Flow visualization (original) (raw)

Continuous coloured smoke-wire technique for flow visualisation

1988

A continuous colored smoke-wire technique has been developed for flow visualization in wind tunnels. The improved contrast of colored smoke sheet facilitates flow visualization. In the present technique, a vertical smoke-wire is used for introducing controlled sheets of smoke streaklines during a wind tunnel run. Regulated drops of a mixture of paraffin oil with colored dye are allowed to fall

Comparative analysis of experimental and numerical flow visualization methods

FME Transactions, 2006

The results of flow visualization around various models in MTI's wind and water tunnels are presented in this paper. They were obtained by different techniques: holographic interferometry, surface oil emulsion, dye and air bubbles. Besides experimental results, the flow simulations by Fluent for the same experimental conditions are presented too. The obtained comparative analyses shows that it is helpful to use both methods, experimental and numerical, in complex flows investigations

Some principles of flow visualization techniques in wind tunnels

Nowadays, there are various ways to study gas and fluid flows in wind tunnels and are still an important field of scientific research. The objectives of the research intended to present the basic principle of flow visualization techniques in wind tunnels and to simulate, visualize, observe, and measure how the flow around the object.

Development and application of streakline visualization in hypervelocity flows

Experiments in Fluids, 2002

In the traditional smoke-wire setup, the streak lines consist of smoke generated by oil that vaporizes as it runs down a heated wire placed upstream of a model in a wind tunnel. Provided that the wind tunnel flow has sufficiently Abstract A method for visualizing streaklines in hypervelocity flows has been developed. The method uses the high temperatures produced in hypervelocity flows to ablate small amounts of sodium deposited onto a wire stretched across the flow and to broaden the lines in the sodium spectrum. By using a dye laser, tuned to a wave length close to one of the sodium D-lines, as the light source in shadowgraph or Schlieren visualization, streaklines seeded with sodium become visible through ab sorption and/or enhanced refractivity. The technique has been used to investigate the stability of the shear layer produced by the curved bow shock on a cylindrically blunted wedge. The results suggest that the shear layer is unstable, exhibiting structures with a wavelength that is comparable to half the nose radius of the body.

Flow visualization techniques in wind tunnels–optical methods (Part II)

Scientific Technical Review, 2007

An attempt is made to describe and review the most widely used methods for flow visualization. The first part described the basis and applications of different visualization methods for subsonic and supersonic flow in wind and water tunnels. This part concentrates on optical methods (shadow, schlieren and interferometry) and their application in compressibe flow visualization. Almost all presented photos have been made in the laboratories of the VTI.

Visualization and picture processing of turbulent flow

Experiments in Fluids, 1984

The tracer method was used to visualize the threedimensional structure of turbulent open-channel flow. A horizontal cross-section of the flow was illuminated by light passing through a thin slit. The illuminated cross-section was shifted upward, and at the time, successive pictures of flow patterns were taken. The picture-taking system was then shifted in downstream direction to follow the flow structures. The pictures obtained were processed by computer. Various kinds of physical properties of the flow were quantitatively evaluated and displayed as graphical outputs. These results contribute to the elucidation of the threedimensional structure of turbulent open-channel flows.

Visualization of Near-Surface Flow Patterns for Air-Water Gas Transfer

2018

Near-surface flow patterns and their influence on local transport processes are investigated in a horizontal plane with visualization techniques. For this, a new method was developed that produces tracer particles with high effective Schmidt number (Sc = O(10 6)) by chemical reaction directly at the water surface. While different chemical systems were tried, best results were achieved using the precipitate AgCl, formed by AgNO 3 in the water body and a controlled influx of HCl gas. Trace amounts of precipitate are made visible by scattering laser light. Using the new method, the influence of wind induced turbulences at the water interface can be investigated with previously unachieved sensitivity. Illumination of the wavy water surface leads to shadowing and lensing effects that become apparent in the image data and cannot fully be compensated for with image processing. The results are qualitatively compared to data from active thermography (heat, Pr ≈ 7) and boundary layer imaging (gas, Sc ≈ 600), showing a close resemblance of the flow pattern. With higher Schmidt number of the tracer, the structure becomes more pronounced and higher sensitivity to surface convergence is observed. Experiments with glass spheres (d = 70 µm-2 mm, Sc → ∞) were conducted for further comparison. Tracking of individual particles allows for a precise measurements of the surface velocity and investigations of the local momentum transfer. Zusammenfassung Strömungsmuster nahe der Wasseroberfläche und ihre Auswirkungen auf lokale Transportprozesse werden mit Visualisierungsmethoden in horizontaler Ebene untersucht. Dafür wurde eine neue Technik entwickelt, die Tracerpartikel mit hoher effektiver Schmidtzahl (Sc = O(10 6)) direkt an der Wasseroberfläche durch chemische Reaktionen erzeugt. Unter verschiedenen getesteten chemischen Systemen ist eine Ausfällung von AgCl, erreicht durch in Wasser gelöstes AgNO 3 und kontrollierte Einfuhr von HCl in den Luftraum, am besten geeignet. Bereits geringe Teilchenkonzentrationen können durch die Streuung von Laserlicht sichtbar gemacht werden. Mit der neuen Methode kann der Einfluss von windinduzierten Turbulenzen an der Oberfläche mit bisher unerreichter Empfindlichkeit nachgewiesen und untersucht werden. Für höhere Windbedingungen führen Abschattungen und Reflektionen der Beleuchtung an der Wasseroberfläche zu Störungen, welche auch mit aufwändigen Bildverarbeitungsmethoden nicht hinreichend behoben werden können. Die Resultate werden qualitativ mit Daten aus der Thermographie (Wärme, Pr ≈ 7) sowie der Grenzschichtdickenvisualisierung (Gas, Sc ≈ 600) verglichen, wobei eine starke Ähnlichkeit der Strömungsmuster beobachtet wird. Mit ansteigender Schmidtzahl der Tracer wird eine klarere Struktur und größere Empfindlichkeit für Oberflächenkonvergenz beobachtet. Zum weiteren Vergleich wurden Experimente mit Glaskugeln (d = 70 µm-2 mm, Sc → ∞) durchgeführt. Tracking der einzelnen Partikel erlaubt eine präzise Bestimmung der Oberflächengeschwindigkeit und eine Vermessung des lokalen Impulstransfers. vii Chapter 1 Chapter 2 Theory Investigations of gas transfer at the water surface are under the influence of multifarious processes. The aim of this chapter is to provide an understandable mathematical background for the natural phenomenons and laboratory observations investigated in this thesis. Basic quantities and conceptual models for the description of air-sea gas transfer are introduced. Special emphasis is on the importance of the Schmidt number as well as the relevance and interpretation of chemical reactions at the interface. To conclude, an overview is given on the turbulent flow patterns at the water surface that are crucial for transport mechanisms and are closely investigated within this work.

VISUALIZATION OF STRATIFIED AND ROTATING FLOWS FINE STRUCTURE

Visualization by sensitive optic methods namely schlieren and shadow as well as electrolytic precipitation and dyeing are widely used for stratified flows. Conditions of experiment completeness and adequacy are discussed. Bright colour schlieren images of the flow are produced using 'natural rainbow method' exploring refraction and dispersion of a light in the fluid. Wide view field and a high spatial resolution of schlieren instruments allow observing simultaneously large and small scale flow components. General features of substances transportation in stratified and vortex flows are marked. Streaky structures in flows are identified and their transformation into vortex system is registered. Anisotropic transport of a dye in a compound vortex contacting a free surface is registered.