Ultra-high-speed time-resolved PIV of turbulent flows using a continuously pulsing fiber laser

Abstract

Abstract The application of a compact pulsed fiber laser for high-speed time-resolved particle image velocimetry (TR-PIV) measurements in the potential core of a turbulent round jet is presented at repetition rates of up to $$500\,\hbox {kHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>500</mml:mn> <mml:mspace/> <mml:mtext>kHz</mml:mtext> </mml:mrow> </mml:math> . The master oscillator power amplifier laser architecture consists of a pulsable seed diode whose emission is amplified in a Yb-doped fiber. The pulsed laser is operated continuously at repetition rates ranging from $$10\,\hbox {kHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>10</mml:mn> <mml:mspace/> <mml:mtext>kHz</mml:mtext> </mml:mrow> </mml:math> to $$1\,\hbox {MHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mspace/> <mml:mtext>MHz</mml:mtext> </mml:mrow> </mml:math> with adjustable pulse widths at an output power of 50 W. The maximum rated pulse energy of $$486\,\upmu \hbox {J}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>486</mml:mn> <mml:mspace/> <mml:mi>μ</mml:mi> <mml:mtext>J</mml:mtext> </mml:mrow> </mml:math> is reached at $$100\,\hbox {kHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>100</mml:mn> <mml:mspace/> <mml:mtext>kHz</mml:mtext> </mml:mrow> </mml:math> , making the laser suitable for measurements of turbulent flows and highly transient phenomena. To demonstrate the feasibility of the laser for flow velocimetry, TR-PIV is conducted in a turbulent round jet. Two different high-speed camera systems are employed: a high-speed CMOS camera running at $$200\,\hbox {kHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>200</mml:mn> <mml:mspace/> <mml:mtext>kHz</mml:mtext> </mml:mrow> </mml:math> and $$400\,\hbox {kHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>400</mml:mn> <mml:mspace/> <mml:mtext>kHz</mml:mtext> </mml:mrow> </mml:math> and an in situ storage CCD camera for burst-mode PIV measurements at $$500\,\hbox {kHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>500</mml:mn> <mml:mspace/> <mml:mtext>kHz</mml:mtext> </mml:mrow> </mml:math> . For the CMOS system, the capability of measuring several characteristic quantities of turbulent flows is discussed with regard to the effects of uncertainty and spatial resolution. The presented system extends the range of suitable laser systems for high-speed PIV measurements offering continuous pulsing at repetition rates of up to $$1\,\hbox {MHz}$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>1</mml:mn> <mml:mspace/> <mml:mtext>MHz</mml:mtext> </mml:mrow> </mml:math> at a compact footprint. The amount of consecutive images is solely limited by the onboard storage of the camera, which enables unprecedented temporal dynamic ranges. Graphical Abstract

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