Counter Rotating Research Articles

Heat transfer in rotating spiral channel with two opposite planar walls roughened by skew ribs

Heat transfer performances in a radially rotating spiral channel with two opposite planar endwalls roughened by in-line 45° ribs at speeds of 0–900 rev/min are experimentally examined. Airflow enters this rotating channel from the spiral eye and flows spirally outward with different co- and counter rotating conditions at which the Coriolis secondary flows respectively enrich and suppress the combined vortices tripped by skew-ribs and centrifugal forces. Local Nusselt numbers along the centerlines of the inner/outer smooth curved walls and the ribbed planar endwall are individually measured at Reynolds numbers (Re) of 750–30,000, rotation numbers (Ro) of 0–3.09 and buoyancy numbers (Bu) of 0.00038–7.88 with co- and counter rotations. In the static channel, the rib-induced sectional flows enrich Dean vortices to raise the mean centerline-averaged Nusselt numbers (Nu¯0,mean) to 5.79–9.84 and 3.37–2.11 times of the straight plain duct references (Nu∞) at laminar and turbulent conditions, respectively. In the rotating channel, the rotation induced Coriolis and centrifugal forces act synergetically to generate various degrees of heat transfer impacts on the inner, outer and ribbed channel walls. A set of selected heat transfer data illustrates the differential rotational-force effects on local Nu and the averaged Nusselt numbers (Nu¯) along the centerlines of rotating inner, outer and ribbed walls by analyzing the interdependent and isolated Re, Ro and Bu impacts on Nu and Nu¯ at co- and counter rotating conditions. Due to the combined Re, Ro and Bu effects, Nu¯/Nu¯0 ratios over the inner, outer and ribbed walls with co- and counter rotations respectively fall in the ranges of 1.08–3.01, 1.03–2.6 and 1.01–2.19 at co-rotating conditions and 1.01–2.63, 2.68–1.87 and 0.74–2.13 with counter rotations. A set of physically consistent heat transfer correlations is generated to permit the evaluation of individual and interdependent Re, Ro and Bu impacts on Nu¯ over each constituent channel wall for this rotating spiral ribbed channel.

Ship Vibration Control Using a Force-Adjustable Mechanical Actuator

A mechanical actuator to generate adjustable force and its control algorithm have been developed to reduce ship structural vibration of a single harmonic component of main engine rotating frequency The actuator generates a unidirectional sinusoidal force using the vectorial sum of centrifugal forces of two coun terrotating unbalanced masses. The adjustable-force generation during its operation has been embodied by the mechanism to adjust the eccentric distance of the mass using a link system. The control algorithm using the vibration magnitude and phase signals of both the actuator and main engine has been adopted to reduce ship structural vibration. The algorithm automatically detects the optimal phase and force magnitude. That should be supplied by using the variation of controlled vibratory response according to the phase difference between the main engine and the actuator. This algorithm can be applied without any prior identification of the dynamic characteristics of ship structures. In the control experiments for the superstructure vibration of two large merchant ships, the developed system showed good performance in reducing the vibration levels to 1/6 ~ 1/2 of the uncontrolled levels.

Efficient hybrid scheme for the analysis of counter-rotating propellers

An efficient solution procedure has been developed for analyzing inviscid unsteady flow past counter rotating propellers. This scheme is first order accurate in time and second order in space, and has been extended to fourth order accuracy in the axial direction. The solution procedure has been applied to a 2-bladed SR-7 single rotation propeller and to a GE F7/A7 counter rotation propeller. The pressure coefficients and the global quantities, power and thrust, show good comparison with experimental measurements.

Nonlinear wave mechanics: Iwo Bialynicki-Birula. Department of Physics, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, and Institute of Theoretical Physics, Warsaw University 00-681 Warsaw, Poland; and Jerzy Mycielski. Institute of Theoretical Physics, Warsaw University 00-681 Warsaw, Poland

We demonstrate the capability to exercise advanced control on the laser-induced periodic surface structures (LIPSS) on silicon by combining the effect of temporal shaping, via tuning the interpulse temporal delay between double femtosecond laser pulses, along with the independent manipulation of the polarization state of each of the individual pulses. For this, cross-polarized (CP) as well as counter-rotating (CR) double circularly polarized pulses have been utilized. The pulse duration was 40 fs and the central wavelength of 790 nm. The linearly polarized double pulses are generated by a modified Michelson interferometer allowing the temporal delay between the pulses to vary from Δτ = −80 ps to Δτ = +80 ps with an accuracy of 0.2 fs. We show the significance of fluence balance between the two pulse components and its interplay with the interpulse delay and with the order of arrival of the individually polarized pulse components of the double pulse sequence on the final surface morphology. For the case of CR pulses we found that when the pulses are temporally well separated the surface morphology attains no axial symmetry. But strikingly, when the two CP pulses temporally overlap, we demonstrate, for the first time in our knowledge, the detrimental effect that the phase delay has on the ripple orientation. Our results provide new insight showing that temporal pulse shaping in combination with polarization control gives a powerful tool for drastically controlling the surface nanostructure morphology.