Implementation Aspects of Uniform Blowing in Turbulent Boundary Layers
Creators: name:  G. FAHLAND 
name:   D. GATTI 
name:   A. STROH 
name:   B. FROHNAPFEL 
Publisher: name: Proceedings of  the 9th European Conference for Aerospace Sciences. Lille, France, 27 June - 1 July, 2022
Year: 2022
Subjects: FLOW CONTROL
AEROSPACE

description: Flow control for drag reduction is a very common research topic to enhance system properties, especially for mobility and energy applications. In particular turbulent flow control is a widespread subject of research due to the dominance of turbulent boundary layers in aforementioned applications and the complexity of turbulent flows.We focus our studies on the scheme of uniform blowing (described by e.g. [8]) also known as micro-blowing technique (described by Hwang [6]) applied on airfoils. Originally, this scheme was conceived as a means to reduce friction drag [7]. However, the implementation on a more complex use case like an airfoil reveals further effects on the overall flow. First of all, since performance of an airfoil does not solely depend on drag but lift also, drag reduction efforts have to coincide with either lift improvement or at least similar lift compared to an uncontrolled case. Several studies showed, that this is not the case for micro-blowing on the upper side of an airfoil [3, 1]. Yet we could show that blowing on the lower side of an airfoil fulfills this basic requirement [4]. This opens-up the question of the distribution of the flow control scheme, both macroscopic (regions of application) and microscopic (the porous surface). The latter has been thoroughly described also for laminar flow control via suction [2] but also for the case of the micro-blowing technique by Hwang [6]. Currently we are in the phase of designing our experimental campaign with the plan of closing the gap in between the researched levels of porosity. Regarding the regions of application we find that increasing scheme performance coincides with decreasing adverse pressure gradient [4]. Considering an implementation on a mobile application another figure becomes relevant: The performance of the support system for this kind of flow control and its impact on the overall performance improvement. We show that for the micro-blowing technique the momentum budget of the control fluid is the main contribution to the drag-like power demands of the support system [5]. Alongside the aspects summarized in this abstract we will present further details on our ongoing research regarding the momentum budget and the resulting significance for measurement quantities in experimental investigation. References: [1] M. Atzori, R. Vinuesa, G. Fahland, A. Stroh, D. Gatti, B. Frohnapfel, and P. Schlatter. Aerodynamic Effects of Uniform Blowing and Suction on a NACA4412 Airfoil. Flow Turbulence Combust, 105:735759, April 2020. [2] N. Beck, T. Landa, A. Seitz, L. Boermans, Y. Liu, and R. Radespiel. Drag Reduction by Laminar Flow Control. Energies, 11(1):252, January 2018. [3] Kaoruko Eto, Yusuke Kondo, Koji Fukagata, and Naoko Tokugawa. Assessment of Friction Drag Reduction on a Clark-Y Airfoil by Uniform Blowing. AIAA Journal, 57(7):27742782, July 2019. [4] G. Fahland, A. Stroh, B. Frohnapfel, M. Atzori, R. Vinuesa, P. Schlatter, and D. Gatti. Investigation of Blowing and Suction for Turbulent Flow Control on Airfoils. AIAA Journal, 59(11):44224436, July 2021. [5] G. Fahland, A. Stroh, D. Gatti, M. Atzori, R. Vinuesa, P. Schlatter, and B. Frohnapfel. Energy Budgets and Performance Development of Turbulent Boundary-Layer Control on Airfoils. In ETMM13 Conference Proceedings, pages 123127, Rhodes, Greece, September 2021. ERCOFTAC. [6] D. Hwang. Review of research into the concept of the microblowing technique for turbulent skin friction reduction. Progress in Aerospace Sciences, 40(8):559575, November 2004. [7] H. S. Mickley. Heat, mass, and momentum transfer for flow over a flat plate with blowing or suction. NACA, TN 3208, pages 125, 1954. [8] A. Stroh. Reactive Control of Turbulent Wall-Bounded Flows for Skin Friction Drag Reduction. Dissertation, Karlsruhe Institute of Technology, Karlsruhe, 2016.