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
A day after posting Part 4. I did a calculation using a spreadsheet. I could either stick to my existing HITEC or get a slightly bigger one. There’s a local Arduino reseller that has lots of TowerPro MG945 which has a stall torque rating of 12kg/cm at 6VDC. I am definitely going to buy this. Although the gears are of metal, due to the power that’s required, I prefer Nylon to take in the additional service demand. I would also need to reduce the surface area by 30% while limiting the angle to not more than 30º. As preparation to accept this servo I had to install a 3 wire cable taken from a power cord extension. The length is about 1.3m which is sufficiently long to have the new controller next to the mid console close to the handbrake. I have routed this through holes that were meant for the rear water jet for the wiper and through one for the spoiler mounting. It’s a bit harder than just that, as I had to remove two panels and I had to make sure the cable was not interfering with the rear seat belt mechanism.
While at the same time, I found the bracket for the reverse sensor a bit too big for my liking. I therefore made holes to shave off 20g. It was not planned. Since it was hard to remove these panels, I would not be seeing it for many years to come.
A few more days and I finished my mechanical build of the spoiler and had it fitted on the car yesterday 27 May 2014. I had a spin in it around Putrajaya, in the most decent of 80km/h speed. It did not fell off even though all of the wooden part was held in place by nothing more than Dunlop Contact Adhesive and two screws. I had another spin today at much more livelier speed around the same track and it is still there on the roof. I might add more screws to keep it all sane. I used normal green coloured Garden Wire to secure the angle of attack. I do not want the angle to be too big that it would add drag and load onto the new assembly.
I am happy to report that on the first test, I recorded an 18% fuel consumption reduction. Initially the average at 80km/h is 5.3l/100km. Now it is 4.3l/100km. Tell me again how much that hybrid costs! This is amazing. Previously I could only make 4.0l/100km on a flat straight road. But with this spoiler. I could drive it normally without having to use hyper-milling techniques to get close to that. It goes to show that it does make sense to make the air separation as late as possible. The angle of the spoiler closely matches the angle of the hatch. I cannot be too sure if I had also reduced the wake.
With that I have completed the mechanical build and managed to clean the wet kitchen area of my house clear from tools and debris. This gives much joy to my wife. The next steps will be to finalize the electronics.
It has been a few weeks of browsing through my den of broken things to put together a test rig. The reason being to please my self doubt about what I am trying to do. A lot of times I have questions floating in my head if I could actually pull this off. I have been messing around on the internet and trying to find something that could show that my half baked ideas is actually worth the time. Time is on my side. I have stopped working for the moment. I ended my previous job as a Manager for Fire and Gas Detection system with Draeger Safety with a small compensation package. That bit of kit would probably last me a few months before I actually need to find a job. At 45 years of age, that is not going to be easy.
I have taken a piece of wood from my hoardings and bought a cheap set of planer. The last time I used this was in Secondary School in the early 80’s where we learned woodworking. I therefore whittled down this piece of wood for two days to come as close as possible to the profile that I needed. I also used my dremel and coarse grit sandpaper to give a good smooth finish. Woodworking is very addictive I must say. I find myself constantly reshaping the profile untul it looked satisfying to my eyes. I was not looking for an effective aerodynamic profile. I wanted it to look good. I had to force myself to stop because I needed to do this rig and reassure myself.
I took the finished piece of wood and proceeded to find the center of gravity. This is crucial as this would help to reduce the torque demand on the servo motor. Placing the servo in line with the axis of rotation means reducing the weight that had to be moved around the axis. I simply held the spoiler by the side of both hands. I slide both hands to the center of the piece. Where the tilted, the weight has gone the other way. I slid the hand which had no resistance because of this shift. I put the wood on a pen and tried to balance it as much as possible. This way, I found the center of gravity and marked with a pen. I then used the grain of the wood to show me the pivot point at each end of the piece.
Then I looked inside the cabin again to find unused TV stands meant for my 42 in plasma TV. I drilled both at an approximate height. The undriven pivot side was held by a simple screw. The driven side had a servo hub which was nailed. The hub has a 24T spline which would normally be attached to the servo shaft and screwed in place. This is another issue that I would need to address. I would need to cut an approximate width of 20mm to enable the screw to tighten the sawn wooden piece against the servo. Once that servo is tightened, it would then be screwed to the main piece.
Finished Test Rig
I have been trawling the pages of Servo City for a few weeks now and have ordered some bits and pieces. I will tell why I need those a few paragraphs later. I have made a test rig to show myself that the small servo could turn the wooden spoiler. A video of which can be found on my facebook link here
Close up of Hitec HS-425BB RC Servo
What I have realized after playing with the test rig is that the weak link lies in the connection to the HITEC Servo. This HITEC HS 425BB was bought from a local Arduino authorised agent at MyDuino.com. It was the biggest RC Servo that they had. I could see that at a speed of 200km/h and with a surface area of 7,500mm2, the wind load on the spoiler would only be contained by the servo hub and the swivel joint. Even though this HS 425BB is a model with bearings, I would think that it would not be sufficient to handle the load. Therefore I decided a redesign is in order. Part of the items I hard ordered online was an aluminium arm to connect to the spoiler. But because the spoiler would have a different pivot point and than the servo, the hole on the arm must be modified to a slot.
Having two support on the driven side would increase load capability. This also means is that the torque demand on the servo would be increased. I am prepared to make the spoiler lighter by hollowing; making more holes where necessary.
People Mover! I hear you shout. Truly agreeable with you on that one. It is NOT a car. Its a bus. Initially it was an embarrassing idea to have one. Yet I have a family with three above average size children with above average appetite. Plus we used to have a lived in maid from Indonesia. Therefore, it is a must have. It is a Hyundai Trajet GLS circa 2002 but we bought it in 2004. The only automatic transmission car that I own. My wife actually owns it. I just pour in the fuel and pay the monthly dues and do all the maintenance on it.
A bit of history. Hyundai made this to compete against the Toyota Estima, Honda Oddysey and the GM/Opel Zafira. Wherever they meet. I would think Asians would be the preferred market as the Europeans are dead set on station wagons. Aisans tend to have a sizeable family extended or not.
It drinks a lot. Petrol I mean. Wherever you go except for national highways which seem to be just about ‘ok’. The fuel consumption is a real issue when it does not travel in one huff. Stop and Go traffic is stressful on the heart and the wallet. It does not have a fuel consumption meter. Which makes it hard to guess how efficient it is at doing its thing. However, big lugs like this are the ones that supposed to get the highest attention. Reducing fuel consumptions on behemoths should be the main focus of car designers.
Therefore, in the spirit of chasing efficiency, I plugged in the washing machine hose thingy into the airbox. Drilled an M25 hole and simply push it in. The other end with the funnel could be placed anywhere. So I did.
Interface done with airbox
Secondary Intake for Hyundai Trajet
I had it go through various orifices. I had to remove the front grille to make my hand accessible to where I want it. I then decided to run it through the bottom grill. I found this not to be the ideal place. The wake from the bumper would have a slight pressure drop where I had it. It ws a bit lengthy and would cause some measure of pressure loss.
Since then I had cut it up and placed it just over the left light cluster. What I do want to see is using a snorkel and mount it right over the radiator. That would be Trajet Snorkel 2.0
I still have no clue if there was any improvement. I leave that one to faith.