The flow over macroscopic patterned/structured surfaces was investigated in a subsonic wind tunnel over Reynolds numbers ranging from 3.14 x 104 to 2.77 x 105 for cylinders and from 5.34 x 105 to 11.27 x 106 for plates. The investigations were accomplished by measuring local and global drag, velocity profiles and by visualization of the flow above the surface. Flow visualization was carried out by using oil-film technique and velocity profile measurements to elucidate the observed effect, and hence present the mechanism responsible for theobserved drag reduction. Investigations on structured plates were performed with the help of hot wire anemometry and oil film interferometry.
The main concern of the experiments on structured plates was to examine the effect of hexagonal structures on local and global drag of a structured plate. It was accomplished by determining and analyzing the boundary layer quantities like shear stress velocities, shear stress coefficients and momentum thicknesses over a selected Reynolds number range and various locations in streamwise direction. Finally, a number of configurations of a wind turbine made of smooth and structured blades were investigated to compare their efficiencies at various flow velocities.
Inhaltsverzeichnis (Table of Contents)
- INTRODUCTION
- Motivation
- Aims and Approaches
- THEORETICAL BACKGROUND
- Pressure drag
- Skin Drag
- Fundamentals of Boundary layer
- STATE OF THE ART
- Drag reduction of bluff bodies
- Drag reduction of streamlined bodies
- EXPERIMENTAL SETUP
- Bluff body investigation
- Streamlined body investigation
- Investigations on experimental wind turbine
- Invested Configurations
- MEASUREMENT TECHNIQUES
- Drag measurement
- Flow visualization
- Smoke flow visualization
- Surface Oil flow visualization
- Oil film interferometric Visualization
- Velocity measurements
- Shear stress measurements
- Clauser chart method
- Oil film interferometric method
- Pressure & Temperature measurements
- Braking moment and angular speed measurement
- RESULTS AND DISCUSSION
- Structured cylinders
- Velocity profiles in the wake region
- Drag Variation
- Location of flow separation
- Flow visualization on the surfaces of cylinders
- Streamwise velocity measurements
- Energy spectra of the flow over cylinders
- Vortex shedding
- Structured plates
- Non dimensional velocity profiles
- Boundary layer quantities
- Flow over individual hexagonal structure
- Optimization of the measurement techniques
- Boundary layer measurements
- Flow structures within the hexagonal depressions and bumps
- Power spectrum
- Visualization of flow over the surface
- Pressure distribution
- Experimental Wind Turbine
- Structured cylinders
- CONCLUSIONS & FUTURE WORK
- Conclusions
- Future work
- LITERATURE
Zielsetzung und Themenschwerpunkte (Objectives and Key Themes)
The dissertation aims to experimentally investigate the flow over macroscopic patterned/structured surfaces in a subsonic wind tunnel. The study investigates how these structures affect drag, flow visualization, and velocity profiles over a range of Reynolds numbers for cylinders and plates. The primary goal is to identify the mechanism by which these structures influence flow behavior and, ultimately, to determine their impact on drag reduction.
- Influence of hexagonal structures on drag reduction in cylinders and plates
- Analysis of flow behavior over structured surfaces through visualization and velocity measurements
- Impact of surface structures on boundary layer characteristics and shear stress distribution
- Evaluation of drag reduction mechanisms associated with structured surfaces, including flow separation and reattachment
- Exploration of the potential for applying structured surfaces to enhance the efficiency of wind turbines
Zusammenfassung der Kapitel (Chapter Summaries)
The dissertation begins with an introduction outlining the motivation for this research, which is to investigate the potential of macroscopic structured surfaces for drag reduction in aerodynamic applications. The introduction also establishes the aims and approaches used in the study. Chapter two provides a theoretical background on pressure drag, skin drag, and the fundamentals of boundary layers, which are essential concepts for understanding the flow phenomena investigated in the dissertation.
Chapter three reviews the existing literature on drag reduction techniques applied to bluff and streamlined bodies. It establishes the context for the current research by summarizing previous findings and identifying gaps in knowledge that the dissertation aims to address.
Chapter four delves into the experimental setup used in the study. This chapter details the wind tunnel facility, the test sections for bluff and streamlined body investigations, and the specific configurations of structured surfaces investigated. It also describes the experimental wind turbine used to assess the potential for drag reduction in a practical application.
Chapter five outlines the measurement techniques employed in the study. It covers drag measurement, flow visualization techniques, velocity measurements, shear stress measurements, and pressure and temperature measurements. The chapter provides a detailed explanation of each technique and its application in the context of the research objectives.
Chapter six presents and discusses the results of the experimental investigations. This chapter focuses on the flow characteristics observed over structured cylinders and plates, including velocity profiles, drag variation, flow separation, and shear stress distribution. It also analyzes the effect of hexagonal structures on the efficiency of the experimental wind turbine.
The final chapter, which is not included in this preview, presents conclusions drawn from the research findings and outlines potential future directions for research in this area.
Schlüsselwörter (Keywords)
The study focuses on the area of aerodynamics and explores the impact of macroscopic structured surfaces on drag reduction, flow visualization, and boundary layer characteristics. Key research methods include oil film interferometry, hot-wire anemometry, and flow visualization techniques. The dissertation investigates the flow over both bluff and streamlined bodies, with specific emphasis on hexagonal structured surfaces. The findings contribute to the understanding of drag reduction mechanisms associated with structured surfaces and explore their potential application in wind turbine technology.
- Citation du texte
- Mohammad Usman Butt (Auteur), 2014, Flow over macroscopic hexagonal structured surfaces. Experimental Investigation, Munich, GRIN Verlag, https://www.grin.com/document/1184440
