In this paper, an approach for control-oriented high–frequency turbomachinery modeling previously developed by the authors is applied to develop 1D unsteady compressible viscous flow models for a generic turbojet engine and a generic compression system. We begin by developing models for various components which are commonly found in turbomachinery systems. These components include: ducting without combustion, blading, ducting with combustion, heat soak, blading with heat soak, inlet, nozzle, abrupt area change with incurred total pressure losses, flow splitting, bleed, mixing, and the spool. Once the component models have been developed, they are combined to form system models for a generic turbojet engine and a generic compression system. These models are developed so that they can be easily modified and used with appropriate maps to form a model for a specific rig. It is shown that these system models are explicit (i.e. can be solved with any standard ODE solver without iteration) due to the approach used in their development. Furthermore, since the nonlinear models are explicit, explicit analytical linear models can be derived from the nonlinear models. The procedure for developing these analytical linear models is discussed. An interesting feature of the models developed here is the use of effective lengths within the models, as functions of axial Mach number and nondimensional rotational speed, for rotating components. These effective lengths account for the helical path of the flow as it moves through a rotating component. Use of these effective lengths in the unsteady conservation equations introduces a nonlinear dynamic lag consistent with experimentally observed compressor lag and replaces less accurate linear first order empirical lags proposed to account for this phenomenon. Models of the type developed here are expected to prove useful in the design and simulation of (integrated) surge control and rotating stall avoidance schemes.
In this article the theoretical foundations of a simplified approach for control of rotating stall are presented. This approach requires two-dimensional sensing, but only a single one-dimensional axisymmetric effector with relatively low bandwidth requirements. The reduced actuation requirements of this approach are a consequence of the fact that in this approach one does not require or act upon rotating stall phase information. This is due to the fact that one does not seek to extend the theoretical stable axisymmetric flow range of the compressor. Rather, one seeks to directly address persistent disturbances that would otherwise throttle the equilibrium into the unstable axisymmetric flow range of the compressor. In addition, one seeks to enlarge the domains of attraction of linearly stable axisymmetric equilibria, thereby addressing impulsive disturbances that would otherwise perturb the system state beyond the domain of attraction of the stable axisymmetric equilibrium. Experimental validation of this approach on a single-stage low-speed axial compressor rig is discussed in Part
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