54,791 research outputs found
Analysis and design of transonic airfoils using streamwise coordinates
A new approach is developed for analysis and design of transonic airfoils. A set of full potential equivalent equations in von Mises coordinates is formulated from the Euler equations under the irrotationality and isentropic assumptions. This set is composed of a main equation for the main variable, y, and a secondary equations for the secondary variable, R. The main equation is solved by type dependent differencing combined with a shock point operator. The secondary equation is solved by marching from a non-characteristic boundary. Sample computations on NACA 0012 and biconvex airfoils show that, for the analysis problem, the present approach achieves good agreement with experimental C sub p distributions. For the design problem, the approach leads to a simple numerical algorithm in which the airfoil contour is calculated as part of the flow field solution
Small radii of neutron stars as an indication of novel in-medium effects
At present, neutron star radii from both observations and model predictions
remain very uncertain. Whereas different models can predict a wide range of
neutron star radii, it is not possible for most models to predict radii that
are smaller than about 10 km, thus if such small radii are established in the
future they will be very difficult to reconcile with model estimates. By
invoking a new term in the equation of state that enhances the energy density,
but leaves the pressure unchanged we simulate the current uncertainty in the
neutron star radii. This new term can be possibly due to the exchange of the
weakly interacting light U-boson with appropriate in-medium parameters, which
does not compromise the success of the conventional nuclear models. The
validity of this new scheme will be tested eventually by more precise
measurements of neutron star radii.Comment: EPJA (2015) in pres
Probing the high-density behavior of symmetry energy with gravitational waves
Gravitational wave (GW) astronomy opens up an entirely new window on the
Universe to probe the equations of state (EOS) of neutron-rich matter. With the
advent of next generation GW detectors, measuring the gravitational radiation
from coalescing binary neutron star systems, mountains on rotating neutron
stars, and stellar oscillation modes may become possible in the near future.
Using a set of model EOSs satisfying the latest constraints from terrestrial
nuclear experiments, state of the art nuclear many-body calculations of the
pure neutron matter EOS, and astrophysical observations consistently, we study
various GW signatures of the high-density behavior of the nuclear symmetry
energy, which is considered among the most uncertain properties of dense
neutron-rich nucleonic matter. In particular, we find the tidal polarizability
of neutron stars, potentially measurable in binary systems just prior to
merger, is more sensitive to the high density component of the nuclear symmetry
energy than the symmetry energy at nuclear saturation density. We also find
that the upper limit on the GW strain amplitude from elliptically deformed
stars is very sensitive to the density dependence of the symmetry energy. This
suggests that future developments in modeling of the neutron star crust, and
direct gravitational wave signals from accreting binaries will provide a wealth
of information on the EOS of neutron-rich matter. We also review the
sensitivity of the -mode instability window to the density dependence of the
symmetry energy. Whereas models with larger values of the density slope of the
symmetry energy at saturation seem to be disfavored by the current
observational data, within a simple -mode model, we point out that a
subsequent softer behavior of the symmetry energy at high densities (hinted at
by recent observational interpretations) could rule them in.Comment: 14 pages, 11 figures, 3 tables; submitted to EPJA Special Volume on
Nuclear Symmetry Energ
- …