# Questions tagged [reynolds-number]

It refers to a dimensionless quantity used in fluid mechanichs. It measures the relevance of inertial terms compared to viscous terms.

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### Why XFOIL predicts a lower drag coefficient at higher Re?

A well known idea is that for aerodynamic/streamlined bodies the friction drag is larger than pressure drag. Hence, a laminar boundary layer is preferable (only looking at minimal drag, no other ...
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1 vote
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### What chord should I use to calculate Reynolds number?

Mean geometric chord of exposed wing, or mean aerodynamic chord of gross wing? It's not particularly clear in the literature.
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### How can I calculate the pressure coefficient and stagnation temperature?

How would we find the critical pressure and stagnation temperature if we are given the Mach number, density, freestream temperature and the pressure on a point along the wing?
1 vote
30 views

### Distance where transition from laminar to turbulent boundary takes place

How do we work out where the distance from the leading edge the laminar boundary layer would turn into a turbulent boundary layer? Assuming we have been given the length of the plate, speed, dynamic ...
1 vote
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### How do i find a supercritical airfoil for my preliminary design?

The following information is available but i don't exactly know where to get the information about SC Airfoils from. Do Airbus , Boeing use secret airfoil that they don't disclose? Cruise Speed = 240 ...
1 vote
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### Why don't we simulate similarity parameters simultaneously in the same wind tunnel?

As 'Fundamentals of Aerodynamics' by JD Anderson suggest Today, for the most part, we do not attempt to simulate all the parameters simultaneously; rather, Mach number simulation is achieved in one ...
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### Leading edge or trailing edge stall?

As I wrote last week, I'm doing a Benedek 10355 airfoil performance report. At this point of the work I am analyzing the stall of the profile at a fixed Reynolds number. The Benedek 10355 airfoil has ...
• 35
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### Is it possible that as the Reynolds number increases, a laminar bubble increases in extension?

I'm studying the Benedek 10355 airfoil (Plot), which should be a profile used in air-controlled models. While I was carrying out a boundary layer analysis, I realized the particularity that I have ...
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1 vote
185 views

### At which point in scale reduction do slats and flaps become unnecessary?

Imagine some Fi-156 Storch, and reduce its scale down gradually to 10cm span. Let's assume full scale Fiesler Storch is 100% efficient at, for example, minimizing stall speed. During this reduction ...
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1 vote
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### Turbulent flows over 6 series airfoils

6 Series Airfoils were developed to enhance the laminar flow region over the airfoil. But, the Reynolds number at which planes fly are high for the flow to be Laminar. Then what's point of introducing ...
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### Is the Reynolds number the same for both the airfoil and wing? If not, why/how does it change?

This question might be stupid, but I don't understand this one thing: does the Reynolds number change when you go from the airfoil to the wing? Or is it the same for both?
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### How does the critical Angle of attack changes with Increasing Reynolds Number?

I am simulating NACA 2415 Airfoil for different Reynolds Number i.e. 2 million,3 million and 4 million on ANSYS Fluent. The difference between the critical Angle of attack is quite vast. For the 4 ...
3k views

### Why does a turbulent boundary layer cause more friction drag than a laminar boundary layer?

From what I understand, friction is caused by viscosity and a bigger Reynolds number signifies lower viscosity. Thus, a higher Reynolds number(i.e. turbulent flow) results in lower friction. But, ...
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### How does drag change with Reynolds number?

If you want to scale down an airframe, i.e., for wind tunnel testing, you have to adjust for the Reynolds number. I want to ask if in case I forgot to adjust the Reynolds number, would the drag on the ...
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### How to calculate Reynolds number?

How do I calculate the Reynolds number of a wing with wing chord,1.2m and speed of 60km/h
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### would a dimpled heat shield reduce heat transfer during reentry? [closed]

Would a large ceramic golfball absorb less heat on reentry than a standard sphere? "The difference in the flowfields around a smooth sphere and a rough, or dimpled, sphere can be seen above. Since ...
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### Does zero-lift angle of attack depend on Reynolds number?

In this post I read that, due to viscous effects, the $C_{l}$ at a given angle of attack increases slightly with the Reynolds number but it seems that it just happens near the stall angle of attack. ...
• 227
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### Does Lift/Drag generally improve at higher Reynolds numbers?

I have been looking at the lift/drag polars for various airfoil profiles. The L/D ratio seems to improve at higher Reynolds numbers. Obviously different wings are optimized for different speeds, and ...
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### Is airflow ever laminar in the boundary layer, near the wing leading edge?

I often see images of the boundary layer over a wing indicating the airflow is laminar over the first portion of the wing: Transition from laminar to turbulent flow over the wing. Left: source, right:...
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1 vote
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### What is the order of Reynolds number inside the Compressor at cruise conditions?

I am doing a CFD study on a probe that will be installed inside a compressor of a civil aircraft for my final year project. I need to know the Reynolds number inside a compressor at cruise conditions. ...
The Reynolds-Number $Re$ is defined as $Re = \frac{c \cdot L \cdot \rho}{\mu} = \frac{c \cdot L}{\nu}$, with the velocity $c~\left[ \frac{m}{s} \right]$, the reference length $L~\left[ m \right]$, ...