Corner Separations Around a NACA65 Blade in a Decelerating Flow

In order to examine the fundamental characteristics of a corner separation in a decelerating cascade flow, an experimental apparatus was made and the separations around a NACA65 blade in a decelerating channel flow were examined both experimentally and numerically. The two-dimensional calculations show that the NACA65 cascade flow that has 45 deg. of the turning, 1.24 of the solidity and 17 deg. of the stagger angle is similar to the channel flow that has 14 deg. of the stagger angle in terms of the pitchwise blade force. The experimental investigation by the five-hole probe shows that the accumulations of the low energy fluid can be seen around the corner part and the overturning flow due to the secondary flow exists. And, as the periodicity of the blade wake in the pitchwise direction is comparably good, the wake of this channel flow is similar to the wake of the cascade flow for the two pitch portion. PIV measurement showed that the focus-type separation was seen in the momentary streamline along the suction surface of the blade, whereas no apparent separation was seen in the flow along the endwalls. SD diagram consideration showed that the present case on the study was consistent with the relation between the stall indicator S and the diffusion parameter D proposed by Lei et al.

Steady and Unsteady Characteristics of Two Corner Separations in a Decelerating Square Channel Flow

The three-dimensional separation in a decelerating channel flow generated by the suction through a porous side wall had been investigated experimentally. Unsteady characteristics of two corner separations were especially focused on. The profiles of time averaged static pressure are two-dimensional in the height direction even in the case with large regions of corner separation. The contour of the turbulence level of the mainstream velocity shows two peak values which correspond to two corner separations. The value of cross-correlation gets large negative values without any lag and the value of coherence gets peak value at around 0.5–2 Hz. The corner separations near the top wall and near the bottom wall are not independent and keep coherent structure both with negative value of cross correlation function and with the frequency of around 0.5–2 Hz.

Vortices Within the Flow Separation in a Decelerating Channel Flow: Time-Averaged Characteristics

An experimental equipment for studying the vortex behavior in 3D flow separation was constructed to have a comprehensive understanding of a separated channel flow. The separation occurs on three side walls of the straight channel by the suction from a porous side wall. Several types of separation can be generated by changing the sucked flow rate and providing the inlet flow with velocity gradient. For a strong decelerating-flow without the inlet velocity gradient, an alternate flow pattern with an opposite vortex occurs at considerably irregular intervals. With the inlet velocity gradient, a vortex appears and disappears along an inclined separation line for a moderate decelerating-flow, and a large stable vortex exists in the separation region for a strong decelerating-flow. The behavior of these vortices was examined and discussed in relation to the vortices including in the inlet flow.