Inlet passage shapes (water and air)

[kach22i]

Before we begin, what is the major differences between water and air propellers and the mediums they operate in?
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SECTION - 1

I see slotted/grated waterjet intakes which look a lot like NACA air intakes, so I'm guess there are many similarities between how water and air acts.

Questions (see figure):

1. Passive air intake (no fan) body moving under 100 mph (if in air), which air intake is most efficient? Is water any different, why?

2. Active powered fan situation, body moving under 100 mph (if in air), which air intake system is most efficient? Is water any different, why?

3. Please direct me to an on-line source of information which explains when, where and why.



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SECTION - 2

Imagine these images turned upside down and in water, what would the answers be?

NOTE: Figure "C" exist in an air-cooled Porsche 911 for the cooling fan in an abstract way. Is there an equal situation in the water world?

[kach22i]

Come on, are the sketches that bad?

[kach22i]

Can this be applied to watercraft to reduce wake and drag?

Boeing makes 'quiet' advances
Noise-reduction efforts pay off at remote airfield in Montana

By JAMES WALLACE
SEATTLE POST-INTELLIGENCER AEROSPACE REPORTER
http://seattlepi.nwsource.com/busine...uietjet11.html

During tests at the Glasgow site with a 777 in 2001, Boeing found that two engines equipped with chevrons made no more noise than a single engine without the chevron.

Photo Caption:

Technology being tested on this Boeing 777 in Montana is expected to find its way into 787s, due to enter service in 2008, and the 747 Advanced. (August 11, 2005)

Credit: James Wallace/Seattle Post-Intelligencer

[charmc]

Originally Posted by kach22i

Before we begin, what is the major differences between water and air propellers and the mediums they operate in?

Hi, George, I just found this thread.

OK, The first and most obvious difference is that, while both air and water are fluids, "standard" water is 773.45 times more dense than "standard" air.

Another is that the density of air changes much more readily than the density of water. So relatively minor changes in air temperature and humidity will affect air propulsion systems significantly. Temperature changes in water have much less impact.

A third is that, under all "normal" circumstances, air is compressible, water is not. Compressing air increases its density, with lots of fun effects on power calculations.

Water propellors are smaller in diameter and stronger (requirement of operating in a denser fluid).

OK, got to get back to work. I'll review your questions and sketches later.

[kach22i]

Originally Posted by charmc

OK, got to get back to work. I'll review your questions and sketches later.

Cool, when ever........no rush.

I was looking up the term inlet flow distortion when I found an interesting image.

http://caltechbook.library.caltech.edu/22/01/chap4.htm

The circumstances are depicted in figure 4.6. Below a certain critical flow coefficient, the pressure difference driving the leakage flow becomes sufficiently large that the tip leakage jet penetrates upstream of the inlet plane of the impeller, and thus forms an annular region of ``backflow'' in the inlet duct..................efforts have been made to insert a ``backflow deflector'' in order to improve pump performance

It's a start.

[kach22i]

Looks like I have the right phrase to Google search with for sure.

http://www.techsburg.com/

Goal:
Realize performance benefits of boundary layer ingesting serpentine inlets by reducing engine-face flow distortion using active flow control methods

http://www.techsburg.com/Case_Studie...rframeInt.html

Goal:
Develop a highly efficient flow sensing and control system to eliminate adverse propulsion inlet/boundary layer interactions common to advanced propulsion-airframe (PAI) integration concepts.

Note: serpentine inlet is another search term I'm trying.

[lazeyjack]

wadda you do when your at work george?

[kach22i]

Originally Posted by lazeyjack

wadda you do when your at work george?

I'm a self employed architect in Michigan, things are real slow right now. I took up to Calculas 4 in college, but nothing stuck - my right side of my brain is far too dominant.

Hey, this looks a little like figure "C".

http://emeraldinsight.com/Insight/vi...&history=false

[USCGRET/E8]

In an open air prop configuration, tip speed is very important.
See: http://www.pponk.com/
http://www.hoverhawk.com/propspd.html

All props (water/air) are more efficient when enclosed. As you know, a water jet has an impeller vs. a propeller. Wikipedia has a good description:
Since impellers have no large blades to turn, they can spin at much higher speeds than propellers. The water forced through the impeller is channelled by the housing, creating a water jet that propels the vessel forward. The housing is normally tapered into a nozzle to increase the speed of the water, which also creates a Venturi effect in which low pressure behind the impeller pulls more water towards the blades, tending to increase the speed.

To work efficiently, there must be a close fit between the impeller and the housing. The housing is normally fitted with a replaceable wear ring which tends to wear as sand or other particles are thrown against the housing side by the impeller.

Vessels using impellers are normally steered by changing the direction of the water jet.

[USCGRET/E8]

Most water jets are axial flow. There also was some centrifgal pumps that monted on the bottom of outboard motors. In that the water had to change direction, they weren't very efficient and they came up with ways to make and attach axial flow oumps.

[kach22i]

Originally Posted by USCGRET/E8

All props (water/air) are more efficient when enclosed.

More or less that is true, I have to admit and as you can see from the sketches "ducted" is where my mind is at.

Mass Flow.......another good term
http://www.adl.gatech.edu/classes/propulsion/prop9.html


1. Inlet flow distortion

2. Serpentine inlet

3. Mass Flow

Any other search terms which will help out my quest?

Google search:
Inlet flow distortion Serpentine inlet Mass Flow
http://scitation.aip.org/getabs/serv...cvips&gifs=yes

This paper discusses the structure of the flow within the engine inlet of an uninhabited combat air vehicle (UCAV). The UCAV features a top-mounted, serpentine inlet leading to an engine buried within the fuselage. The performance of the inlet is found to depend strongly on a flow separation that occurs within the inlet. Both the time-averaged and the unsteady structure of this separation is studied, and an argument relating the inlet performance to the behavior of this separation is suggested. The results presented in this paper also suggest that there are considerable aerodynamic limitations to further shortening or narrowing of the inlet. Since there are substantial, system level benefits from using a smaller inlet, the case for separated flow control therefore appears clear.

Sounds like an old Williams Internations cruise jet missile.

[USCGRET/E8]

Some performance is lost using a water jet on a boat vs. a propeller. Case in point: I had a 21' boat with a 320Hp Ford 460 and Berkely water jet. Top speed was 50 mph. The same engine and boat hooked to an outdrive w/prop would have a top speed of 60-65 mph. The jet was way quicker out of the hole, however, because the impeller let the engine rev up instantly into it's high power range. A jet has only one moving part vs. several gears, thus far less expensive maintenance required.

[kach22i]

Originally Posted by USCGRET/E8

Some performance is lost using a water jet on a boat vs. a propeller.

Have you seen the snowmobile verses jetski race? The surface area of the track allowed the snowmobile to beat the jet ski even on a course with many turns.

Just an interesting weird thing.

STRICT inlet by Lockeed Martin:
http://scholar.lib.vt.edu/theses/ava...rabe_final.pdf

More STRICT from an Air Force site:
http://www.afrlhorizons.com/Briefs/Aug04/VA0309.html

Current design methods require inlet duct length-to-diameter (L) ratios of approximately 4 to produce satisfactory pressure recovery and distortion characteristics at the engine inlet. As part of the STRICT program, scientists developed a duct with an L of 2.5 that performs favorably compared to current designs. Scientists also demonstrated that the active flow control in the STRICT duct, at a throat Mach number of 0.65, contributed a 5% increase in pressure recovery (92% to >97%) and a greater than 90% decrease in circumferential distortion compared to the same duct without flow control.

[USCGRET/E8]

I guess what I am trying to say, is that when a prop is changed into an impeller, when ducted, the output force is changed. When actual props are ducted, they become more efficient. Many of the tugboats now have ducted props. I saw an experimental plane a while back, that had ducted props and it could take off in a lot less distance. The impellers seem to require more rpm's, which with a smaller diameter is possible.

[USCGRET/E8]

Have you seen the Jet model airplanes? They have a ducted prop that looks like the impeller on a marine bilge blower.