Measuring air flow changes through the radiator after adding splitter and air dam

[496BBC]

Back when I was having heating issues with my car Matt G. had suggested that I could measure air flow changes through the radiator by measuring voltage from the fan motor while not energized. Back then I was so caught up with fixing my heating issue that I let this one fall to the back of the list.

I recently had to re-rout my data logging cables so I decided to try Matt’s idea. I ran a wire from one of my 11” SPAL fans into the cabin and connected a DVM and sure enough I can get a good voltage reading from the fan motor. I’m seeing around 1.5 volts at 50 mph, 2.4 volts at 60 mph and around 3.2 volts at 70 mph. I was able to run 3 tests and the voltage was pretty close to these readings each run. I was able to see when my seal ( a piece of pipe insulation) between the top of the radiator and the core support partially blew out allowing air to bypass the radiator during one of my carburetor tuning test runs.

It’s a little hard to keep an eye on the DVM and the road when doing carb tuning test runs so I’ve connected the fan motor leads to my data logger so I can log the voltage while driving. This will also allow me to compare RPM’s with air flow to see if any changes I make to the cars front end effect air flow. My plan is to add a splitter and an air dam under the front of the car as BeeJay has done to see if it’ll increase air flow through the radiator.

The voltage readings are form memory so they may be off a little but they’re close, I was busy watching AFR, RPM and the road. This is why I’m wiring it through the logger, I’ll be able to down load it to my laptop and study the voltage compared to RPM’s.

Neal

 

[mrvette]

I would think that voltage/airflow relationship should be fairly accurate and consistent....I would maybe rather monitor the current drawn by the fans it should be rather minimal at say 40 mph.....

:quote::thumbs:

 

[BBShark]

That's a good idea. Turn your fan into an anemometer(sp?).

 

[phantomjock]

WOW - want to do a TEST!?

I have a Japanese text (fortunately translated!) titled, "Automobile Aerodynamics". One of the things I noted with GREAT interest is this tidbit:

"How fast does wind pass through the radiator?
The wind that pass through present-day radiators is
slowed to about 1/3 its speed of travel in the process."​

That may be quite significant! You could make some assumptions regarding the velocity by using the fan outside the window at speed and record the same info - volt/amps. Or, an interesting verification could be put your fan on the front (exposed side) of the radiator and compare at the same speeds. Either way a little data collection to verify the academic assertion would be nice.

Now, back to my book; the text is quite interesting (aside from the obvious translation chuckles) and includes some tables showing the Cd for various configurations of radiator and duct to the radiator. There is also a very nice set of graphs showing velocity ratios vs air passage for various configurations of rows, style of fin, and fins per inch.

If I can get a decent shot with the camera I'll add it to the mix here. Sorry no scanner available. Work keeps me humping so it may be a little bit, but I'll do it asap if there is interest.

Cheers - Jim

 

[69427]

I have a Japanese text (fortunately translated!) titled, "Automobile Aerodynamics". One of the things I noted with GREAT interest is this tidbit:

"How fast does wind pass through the radiator?
The wind that pass through present-day radiators is
slowed to about 1/3 its speed of travel in the process."​

.................................

Cheers - Jim

That's the function of the diffuser volume/area in front of the radiator. It's not efficient to allow the air to just slam into the radiator surface.

 

[mrvette]

I have a Japanese text (fortunately translated!) titled, "Automobile Aerodynamics". One of the things I noted with GREAT interest is this tidbit:

"How fast does wind pass through the radiator?
The wind that pass through present-day radiators is
slowed to about 1/3 its speed of travel in the process."​

.................................

Cheers - Jim

That's the function of the diffuser volume/area in front of the radiator. It's not efficient to allow the air to just slam into the radiator surface.

But wouldn't opening up the grills like I did, and putting in tray headlights and eliminating that restriction, and obviously removing license plate gear, but I know I added in two 'driving lights'.....still a overall inrush increase....
so you saying it did almost no good??

:shocking:

 

[phantomjock]

mrvette -
No - I wasn't saying that. In fact there is a a marked increase in flow by removing the grillwork and the licence plate. I read the text as meaning the velocity of the air is sufficiently decreased from the front (face) of the radiator to the back face (through the radiator -- free stream to free stream). The text is suggesting by 2/3. There will be a pressure spike on the front face as the flow goes from free stream and smashes against the radiator coils. By removing the grillwork - you have eliminated a similar problem in front of the radiator.

69427 -
I am not convinced the inlet on the C3 is optimum and much of the air does, "just slam into the front of the radiator surface." The tilt-back of the radiator also fails in ensuring efficiency (for flow purposes).As ductwork goes, the space behind the grill, the lower valance, is all fairly inelegant, rough, and not supportive of good flow" to the face of the radiator. Then once through the radiator - the air has to go somewhere - and more turbulence opportunity found in the engine compartment.

496BBC -
All which is why it would be so interesting to get the "instrumentation" on the front side of the radiator - and then we'd have a comparison. And be able to make some observations about the actual loss through the radiator! Then, build/install the splitter, measure front side flow, then back side flow and - Voilà! Real before and after conclusions cold be made - regarding improvement/efficiency.

Cheers - Jim
(somewhere around 89 days to go...)

 

[mrvette]

Jim, first off, Thanks for your service, come back safe...:beer:

second thing is on my airflow, I have the dual spal fans running directly parallel to the back of the radiator....about 2" or so off the core... so obviously the airflow from them is angled down, where as the stock fans aimed straight back over the engine.....so I wonder if changing that to straight back would help much with engine compartment heat....or what??

thinking of FLORIDA heat we know and headers and a/c and all that shit....

comments??

:clap::search:

 

[69427]

...................................

69427 -
I am not convinced the inlet on the C3 is optimum and much of the air does, "just slam into the front of the radiator surface." The tilt-back of the radiator also fails in ensuring efficiency (for flow purposes).As ductwork goes, the space behind the grill, the lower valance, is all fairly inelegant, rough, and not supportive of good flow" to the face of the radiator. Then once through the radiator - the air has to go somewhere - and more turbulence opportunity found in the engine compartment.

.........................

Cheers - Jim
(somewhere around 89 days to go...)

I made no claim that the C3 configuration was efficient. I was merely stating a prime reason for the reduced flow velocity in a properly designed cooling system (think P-51 radiator assembly).

 

[496BBC]

The front of my car is highly modified, I've removed the vacuum canister and the crash bar form the front end and fabbed a new core support that would not interfere with air flow to support the radiator.

I have a 80 model front bumper and have opened the area in the center and added thin wire grills on all the openings on the front of the bumper.

I built an air diverter to better direct the air from the lower spoiler up into the radiator and sealed the frontal area so all air would be directed through the radiator.

I have a couple areas at the top of the radiator that needs some attention and I'll take care of that soon as I get the motor back together.

I'll get some data logged prior to making anymore changes. Wish I would've done this before doing all the mods I've made to date.

Oh well live and learn

thanks for all the input and help

Neal

 

[010752]

diffusion and optimized air flow example

http://www.beta-cae.gr/events/c1pdf/05_chacko_radiator_efficiency_paper.pdf

 

[mrvette]

diffusion and optimized air flow example

http://www.beta-cae.gr/events/c1pdf/05_chacko_radiator_efficiency_paper.pdf

So the shape of the shroud behind the radiator seems to be most critical in the airflow through it.....interesting....here I keep thinking anything in front, and the sealing.....so IF I try remounting the fans....what would be a proper shape and angle??

maybe to get a stock shroud again, and fasten the Spals to that, somehow??

:amazed::quote:

 

[phantomjock]

I type while the slow conection to the 'net gets me to the link - could be interesting! 010752 - Thanks for locating that - its going in my files!!

69427 - I'm with you on the P-51 ducting. Most everyone may recall the inlet was stepped off the fuselage to get clear of bound flow. Sort of a splitter but maybe in reverse. And ducting (interior surface roughness/shape and cross-section) plays a factor in getting good flow.
[BTW - Its always seemed to me a good idea to do the dual fans/mounts on the radiator and pull through the radiator. Gets the flow through more efficiently - but nothing is free - you gotta pay for the fans and the energy to run them. Then the air needs to be exhausted somewhere.]

mrvette - that article just finished downloading here - and a quick look -- it is very interesting. One of the very disturbed areas aft of the radiator is of course the engine "space" and as you mention he heat and headers and "stuff" all contribute to inefficient flow - maybe not directly to the radiator - but it won't help with lowering Cd.

There are more than a few examples of efficient radiator exits - some I've seen here - on TTs site - notably the yellow, the blue (turquoise - with the shovel splitter and airbox, and the blue (german racing team-I think) has an airbox too as I recall.

A Splitter like BeeJays should help provide better flow into the radiator - (top side) and the bottom surface of the splitter would improve flow under the car as well.

All options to put into the mix. Right now I'm designing an airbox for my radiator, but the radiator will be in a forward laydown profile - not OEM aft leaning. I plan on a large-ish exit through the hood - like a few of the vehicles here. I'll load some pics this weekend - thats the soonest I'll have time to find-em!

For now - I'll spend a bit of time with the CFD article -- like I said looks interesting - but then maybe I have a twisted sense of priorities -- oh yeah no beer here -- ARGHH.

Cheers - Jim

 

[rodeck350]

I’m seeing around 1.5 volts at 50 mph, 2.4 volts at 60 mph and around 3.2 volts at 70 mph. I was able to run 3 tests and the voltage was pretty close to these readings each run. I was able to see when my seal ( a piece of pipe insulation) between the top of the radiator and the core support partially blew out allowing air to bypass the radiator during one of my carburetor tuning test runs.

This is a very interesting test. I don't want to encourage you to speed but i'd be interested in at what speed you first start seeing voltage and up to as fast as safely possible to see if the air speed saturates ie, reaches a limiting value.

That may be quite significant! You could make some assumptions regarding the velocity by using the fan outside the window at speed and record the same info - volt/amps. Or, an interesting verification could be put your fan on the front (exposed side) of the radiator and compare at the same speeds.

I agree that a passenger could hold a spare fan out the window to get a unimpeded air flow voltage reading. That would be very good info as a comparison.

But i disagree that you will find different speeds in front vs behind the rad. The airflow will be the same. The pressure would be higher in front vs the rear but that would need an electronic barometer or such. All that's going to do is measure the airflow resistance of the radiator itself. It would be expected that more rows and wider tubes would be more resistant. The rule of thumb on a aluminum radiator is that more than 2 rows produces diminishing returns.

 

[496BBC]

010752; I quickly looked over the article the thing that sticks out is that these tests appear to have been done with the truck sitting still. Looking at the flow of the air at the recirculation points if the truck was in forward motion than the recirculation would be less to null with the air pressure generated by the forward motion. It seems that with forward motion air flow becomes a pressure and resistance issue. The pressure in front of the radiator will be higher than at the outlet of the radiator. Any changes that will increase the DP should increase air flow through the radiator.

Rodeck350; The three tests I’ve done the first sign of voltage was around 35 mph. The highest voltage I’ve seen has been around 3.85 volts but this has been at deceleration after a WOT run. Just to much going on to look over at the DVM. My data logger will log voltage up to 5 volts so I should get more accurate readings once logging.

I’ve been looking at some MAP sensors that are used on turbocharged cars that will allow me to measure pressure in front and at the outlet of the radiator (vacuum and boost). If I can find one at a reasonable cost I may add one to the mix. It would be interesting to be able to mount the sensing leg of a MAP sensor at different locations on the car.

Neal

 

[phantomjock]

Using a MAP sensor and your datalogger seems very elegant. And with a bit of wire and tape you could get flow measurements in a lot of locations! Wow - imagine the possibilities.

I picked up a "magnehelic gauge" a year back - with the intention of doing what we are talking about. sort of like this one:
http://cgi.ebay.com/Dwyer-Magneheli...ultDomain_0&hash=item256002b773#ht_2282wt_950

They list at close to 100 bucks - but some clever shopping I did ok. Unfortunately it waits for my return and the car reassembly.

Downside to this set up is it requires a bunch of tubing and a passenger to do the data collection. My co-pilot (a cute datalogger) doesn't scare too easy - but she requires a nice meal + wine+ flowers as payback!

I have no clue on the MAP outputs, range of values it will measure, or the datalogger, and if the measurement system will have the fidelity or range to capture the information -- but it sure sounds cool. Keep us posted on the approach.

Off to work -
Cheers - Jim

 

[mrvette]

Early 60's Univ/Maryland college park...Glen Martin Aero college, I wanted to be...the father of a old HS electronic geek buddy was a Professor there....

I wanted engineering, but was piss poor/LOUSY at math, so never tried....

but turns out they were doing lots of work with CHRYSLER on aero for cars back in the daze....had I known....

:goodnight:

 

[010752]

diffusion and optimized air flow example

http://www.beta-cae.gr/events/c1pdf/05_chacko_radiator_efficiency_paper.pdf

So the shape of the shroud behind the radiator seems to be most critical in the airflow through it.....interesting....here I keep thinking anything in front, and the sealing.....so IF I try remounting the fans....what would be a proper shape and angle??

maybe to get a stock shroud again, and fasten the Spals to that, somehow??

:amazed::quote:

I did quite a bit of research quite a few years ago on shrouds and fans etc and a rule of thumb that sticks in my mind was that for optimum cfm, the shroud should be approx the same distance from the radiator as it’s diameter.
Of course that’s not possible in a C3, but the old Monte Carlo and Grand Prix of the early 70’s did have a shroud that seemed to be almost 2 feet long.
If I were mounting electric fans, I think I would go for the large Ford single fan, and reglass the original shroud for it to fit properly vertically.
Another tidbit I remember from similar test results was that a single larger fan will draw more cfm at less horespower and rpm that smaller or multiple fans.

Just this area of fans and shrouding is a science all to itself and gets pretty complex in a hurry, especially if you aren’t specifically trained for it. A lot of factors involved.

A Splitter like BeeJays should help provide better flow into the radiator - (top side) and the bottom surface of the splitter would improve flow under the car as well.

All options to put into the mix. Right now I'm designing an airbox for my radiator, but the radiator will be in a forward laydown profile - not OEM aft leaning. I plan on a large-ish exit through the hood - like a few of the vehicles here. I'll load some pics this weekend - thats the soonest I'll have time to find-em!

For now - I'll spend a bit of time with the CFD article -- like I said looks interesting - but then maybe I have a twisted sense of priorities -- oh yeah no beer here -- ARGHH.

Cheers - Jim

I've got quite a few pdf test results, if I can find them.

As to a splitter, I remember that the tests showed it did not increase the pressure to the radiator, but did of course help in cf.

I assume you're talking basically the radiator/flow design of the old GT40s, my favorite. Optimum design for what little I know, helped in all areas. Even the C6r's copied it as best they could.

010752; I quickly looked over the article the thing that sticks out is that these tests appear have been done with the truck sitting still. Looking at the flow of the air at the recirculation points if the truck was in forward motion than the recirculation would be less to null with the air pressure generated by the forward motion. It seems that with forward motion air flow becomes a pressure and resistance issue. The pressure in front of the radiator will be higher than at the outlet of the radiator. Any changes that will increase the DP should increase air flow through the radiator.

Neal

Or it will make it worse.:search:
I've got other test results here somewhere showing that increased pressure is much worse for radiator cooling than a diffused flow (assuming min requirement is met).
If you think of it as a separate system, like a water valve, internally there is always going to be turbulence, usually more with more flow and pressure.
Notice that NASCAR has relatively small air inlets.
Interesting thing about these test results is that it is not always what one would predict.
On the other hand, another test result predicted by increasing the surface areas of your radiators, you would increase cooling, which you did by adding more. A trick used is to angle the radiator, not because of physical restraints like in a C3, but simply because it increases the area, thus cooling.

Looking forward to your results, interesting stuff.:clap:

 

[larrywalk]

Using the electric radiator fan as a generator and measuring the electrical voltage is a neat idea. It is similar to using a propeller or fan for measuring water or wind speeds. In this case, it is not a measurement of absolute values, but it is a proxy for flow through the radiator.

I have recently thought that a good way to improve flow through the engine compartment, thereby lowering carburetor inlet temperatures and improving cooling was to remove the upper control arm flaps that separate the wheel wells from the engine compartment since I believe that the pressure under hood is greater than that in the front wheel wells. If you are looking for things to test, I'd sure like to see results at a given speed, say 70 or 65 mph (the higher the better, but wind velocity will be critical for comparison, so two runs - one each way would be required in each configuration.)

Good luck with your testing!

 

[vette427sbc]

With all of the mods people do to increase airflow to the radiator area, I think you can pass the point of increasing performance, and begin to force too much air to the radiator and under the hood which begins to create lift. I would think you want the LEAST amount of air that the car can handle without overheating. I put my front license plate on to reduce air going though the front grills (and to keep the cops away ), and I put the rubber flaps back on that cover the lights in the grill when they are down. So I have very minimal air entering through the grill. The majority of my airflow is from the bottom. No overheating, and less air being forced under the hood.

Ive been wanting to do a heat extractor setup for my radiator too... Ive also been wanting to add those greenwood (?) fender arch vents. I think they would be a pretty big help for cars that dont have pace-car spoilers to block off the front wheels.