- Research Background
In the new design and optimization process of aircraft, ships, automobiles and other carriers, it is necessary to study the phenomenon of unsteady flow across supersonic speed. Under the interaction of shear layer, vortex and shock wave, the phenomenon of unsteady flow is usually very complex, and the traditional 2D2C two-dimensional plane measurement technology can not fully understand the change rule and structural characteristics of complex flow field.
2.Technical Introduction
Tomo-PIV technology combines traditional PIV technology with reconstruction techniques. Based on the multiplicative algebraic method, it performs three-dimensional cross-correlation calculations on particle distributions reconstructed at two adjacent time moments, thereby achieving full-field velocity measurements of the three-dimensional spatial flow field.
3.Experiment
Due to the release or absorption of heat caused by gas-liquid phase change, the temperature and pressure of two-phase flow will be affected. Therefore, gas-liquid two-phase flow is a typical unsteady flow phenomenon. The study of gas-liquid two-phase flow helps to understand complex flow phenomena.
4.Equipment and Process
Equipment
A set of Tomo-PIV experimental equipment typically consists of a high-energy laser, volume lens group, four Revealer PIV dual-frame high-speed cameras, a synchronous controller, a stereo calibration board and RFlow 3D3C software, etc.
Process
First step --build a high-energy volume laser illumination system, utilizing the volume lens group to expand the laser beam emitted by the high-energy laser into a volumetric light source, illuminating the tracer particles in the three-dimensional space to be measured.
Second step --set up a layer-resolved image acquisition system. Four high-speed cameras are used to target the area from different angles, as shown in the figure below. Focus until the particle images are clear. All four high-speed cameras are connected to a synchronous controller to capture images simultaneously with the same timing sequence.
Third step -- calibrate the layer-resolved image acquisition system. By capturing multiple sets of calibration board images with multiple cameras, the projection model for the object and image space is calibrated. To improve the measurement accuracy of Tomo-PIV, stereo self-calibration is performed on particle images, as shown in the figure below.
Fourth step -- use RFlow software for multi-view image reconstruction, the layer-resolved image acquisition system captures particle images at different moments. One set of these images is input, and the MART method is used to reconstruct the three-dimensional particles, obtaining a three-dimensional spatial particle distribution at a specific moment, as shown in the figure below.
Fifth step -- use RFlow software for subsequent analysis of the three-dimensional velocity field and vortex structures.
5.Results
Tomo-PIV image acquisition system: High-speed camera 1 captures images of gas-liquid two-phase flow.
Three-dimensional flow field around the bubble.
Distribution of velocity iso-surfaces around the bubble.
Vortex structures around the bubble calculated using the Q-criterion.
- Application Prospects
Tomo-PIV reconstruction technology, as an advanced optical measurement technique, is an effective tool for measuring three-dimensional unsteady complex flow fields such as turbulence and multi-vortex interference. The Revealer Tomo-PIV system features high spatiotemporal resolution and accurate reconstruction, making it suitable for aerodynamics, hydrodynamics, and other research areas in aerospace, naval engineering, and automotive engineering. This technology helps engineers continuously improve design performance.
