Active control of laminar-turbulent transition

Instability waves, commonly called T-S waves, can be introduced in a laminar boundary layer by periodic heating of flush-mounted heating elements. Experiments have demonstrated that nearly complete cancellation of a T-S wave excited in this way can be achieved by using a second downstream heating element with a suitable phase shift. As one application of the technique, a single element together with a feedback loop activated by measured wall shear stress has been used to reduce the amplitude of naturally occurring laminar instability waves. A significant increase in the transition Reynolds number has been achieved

Control of laminar-instability waves using a new technique

A new technique using surface-film activators has been developed to induce and control laminar-instability waves by periodic heating. A flat plate was instrumented and installed in the GALCIT High-speed Water Tunnel with flush-mounted surface heaters and probes. Extremely two-dimensional naturally occurring Tolmien-Schlichting (TS) waves were observed along with the subsequent formation of turbulent spots. Laminar-instability waves were then excited in a controlled fashion using the surface-mounted heaters. A preliminary experiment on cancellation of excited laminar-instability waves was carried out. Finally, turbulent spots were produced using amplitude-modulated bursts to form Gaussian TS wave packets. Flow visualization, along with wall shear measurements, was used to infer the velocity and vorticity field near the wall

Active Control of Transition Using the Lorentz Force

A new concept and technique has been developed to directly control boundary-layer transition and turbulence. Near-wall vertical motions are directly suppressed through the application of Lorentz force. Current (j) and magnetic (b) fields are applied parallel to the boundary and normal to each other to produce a Lorentz force (j x B) normal to the boundary. This approach is called magnetic turbulence control (MTC). Experiments have been performed on flat-plate transitional and turbulent boundary layers in water seeded with a weak electrolyte

The Coming Age of Parallel-Processing Supercomputer

It is anticipated that the needs of scientific computation will dramatically outpace the performance of general-purpose supercomputers over the next decade. These needs will, however, be addressed by an emerging class of parallelprocessing supercomputers (PPS). The Princeton University Navier-Stokes Computer (NSC) is a PPS geared toward simulating complex flows. It has a projected speed and capacity two orders of magnitude beyond that of current supercomputers. The architecture of the NSC and a discussion of a working prototype is presented

Multinode reconfigurable pipeline computer

A multinode parallel-processing computer is made up of a plurality of innerconnected, large capacity nodes each including a reconfigurable pipeline of functional units such as Integer Arithmetic Logic Processors, Floating Point Arithmetic Processors, Special Purpose Processors, etc. The reconfigurable pipeline of each node is connected to a multiplane memory by a Memory-ALU switch NETwork (MASNET). The reconfigurable pipeline includes three (3) basic substructures formed from functional units which have been found to be sufficient to perform the bulk of all calculations. The MASNET controls the flow of signals from the memory planes to the reconfigurable pipeline and vice versa. the nodes are connectable together by an internode data router (hyperspace router) so as to form a hypercube configuration. The capability of the nodes to conditionally configure the pipeline at each tick of the clock, without requiring a pipeline flush, permits many powerful algorithms to be implemented directly

Investigation of wall normal electromagnetic actuator for seawater flow control

Submitted versio

Lamination and folding in electromagnetically driven flows of specified geometries

Accepted versio

Control of flow geometry using electromagnetic body forcing

Accepted versio

Effectiveness of active flow control for turbulent skin friction drag reduction

The effectiveness of the opposition control method proposed by Choi et al. [J. Fluid Mech. 262, 75 (1994)] has been studied using direct numerical simulations. In this study, the effects of the amplitude and the phase of wall blowing and suction control input were considered separately. It is found that the amplitude of wall blowing and suction as well as the detection plane location played an important role in active control for skin-friction drag reduction. By changing the amplitude, a substantial drag reduction was achieved for all detection plane locations considered, and the efficiency of the opposition control was also improved. When the control was effective, the drag reduction was proportional to the wall blowing and suction strength. There existed a maximum wall blowing and suction strength, beyond which the opposition control became less effective or even unstable. Turbulence characteristics affected by various wall blowing and suction parameters were analyzed to understand the underlying mechanisms for drag reduction. The wall-normal velocity and vorticity fluctuations showed a strong correlation with drag reduction. © 2011 American Institute of Physic