Energetic and exergetic performance evaluation of an AC and a solar powered DC compressor

This study represents experimental performance analyses of an alternative current (AC) and a direct current (DC) refrigeration compressors implemented in a 79 liter refrigerator. Experiments were carried out at continuously running (ON) and periodically running (ON/OFF) operation modes. Data was analyzed and a comparison in terms of cooling capacity, power input, coefficient of performance (COP), Carnot COP, and exergy efficiency was conducted. The comparison showed that DC compressors can be much more efficient than AC compressors in refrigeration units. © Springer-Verlag Berlin Heidelberg 2013

Accurate induced drag prediction for highly non-planar lifting systems

The impact of wake model effects is investigated for two highly non-planar lifting systems. Dependent on the geometrical arrangement of the configuration, the wake model shape is found to considerably affect the estimation. Particularly at higher angles of attack, an accurate estimation based on the common linear wake model approaches is involved

Investigation of Transitional Flow Structures Downstream of a Backward-Facing-Step by Using 2D-2C- and High Resolution 3D-3C- Tomo- PIV

Transitional flow structures in the shear layer of a laminar separation bubble downstream of a backward facing step (BFS) have been investigated by means of 2D-2C- und highly resolved 3D-3C- tomographic Particle Image Velocimetry (PIV) for Reynolds numbers between Reh = 1420 and 3000 based on free-stream velocity U and step height h. By using an external acoustic excitation of the shear layer it was possible to arrange phase locked measurements of the wavy flow structures which emanate from instabilities according to Kelvin-Helmholtz [1] (KH). Snapshots of fully 3D-3C velocity vector volumes show complex flow topologies of the non-linear part of the laminar-turbulent transition scenario. This part seems to be governed by hairpin-like, streamwise elongated vortices on top of the classical spanwise oriented 2-D waves. These vortices organize a rapid fluid exchange normal to the shear layer leading to turbulent reattachment of the flow and subsequent development of a turbulent boundary layer