LP Turbine Laminar Separation With Actuated Transition: DNS, Experiment and Fluidic Oscillator CFD

Abstract

Laminar separation bubbles form on the back surfaces of aero-engine LP turbine blades. In recent years significant weight and cost reductions and performance improvements have been achieved through a better understanding of the behavior of such separation bubbles. A project is underway at the Universita¨t Stuttgart to study a possible technique to suppress laminar separation bubbles using actuated transition. This paper reports on DNS results with and without actuation for different frequencies, amplitudes and Reynolds numbers, revealing the nature of the transitional process. Early results from an experimental simulation are included. In addition numerical simulations of fluidic oscillators which are capable to provide the required frequencies at a size which would fit into an LP turbine are presented.

Actuated Transition in an LP Turbine Laminar Separation: An Experimental Approach

“…These findings confirm the numerical investigations of Rist and Augustin [12] and Ries et al [15,16] who describe the separation bubble control by means of actuation.…”

“…Through this amplification process the boundary layer gets more stable and the separation bubble gets smaller without need of a large air mass flow as for vortex generating jet control. Numerical investigations by means of URANS and DNS that were done prior to the presented work as well as preliminary experimental results were published by Ries et al and Baumann et al in [15][16][17]. Experimental results showing the effect of actuation on the boundary layer are presented here.…”

“…A stability analysis in the location of the actuation slot results in possible frequencies for exciting transition. The analysis was done by Ries et al [15,16]. Given that these frequencies range from 25 to 85 Hz, depending on the Reynolds number in the flow, a woofer (300 W, 270 mm in diameter) was chosen to produce the signal.…”

“…The area of the disturbance strip is 0.3 × 100 mm. The sensitivity of actuation location on actuation effectiveness was investigated by means of DNS calculations [16]. Starting at a locationx act = 0.614 for Re = 79, 000, the impact of actuation location on the bubble was shown to be very small.…”

A Review of Fluidic Oscillator Development and Application for Flow Control

“…Ries et al [61] performed numerical and some preliminary experimental studies on a feedback fluidic oscillator that is designed to be used for controlling the laminar separation bubble formation by exciting the instability modes of the flow at specific frequencies. The comparison was done with and without actuation at different frequencies, amplitudes, and Reynolds numbers.…”