Relative Ratio

Calculate relative atmospheric ratios

• Library:

• Aerospace Blockset / Flight Parameters

• 

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Description

The Relative Ratio block computes the relative atmospheric ratios, including the relative temperature ratio (θ), $$\sqrt{\theta }$$, relative pressure ratio (δ), and relative density ratio (σ).

θ represents the ratio of the air stream temperature at a chosen reference station relative to sea level standard atmospheric conditions:

$$\theta =\frac{T}{T_0}.$$

δ represents the ratio of the air stream pressure at a chosen reference station relative to sea level standard atmospheric conditions:

$$\delta =\frac{P}{P_0}.$$

σ represents the ratio of the air stream density at a chosen reference station relative to sea level standard atmospheric conditions:

$$\sigma =\frac{\rho }{{\rho }_0}.$$

The Relative Ratio block icon displays the input units selected from the Units parameter.

Limitations

For cases in which total temperature, total pressure, or total density ratio is desired (Mach number is nonzero), the total temperature, total pressure, and total densities are calculated assuming perfect gas (with constant molecular weight, constant pressure specific heat, and constant specific heat ratio) and dry air.

Ports

Input

Mach — Mach number

scalar

Mach number, specified as a scalar.

Data Types: double

γ — Ratio

scalar

Ratio between the specific heat at constant pressure (C_p) and the specific heat at constant volume (C_v), specified as a scalar. For example, (γ = C_p/C_v).

Data Types: double

To — Static temperature

scalar

Static temperature, specified as a scalar.

Data Types: double

Po — Static pressure

scalar

Static pressure, specified as a scalar.

Data Types: double

ρo — Static density

scalar

Static density, specified as a scalar.

Data Types: double

Output

θ — Relative temperature ratio

scalar

Relative temperature ratio (θ), returned as a scalar.

Dependencies

To enable this port, select Theta.

Data Types: double

sqrt(θ) — Square root of relative temperature ratio

scalar

Square root of the relative temperature ratio ( $$\sqrt{\theta }$$), returned as a scalar.

Dependencies

To enable this port, select Square root of theta.

Data Types: double

δ — Relative pressure ratio

scalar

Relative pressure ratio, (δ), returned as a scalar.

Dependencies

To enable this port, select Delta.

Data Types: double

σ — Relative density ratio

scalar

Relative density ratio, (σ), returned as a scalar.

Dependencies

To enable this port, select Sigma.

Data Types: double

Parameters

Units — Units

Metric (MKS) (default) | English

Input units, specified as:

Units	Tstatic	Pstatic	rho_static
Metric (MKS)	Kelvin	Pascal	Kilograms per cubic meter
English	Degrees Rankine	Pound force per square inch	Slug per cubic foot

Programmatic Use

Block Parameter: units

Type: character vector

Values: 'Metric (MKS)' | 'English'

Default: 'Metric (MKS)'

Theta — Relative temperature ratio

on (default) | off

When selected, the block calculates the relative temperature ratio (θ) and static temperature is a required input.

Programmatic Use

Block Parameter: theta

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Square root of theta — Square root of relative temperature ratio

on (default) | off

When selected, the block calculates the square root of relative temperature ratio ( $$\sqrt{\theta }$$) and static temperature is a required input.

Dependencies

Selecting this check box enables the sqrt(θ) output port.

Programmatic Use

Block Parameter: sq_theta

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Delta — Relative pressure ratio

on (default) | off

When selected, the block calculates the relative pressure ratio (δ) and static pressure is a required input.

Programmatic Use

Block Parameter: delta

Type: character vector

Values: 'on' | 'off'

Default: 'on'

Sigma — Relative density ratio

on (default) | off

When selected, the block the relative density ratio (σ) and static density is a required input.

Programmatic Use

Block Parameter: sigma

Type: character vector

Values: 'on' | 'off'

Default: 'on'

References

[1] Aeronautical Vestpocket Handbook, United Technologies Pratt & Whitney, August, 1986.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using Simulink® Coder™.

Introduced before R2006a