SDF Aerospace and Aerodynamics Corner

From , the difference between actual and required flow is either spilled or bypass:


The same source then mentioned again that excess air needs to be bypassed:


The source does not say anything regarding using intake ramps to reduce excess air, contrary to your claim. The fact remains that the bypass system is what regulates air flow in an inlet. As for spillage, it can occur on fixed-inlet and DSI. It can also occurs with pitot intake at subsonic speed, as you can see .

Engineer said:

From

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, the difference between actual and required flow is either spilled or bypass:

The same source then mentioned again that excess air needs to be bypassed:

The source does not say anything regarding using intake ramps to reduce excess air, contrary to your claim. The fact remains that the bypass system is what regulates air flow in an inlet. As for spillage, it can occur on fixed-inlet and DSI. It can also occurs with pitot intake at subsonic speed, as you can see

.

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you forget to highlight the variable inlet ramp will reduce excess air mass flow by 13%

how engineer it does it why Sr-71 reduces throat area like F-14?

MiG-29 said:

As the SR-71 increases its speed, the inlet varies its exterior and interior geometry to keep the cone-shaped shock wave and the normal shock wave optimally positioned. Inlet geometry is altered when the spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach. At Mach 3.2, with the spike fully aft, the air-stream-capture area has increased by 112 percent and the throat area has shrunk by 54 percent


This type of intake produces a series of mild shockwaves without excessively reducing the intake efficiency.12. As aircraft speed increases still further, so also does the intake compression ratio and, at high Mach numbers, it is necessary to have an air intake that has a variable throat area and spill valves to accommodate and control the changing volumes of air (fig. 23-9).


Variable geometry capability in the ramp angle
changes for mass flow regulation




tell me why F-14 and SR-71 have variable geometry throats and the SR-71 reduces the throat area to reduce mass flow?

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Using large font size is not going to magically make your position stronger. The purpose of variable-geometry is to optimally position the shock waves, this is stated in your very own citation above. I have highlighted some extracts for your convenience, and you can read the entire thing at




In addition, your own source has the following to say:



Thus, bypass system is what regulates air flow. We can see that inlets on the F-22 have only bypass doors with no variable-geometry. Recall what you have said:

MiG-29 said:

If you were right you only would need the by pass doors, not variable geometry throats.

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Right now, you are claiming I am incorrect just for the sake of arguing.

MiG-29 said:

you forget to highlight the variable inlet ramp will reduce excess air mass flow by 13%

how engineer it does it why Sr-71 reduces throat area like F-14?

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Throat area is reduced as a consequent of having to adjust the position of oblique shock waves. It is that simple. Note how it is the bypass system that regulates air flow in the following illustration for Concorde's intake:







The same source states the following:

The air intake ramp assemblies main job is to slow down the air being received at the engine face to subsonic speeds before it then enters the engines.

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On the F-22, the inlets are fixed with only bypass doors present. Recall what you have said:

MiG-29 said:

If you were right you only would need the by pass doors, not variable geometry throats.

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Right now, you are claiming I am incorrect just for the sake of arguing.

Engineer said:

Throat area is reduced as a consequent of having to adjust the position of oblique shock waves. It is that simple. Note how it is the bypass system that regulates air flow in the following illustration for Concorde's intake:

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The same source states the following:


On the F-22, the inlets are fixed with only bypass doors present. Recall what you have said:


Right now, you are claiming I am incorrect just for the sake of arguing.

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you are still wrong and i will prove it

this is variable geometry intake


if you see the numbers for a fixed intake


what can you see? well the intake is smaller so the engine demands needs are closer to the intake supply, why simple you are sizing the intake smaller, plus the throat at lower speeds is bigger, so you do not need a bigger fixed intake to avoid the engine from choking at low subsonic speeds, yes you need still by pass doors, but a bigger throat at speeds below Mach 1.4 reduces bigger sizing on variable geometry throat intakes

MiG-29 said:

you are still wrong and i will prove it

this is variable geometry intake

if you see the numbers for a fixed intake

what can you see? well the intake is smaller so the engine demands needs are closer to the intake supply, why simple you are sizing the intake smaller, plus the throat at lower speeds is bigger, so you do not need a bigger fixed intake to avoid the engine from choking at low subsonic speeds, yes you need still by pass doors, but a bigger throat at speeds below Mach 1.4 reduces bigger sizing on variable geometry throat intakes

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Nope. There is nothing wrong about my statements. The fact that you are yet unable to specifically point out where I am wrong speaks volume.

The different between plots 10.52 and 10.53b is due to different capture area used in the two examples. Since these are two different inlets, of course their mass flow ratio will be different. This is clearly stated in the source:



It remains a fact that variable-geometry does not regulate air flow. The amount of air that flows through the inlet mouth is the same as the amount of air that flows through the throat. Narrowing of the throat only causes air at that region to move faster to compensate, and this is Bernoulli's principle.



Bypass system is what regulates air flow, and as we have seen of fixed and variable-geometry inlets, an inlet can operate without a variable intake ramp but cannot function without a bypass system. Recall what you have said:

MiG-29 said:

If you were right you only would need the by pass doors, not variable geometry throats.

Click to expand...

F-22 does not have variable-geometry in its inlets, only bypass doors. Right now, you are claiming I am incorrect just for the sake of arguing.

Engineer said:

Nope. There is nothing wrong about my statements. The fact that you are yet unable to specifically point out where I am wrong speaks volume.

The different between plots 10.52 and 10.53b is due to different capture area used in the two examples. Since these are two different inlets, of course their mass flow ratio will be different. This is clearly stated in the source:

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It remains a fact that variable-geometry does not regulate air flow. The amount of air that flows through the inlet mouth is the same as the amount of air that flows through the throat. Narrowing of the throat only causes air at that region to move faster to compensate, and this is Bernoulli's principle.

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Bypass system is what regulates air flow, and as we have seen of fixed and variable-geometry inlets, an inlet can operate without a variable intake ramp but cannot function without a bypass system. Recall what you have said:


F-22 does not have variable-geometry in its inlets, only bypass doors. Right now, you are claiming I am incorrect just for the sake of arguing.

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of course they are smaller, the variable geometry throat intake is smaller and more effective than the bigger fixed intake, that is the first advantage and that is thanks to a variable geometry throat and ramp, the second advantage is by bypassing less air pressure recover is better and do you want and example

F-14 has better pressure recovery than DSI


So you not not only can develop smaller capture area intakes but also better pressure recovery.

F-14 and Concorde have for a reason variable geometry intakes.

Ah and by the way spilling air means A1 is free stream flow outside the intake hahaha not inside the intakee hahaha

MiG-29 said:

of course they are smaller, the variable geometry throat intake is smaller and more effective than the bigger fixed intake, that is the first advantage and that is thanks to a variable geometry throat and ramp, the second advantage is by bypassing less air pressure recover is better and do you want and example

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This does not prove your claim that variation in throat area regulates flow, nor does it invalidate anything that I have said. Variable-geometry's purpose is to position the oblique shock waves. It is the bypass's job to regulates air flow. Your citations say the same thing.

MiG-29 said:

F-14 has better pressure recovery than DSI


So you not not only can develop smaller capture area intakes but also better pressure recovery.

F-14 and Concorde have for a reason.

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And J-10B's DSI has better pressure recovery than variable-geometry inlet on F-4D.

I have pointed this out before and I will do so here again: you can install as many variable ramps as you want to increase pressure recovery, but for each ramp you installed complexity will increase. This results in increase weight which offsets advantage gained.

MiG-29 said:

Ah and by the way spilling air means A1 is free stream flow outside the intake hahaha not inside the intakee hahaha

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A1 is the capture area, A0i is the cross sectional area of free stream flow.


Also, spilled air doesn't enter the inlet's mouth. Air spilling doesn't contradict Bernoulli's principle, and the amount of air flowing into the inlet mouth equates to the amount of air flowing through the throat.

Engineer said:

This does not prove your claim that variation in throat area regulates flow, nor does it invalidate anything that I have said. Variable-geometry's purpose is to position the oblique shock waves. It is the bypass's job to regulates air flow. Your citations say the same thing.



And J-10B's DSI has better pressure recovery than variable-geometry inlet on F-4D.

I have pointed this out before and I will do so here again: you can install as many variable ramps as you want to increase pressure recovery, but for each ramp you installed complexity will increase. This results in increase weight which offsets advantage gained.



A1 is the capture area, A0i is the cross sectional area of free stream flow.

Also, spilled air doesn't enter the inlet's mouth. Air spilling doesn't contradict Bernoulli's principle, and the amount of air flowing into the inlet mouth equates to the amount of air flowing through the throat.

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the intake with variable throat has a bigger throat at Mach 1.4 and smaller above Mach 1.4.

A1 is spilled and As=throat or mouth so tell me why the variable intake gets a bigger throat?


Why the variable can be made smaller?

answer the larger throat area gets more air

If A1=As they have the same area, and air is spilled because A1 is bigger than As area, the engine is like a toilet plunger that increases or decreases the suction force inside the intake

MiG-29 said:

the intake with variable throat has a bigger throat at Mach 1.4 and smaller above Mach 1.4.

A1 is spilled and As=throat or mouth so tell me why the variable intake gets a bigger throat?


Why the variable can be made smaller?

answer the larger throat area gets more air

If A1=As they have the same area, and air is spilled because A1 is bigger than As area, the engine is like a toilet plunger that increases or decreases the suction force inside the intake

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Change in throat area is a consequent of having to adjust the intake ramp to position the shock waves. Air spillage is caused by the position of normal shock wave, not by variation in throat area. Air can get spilled regardless of whether the inlet can vary its inlet geometry or not as shown in the following diagram.


Spill air doesn't enter the inlet mouth, but the amount of air that does is going to be the same as the amount of air that flows through the inlet throat. This is Bernoulli's principle shown in the diagram below.


In addition, air is a compressible fluid. Your water-in-the-sink and toilet-plunger examples are flawed because water is incompressible and do not behave like air. What does it mean by compressible? Think of a spring, now squeeze it and fit it into a small area. That's what going to happen to the intake air too when it encounters narrower space.

Thus, variation in throat area is not going to regulate air flow. To regulate air flow, bypass system are needed. In fact, air inlet with bypass doors only can operate without intake ramp, as is the case on F-22. Remember what you have said:

MiG-29 said:

If you were right you only would need the by pass doors, not variable geometry throats.

Click to expand...

Right now, you are arguing just for the sake of arguing.