I have found a nifty free program that could do a flow simulation and show it graphically as a video clip in .avi format. It is called Flow Illustrator. It is not accurate to replace a full blown Computational Fluid Dynamics software but it is free. You will need to do your own model. This is simply done by using a side view of the model. You can do this by using an existing picture with non essential details such as background and people deleted. I use Microsoft paint to edit my picture. Please note that it is advisable for you to use the CUT function using SELECTION. Once the image you need is cut from the original, you crop the rest leaving with a totally white background. You can upload the picture and set three (3) variables; Reynolds number, time between frames and video length in seconds. I only change the setting for video length. If you want to do comparison of flow between two designs, you need to have the picture in the exact dimensions. The value of the Reynold’s number will be shown on the video.
You can see the comparison video on this link.
A screen capture of the comparison is shown below
Simulated flow on Satria Neon with Deflector
Simulated Flow over Satria Neo with Standard Spoiler
Notice I have cut out the wheels to indicate flow of air under the floorpan. Green coloured areas indicate high pressure/low velocity and Red indicates low pressure/high velocity. The comparison helps to show that the original design with standard spoiler has a bigger wake left in the trail of the car. The one with the deflector has a smaller wake as the height of the turbulence is reduced.
If you do another comparison with a sedan design, you would see that the wake is about the height of the boot. The deflector now looks like what we intended it to be. It is to reduce the wake by delaying air separation from the hatch. This partly answer the previous question of why the Fuel Consumption curve is not logarithmic. The deflector has therefore made the car more aerodynamic. It makes it easier to cut through the air. I would not be surprised if it has reduced the Cd value of the car.
Making the car aerodynamic has the added bonus of reducing drag and obtain faster acceleration and top speed.
It came as an afterthought. It was never my direct intention to have done what I made. I had initially made a Secondary Intake for reducing fuel consumption of this car. See my previous article. Then I wanted to make the spoiler adjustable so that it can actually be useful. This was on my previous thinking that the spoiler functioned as perceived. That it provided down force and that if I took it out, the handling would suffer.
This then changed somehow without any premeditated intentions. What I have right now is a combination of efficiency solutions. The secondary intake initially showed that I could save money in the movement of the throttle. That was fine. Then the aerodynamics were sorted. Never did I thought the two combined mods made significant fuel saving changes.
I did a test run yesterday for 230km in total. This was a return trip on the North South Highway. It was to test the Deflector at speeds above 90km/h. It performed admirably by registering an Indicated average Fuel Consumption (FC) of less than 5.0 l/100km. You can see the YouTube video here . Yes, this means I now have a YouTube account. Forgive me I am rather slow at 46 years old. I have only now found the use for it.
During the same journey I made similar tests for speeds of 100, 120 and inadvertently 130km/h. All of these test results were on solid straight roads with the AC switched on. I plotted the values which I had observed on a spreadsheet. I had expected a exponential curve from 100 to 130km/h. But I could not get it. The only time I observed a high FC is when the car was being driven at 100km/h up a 20 degree incline.
The table is now UPDATED on 9 November 2014.
The data is based on observed data from factory standard equipment. They are not absolute and the value is AVERAGE Fuel Consumption. The last data if drawn to scale should be closer but it should also be higher.
A few things floated in my mind. As engineers we are told that aerodynamic load is very much affected by speed of the object or vehicle. This aerodynamic load increases . Fuel consumption will increase dramatically as speed increases. Perhaps it is too early and too easy to say that somehow with the combination of both modification, we have come to a point where the world is no longer flat. I might need to spend more day trips to Melaka to do more tests. One might say that these values at these speeds are insignificant as the speeds are low. But these speeds are what normal people are driving at. This is the whole point of doing these modifications. It is so normal people could save money driving normally.
Should anyone ask about performance degradation; I simply did not see any. The maximum top speed is still attainable.
Just a quick one as I do not want to give away too much. Finally managed to do up the fibre glass work with Chooped Mat and Roving. The Roving is better suited to hold the surface on the edges as it is stronger.
Needed to brace this securely on this working design. I would not need to get a really solid grip on the production model as it will totally be fibre glass. As it is now, wood is used as the main structural material. I would only need this working design to make some sets of mould. The finished product would therefore be much lighter and look nice.
Deflector mounted on car
Had a spin around Putrajaya. About 45km distance. First round registered 4.3 l/100km while the second registered 4.5l/100km. Will keep doing test and maybe try to add more surface area on the bottom. I am very happy as it is, there was little effort to try and clean it up. Not even fillers and it still meets the target. Probably I might get better results with the extension.
Posted in Aerodynamics, Fuel Economy, Spoilers
- Tagged Aerodynamics, Composite, Deflector, DIY, Fuel Consumption, Prototype, scratch buiding, spoilers, Woodwork