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Mechanical Engineering Home > Labs and Centers: Shear Flow Control Laboratory

Shear Flow Control Laboratory

  Researchers:

       David Forliti

       Alison Behrens

       Michael Hallberg

  Recent Students:

       Brian Tang

  Documents:

       Key Papers
 

The objective of the Shear Flow Control Laboratory is to advance our fundamental understanding of free shear flows, and in the process, develop control strategies to solve applied problems in fluid dynamics. The class of flows of particular interest include: subsonic and supersonic jets; two- and three-dimensional wakes flows; wall-bounded flows experiencing significant free shear effects; and combustion applications where free shear flow control can be employed to influence flame speed and emissions.

The Shear Flow Control Lab incorporates passive techniques where the known stability aspects of the flow are exploited to cause desired changes in the flow. Our approach contrasts those used in other research groups, where flow control relies on the introduction of disturbances of controlled amplitude and phase to produce the desired changes in the flow field. These methods tend to be complicated, requiring sensors and actuators, which are typically too fragile to survive the harsh environments encountered in practice. In our laboratory, flow control has been used in several applications, including: mixing enhancement of shear layers and jets; the thrust vector control of high-speed jets for propulsion; entrainment studies in plasma and low density jets; and in rotating, high-heat-release combustors. State of the art instrumentation is used to study these fluid dynamic problems, including Particle Image Velocimetry (PIV) and Laser Doppler Anemometry (LDA), as well as more traditional methods such as hot-wire anemometry and pitot probe surveys.

Dave Forliti, a Ph.D. student advised by Prof. Strykowski, is pictured here with a low-speed air jet. A laser light sheet is passed through the jet, and tiny olive oil droplets seeded in the jet flow scatter the laser light. The motions of the particles are used to measure two-dimensional instantaneous velocity fields. The structure of the instantaneous flow is seen in the PIV image, which is not available using traditional single-point measurement techniques. In addition to the measurement of instantaneous flow features, several velocity fields can be measured and ensemble statistics can be obtained of the flow field. The computer screen shows the distribution of mean velocity gradients for the free jet flow, which gives insight into the level of mixing and entrainment of the jet with the surrounding fluid.