# Questions tagged [fluid-dynamics]

Is a subdiscipline of fluid mechanics that describes the flow of liquids and gases

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1 vote
101 views

### Why can't supersonic flow work its way upstream?

I am reading this textbook today. And it described supersonic flow as follows: In a supersonic flow, because the local flow velocity is greater than the speed of sound, disturbances created at some ...
3k views

### Will computational fluid dynamics (CFD) ever be 100% correct?

CFD results never match real world numbers especially in turbulent 3D complex flow... What stops CFD being perfect, and will it ever be 100% correct? If the Navier-Stokes Millennium problem is solved, ...
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63 views

### How to find the velocity of the working fluid through the fan in a turbofan engine?

Is there any formula for the velocity of the working fluid (air) through /the fan of a turbofan engine? If not, how can I find the velocity?
102 views

### Is it possible to have a separated boundary layer without having reversal flow?

To fix the ideas, let's consider an airfoil instead of a generic shape. As far as I understand, the separation of the boundary layer takes place after there is a region of reversal flow on the suction ...
50 views

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1 vote
378 views

### Calculate resultant force from pressure distribution?

Can you explain with example how can I calculate magnitude and direction of resultant force from pressure distribution over airfoil?
70 views

### Does low pressure induces high velocity or high velocity induces low pressure?

Does low pressure induces high velocity or high velocity induces low pressure? I am wandering what is the cause and what is the result. I mean i.e. Bernoulli principle or situation in the core of a ...
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175 views

### Does flow separation starts earlier at higher airflow speeds?

For same AoA,will flow separation starts earlier (point of separation more upstream) at higher airflow speeds (=higher air inertia) compare to lower airflow speeds? High speed airflow has more air ...
212 views

### Velocity induced by a straight vortex filament

Consider a straight vortex filament as shown below. At each point, there's a point vortex of strength $\it T$. Consider that a point $P$ is there on the outermost circle of flow induced by the vortex ...
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95 views

### What happens when a "ground effect" plane approaches the sound barrier?

Does the shock wave inhibit or contribute to lift? What is the ideal speed to fly near or on the speed of sound while using the ground effect?
715 views

### Is multi element wing good option for slow flight airplanes?

Can we use multi element wing for slow flight planes, like F1 multi element rear wing? If we know that pressure act prependicular to the surface why this two upper elements are "almost" ...
472 views

### Why high air speed at flat surface don't always produce low pressure?

Can you explain why flat surfaces don't produce low pressure in both experiments ,even air has high speed in both case? 1)experiment where flat surface DON'T produce low pressure: http://www.cabrillo....
103 views

### On an aerofoil or circular cylinder why does the airflow stay attached after passing the point of maximum thickness?

Why does it follow the curvature rather than separating? Its not due to the coanda effect as the accelerated flow near the surface of the aerofoil can't be considered a jet. It's not due to surface ...
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59 views

### How accurate is CFD software compared to wind tunnel tests? [duplicate]

How accurate is computational fluid dynamics (CFD) software compared to wind tunnel tests? (I mean CFD computed with super-computers like the aircraft industry has.)
323 views

### How does a diffuser (in ground effect) accelerate the air in front of it?

A diffuser reduces speed and increases pressure, so how does a diffuser accelerate air in front of it if we have an adverse pressure gradient situation? Wouldn't be better that we put the lower ...
338 views

### Why does turbofan exhaust appear to reverse direction?

Yesterday I was at the airport planespotting. I observed the exhaust of a couple of turbofan engines, and found it curious how the fluid seemed to behave as it was leaving the engine and gaining ...
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338 views

### What causes lift in aerofoil: Bernouli's principle or Newton's third law? [duplicate]

Reading materials online, I observe some explanation based on Bernoulli's principle, quoting the difference of air pressure above/below and difference of speed of airflow. While some say's Bernoulli's ...
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1 vote
165 views

### Is it possible to have the laminar flow above $Re=10^7$?

For pipe flow I came across the information that the onset of turbulent flow occurs at approximately $Re=10^3$ to $Re=10^4$, while for boundary layers on the airfoil the onset occurs in between \$Re=10^...
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2k views

### What is boundary layer tripping?

I came across the term "Boundary layer tripping" but I can't really underastand it. After searching on internet I cannot find any video or an image explaining that concept. Could you please explain ...
410 views

### Why do shockwaves progressively move aft as speed increses?

As an airfoil moves from subsonic to supersonic, the shocks that develop over the surface move progressively toward the trailing edge. What is the physical explanation for this behavior? As a side ...
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173 views

### What causes the vortex on the tip of this vertical stabilizer (CFD Simulation)

This is a computational fluid dynamics simulation of an airfoil that is oriented to look like a vertical stabilizer. After watching the video, it becomes clear that the tip of the stabilizer causes a ...
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361 views

### How far can the sound of a sonic boom travel? [closed]

Are there conditions or distances from the plane to cloud to the observer in which a sonic boom from a plane is muted?
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1 vote
399 views

### What happens to the high pressure below an airfoil when the angle of attack increases?

I recently came across this question in a principles of flight exam: When the angle of attack of an airfoil increases the high pressure below the airfoil increases, the induced drag increases the ...
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923 views

### Why does the Biot-Savart law give the induced velocity of a infinitesimal segment of a vortex filament at point P?

My question is about the proof of how the Biot-Savart law can be used for vortex filaments. This is what I have in my textbook: However, I'm not certain how it was derived - I understand that the ...
1 vote
459 views

### Why is the stagnation point on the upper surface before the start of circulation?

In many textbooks, such as Anderson (Fundamentals of Aerodynamics), Bertin (Aerodynamics for Engineers), and Houghton (Aerodynamics for Engineering Students), the authors present the idea that there ...
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488 views

### What are accurate flight simulation models called? Is there a standard model?

I'm risking a question that might be "opinion based", but I hope it will not be seen as that. This question is touched upon in the following questions: What are the differences between PC and ...
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322 views

### How is the flow of air through a NACA submerged inlet determined?

This question pertains to the design and/or selection of NACA submerged inlets. I am trying to understand what kind of airflow would enter a NACA submerged inlet/scoop and am looking for a good ...
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1 vote
511 views

### Why do wingtip vortices affect the upwash ahead of the aerofoil?

I understand that wingtip vortices increase the downwash aft of the aerofoil and the theory that they will alter the effective airflow angle, reducing effective angle-of-attack, with the total ...
1 vote
914 views

### Boundary layer momentum thickness

Could someone please explain the concept of the boundary layer momentum thickness and its difference to boundary layer thickness calculation? Some explanation about the application of the boundary ...
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2k views

### What is the difference between static and dynamic stall?

What are the static and dynamic stalls on the aircrafts wing? When would we encounter static and when dynamic one? What is the difference between them?
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1 vote
1k views

### Is the shear centre of a wing the same as its aerodynamic centre?

How can the shear centre of a wing be located and is it the same as the aerodynamic centre of a wing? Lastly, I know how the centre of pressure interacts with the aerodynamic centre but not the wing'...
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735 views

### Transonic buffet - reason for a rapid movements of the shockwave along the wing chord line?

I know that transonic aerodynamic buffet is caused by the separated turbulent boundary layer striking the airframe (horizontal stabilizer, wings, fuselage) with considerable force causing a high ...
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810 views

### Why is the delta wing naturally stable in pitch?

Any thoughts on why the delta wings are naturally more stable in pitch, so they don't require any tail surface? What's the physics behind this?
• 1,090
709 views

### Do stall strips mean that wing washout is not required?

The Wikipedia page on stall strips states that AA-1 Yankee airplanes used stall strips to avoid tip stalls (and spins) because wing washout couldn't be used. So my question is: can two stall strips ...
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645 views

### Bed sheet as wing skin?

https://en.m.wikipedia.org/wiki/Aircraft_fabric_covering This article states several early aircrafts that successfully used cotton as wing skin including Wright flyer. "Colditz Cock" glider had its ...
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198 views

### How does pitot tube shape affect indicated airspeed? [closed]

Air flow over wings and engine inlets greatly changes due to a number of factors, such as atmospheric conditions, speed, and the design of the surfaces. On some engines you can see mist behind the ...
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