Scanning stereo-PLIF method for free surface measurements in large 3D domains

Abstract

Abstract In this work, we extend a planar laser-induced fluorescence method for free surface measurements to a three-dimensional domain using a stereo-camera system, a scanning light sheet, and a modified self-calibration procedure. The stereo-camera set-up enables a versatile measurement domain with self-calibration, improved accuracy, and redundancy (e.g., possibility to overcome occlusions). Fluid properties are not significantly altered by the fluorescent dye, which results in a non-intrusive measurement technique. The technique is validated by determining the free surface of a hydraulic flow over an obstacle and circular waves generated after droplet impact. Free surface waves can be accurately determined over a height of $$L=100$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>L</mml:mi><mml:mo>=</mml:mo><mml:mn>100</mml:mn></mml:mrow></mml:math> mm in a large two-dimensional domain ( $$y(x,z) = 120\times 62$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>y</mml:mi><mml:mo>(</mml:mo><mml:mi>x</mml:mi><mml:mo>,</mml:mo><mml:mi>z</mml:mi><mml:mo>)</mml:mo><mml:mo>=</mml:mo><mml:mn>120</mml:mn><mml:mo>×</mml:mo><mml:mn>62</mml:mn></mml:mrow></mml:math> mm $$^2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mrow/><mml:mn>2</mml:mn></mml:msup></mml:math> ), with sufficient accuracy to determine small amplitude variations ( $$\eta \approx 0.2$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>η</mml:mi><mml:mo>≈</mml:mo><mml:mn>0.2</mml:mn></mml:mrow></mml:math> mm). The temporal resolution ( $${\varDelta }t = 19$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Δ</mml:mi><mml:mi>t</mml:mi><mml:mo>=</mml:mo><mml:mn>19</mml:mn></mml:mrow></mml:math> ms) is only limited by the available scanning equipment ( $$f = 1$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>f</mml:mi><mml:mo>=</mml:mo><mml:mn>1</mml:mn></mml:mrow></mml:math> kHz rate). For other applications, this domain can be scaled as needed. Graphic abstract

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