304 research outputs found
Inverse design technique for cascades
A numerical technique to generate cascades is presented. The basic prescribed parameters are: inlet angle, exit pressure, and distribution of blade thickness and lift along a blade. Other sets of parameters are also discussed. The technique is based on the lambda scheme. The problem of stability of the computation as a function of the prescribed set of parameters and the treatment of boundary conditions is discussed. A one dimensional analysis to indicate a possible way for assuring stability for any two dimensional calculation is provided
Two-vortex equilibrium in the flow past a flat plate at incidence
The two-dimensional inviscid incompressible steady flow past an inclined flat plate
is considered. A locus of asymmetric equilibrium configurations for vortex pairs
is detected. It is shown that the flat geometry has peculiar properties compared to
other geometries: (i) in order to satisfy the Kutta condition at both edges, which
ensures flow regularity, the total circulation and the force acting on the plate must be
zero; and (ii) the Kutta condition and the free vortex equilibrium conditions are not
independent of each other. The non-existence of symmetric equilibrium configurations
for an orthogonal plate is extended to more general asymmetric flows
Generic features of the fluctuation dissipation relation in coarsening systems
The integrated response function in phase-ordering systems with scalar,
vector, conserved and non conserved order parameter is studied at various space
dimensionalities. Assuming scaling of the aging contribution we obtain, by numerical simulations
and analytical arguments, the phenomenological formula describing the
dimensionality dependence of in all cases considered. The primary
result is that vanishes continuously as approaches the lower
critical dimensionality . This implies that i) the existence of a non
trivial fluctuation dissipation relation and ii) the failure of the connection
between statics and dynamics are generic features of phase ordering at .Comment: 6 pages, 5 figure
The N-Vortex Problem on a Symmetric Ellipsoid: A Perturbation Approach
We consider the N-vortex problem on a ellipsoid of revolution. Applying
standard techniques of classical perturbation theory we construct a sequence of
conformal transformations from the ellipsoid into the complex plane. Using
these transformations the equations of motion for the N-vortex problem on the
ellipsoid are written as a formal series on the eccentricity of the ellipsoid's
generating ellipse. First order equations are obtained explicitly. We show
numerically that the truncated first order system for the three-vortices system
on the symmetric ellipsoid is non-integrable.Comment: 14 pages, 1 figur
Crossover in Growth Law and Violation of Superuniversality in the Random Field Ising Model
We study the nonconserved phase ordering dynamics of the d = 2, 3 random
field Ising model, quenched to below the critical temperature. Motivated by the
puzzling results of previous work in two and three di- mensions, reporting a
crossover from power-law to logarithmic growth, together with superuniversal
behavior of the correlation function, we have undertaken a careful
investigation of both the domain growth law and the autocorrelation function.
Our main results are as follows: We confirm the crossover to asymptotic
logarithmic behavior in the growth law, but, at variance with previous
findings, the exponent in the preasymptotic power law is disorder-dependent,
rather than being the one of the pure system. Furthermore, we find that the
autocorre- lation function does not display superuniversal behavior. This
restores consistency with previous results for the d = 1 system, and fits
nicely into the unifying scaling scheme we have recently proposed in the study
of the random bond Ising model.Comment: To be published in Physical Review
Set of Boundary Conditions for Aerodynamic Design
Robust and flexible numerical methodologies for the imposition of boundary conditions are required to formulate well-posed problems. A boundary condition should be Robust and flexible numerical methodologies for the imposition of boundary conditions are required to formulate well-posed problems. A boundary condition should be nonreflecting, to avoid spurious perturbations that can provocate unsteadiness or instabilities. The reflectiveness of various boundary conditions is analyzed in the context of the Godunov methods. A nonlinear, isentropic wave propagation model is used to investigate the reflection mechanism on the flowfield borders, and a parameter Ï„ is defined to give a measure of the boundary reflectiveness. A new set of boundary conditions, in which Ï„ =0, that is, totally nonreflecting, is then proposed. The approach has been integrated in an aerodynamic design procedure using a distributed boundary control
Nonlinear response and fluctuation dissipation relations
A unified derivation of the off equilibrium fluctuation dissipation relations
(FDR) is given for Ising and continous spins to arbitrary order, within the
framework of Markovian stochastic dynamics. Knowledge of the FDR allows to
develop zero field algorithms for the efficient numerical computation of the
response functions. Two applications are presented. In the first one, the
problem of probing for the existence of a growing cooperative length scale is
considered in those cases, like in glassy systems, where the linear FDR is of
no use. The effectiveness of an appropriate second order FDR is illustrated in
the test case of the Edwards-Anderson spin glass in one and two dimensions. In
the second one, the important problem of the definition of an off equilibrium
effective temperature through the nonlinear FDR is considered. It is shown
that, in the case of coarsening systems, the effective temperature derived from
the second order FDR is consistent with the one obtained from the linear FDR.Comment: 24 pages, 6 figure
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