Data Structures

This page documents the internal data structures used in turbigen. It is intended as a reference for users extending the program using custom plugins or developers modifying the source code.

Working fluids

Both perfect and real working fluids are represented by a State class, which has a common interface for setting and reading thermodynamic properties. The interface allows the same mean-line design code to work with any working fluid. State does not store velocity information and hence makes no distinction between static and stagnation states, the handling of which is left to the calling code.

Setter methods

The following methods are used to set the thermodynamic state of the fluid to a new value. The object is updated in-place; a copy can be explicitly created using State.copy(). By the two-property rule, the setters all take two arguments to uniquely specify the thermodynamic state. The following methods are available:

Method	Arguments
State.set_h_s(h, s)	Enthalpy	Entropy
State.set_P_h(P, h)	Pressure	Enthalpy
State.set_P_rho(P, rho)	Pressure	Density
State.set_P_s(P, s)	Pressure	Entropy
State.set_P_T(P, T)	Pressure	Temperature
State.set_rho_u(rho, u)	Density	Internal energy

Property attributes

Thermodynamic and transport properties of the fluid are accessed as attributes of the State object. The following properties are available:

Property	Description	Units
State.a	Acoustic speed	m/s
State.cp	Specific heat at constant pressure	J/kg/K
State.cv	Specific heat at constant volume	J/kg/K
State.gamma	Ratio of specific heats	–
State.h	Specific enthalpy	J/kg
State.mu	Kinematic viscosity	m^2/s
State.P	Pressure	Pa
State.Pr	Prandtl number	–
State.rgas	Specific gas constant	J/kg/K
State.rho	Density	kg/m^3
State.s	Specific entropy	J/kg/K
State.T	Temperature	K
State.u	Specific internal energy	J/kg

Flow fields

Augmenting a thermodynamic state with velocity and coordinate data allows the FlowField class to represent a flow field. Composite properties such as stagnation pressure and Mach number can then be computed from the thermodynamic state and velocity vector. Setting an angular velocity allows evaluation of quantities in a rotating frame. Circumferential periodicity is represented by a number of blades.

Setter methods

The FlowField class has the same thermodynamic setter methods as the State class. Velocity and coordinate data are set directly by assigning to the corresponding attributes.

Property attributes

In addition to all the pure thermodynamic properties defined in State, incorporating velocity and coordinate data allow the FlowField to provide the following other properties:

Property	Description	Units
FlowField.Alpha	Yaw angle	deg
FlowField.Alpha_rel	Relative frame yaw angle	deg
FlowField.ao	Stagnation acoustic speed	m/s
FlowField.Beta	Pitch angle	deg
FlowField.e	Specific total energy	J/kg
FlowField.halfVsq	Specific kinetic energy	J/kg
FlowField.halfVsq_rel	Relative frame specific kinetic energy	J/kg
FlowField.ho	Stagnation specific enthalpy	J/kg
FlowField.ho_rel	Relative frame stagnation specific enthalpy	J/kg
FlowField.I	Rothalpy	J/kg
FlowField.Ma	Mach number	–
FlowField.Ma_rel	Relative frame Mach number	–
FlowField.Omega	Reference frame angular velocity	rad/s
FlowField.Po	Stagnation pressure	Pa
FlowField.Po_rel	Relative frame stagnation pressure	Pa
FlowField.r	Radial coordinate	m
FlowField.rhoe	Volumetric total energy	J/m^3
FlowField.rhorVt	Volumetric angular momentum	kg/m^2/s
FlowField.rhoVr	Volumetric radial momentum	kg/m^2/s
FlowField.rhoVt	Volumetric angular momentum	kg/m^2/s
FlowField.rhoVx	Volumetric axial momentum	kg/m^2/s
FlowField.rpm	Reference frame revolutions per minute	rpm
FlowField.t	Circumferential coordinate	rad
FlowField.tanAlpha	Tangent of yaw angle	–
FlowField.tanAlpha_rel	Tangent of relative frame yaw angle	–
FlowField.tanBeta	Tangent of pitch angle	–
FlowField.To	Stagnation temperature	K
FlowField.To_rel	Relative frame stagnation temperature	K
FlowField.U	Blade speed	m/s
FlowField.V	Absolute velocity magnitude	m/s
FlowField.V_rel	Relative frame velocity magnitude	m/s
FlowField.Vm	Meridional velocity magnitude	m/s
FlowField.Vr	Radial velocity	m/s
FlowField.Vt	Circumferential velocity	m/s
FlowField.Vt_rel	Relative frame circumferential velocity	m/s
FlowField.Vx	Axial velocity	m/s
FlowField.x	Axial coordinate	m

Mean line

The MeanLine class encapsulates the quasi-one-dimensional geometry and flow field of a turbomachine. In addition to thermodynamic states and velocity vectors, it also contains a root-mean-square radii and annulus areas. Assuming the span is perpendicular to the mean-line pitch angle, These data are sufficient to determine hub and tip radii, and the midspan blade angles.

Property attributes

In addition to the properties defined in State and FlowField, the MeanLine class provides the following

Property	Description	Units
MeanLine.A	Annulus area	m^2
MeanLine.eta_poly	Total-to-total polytropic efficiency	–
MeanLine.eta_ts	Total-to-static isentropic efficiency	–
MeanLine.eta_tt	Total-to-total isentropic efficiency	–
MeanLine.htr	Hub-to-tip radius ratio	–
MeanLine.mdot	Mass flow rate	kg/s
MeanLine.Nb	Number of blades	–
MeanLine.PR_ts	Total-to-static pressure ratio	–
MeanLine.PR_tt	Total-to-total pressure ratio	–
MeanLine.rhub	Hub radius	m
MeanLine.rmid	Midspan radius	m
MeanLine.rrms	Root-mean-square radius	m
MeanLine.rtip	Tip radius	m
MeanLine.span	Span	m