Impeller > Main dimensions > Radial-inflow Gas Turbine

In the panel Shaft, the required shaft diameter is computed.
¢ Shaft/ Hub

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
Peripheral speed at inlet
Machine Mach Number
Blade width at inlet
Peripheral speed at outlet
Mean diameter at outlet
Width at outlet
Ratio Width-diameter at inlet	b1/d1	guideline: 0.05..0.15
Diameter ratio	d2/d2min with:	guideline: 1.005..1.05
Ratio radius-width at outlet		guideline: 1.005..1.05
Isentropic velocity ratio

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 guidelines given in the last column should be matched within the design.

It might be that for the chosen configuration of global setup and main dimensions a reasonable thermodynamic state cannot be calculated. This may be the case if e.g. the mass flow is too high for the chosen cross sections. Then a warning is generated.

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
β1 differs by more than 25° from the flow imposed by the upstream component.
β1 differs by more than 25° from β1mean.
β1 differs by more than 25° from the flow imposed by the degree of reaction.
The dimensions and the design point yield an estimated average relative inlet flow angle β1 that differs by more than 25° from the relative inlet flow angle imposed by the either of •swirl of the upstream component •β1mean •degree of reaction R see Setup.	Change the dimensions (width, diameters etc.) or change the Global setup (e.g. mass flow, pressure ratio) or change inlet swirl in the Setup by either of parameters given on the left hand side.

Thermodynamic state cannot be calculated at inlet/outlet. Possible reason: choked flow. Consider change of main dimensions or Global setup.
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 condition and the respective cross section.	Increase the dimensions (width, diameters etc.) or change the Global setup (e.g. decrease mass flow, increase pressure, decrease temperature).

In/outlet cross section ratio is unusual. Meridional contour should be defined with an appropriate in/outlet width.
Inlet and outlet cross section area are not in the same order of magnitude. The ratio A2/A1 is outside the range of 0.1 to 10. This can result in high level of meridional acceleration or deceleration.	You may change the in/ outlet geometry or ignore the warning because the real cross sections will be estimated based on the meridional contour in subsequent design steps.

In/outlet cross section ratio is unusual.
Meridional contour should be defined with an appropriate in/outlet width.

Inlet and outlet cross section area are not in the same order of magnitude. The ratio A2/A1 is outside the range of 0.1 to 10.

This can result in high level of meridional acceleration or deceleration.

You may change the in/ outlet geometry or ignore the warning because the real cross sections will be estimated based on the meridional contour in subsequent design steps.

Inlet/ Outlet: Pressure and temperature not within the gaseous phase of the fluid. Check inlet condition and geometry.
If the fluid model is CoolProp or REFPROP, fluid properties will be calculated as function of pressure and temperature. In case the local pressure is not below the vapor pressure at the temperature, the fluid state is not valid.	Decrease main dimensions (width, diameter etc.) or change Global setup (e.g., increase mass flow, decrease pressure, increase temperature).

Dimensions

Dimensions

Information