Mass at intake area and mass flow rate are two different things. Mass per area is what spill is about. Mass flow rate is how much fast mass passes through.
Last edited:
SDF Aerospace and Aerodynamics Corner
- Thread starter paintgun
- Start date
MiG-29
Banned Idiot
The video of engineer is a pretty neat one but he fails to know the XB-70 has mixed compression, a Mach 3 its intakes are started, a F-14 has not a mixed compression but an external compression system, on a XB-70 the ramps are inside the intake duct and the shock waves are swallowed and inside the intake duct, on the F-14 the ramps are ahead of the throat and never are started, the Xb-70 at mach 3 can not spill air because it is working at supercritical conditions, so the second throat analogy of the video is correct for a mixed compression system such as a XB-70.
Notable examples of inlets employing external compression include those used on the Concorde, the F-14 Tomcat, and the F-15 Eagle
Attachments
-
xb-70 intake.jpg
Last edited:
Engineer
Major
Nope. Fallacy refers to improper reasonings, such as those you used in your argument. There is no fallacy in my statement.
The amount of air entering the inlet is the same as the amount of air flowing through the throat. Mass flow rate is conserved, and it is said so in the book here:
So, the book disagrees with you.
Furthermore, mass flow rate is fixed. All variable-geometry does is move the terminal shock, and it is said so in the video . Mass flow is fixed because of choke, said so in video . Density at the throat changes as area of the throat changes because of fixed mass flow, said so .
Correct. Bypass doors are what changes the mass flow, not variable-geometry. A variable-geometry inlet requires bypass doors to control mass flow, but a fixed-inlet with bypass doors does not require variable-geometry to do the same thing. This says variable-geometry throat does not regulate mass flow as you claimed it does. Recall what you have said.
Right now, you are just arguing for the sake of arguing.
Engineer
Major
Spill air does not enter the inlet, but the amount of air that does is equal to the amount of air that passes through the throat. Mass flow rate is conserved. This is Bernoulli's effect:
spill air is like a sink overflowing, you like it or not hahaha
Wrong. Air is compressible fluid, while water is incompressible. So your water-in-a-sink analogy for air flow within an aircraft's inlet is flawed. I neither need to like or dislike it, because I know you are wrong.
Engineer
Major
The video of engineer is a pretty neat one but he fails to know the XB-70 has mixed compression, a Mach 3 its intakes are started, a F-14 has not a mixed compression but an external compression system, on a XB-70 the ramps are inside the intake duct and the shock waves are swallowed and inside the intake duct, on the F-14 the ramps are ahead of the throat and never are started, the Xb-70 at mach 3 can not spill air because it is working at supercritical conditions, so the second throat analogy of the video is correct for a mixed compression system such as a XB-70.
Wrong. The phenomena explained in the video is applicable to any type of supersonic inlet, as the video shows how compressible flow behaves inside a duct. Mass flow rate is conserved as air is moved from a wider area to the narrow throat. Thus, mass flow rate at the inlet mouth and mass flow rate at the throat is the same.
The citations, pictures and videos show that your claim that variation in throat geometry regulates air flow is incorrect.
Spill air can occur on fixed-inlet as well, showing spilling is not an effect of varying throat geometry. With DSI, excess air is spilled exclusively, as explained in .
In the discussion of the right picture, the paper points out that pressure recovery ratio at sub-critical condition is higher than traditional inlet. This is because the oblique shock wave becomes stronger at high Mach number.
The pressure recovery ratio of DSI at sub-critical condition is higher than traditional inlet. This is the finding of the paper.
Last edited:
Engineer
Major
Actually, what MiG-29 doing is discarding effects of Bernoulli's principle and compressibility to justify his opinion that throat geometry changes regulates air flow. Obviously, the pseudo-aerodynamics theories invented by him, such as air behaves like water in a sink, have little to do with reality.
The reality is this: after air has been spilled, the amount of remaining air which enters the inlet mouth can be measured in X kg/s. This air then enters the narrower throat region, and measuring the amount of air here would give the same X kg/s. This is conservation of mass. It is even said so here:
MiG-29
Banned Idiot
you are the one who does not understand mixed compression intakes swallow the shocks and operate in supercritical conditions they have internal compression, the video has a XB-70 at the end and no external intakes swallow the shocks, starting is only applied to mixed compression intakes
MiG-29
Banned Idiot
actually external compression works for only critical states, mixed compression swallow the shock and start the intake, you did not know that mixed compression has supercritical states
Engineer
Major
Whether it is internal, external, or mixed compression inlet, does not negate the fundamental employed in the design of supersonic inlet, which is that of a compressible flow. The behavior of compressible gas is shown in the video, and we see when air encounters a narrower space, the flow rate is increased to compensate. The air at the narrower space also compresses. The combined result of the two is the terminal shock wave.
You do not know about compressible gas. You assumed air acts like water. You do not know about Bernoulli's effect either. This shows you have no understanding whatsoever of aerodynamics.
MiG-29
Banned Idiot
Wrong. The phenomena explained in the video is applicable to any type of supersonic inlet, as the video shows how compressible flow behaves inside a duct. Mass flow rate is conserved as air is moved from a wider area to the narrow throat. Thus, mass flow rate at the inlet mouth and mass flow rate at the throat is the same.
The citations, pictures and videos show that your claim that variation in throat geometry regulates air flow is incorrect.
Spill air can occur on fixed-inlet as well, showing spilling is not an effect of varying throat geometry. With DSI, excess air is spilled exclusively, as explained in .
In the discussion of the right picture, the paper points out that pressure recovery ratio at sub-critical condition is higher than traditional inlet. This is because the oblique shock wave becomes stronger at high Mach number.
The pressure recovery ratio of DSI at sub-critical condition is higher than traditional inlet. This is the finding of the paper.
To start DSI can not swallow the shock unless is a DHI, DSI are external compression simply because the shocks are outside the lip cowl and do not get supercritical states.
F-14 also does not swallow the shocks, a mixed compression at Mach 3 does not spill you unchoke the intake throat how engineer? well by moving the shock outside the intake and impinging on the intake cowl lip, in an subcritical state you will see the shock outside the cowl not even impinging the intake lip and spilling