Control of Turbulence Using Ultrasound
Publication Date: 2002-Feb-21
The IP.com Prior Art Database
Using the right frequency and intensity of ultrasound, applied on the hull of a vessel, it is possible to control the onset of turbulence in the surrounding medium, such as water, or air. By such a process, the onset of turbulence may be controlled, resulting in the reduction of drag due to turbulence. In this way, it may be possible to reduce the cost of fuel to move at higher speeds.
Is the Critical Reynolds Number a Universal Constant?
Due to reports accumulated over several years about the observed differences of the critical Reynolds number for different pure gases, and even for liquids, we raise the question of the universality of the critical Reynolds number for the onset of turbulence. We summarize the results, and briefly discuss the physical idea which prompted these experiments in the first place. These experiments, and it is strongly suggested, even more experiments in the future, raise the fundamental question on whether the Navier-Stokes equation should be the sole and unique starting point of turbulence research.
Critical Reynolds number, turbulent-laminar transition, molecular hydrodynamics, control of turbulence
The mystery of turbulent flows has been intriguing researchers in mechanics, synergetics, hydrodynamics, plasma physics, geophysics, chemistry and biology. In spite of more than a century of history (Lumley and Yaglom, 2001), this problem is still unsolved. Numerous experiments since Reynolds' paper (1883) show that the stationary flow of fluids is possible only if the Reynolds number is less than some critical value. It is known that the Navier-Stokes equations govern laminar flows. Furthermore, the theoretical analysis is considerably simplified for incompressible flows. In this case, only the dimensionless Reynolds number defines the regime of the flow. The breakdown of the stationary flow is associated with the loss of the stability with increasing Reynolds number. The value of the critical Reynolds number depends on the nature of the flow, but should be the same for different fluids in the same flow. This statement is considered a fundamental tenet for understanding the nature of the turbulent flows.
Hagen-Poiseuille flow (Schiller, 1882; Prandtl and Tietjens,1931) or flow in a
long circular pipe, is stable with respect to infinitesimal disturbances . The transition to
turbulence occurs as a result of finite perturbations or insufficiently smooth boundary
conditions at the pipe entrance. In the transition to the turbulent regime, the drag
coefficient increases sharply, which makes it possible to monitor the critical Reynolds
number reliably. To avoid objections arising out of experiments with compressible gases
(Nerushev and Novopashin, 1996, 1997 ; Novopashin and Muriel, 1998, 2000) , we
studied the transition to turbulence of normal water and heavy water. For as long as the
viscosity and densities are accurate, these two liquids should have the same critical
Reynolds number according to classical hydrodynamics.
The experimental set-up is shown on Fig.1. A basin with liquid (2) is installed inside a hermetically sealed chamber (1). The air pressure in the chamber may be compressed up to 500 Torr above atmospheric pressure by a...