Planar PIV

Planar Particle Imaging Velocimetry (PIV) systems allow non-intrusive measurements of two or three velocity components (2C or 3C) in a planar section of gas or liquid flows. The plane (2D) is defined by a light-sheet illuminating seeding particles following the flow. The 2D2C configuration measures the in-plane velocity components whereas the 2D3C system also captures the out-of-plane velocity component.

The flow must contain seeding particles that follow the flow. The laser will fire two light pulses at a small time delay, and the camera records two images of the particles with that small time delay between them. The movement of particles due to the flow is analysed by the software to extract velocity information.

The main system components for this imaging technique are the camera and light source. Based on the image acquisition rate of the system, spanning from 10 Hz to 20 kHz, these systems can be used to acquire ensembles of single-shot images (at 10 – 200 Hz) of a flow field or ensembles of Time Resolved (TR) images (at 0.5 – 20 kHz).

DynamicStudio, our imaging software, guides the user through the entire measurement process from calibration to visualization of results. The guidance includes basic features such as help to focus a camera and advanced post-processing such as pressure from PIV computations, which derives pressure fields from the vector maps.

10 – 200 Hz systems, 2D2C

The simplest system configuration for measuring two velocity components in a plane (2D2C) consists of:

• Camera  
• Light source
• Optics to create a light sheet
• Synchronizer
• PC and software for analysis

Stereo PIV, 10 – 200 Hz systems, 2D3C

Stereo PIV is a method for measuring three velocity components in a plane (2D3C) based on the principle of parallax.

By placing two cameras so that they observe the light-sheet plane from two different angles, you obtain slightly different particle images from each camera due to the parallax effect.

The differences between them arise from the third, out-of-plane velocity component and the different observation angles of the two cameras.

After image calibration, this third velocity component can be evaluated. In addition, the two in-plane velocity components can be corrected for parallax errors.

A 2D2C PIV system can be upgraded to a Stereo PIV (2D3C) system by adding:

• Additional camera
• Scheimpflug mounts
• Calibration target
• Stereo PIV software module

TR-PIV systems for 2D2C and 2D3C, 0.5 – 20 kHz

Both the 2D2C and 2D3C configurations can be upgraded for Time Resolved (high image acquisition rate) measurements. TR-PIV systems relies on the use of high-repetition rate lasers combined with matching high-frame rate cameras. Depending on the application, a TR-PIV system can be a 500 Hz system for measurements in liquids and a >10 kHz system for high speed gas flows.

Components for 2D2C PIV

• Light source (laser or LED) and light sheet optics
• Camera
• DynamicStudio Base Package for easy setup and control of hardware devices, data acquisition, image pre-processing and data storage
• DynamicStudio 2D PIV add-on for Dynamic Studio: 2D vector field calculation, Least Squares Matching method (LSM) for high accuracy velocity and direct calculation of the velocity gradients, Adaptive PIV with multi-grid cross correlation and average correlation for µPIV. Supports deforming windows and high accuracy calculation, proven by the 2014 PIV challenge. Furthermore, this Add-on includes TR and 2-Frame particle tracking methods to directly and accurately compute particle paths.  Proper Orthogonal Decomposition (POD) allows for investigation of the main spatial modes.
• For TR PIV, the Oscillating Pattern Decomposition (OPD) add-on allows for investigation of dominant flow structures in the TR data ensemble  
• Synchronizer for correct timing of laser pulses and camera shutter

Additional components for 2D3C Stereo PIV

• DynamicStudio StereoPIV software including camera calibration routines that measure and account for perspective distortion arising from the skewed orientation of the cameras, routines to compute the third velocity component from the two camera data sets, and presentation of 3-component velocity information.
• Calibration targets. Camera calibration requires calibration images to be recorded in the light sheet as well as in front of and behind it. DynamicStudio StereoPIV allows automatic recording of these calibration images.
• Scheimpflug mounts. The user has to fine-adjust the angle between the CCD (CMOS) array and camera lens in order to focus correctly. To do this, the so-called Scheimpflug condition must be fulfilled. This is achieved by mounting the cameras on Scheimpflug mounts. DynamicStudio StereoPIV includes a focus-assist tool.