Impeller > Main dimensions > Axial Gas Turbine / Compressor

The main dimensions can be seen on Main dimensions panel. They can be recomputed by pressing the Calculate-button. The computation is based on "Euler's Equation of Turbomachinery", on the continuity equation and the relations for the velocity triangles as well as on the parameters given in the tab sheets Setup and Parameters.

Individual main dimensions can be calculated separately using the button inside the value field.

You may accept the proposed values or you can modify them slightly, e.g. to meet a certain normalized diameter.

In case the checkbox Automatic is activated a new calculation will accomplished after any change of parameter. Then the manual alteration of the main dimensions is not possible.

Neighboring components

In specific cases the dimensions of the neighboring components at inlet and/ or outlet can be used to get exactly matching geometry.

This feature is available only for explicitly uncoupled components or side-by-side impellers.

Information

In the right panel of any tab sheet an information panel is situated, which holds the computed variables in accordance to the actual state of design, the resulting Meridional section as well as the Cordier-Diagramm with the location of the best point. These three sections can be chosen by the appropriate soft buttons in the heading.

In the Value section the following variables are displayed for information which result from calculated or determined main dimensions:

Flow properties at: - impeller inlet - impeller outlet	density ρ static pressure p temperature T total density ρt total pressure pt total temperature Tt volume flow Q mass flow ṁ swirl s
Velocity triangles at: - impeller inlet - impeller outlet	velocities u, cm, cm*, cu, c, wu, w flow angles α, β Mach numbers Mac, Maw, Mau

Work coefficient
Flow coefficient
Meridional flow coefficient

Specific diameter
Isentropic velocity ratio		only turbines
Pressure rise coefficient		only compressor
Suction capacity		only compressor

Reynolds number	with d1 = highest diameter at inlet
	with b1 = width at inlet
	with d2 = highest diameter at outlet
	with b2 = width at outlet

The Meridional preview is based on the main dimensions designed until this point.

The Cordier diagram can be used for checking the impeller diameter d2.

See Cordier.

The Velocity triangles are the result of a mid-span calculation and are based on the design point and the main dimensions.

Possible warnings

Problem	Possible solutions
Thermodynamic state cannot be calculated at inlet/outlet. Possible reason: choked flow. The cu-specification will not be available.
The dimensions might be too tight for the specified mass flow and inlet conditions. In other words the mass flow is higher than the choked mass flow rate for the particular inlet conditions and the respective cross section.	Increase the dimensions (diameters etc.) or change the Global setup (e.g. decrease mass flow, increase pressure, decrease temperature).

Problem

Possible solutions

Thermodynamic state cannot be calculated at inlet/outlet. Possible reason: choked flow.

The cu-specification will not be available.

The dimensions might be too tight for the specified mass flow and inlet conditions. In other words the mass flow is higher than the choked mass flow rate for the particular inlet conditions and the respective cross section.

Increase the dimensions (diameters etc.) or change the Global setup (e.g. decrease mass flow, increase pressure, decrease temperature).

Dimensions

Dimensions

Information