SYSTEM AND METHOD OF CONTROLLING CLEARANCE BETWEEN TURBINE ENGINE BLADES AND CASE BASED ON ENGINE COMPONENTS THERMAL GROWTH MODEL

A system and method of controlling clearance in a turbomachine includes adjusting the machine case cooling air in response to the difference between the desired clearance and the actual clearance. An accurate estimate of the actual clearance is made with a real time mathematical model on-board engine controller. The model computes thermal growth of the turbomachine components each with a difference equation derived from a closed form solution to the 1st order differential equation obtained through the application of 1st law of thermodynamics. The resulting equation is conveniently formulated in terms of equivalent time constant and steady state growth both correlated with thermo-physical characteristics of multiple fluid streams exchanging heat with the component. The solution is applied over a time step of the control software. Approximating coefficients are strategically placed in the model to allow calibration of the model to a particular version of the engine hardware.