Flow field investigation in rotating rib-roughened channel by means of particle image velocimetry

Abstract

The turbulent velocity field over the ribroughened wall of an orthogonally rotating channel is investigated by means of two-dimensional particle image velocimetry (PIV). The flow direction is outward, with a bulk Reynolds number of 1.5 9 10 4 and a rotation number ranging from 0.3 to 0.38. The measurements are obtained along the wall-normal/streamwise plane at mid-span. The PIV system rotates with the channel, allowing to measure directly the relative flow velocity with high spatial resolution. Coriolis forces affect the stability of the boundary layer and free shear layer. Due to the different levels of shear layer entrainment, the reattachment point is moved downstream (upstream) under stabilizing (destabilizing) rotation, with respect to the stationary case. Further increase in rotation number pushes further the reattachment point in stabilizing rotation, but does not change the recirculation length in destabilizing rotation. Turbulent activity is inhibited along the leading wall, both in the boundary layer and in the separated shear layer; the opposite is true along the trailing wall. Coriolis forces affect indirectly the production of turbulent kinetic energy via the Reynolds shear stresses and the mean shear. Twopoint correlation is used to characterize the coherent motion of the separated shear layer. Destabilizing rotation is found to promote large-scale coherent motions and accordingly leads to larger integral length scales; on the other hand, the spanwise vortices created in the separating shear layer downstream of the rib are less organized and tend to be disrupted by the three-dimensional turbulence promoted by the rotation. The latter observation is consistent with the distributions of span-wise vortices detected in instantaneous flow realizations.

Simulation of the Flow in a Ribbed Rotating Duct with a Hybrid k-ω RANS/LES Model

“…In the current work, numerical results by a hybrid k-ω RANS/LES model and the originating RANS k-ω model are compared with the experimental results by Coletti and Arts [6] and Coletti et al [7]. Coletti et al [7] observed that the Coriolis force affects the dynamics of both large and small scales, leading to complicated flow patterns with recirculation zones and secondary vortex motions.…”

“…The objective was fundamental study of the effect of the Coriolis force on turbulence enhancement or damping in a nominally 2D channel. The first, and probably still the only, PIV measurements of flow in a ribbed rotating duct, relevant for internal cooling channels of gas turbine blades, with the equipment rotating together with the duct, were realised by Coletti and Arts [6] and Coletti et al [7]. The cross-section of the duct is approximately square.…”

“…This leads to a shorter length of the separation bubble behind a rib compared to the non-rotating case. Coletti et al [7] recorded mean-flow streamlines in the mid-span plane of the channel and profiles of mean and fluctuating streamwise velocity components on 6 positions in the mid-span plane. They also recorded the streamwise evolution of the mean wall-normal velocity component on a line just above the ribs.…”

“…Coletti et al [7] observed that the Coriolis force affects the dynamics of both large and small scales, leading to complicated flow patterns with recirculation zones and secondary vortex motions. As discussed above, the applicability of a hybrid RANS/LES technique of DES type to flow in a ribbed rotating duct was already investigated by Viswanathan and Tafti [12,13], but comparison was made with LES results.…”

Large eddy simulation for predicting turbulent heat transfer in gas turbines

“…Computational modelling has played a very important role in identifying the underlying physics of cooling flows. Experiments have mostly measured the heat transfer coefficients without much regard to the underlying hydrodynamic mechanisms for a number of reasons, chief among them being the singular importance of heat transfer coefficients to the design process and the difficulty of making velocity measurements particularly in a rotating geometry, which is a challenge even to this day [2]. A vast number of numerical investigations have been performed to investigate the ability of numerical models, in particular turbulence models, to predict the heat transfer.…”