# Questions tagged [aerodynamics]

A subset of the [fluid-dynamics] tag concerning primarily forces such as lift and drag generated on bodies as they move through gasses or as gasses move through the body (typically air).

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55 views

### Does spinning the umbrella slow down the fall more?

Ignoring its structural weakness, if you jump from some height and use an umbrella to slow down the fall, would making it spin while you're falling affect the speed in any way?
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### Does Navier-Stokes equations get correct result for complex turbulent flow without turbulence model?

Does Navier equations (1822 formulation) get correct result for complex turbulent flow without turbulence model? Is this 1822 formulation?
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### Static pressure vs ambient pressure

If in a real scenario, a flat surface with a flush perpendicular closed duct of small diameter is exposed to a tangential fluid flow(laminar and naturally with the presence of boundary layer effect), ...
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### Can I solve the drag equation without any experimental data? (I have a 3d model of a rocket and want to see how fast it can go using math) [closed]

I made a rocket in a cad software and tried to do the math to solve speed. Is there any way to solve the drag coefficient of a rocket (pointed for simplicity) cone and fins that goes up then goes to ...
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### For incompressible fluids, does the velocity increase or decrease when the fluid enters the divergent nozzle through an equal diameter pipe?

For incompressible fluids, does the velocity increase or decrease when the fluid enters the divergent nozzle through an equal diameter pipe? People generally believe that speed decreases, but I ...
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### Will the wind vane at the airport also generate thrust?

We all know that when the converging nozzle rushes out of the fluid, it will generate thrust opposite to the direction of the fluid, so will the wind vane of the airport also generate thrust opposite ...
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### Why will a cylinder tend to freefall on its side?

In a video I saw about the U.S. military’s idea “Rods from God”, it said a uniform steel cylinder will tend to freefall in the air on its side if not corrected. It won't freefall vertically if left to ...
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### How can I find out how much parasitic drag will slow an object traveling vertically from a single impulse?

For my high school physics final I'm doing a project on the manhole cover launched vertically by a nuke from Project Plumbob and assuming it didn't melt in the atmosphere. How can I calculate the ...
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### Does a helicopter fly because air is forced downwards, or because each rotor acts as an aerofoil to generate lift? [duplicate]

The answer may be a combination of the two. Does a helicopter fly because air is caught by the rotor and thrown downwards, which causes an equal reaction in the opposite direction and 'throws' the ...
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### Parachute extension when it is connected to a moving Dynamics Cart

So, I was trying to see the effect of the surface area of the parachute on the velocity of a cart(with a parachute horizontally attached to it) after it passes a certain distance. It is supposed to be ...
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### Is is possible to design a cup lid that doesn't alter the trajectory of the cup when thrown?

First, some context to my question. Second, I do not have a background in fluid dynamics/engineering. Liberal Arts major FTW. I've been running observational experiments with my 14 year old to ...
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### How do shockwaves interact?

As seen here, there are two T-38's going supersonic. What happens when those shockwaves interact? They seem to dissipate in some places on this photo when they interact. Any source online says that ...
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### Floating Elevator

Balloons can be balanced to have just enough string to be suspended off the floor with the end of the string touching the floor. Another balloon could then also be stacked and top of that balloon in ...
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### Entry equation for objects with different characteristics

The question, which weighs more, one pound of feathers or one pound of black hole, comes to mind. Each would react wildly different reentering Earth's atmosphere. In order to narrow the question: Is ...
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### Why cornering wind tunnel rotate?

Why cornering wind tunnel rotate, why is not just curved? A curved wind tunnel has a radial pressure gradient, but this pressure gradient doesn't exist in a real turn, so how do you get zero pressure ...
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### Does high pressure make drag on a wing?

Say you have a plate facing the airflow right over a wing. Not attached, but just right over it. If flow separation and drag on the rear side of the plate (rear meaning the trailing edge of a wing) ...
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### Why aren't helicopter blades tapered?

From my understanding helicopter blades work similar to a planes wings, ie the air going over is faster due to the shape. So my question is why then are the blades rectangular? ie they are the same ...
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### Does (and how) a shark fin on car top (or fan blade) reduce drag?

I've heard this kind of shark fin on the roof reduces drag by breaking the wave that forms behind, where the roof bends into rear window. image source The story goes that it's similar to these fins ...
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### Does a second fan in the tube accelerate the flow even more?

For example, if there is a tube with a certain diameter and one fan in this tube that generates a flow of air with velocity X, will an additional fan (or several fans) accelerate the air even more? If ...
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### How does a shear layer make vortices?

How does a shear layer make vortices? If you have 2 streams of air that are moving at different speeds or opposite directions right beside each other, how does that make a vortex? What causes the ...
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### Can sail be fixed or simple aerodynamic shape split?

Is it possible to create small shape that would be aerodynamic in most directions and not much in one of (kind of fixed sail) ? Performed some experiments with pyramid like shape in front of bike (...
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### Why are cylinders more aerodynamic than spheres?

Why are cylinders more aerodynamic than spheres? Say you have a cylinder falling vertical that has rounded ends. Now remove the cylinder part. Now you’re left with a sphere but without the skin ...
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### How is the second shock in a lambda shock able to form?

For an oblique shock to form, there has to be an angle in which the flow turns into itself. Usually, that angle is caused by flow separation, in which the separation is caused by a normal shock first, ...
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### Spin velocity in table tennis

I have read on papers that argued, when flying, we have constant spin velocities $\omega_x, \omega_y, \omega_z$, that primarily depend on the initial spin setting e.g., topspin, bottom spin and ...
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### Is there a theoretical limit to the thrust produced by a propeller in amosphere?

Assumptions: Indestructible variable-pitch aircraft propeller Arbitrary motor torque and velocity Standard pressure and atmospheric conditions at sea level Low, near-zero relative airspeed This may ...
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### Trouble understanding why ideal gas law explains that can of compressed air gets cold when you spray it [duplicate]

I was told that a canister of compressed air gets cold because of the ideal gas law, you are lowering the pressure and since the density of air is the same, the temperature of the can gets cold. I was ...
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### Frequence vs speed of a moving object

Imagine swinging wood stick using hand (say it's a 1-meter long cylinder with 2 centimeter diameter, just for the sake of argument). When doing it fast (angular velocity = $\omega_1$), it will create ...
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### Relation between blast wind and overpressure

Suppose we have the ambient air pressure, density, speed of sound and blast overpressure. How can we use this data to get the speed of the blast wind? Currently I simply assume that 50% of the wave's ...
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### Why does the density decrease equal the speed gain at Mach 1?

In this answer, it says : "At small Mach numbers, changes in speed cause negligible changes in density, but as Mach approaches unity, both are of similar magnitude. With Ma>>1 , changes in ...
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### Do airfoils need narrowing tails to create a forward force?

All airfoils I have seen become narrow towards the trailing edge. Is it still possible to create a forward vector force if the shape becomes wider again after a narrow middle section? I read that the ...
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### Is air resistance totally dependent on surface area?

Two objects of varying mass, but of the same surface area, are dropped from the same height. Which will strike the ground earlier?
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### Rocket-assisted drag cancellation in artillery shell

The main limit on artillery range is drag. Hence for the same muzzle velocity, the WWII 800mm Schwerer supergun had twice the range of the modern 155mm M777 gun, because the super shell had a much ...
1 vote
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### Has Biot–Savart law real physics in fluids?

In this video from 28:27-36:50 author talk how Bio Sawrt law dont have any physics in aerodynamics, he say it is just math concept and how vorticity cant induce velocity in fluid somewhere in the ...
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### Doubt regarding the working of aerofoils

While reading about the physics of airplane wings... I came across this paragraph. On account of its shape, when the aerofoil moves through the air, the molecules of the air which separate from each ...
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### How does the rate of change of momentum due to unsteady flow inside a control volume not always equal 0 due to momentum conservation?

I apologize for the bad title, I am struggling to shorten the question; essentially, in J.D.Andersons Fundamentals of aerodynamics, there is a section where he derives the momentum equations. Starting ...
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### Contact force to air pressure ratio

Preamble Just to preface, I am not a physicist or physics student. So my question is not related to any real world application or projects. It is more of a shower thought than anything else. Therefore,...
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### How does the Dzhanibekov Effect change if replaced with a propeller?

Every explanation and example uses a t-bar. But what if the "bar" was a propeller? I can understand there being no difference if it's a vacuum, but I would think the aerodynamics would ...
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### How do rifled-bore shells remain pointing into the airflow?

I can understand the logic behind spin-stabilizing bullets, which travel only a few hundred meters on fairly flat trajectories. But I cannot understand the logic for artillery. Won't spinning shells ...
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### Under what conditions is the material derivative of an integral not equal to the integral of the material derivative of a quantity?

I have always been curious, but the general form of the Helmholtz equation in fluid mechanics states that $\frac{D}{Dt}\int_{C}\vec{v}\cdot\vec{dl}$ = 0 which is the statement that the circulation ...
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### Is the wing drag of induced drag + 2d drag at 0lift still accurate for cambered airfoils?

I have some work at uni that requires some aerofoil analysis to create a wing, but from the polar plots its clear that the cambered aeros have lower total 2d viscous drag (from xfoil) at the cl its ...
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1 vote
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### How does a helicopter rotor keep spinning in the same direction when autorotating without reversing the pitch

I have read that if helicopter's engine fails, you set the pitch to minimum but not reverse pitch. The rotor would have to be tilted back to provide an angle of attack on the blades so it glides like ...
1 vote
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### The proportionality of a Drag force and speed

At low speeds, Drag force is proportional to speed due to Stokes law. At higher speeds, Drag is proportional to the square of speed. While modelling the speed of a water rocket, I realised that when ...
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### Why is windspeed proportional to inflated area in windsock?

I have come across this image on Twitter on how to measure wind speed with a windsocket. I noticed that the rings look equally long in the photograph (and others) and measure a speed increase of 3 ...
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### Does heavier car need more aerodynamic downforce in turn than lighter car for same cornering speed?

When a car turns, the frictional force $F_f = (mg\mu + A\mu)$, where A is aerodynamic downforce and $\mu$ the friction coefficient, needs to match the centrifugal force $F_c = m \times V^2/r$. If the ...
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### Understanding lift on a rotating cylinder (inviscid)

From J.D Andersons Aerodynamics book, under the category of describing inviscid flow (over a rotating cylinder in this case), it states "...the friction between the fluid and the surface of the ...
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### What causes an arrow to rotate? [duplicate]

My intuition: In a system without air resistance, I would expect an arrow shot at an angle with its head pointing upwards to follow a ballistic trajectory without rotating around the horizon - because ...
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1 vote
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### Theta-Beta-Mach relation for small deflections

I'm currently studying shockwaves, particularly their effects on drag. I've stumbled upon an odd formula in "Elements of Gasdynamics" (Liepman and Roshko, pages 52-53), in there I saw an ...
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### How can the pressure distribution observed in a Venturi tunnel be explained on a molecular level?

If we consider the flow of an ideal gas through a Venturi tunnel and we assume it to be incompressible, we can show through mass conservation that the velocity must increase as area decreases and vice ...
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