Development of Particle Image Velocimetry local apparatus for experimental fluid mechanics studies

Particle Image Velocimetry is an experimental technique that can be used to quantitatively visualize any type of flow field irrespective of the type of fluid. We are assigned to design and develop a 2D experimental facility of Particle Image Velocimetry for the visualization of the

Project Title

Development of Particle Image Velocimetry local apparatus for experimental fluid mechanics studies

Project Area of Specialization

Mechanical Engineering

Project Summary

Particle Image Velocimetry is an experimental technique that can be used to quantitatively visualize any type of flow field irrespective of the type of fluid. We are assigned to design and develop a 2D experimental facility of Particle Image Velocimetry for the visualization of the laminar boundary layer profile of internal pipe flow. The basic principle of particle image velocimetry is that fluid flow is illuminated with the help of a laser light sheet which is seeded with fluorescent microparticles. The particle image velocimetry consists of several subassemblies such as:

Seeding

Particles with a density equal to the density of the flowing fluid and having high light scattering characteristics need to be illuminated to record them. The size of these particles must be larger than the wavelength of the incident light however the upper limit of their size is controlled with their inertial characteristics. 

Recording

These illuminated tracer particles are recorded by capturing stationary images of these particles with the help high speed, high-resolution CCD camera which offers high frame rate and small response time.

Calibration

Displacement of the images of the particles as well as the displacement of the particles in the images needs to be calibrated.

Post-Processing

To counter complex fluid flows and delete invalid flow measurement, post-processing is essential. One such post-processing tool is the PIV lab which is a which is an open-source PIV simulation module in MATLAB.

In this PIV facility, we can see that the flowing fluid is mixed with the seeding particles and is moving through the test section. A laser source is generating a high-intensity laser and its geometry is changed into a sheet configuration with the help of light-sheet optics. Then this light sheet incident on the fluid flowing through the test section. The particles which lie in the plane of this sheet will be illuminated and they will be recorded with the help of a high-speed CCD camera and a high-resolution optical lens. The stationary images of the particles recorded at the two consecutive instants will have a slight displacement of the particles. This displacement, as well as the time difference of the recording of these two frames, will be calculated to get the velocity vectors at each illuminated particles by the PIV simulation software. The basic framework of this facility is shown below.

Project Objectives

The main objectives of the project are as follows 

• To study the effects of particle size and density on their light scattering and fluid mechanical properties and the error in the PIV results associated with these parameters of the seeding particles.
• To study the effects of the wavelength, intensity and type of the illumination light source on the contrast of the illuminated particles and their background and ultimately their contribution to the error in the PIV results.
• Understanding of the fluid mechanics of internal pipe flow and its application to determine different flow parameters such as flow rate, velocity, and head losses, etc.
• Determination of the optimum light-sheet configuration which is as thin as possible and is uniformly intense and the effect of its thickness on the contrast of the images of the particles.
• Determine the effects of the laser light reflections of the circular walls on the final PIV images and finding a way to reduce these curvature effects as much as possible.
• Know the effects of the basic parameters of the camera like response time, shutter speed, frames per second and resolution on the resolved PIV images and finding the best combination of these parameters on the final simulated results.
• Understanding different calibration techniques and apply suitable one to calibrate the distance the particles actual travel and the distances they travel in the consecutive images.
• Understanding of the cross-correlation and its coding for the simulation of the PIV images to get our desired velocity field.
• Computational fluid dynamic simulation of the fluid flowing through the test section to check the difference of over result with the ideal one
• Calculation of the laminar velocity profile analytically to check the accuracy of our experimental facility.
• Recording the velocity profiles over different airfoils using experimental facilities like low-speed water tunnel and PIV.  
• Utilize the research potential of this facility to determine the bubble dimension of the bubbling fluidized bed.

Project Implementation Method

This project was started in June. The first three to four-month were used for Literature Review and building the basic concepts behind Particle Image Velocimetry Technique. One month was dedicated to the design of different components. The manufacturing was started immediately after the design in October. About 80% of the project has been implemented practically until now. First of all, we would like to tell the implementations that have been already applied following by the implementations that we would make in the coming three months. We would also tell about the financial barriers that we creating hindrances in the completion of the project.

1. The project was to make a loop of fluid in a circular pipe following by the development of the PIV technique to study that profile. The loop was made in the month of October. The basic concepts of fluid mechanics were utilized in doing this.
2. After the loop manufacturing, the challenging task was to make a light sheet from the laser. Cylindrical lenses and Laser were needed for this. We borrowed Laser from Physics lab of PIEAS but the cylindrical lenses were not available in PIEAS. The lenses were borrowed from the National Institute of Lasers and Optronics ( NILOP). The light sheet was successively made at the start of November.
3. Next challenging thing was to find the camera that can capture the stationary images of the micro-level moving particles. After a lot of struggle, a camera was found in the Biophotonics lab PIEAS. They already using that camera to study microorganisms. The camera was borrowed for a month and we starting to take the pictures of the fluid. As the micro fluorescent particles were very expensive. We used the cornflour as our tracer particles for the initial start of the apparatus.
4. We got our first result on 31 December by doing the simulation of captured images. But the result was not so good.

There are many reasons for this. Some of them are the following:

• In all PIV, apparatus green laser is used. But we are using the Red laser which causes a lot of scattering of light sheet.
• The lens of camera is not good. It has a very small area of field.

1. After December, the month of January and February was used to make the optimization of the light sheet and making the lenses mounts in the workshop of the PIEAS.

We want to make the following implementation the coming three months.

1. We want to purchase a lens for the camera that has a large area of field so that our entire pipe profile can be studied.
2. We want to purchase a green laser as I will give much accurate results as compared to the red one.
3. After the above changes, we will do the experiments on the different flow rates and study the profile of fluid in the pipe.
4. The Computational Fluid Dynamics (CFD) simulation will be made on the ANSYS and the experimental and simulation results will be compared.
5.  After we found that, our apparatus is giving accurate results, we will carry out the research on the study of bubbles size in fluidized bed using PIV.

Benefits of the Project

The sole purpose behind offering this project of Particle Image Velocimetry on the BS level was to build the apparatus that will be further utilized on MS and Ph.D. to carry out the advance research in fluid mechanics using Particle Image Velocimetry technique. There is no local manufacturing this project in Pakistan. The cost of this equipment is quite high as many companies are using patents. Many times PIEAS tried to purchase this equipment from the foreign countries but they did not provide this apparatus to PIEAS due to affiliation with Pakistan Atomic Energy Commission. So, our project main advantage is that it will be extensively used afterward for the cutting edge research in turbulent flow, two-phase flow, and multiphase flows. Our supervisor Dr. Atta Ullah has the plan to make a lab of experimental multiple flows for research and development in PIEAS.

The main advantages of Particle Image Velocimetry are the following

• PIV is the most versatile and advanced fluid visualization technique. It is non-intrusive which means that it does not affect the fluid flow profile in the process of recording or measuring the fluid flow characteristics.
• It is independent of the type of fluid flowing whose profile is to be recorded, we just need particles of good light scattering characteristics and comparable densities to the fluid.
• It is independent of the type of flows such as laminar or turbulent. We can also simulate the velocity results of highly accelerated flow by decreasing the response time of the recording device.
• It is a quantitative technique in which we not only get the velocity magnitude at a single point but we also get the entire velocity field on the entire flow domain. So it is the most efficient technique in the phenomenon of designing of various floating geometries, as we are able to visualize the response of the body to the entire incident flow.

Other than aerodynamic and fluid mechanical research PIV has many other diverse applications like:

• Endoscopic PIV is used in the medical applications in the phenomenon of the recording of the blood flowing profile in human arteries and this profile can be used to estimate the point of blockage of the arteries so it can be used to cure the human heart diseases.
• Micro PIV and Nano PIV are being utilized in the field of microfluidics in which they are used to record the flowing profile of the microchannel hence they find their application in the designing of MEMS.
• Underwater PIV can be used to estimate the flow profile of or seas or any water body at a specific depth from the surface.

There is a huge world of PIV and the designing of the basic 2D PIV will provide the PIEAS the entrance gate to this world of opportunities.

Technical Details of Final Deliverable

Technical details of the final deliverable are the following 

Fluid Flow Loop

Our test section is made up of Perspex with a refractive index of 1.47 and is of circular cross-section. It offers a lot of issues like a scattering of the light sheet over the surface of the pipe and this can be avoided with the help of a cubical water jacket around the surface of the pipe to minimize the curvature effects of the pipe. The flow is straightened with the help of a flow straightening device composed of a large number of tubes having the length to diameter ratio of 150. The block diagram of the experimental setup is as follows:

Seeding particles

We are using 40-60 micron silver coated hollow glass spheres with a density of 1.05g/cm3 for the visualization of water as a flowing medium.

Laser and light sheet

We are using continuous He-Ne 650nm and 10mW red laser and an arrangement of 3 cylindrical lenses to change its geometry into a sheet configuration. Our light-sheet configuration can be seen in the figure below. The focal lengths of the leases are mentioned in the configuration.

Recording

We are using a high resolution 120 fps CCD camera with a lens having a 10X optical zoom and the maximum area it can capture is 5cm. Its shutter speed is 100000. Because of the limitation of the shutter speed and frames per second of the camera we have to restrict the velocity of our flow and we can only measure the velocity profile up to 500 Reynolds number.

Image Processing and Cross-Correlation 

The processing of the images in PIV is performed by using the principle of cross-correlation. Below are the sample images that have been taken at a very little time difference. We can see that in the right image, the particles have moved a little bit in the downward direction i.e. in the negative y-direction. In the right image, there may be some particles at the downward that have come out of the image and at the top of the image, the new particles entering the image have also been not shown here.

Now, to process the images we have to divide the images into the sub-domains called windows. For simplicity here, we divide the left image into the four windows here as shown here

We take the one window of the left image and scan it in the right image to see where it matches with the right image. As the left image at the instant one and the right image is at the instant two. So, the distance between these is the distance that image right has traveled during the small instant of time. Using this distance and the time that we already know, we can easily find the velocity.

Once, we have found the velocity of one window, we need to find the velocity of all other windows in the same way. For each window, we get a vector having a magnitude proportional to the velocity and direction in the direction of the velocity.

Once we find the velocity field of a fluid, we can find all the other parameters of fluid-like shear, pressure, forces, vorticity, etc. by using this velocity field.

Final Deliverable of the Project

Hardware System

Core Industry

Energy

Other Industries

Medical , Petroleum , Health

Core Technology

Clean Tech

Other Technologies

Others

Sustainable Development Goals

Good Health and Well-Being for People, Affordable and Clean Energy, Industry, Innovation and Infrastructure, Life Below Water

Required Resources

If you need this project, please contact me on contact@adikhanofficial.com