared with the time-averaged vorticity field (right) for Re 18000. Time-averaging reveals the Dean motion, though vorticity levels are considerably weaker.