EXP 1-4 Measurement Quantities and Techniques

Axisymmetric drop impact dynamics on a wall film of the same liquid

Front Page

Introduction

Review of experimental studies

Description

Experimental Set Up

Measurement Quantities and Techniques

Data Quality and Accuracy

Measurement Data and Results

Measurement quantities and techniques

Describe the measurement techniques and indicate which quantities were measured and where. Describe how well conditions at boundaries of the flow such as inflow, outflow, walls, far fields, free surface are given or could be reasonably estimated to provide boundary conditions for CFD calculations.

When carrying out the experiments, a uniform film of 500 μm thickness is prepared utilizing the film thickness sensor. In the next step, the film thickness sensor is moved and a drop is generated. During the drop impact onto the liquid film shadowgraphy images are taken. A synchronized high-performance LED (Constellation 120E) in combination with a diffuser plate provides a uniform background illumination. Images are taken with a high-speed CMOS camera (Photron SA-X2), recording the impact at a frame rate of 20000 fps with a magnification of 31 μm/px.

The dynamics of the drop-film interaction is characterized by three parameters as indicated in Fig. 3.

• The crown diameter at the crown base d_CB, measured 0.13 mm above the film surface
• The crown diameter at the free rim forming the crown top d_CT
• The crown height h_C

These parameters are obtained from preprocessed images with the help of the MATLAB Image-Processing Toolbox. For this, a background subtraction from raw images is first performed to be able to distinguish the crown from the background. Then the images are binarised, using a global thresholding method, as shown on the left side of Fig. 3. From the evaluation of consecutive binarised images, the temporal evolution of dCB, dCT and hC can be determined. Reflections on the crown surface can lead to nonphysical interpretations of the crowns dimensions in individual frames. To eliminate erroneous values from the results, all values with a deviation of more than three standard deviations from a running median of 20 consecutive frames are considered as outlier.

Fig. 3: Montage of binarized picture on the left and a raw picture on the right. The crown diameter at the free rim d_CT and the crown diameter at the base d_CB are depicted in red. The crown height h_C is depicted in green. The dashed blue line indicates the film level.

A suitable setup for CFD calculations including domain size and boundary conditions can be found in the following publication:

M. Bagheri, B. Stumpf, I.V. Roisman, C. Tropea, J. Hussong, M. Wörner, H. Marschall, Interfacial relaxation – Crucial for phase-field methods to capture low to high energy drop-film impacts, Int. J. Heat Fluid Flow 94 (2022) 108943, https://doi.org/10.1016/j.ijheatfluidflow.2022.108943

---

Contributed by: Milad Bagheri, Bastian Stumpf, Ilia V. Roisman, Cameron Tropea, Jeanette Hussong, Martin Wörner, Holger Marschall — Technical University of Darmstadt and Karlsruhe Institute of Technology

Front Page

Introduction

Review of experimental studies

Description

Experimental Set Up

Measurement Quantities and Techniques

Data Quality and Accuracy

Measurement Data and Results

© copyright ERCOFTAC 2024