Investigation to optimize the passive shock wave-boundary layer control for supercritical airfoil drag reduction

The optimization of passive shock wave/boundary layer control for supercritical airfoil drag reduction was investigated in a 3 in. x 15.4 in. Transonic Blowdown Wind Tunnel. A 14% thick supercritical airfoil was tested with 0%, 1.42% and 2.8% porosities at Mach numbers of .70 to .83. The 1.42% case incorporated a linear increase in porosity with the flow direction while the 2.8% case was uniform porosity. The static pressure distributions over the airfoil, the wake impact pressure data for determining the profile drag, and the Schlieren photographs for porous surface airfoils are presented and compared with the results for solid-surface airfoils. While the results show that linear 1.42% porosity actually led to a slight increase in drag it was found that the uniform 2.8% porosity can lead to a drag reduction of 46% at M = .81

Analysis of Quiet-Sun Internetwork Magnetic Fields Based on Linear Polarization Signals

We present results from the analysis of Fe I 630 nm measurements of the quiet Sun taken with the spectropolarimeter of the Hinode satellite. Two data sets with noise levels of 1.2{\times}10-3 and 3{\times}10-4 are employed. We determine the distribution of field strengths and inclinations by inverting the two observations with a Milne-Eddington model atmosphere. The inversions show a predominance of weak, highly inclined fields. By means of several tests we conclude that these properties cannot be attributed to photon noise effects. To obtain the most accurate results, we focus on the 27.4% of the pixels in the second data set that have linear polarization amplitudes larger than 4.5 times the noise level. The vector magnetic field derived for these pixels is very precise because both circular and linear polarization signals are used simultaneously. The inferred field strength, inclination, and filling factor distributions agree with previous results, supporting the idea that internetwork fields are weak and very inclined, at least in about one quarter of the area occupied by the internetwork. These properties differ from those of network fields. The average magnetic flux density and the mean field strength derived from the 27.4% of the field of view with clear linear polarization signals are 16.3 Mx cm-2 and 220 G, respectively. The ratio between the average horizontal and vertical components of the field is approximately 3.1. The internetwork fields do not follow an isotropic distribution of orientations.Comment: To appear in APJ, Vol 749, 201

On the inversion of Stokes profiles with local stray-light contamination

Obtaining the magnetic properties of non-resolved structures in the solar photosphere is always challenging and problems arise because the inversion is carried out through the numerical minimization of a merit function that depends on the proposed model. We investigate the reliability of inversions in which the stray-light contamination is obtained from the same observations as a local average. In this case, we show that it is fundamental to include the covariance between the observed Stokes profiles and the stray-light contamination. The ensuing modified merit function of the inversion process penalizes large stray-light contaminations simply because of the presence of positive correlations between the observables and the stray-light, fundamentally produced by spatially variable systematics. We caution that using the wrong merit function, artificially large stray-light contaminations might be inferred. Since this effect disappears if the stray-light contamination is obtained as an average over the full field-of-view, we recommend to take into account stray-light contamination using a global approach.Comment: 5 pages, 3 figures, accepted for publication in Ap