Port Vanes?

[fredman]

Have any of you guys ever created some sheetmetal port vanes that redirect port flow on the flow bench just for giggles? I was thinking of the port inlet not the throat area. Reading Darin's post this popped into my head and was wondering.

Fred

[Unkl Ian]

Tried it very briefly,on a 2 valve Hemi head,didn't see any improvement.

Which doesn't mean it won't work.

[fasteach]

I personally have not seen them, but have it on good authority that this was a common practice among ford 351C drag racers "back in the day".

[Mpcoluv]

The ones I have seen in the old race 351C heads look to be more of a "Fuel shear" designed to break up large droplets of fuel caused by poor velocity.
I have heard of people epoxying a paperclip in a boss 302 port back in the trans am days for that reason.

[fredman]

Thanks for the replies. My thoughts were "dividers" (horiz or vert) placed in the port runner to redirect flow from high (pressure or velocity) to low areas to "fill in" those area for a higher quality port flow. Obviously swirl could also be induced this way also. My sound silly but given the quality of players on this forum, I figure I could get the experience one's to respond.

Fred

[MadBill]

Wind tunnels use turning vanes, and I've found flow benefits (~5% per vane, for one down the center of each of the two 90° bends in a Firebird TPI intake tube. I always wanted to try it on a intake port, maybe one that was a little too big to start with, to make up for the added resriction. (or maybe one that was too small, to keep the air from flying off a tight SSR...)

[fredman]

Possibly in a restricted porting class this could assist the ssr by changing the flow characteristics and fill in a flow separation condition and actually increase cfm and flow quality.

Fred

[Telvm]

Picture of the long, S-shaped air duct for the centerline jet engine in a Boeing 727 airliner:



Air is ingested from the intake (in the background of the gentleman), then has to negotiate two bends until it finally reaches the jet engine (approximately at camera position).

Notice row of vortex generators in each 'short side radius', to energize boundary layer and prevent flow separation.

I wonder if this aerodynamic trick could be of use in shallow intake ports of piston engines.
.

[Unkl Ian]

I've seen some people grinding lines across the floor of the port.
I think they act like small Vortex Generators.

Some have gone as far as making deeper grooves,in the same spot.

Kinda like the dimples on the golf ball theory ?

[Crutch]

Airplane wings also use small tabs like these to induce a small amount of turbulence to prevent the flow from seperating before it reaches the back of the wing. What I don't quite get, does the vortex created keep the boundry layer small and next to the ??low pressure?? area or what.

This part is hear say........

I think the golf ball dimples have been experimented with a lot but the effect isn't the same in a port. Dimples were used where tits (for lack of a better word) should have been used. One other thing I have heard, (can't prove any of it) related to guys cleaning up ports that were CNC cut. Sure the cfm picked up after cleaning up marks from the tool bit however torque and HP went down. I didn't find out if it was caused by boundry layer changes or better fuel suspension due to the cutter marks.

[Telvm]

This is how VGs work on aircraft wings:



.

[fredman]

How much or how tight a radius in a ssr could vg's help keep the boundry layer attached? My initial question was more from a simplistic pov that while flowing a port, hold a divider at various positions that alters or repositions flow into lower depressions or flow areas. Try to "fill in" a port to attain a higher quality of flow. Would even be more interesting in a wet flow bench!

Fred

[Telvm]

Excerpts from Ian Postlethwaite, Lotus Engineering:

"The design of a modern intake port geometry is a compromise between high speed flow and low speed tumble. The tumble is used at low speed to augment combustion at a time when the flow has generated little turbulence during induction.

As the speed/flow rate increases, the tumble increases and flow coefficients decay. At the higher speed/flow rates the flow has sufficient turbulence, and high tumble is not required. Therefore, a port designed to deliver sufficient tumble at low engine speed will produce a surfeit of tumble at the higher speed/flow condition, at the expense of flow coefficient.

The port for a high performance engine has a steep angle, which endows it with a good flow coefficient. The lack of tumble is not a shortcoming since, in this type of engine, the high engine speed and flow generate the
turbulence required. This type of port would produce relatively poor low speed performance. On the other hand a port for a typical passenger car engine has a much shallower port giving good tumble at low speeds but compromised flow at high speed. The bulk flow structure in the cylinder, described as tumble, is generated by separating the flow from the floor of the port just upstream of the valve. This effectively forces the flow over the top of the valve and produces the tumble. Clearly this does not use the full flow area effectively. If the separation could be reduced at high speed then the port flow capacity would increase.

With this in mind Lotus has developed an innovative port design (figure 2) which has shown improvements in flow coefficient of about 8%. Vortices are generated that draw the flow back towards the port floor and re-energize the boundary layer to offset the flow separation which causes the tumble, the flow attaches more to the inner radius of the port with the modified geometry. The modified geometry shows a similar effect at lower speed and consequently reduces the tumble also. However, the reduction in tumble at low speeds is small and is more than compensated for by the increased flow."

[fredman]

Telvm;

I'm a little lost in the diagram of where the port opening (left of picture?) is at and is somethiing being done to the port surface to cause the reattachment. Or is it the vane or divider creating it?

Interesting article, where did it come from?

Fred

[GregGood]

The port entrance is on the right hand side of the diagram. The old Buick NASCAR Stage 2 heads that were run in Busch Grand National years ago had this cast into their intake ports. Most head porters ground them out.

Next time you flow an intake port take a ballpoint pen and lay it on the floor of the intake port. Move it around and see if you can find a position where the manometer loses an inch or two of water.