Nomenclature C = chord length, m C T = thrust coefficient f = flapping frequency, Hz h tip = plunge amplitude at the wing tip, m k = ωC∕U ∞ , reduced frequency l span = wingspan, m Re = U ∞ C∕ν, Reynolds number r z = z-directional distance away from the wing tip, m S wing = wing area, m 2 St = fh tip ∕U ∞ , Strouhal number U ∞ = freestream velocity, m∕s ν = kinematic viscosity of fluid, m 2 ∕s ...

Turbulence, produced by an impulsive spin down from angular velocity Omega to rest of a cube-shaped container, is investigated in superfluid 4He at temperatures 0.08 K-1.6 K. The density of quantized vortex lines L is measured by scattering negative ions. Homogeneous turbulence develops after time t approximately 20/Omega and decays as L proportional, t-3/2. The corresponding energy flux =nu'(k...

We study the shearing of polydisperse and bidisperse media with a size ratio of 10. Simulations are performed with a two-dimensional shear cell using contact dynamics. With a truncated power law for the polydisperse media we find that they show a stronger dilatancy and greater resistance to shearing than bidisperse mixtures. To model additives used to control viscosity we introduce so-called "p...

To elucidate the influence of shear flow on the generation of magnetic field (the dynamo effect), we study the kinematic limit where the magnetic field does not backreact on the velocity field. By non-perturbatively incorporating the effect of shear in a helically forced turbulence, we show that turbulence intensity and turbulent transport coefficients (turbulent viscosity, α and β effect) are ...

By injecting negative ions in superfluid 4He in the zero-temperature limit (T<or=0.5 K), we have generated tangles of quantized vortex line with negligible large-scale flow. For this quantum regime of superfluid turbulence, the vortex line length L was found to decay at late time t as L proportional to t{-1}, the prefactor being independent of the initial value of L. The corresponding effective...

where U is the root-mean-square velocity, kf is a wavenumber (inverse length scale) related with the forcing function, and Re = U/νkf . The positive coefficients C1 and C2 are uniform in the the kinematic viscosity ν, the amplitude of the driving force, and the system size. We compare these results with previously obtained bounds for body forces involving only a single length scale, or for velo...

We present an analytical scheme, easily implemented numerically, to generate synthetic Gaussian 2D turbulent flows by using linear stochastic partial differential equations, where the noise term acts as a random force of well-prescribed statistics. This methodology leads to a divergencefree, isotropic, stationary and homogeneous velocity field, whose characteristic parameters are well reproduce...

Seven patients with status asthmaticus intubated for respiratory failure who had elevated airway pressures and persistent respiratory acidosis were successfully ventilated using a mixture of 60 percent helium and 40 percent oxygen. All patients experienced a rapid reduction in airway pressures, CO2 retention, and resolution of acidosis while breathing a helium-oxygen mixture. There were no unto...

In this paper we consider a coupled system made of the Stokes and Darcy equations, and we propose some iteration-by-subdomain methods based on Robin conditions on the interface. We prove the convergence of these algorithms, and for suitable finite element approximations we show that the rate of convergence is independent of the mesh size h. A special attention is paid to the optimization of the...

Ax, A = amplitude of stroke amplitude in x direction, m, and orientation angle, deg CL, CL = lift coefficient and its average over flapping cycles CD, CD = drag coefficient and its average over flapping cycles CPW, CPW = input power coefficient and its average over flapping cycles c, h = chord and thickness of the plate, m; c is chosen as characteristic length Re = Uc v , Reynolds number, v is ...