Accidental Discoveries of the 20th Century
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Conflicting Traffic
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[quote author=Strega link=topic=562.msg2371#msg2371 date=1439168315]
read up on compressible Bernoulli.
[/quote]
There's no such thing as "compressible Bernoulli". Bernoulli's equation is obtained by applying the condition/approximation of [i]incompressibility[/i] and integrating Euler's equation. So by definition, Bernoulli's equation applies only to incomressible flow. Maybe you mean the energy equation? Not really sure how that resolves the discussion here.
Flow behind a normal shock is always subsonic. But flow behind an oblique shock can and often does remain supersonic. A bow shock is curved. So at the leading point, it's a normal shock, but elsewhere it's oblique.
The possibility of having supersonic flow behind a shock is why the schlieren photo posted by 'pie shows a series of shocks, one behind the other.
As for accidental Discoveries/Inventions:
[b]Teflon[/b] - Developed by accident when pressurizing a gas to experiment on refrigeration systems.
[b]Microwave ovens[/b] - Discovered by an engineer at Raytheon who melted chocolate bar in his pants while working on a RADAR system.
CT
read up on compressible Bernoulli.
[/quote]
There's no such thing as "compressible Bernoulli". Bernoulli's equation is obtained by applying the condition/approximation of [i]incompressibility[/i] and integrating Euler's equation. So by definition, Bernoulli's equation applies only to incomressible flow. Maybe you mean the energy equation? Not really sure how that resolves the discussion here.
Flow behind a normal shock is always subsonic. But flow behind an oblique shock can and often does remain supersonic. A bow shock is curved. So at the leading point, it's a normal shock, but elsewhere it's oblique.
The possibility of having supersonic flow behind a shock is why the schlieren photo posted by 'pie shows a series of shocks, one behind the other.
As for accidental Discoveries/Inventions:
[b]Teflon[/b] - Developed by accident when pressurizing a gas to experiment on refrigeration systems.
[b]Microwave ovens[/b] - Discovered by an engineer at Raytheon who melted chocolate bar in his pants while working on a RADAR system.
CT
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Strega
- Posts: 384
- Joined: Tue May 05, 2015 1:43 am
Bernoulli developed his principle from his observations on liquids, and his equation is applicable only to incompressible fluids, and compressible fluids up to approximately Mach number 0.3.[17] It is possible to use the fundamental principles of physics to develop similar equations applicable to compressible fluids. There are numerous equations, each tailored for a particular application, but all are analogous to Bernoulli's equation and all rely on nothing more than the fundamental principles of physics such as Newton's laws of motion or the first law of thermodynamics.
From wiki... CT you will figure it out....
Mr pie... your schlieren photo doesnt tell the entire story..it would suggest the tail is flying is supersonic air...it is not...
From wiki... CT you will figure it out....
Mr pie... your schlieren photo doesnt tell the entire story..it would suggest the tail is flying is supersonic air...it is not...
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Conflicting Traffic
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[quote author=Strega link=topic=562.msg2387#msg2387 date=1439269206]
CT you will figure it out....
[/quote]
I'm pretty sure I've got it figured out already, thanks.
[quote author=Strega link=topic=562.msg2411#msg2411 date=1439355060]
Explain to us how the engine on the f104 stays running at speeds of <M1 or M2?
[/quote]
A major design driver of engine inlets is pressure recovery (converting total pressure into static pressure rather than heat). Normal shock waves are strong and generate lots of entropy, and therefore are poor for pressure recovery. However, sooner or later, the airflow has to be brought to subsonic for combustion. This is done with a normal shock. But to minimize losses across the normal shock, the airflow is first slowed down with a series of oblique shocks. On the F-104, you can see the semi-conical spike protruding from the inlet. That spike is there to generate the oblique shock(s) before the main inlet creates the normal shock at a suitably reduced Mach number. Similarly purposed features are common on supersonic inlets.
Of course, this says nothing about the flow over the tail in the schlieren photo. The photo doesn't include any normal shocks, but there are almost-normal shocks at the leading edge of the wing roots. With viscous effects, it's possible that there is a small region of subsonic flow around there. But if I were a betting man I'd say that's it. Most (possibly all) of the wing and all of the tail is likely in supersonic flow.
More accidental discoveries:
- [b]The Slinky[/b] -- Originally intended as springs for calibrating naval instruments.
- [b]The cosmic background radiation[/b] -- Originally thought to have been caused by pigeon droppings.
CT you will figure it out....
[/quote]
I'm pretty sure I've got it figured out already, thanks.
[quote author=Strega link=topic=562.msg2411#msg2411 date=1439355060]
Explain to us how the engine on the f104 stays running at speeds of <M1 or M2?
[/quote]
A major design driver of engine inlets is pressure recovery (converting total pressure into static pressure rather than heat). Normal shock waves are strong and generate lots of entropy, and therefore are poor for pressure recovery. However, sooner or later, the airflow has to be brought to subsonic for combustion. This is done with a normal shock. But to minimize losses across the normal shock, the airflow is first slowed down with a series of oblique shocks. On the F-104, you can see the semi-conical spike protruding from the inlet. That spike is there to generate the oblique shock(s) before the main inlet creates the normal shock at a suitably reduced Mach number. Similarly purposed features are common on supersonic inlets.
Of course, this says nothing about the flow over the tail in the schlieren photo. The photo doesn't include any normal shocks, but there are almost-normal shocks at the leading edge of the wing roots. With viscous effects, it's possible that there is a small region of subsonic flow around there. But if I were a betting man I'd say that's it. Most (possibly all) of the wing and all of the tail is likely in supersonic flow.
More accidental discoveries:
- [b]The Slinky[/b] -- Originally intended as springs for calibrating naval instruments.
- [b]The cosmic background radiation[/b] -- Originally thought to have been caused by pigeon droppings.
