Control and Identification of Turbulent Boundary Layer Separation

Abstract

Abstract:Effective delay of turbulent boundary layer separation could be achieved via closed-loop control. Constructing such a system requires that sensor data be processed, real-time, and fed into the controller to determine the output. Current methods for detection of turbulent boundary layer separation are lacking the capability of localized, fast and reliable identification of the boundary layer state. A method is proposed for short-time FFT processing of time series, measured by hot-film sensors, with the purpose of identifying the alternation of the balance between small and large scales as the boundary layer separates, favoring the large scales. The method has been validated by comparison to other criteria of separation detection and over a range of baseline and controlled flow conditions on a "simplified" high-lift system, incorporating active flow control.

Experimental detection of flow separation over a plain flap by wall shear stress analysis with and without steady blowing

“…The amplification of wall shear stress fluctuations within the 100-300-Hz frequency range appears then as a precursor to flow separation. This result was already reported by Seifert and Pack-Melton [9] and Simpson et al [19], but for pressure fluctuations in the latter case.…”

“…Other authors (Rethmel et al [5], Packard & Bons [3] and Troshin & Seifert [7]) prefer to use the rms value (or a calculated value assimilated to the rms value) to detect flow separation. Indeed, flow separation is generally marked by a sharp increase of the rms value of hot-film voltage, as shown by Pack et al [8] and Seifert & Pack-Melton [9]. One advantage of the rms method over the calibration-based method is that the hot films do not need to be calibrated in the former case.…”

Manipulating flow separation: sensitivity of stagnation points, separatrix angles and recirculation area to steady actuation

“…In contrast, separation yields a recirculation region that is often desirable in combustion devices. It is thus not a surprise that there is extensive research on the control of flow separation [1]. Attempts include, in decreasing order of complexity, closed-loop separation control, harmonic or steady active open-loop control and passive control devices.…”

Experimental Detection and Pulsed Jets Control of Turbulent Boundary Layer Separation

“…In the same way, Pack et al 8 first proposed an equivalent method but on wall shear stress measurements, further developed by Seifert & Pack-Melton. 17 Beyond the closed-loop control framework, the ability of wall shear stress measurement to detect turbulent boundary layer separation has already interested several authors and detection criteria have been developed. The so-called phase reversal phenomenon is known to be a particularly well suited criterion to detect laminar boundary layer separation since its first description by Stack et al 20 .…”