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Compressible Flow Calculator

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In the fascinating world of fluid dynamics, understanding how gases move and behave under various conditions is crucial for engineers and scientists. This is where the Compressible Flow Calculator becomes an invaluable tool. It's designed to make complex calculations related to the flow of gases more accessible and understandable, even for those not deeply versed in the subject.

What is Compressible Flow?

Compressible flow refers to the movement of a gas where changes in pressure and temperature significantly affect its density. Unlike liquids, gases can compress and expand; thus, their flow characteristics can vary dramatically with speed and environmental conditions. This behavior is most noticeable at high velocities, close to or exceeding the speed of sound in the gas.

The Core of the Calculator: Mach Number and Speed of Sound

Mach Number

The Mach number (M) is a dimensionless figure representing the ratio of the flow velocity (V) to the speed of sound (a) in the medium. The formula to calculate it is surprisingly straightforward:

M = V / a

Speed of Sound

The speed of sound in a gas is not constant; it varies with temperature and the gas's specific properties. For an ideal gas, the speed of sound (a) can be calculated using the formula:

a = sqrt(gamma * R * T)


  • a is the speed of sound in meters per second (m/s),
  • γ represents the specific heat ratio (Cp​/Cv​), approximately 1.4 for air,
  • R is the specific gas constant, roughly 287 /J/(kgK) for air,
  • T is the absolute temperature of the gas in Kelvin (K).

How Does the Compressible Flow Calculator Work?

Input Parameters

To use the calculator, you'll need three key pieces of information:

  • The flow velocity (V) in meters per second (m/s).
  • The absolute temperature of the gas (T) in Kelvin (K).
  • The specific heat ratio (γ), which is dimensionless.

Step-by-Step Example

Imagine we have air flowing at a velocity of 340 m/s at a temperature of 300 K. Let's calculate its Mach number.

  1. Calculate the speed of sound: First, we use the speed of sound formula. Plugging in the values (1.4γ=1.4, 287/R=287J/(kgK), 300T=300K), we get:

a = sqrt(1.4 * 287 * 300) ≈ 347.22 m/s

  1. Calculate the Mach number: With the speed of sound known, we find the Mach number using the flow velocity (340 m/s):

M = 340 / 347.22 ≈ 0.979

The flow is subsonic since the Mach number is less than 1.

Relevant Information Table

Flow VelocityV340m/s
Specific Heat Ratioγ1.4Dimensionless
Speed of Sounda347.22m/s
Mach NumberM0.979Dimensionless


The Compressible Flow Calculator demystifies the complex calculations involved in predicting gas flow behavior at high speeds. It's not just a tool for experts but an educational resource for students and enthusiasts, helping them grasp the fundamental concepts of compressible flow dynamics. Whether for designing aircraft, understanding weather phenomena, or simulating high-speed exhaust gases, this calculator opens up a world of possibilities by making complex calculations both accessible and manageable.

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