572 research outputs found
Characteristics of vertical and lateral tunnel turbulence measured in air in the Langley Transonic Dynamics Tunnel
Preliminary measurements of the vertical and lateral velocity components of tunnel turbulence were obtained in the Langley Transonic Dynamics Tunnel test section using a constant-temperature anemometer equipped with a hot-film X-probe. For these tests air was the test medium. Test conditions included tunnel velocities ranging from 100 to 500 fps at atmospheric pressure. Standard deviations of turbulence velocities were determined and power spectra were computed. Unconstrained optimization was employed to determine parameter values of a general spectral model of a form similar to that used to describe atmospheric turbulence. These parameters, and others (notably break frequency and integral scale length), were determined at each test condition and compared with those of Dryden and Von Karman atmospheric turbulence spectra. When the data were discovered to be aliased, the spectral model was modified to account for and 'eliminate' the aliasing
Optimization of flux-surface density variation in stellarator plasmas with respect to the transport of collisional impurities
Avoiding impurity accumulation is a requirement for steady-state stellarator
operation. The accumulation of impurities can be heavily affected by variations
in their density on the flux-surface. Using recently derived semi-analytic
expressions for the transport of a collisional impurity species with high-
and flux-surface density-variation in the presence of a low-collisionality bulk
ion species, we numerically optimize the impurity density-variation on the
flux-surface to minimize the radial peaking factor of the impurities. These
optimized density-variations can reduce the core impurity density by
(with the impurity charge number) in the Large Helical Device case
considered here, and by in a Wendelstein 7-X standard configuration
case. On the other hand, when the same procedure is used to find
density-variations that maximize the peaking factor, it is notably increased
compared to the case with no density-variation. This highlights the potential
importance of measuring and controlling these variations in experiments.Comment: 19 figures, 17 pages. Accepted into Nuclear Fusio
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