The performance of high resolution particle velocimetry : algorithm, simulations and experiments

In this report we investigate the performance of particle tracking, exploring the influence of an increasing amount of estimators. Basically, a simple method to determine particle matchings was used. Then, first, temporal extrapolation as well as spatial interpolation are employed. Second, a PlY processing step was incorporated. Tests from simulations show that at relatively high seeding densities the performance was increased with a factor of 4 and 13 for the first and second step, respectively. In a physical experiment of a wake behind a heated cylinder a clear performance improvement in the case of PlY preprocessing was observed

Mixed convection behind a heated cylinder

+157hlm.;24c

Near wake effects of a heat input on the vortex shedding mechanism

This article presents the investigation on the vortex formation and shedding process behind a heated cylinder which is exposed to a cold cross flow. The Reynolds number is chosen to be 75 while the Grashof number is varied between 0 and 5000 (resulting in a variation from forced to mixed convection). The numerical results show that the addition of heat disturbs the vortex formation process. The vortices shed from the upper half of the cylinder become stronger for increasing heat input. Therefore, the shedding process at the upper half of the cylinder becomes more effective compared with the process at the lower half. Consequently, the vortices shed from the upper half of the cylinder have a higher vorticity extreme and a higher temperature. The results show that the difference in effectiveness is mainly caused by a decreasing effect of strain rate during the formation of an upper vortex. This change in strain rate is caused by a change in flow pattern around the cylinder for increasing Grashof number. For higher heat input more fluid flows underneath the cylinder, resulting in weaker shear layers at the upper part of the cylinder

Near wake effects of a heat input on the vortex shedding mechanism

This article presents the investigation on the vortex formation and shedding process behind a heated cylinder which is exposed to a cold cross flow. The Reynolds number is chosen to be 75 while the Grashof number is varied between 0 and 5000 (resulting in a variation from forced to mixed convection). The numerical results show that the addition of heat disturbs the vortex formation process. The vortices shed from the upper half of the cylinder become stronger for increasing heat input. Therefore, the shedding process at the upper half of the cylinder becomes more effective compared with the process at the lower half. Consequently, the vortices shed from the upper half of the cylinder have a higher vorticity extreme and a higher temperature. The results show that the difference in effectiveness is mainly caused by a decreasing effect of strain rate during the formation of an upper vortex. This change in strain rate is caused by a change in flow pattern around the cylinder for increasing Grashof number. For higher heat input more fluid flows underneath the cylinder, resulting in weaker shear layers at the upper part of the cylinder

The wake behaviour behind a heated horizontal cylinder

The behaviour of vortex structures shed from a heated cylinder is experimentally investigated by means of 2-D particle tracking velocimetry. Within this investigation the ReD number was chosen to be 73. The RiD number, the dimensionless number which presents the relative importance of the induced heat, varies between 0 and 1. The experiments were carried out in a large towing tank where the disturbances caused by boundary layers could be minimised. The results show that for small RiD numbers the induced heat results in a deflection of the vortex street in negative y-direction. Within the vortex street a linking of two subsequently shed vortices occurs where the vortex shed from the lower half of the cylinder rotates around the vortex shed from the upper half. These phenomena are assumed to be caused by a strength difference between the vortices shed from the upper half of the cylinder and the lower half. For RiD=1 the effect of the induced heat and buoyancy becomes even more pronounced resulting in a more upwards directed vortex street

Heat induced transition of a stable vortex street

A combined numerical and experimental investigation is presented showing the effect of heat on the stability of a horizontal vortex street for ReD=75 and RiD between 1 and 2. Detailed 2D-HiRes PV experiments are compared with 2D numerical results. The results show that an early transition to 3D of the vortex street takes place for RiD>1. Furthermore, the location at which the 2D wake becomes essentially 3D turns out to be dependent on RiD. For an increasing addition of heat (increasing RiD), this location is shifted into the direction of the cylinder. By applying 3D measuring techniques, such as 3D-PTV and 3D visualisation techniques, the transition process and the behaviour downstream of the transition point are investigated

The performance of a new PTV algorithm applied in super-resolution PIV

In this paper, we investigate the performance of particle tracking, exploring the influence of an increasing amount of estimators. Basically, a simple method to determine particle matchings was used. Then, first, temporal extrapolation as well as spatial interpolation are employed. Second, a PIV processing step was incorporated. Tests from simulations show that at relatively high seeding densities the performance was increased by a factor of 4 and 13 for the first and second step, respectively. In a physical experiment of a wake behind a heated cylinder, a clear performance improvement in the case of PIV preprocessing was observed