31,650 research outputs found
A rational approach to comparing the performance of coaxial and conventional rotors
The merit, in terms of its efficiency and performance, of the twin, contrarotating coaxial rotor configuration over the more conventional single rotor system has long been a point of contention. Previously published comparisons yield seemingly inconsistent and conflicting conclusions. In this paper, the basis for a fair, like-for-like comparison of the performance of coaxial and single rotor systems is discussed. A comparison between experimentally measured data and numerical predictions of rotor performance obtained using the vorticity transport model shows that a computational approach can be used reliably to decompose the power consumption into induced and profile constituents. These comparisons show that a somewhat stronger similarity in geometry needs to be enforced between the two types of rotor system than previously suggested in order that the systems be directly comparable. If the equivalent single rotor system is constructed to have the same disk area, blade geometry, and total number of blades as that of the coaxial rotor, then the geometric differences between the two systems are confined to the defining characteristics of the two types of rotor system, in other words to the vertical separation between the rotor blades and their relative direction of rotation. The differences in aerodynamic performance between a coaxial rotor and an equivalent single rotor defined in this way then arise solely as a result of the differences in the detailed interaction between the blades and their wakes that arise within the two types of system. Using this form of comparison, the articulated coaxial system is shown to consume marginally less induced power than the equivalent single rotor system. The difference is small enough, however, to be obscured if the profile drag of the blades is overtly sensitive to operating condition, as for instance might be the case at low Reynolds number
Entropy of (2+1)-dimensional de Sitter black hole to all orders in the Planck length
We calculate the statistical entropy of a scalar field on the background of
(2+1)-dimensional de Sitter space without an artificial cutoff considering
corrections to all orders in the Planck length from a generalized uncertainty
principle (GUP) on the quantum state density. The desired entropy proportional
to the horizon perimeter is obtained.Comment: 10 pages, two references adde
Lagrangian approach to local symmetries and self-dual model in gauge invariant formulation
Taking the St\"uckelberg Lagrangian associated with the abelian self-dual
model of P.K. Townsend et al as a starting point, we embed this mixed first-
and second-class system into a pure first-class system by following
systematically the generalized Hamiltonian approach of Batalin, Fradkin and
Tyutin. The resulting Lagrangian possesses an extended gauge invariance and
provides a non-trivial example for a general Lagrangian approach to unravelling
the full set of local symmetries of a Lagrangian.Comment: LaTeX, 15 page
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