58503 - A Mathematical Model for Windmilling of a Turbojet Engine 

The transient windmilling characteristic of a modern turbojet engine under different flight conditions and altitudes is obtained with numerous tests conducted at an Altitude Test Facility (ATF). A simple mathematical model for predicting the transient and steady-state windmilling characteristics such as rotational speed and air mass flow rate of a simple turbojet engine in flight has been developed. The method is derived from Froude's momentum theory or disk actuator theory and implemented to a turbojet engine. A correction factor is introduced to match with test results of KTJ-3200 being indigenously developed by Kale R&D Inc. The present model’s predictions are compared with the test data of Microturbo TRI 60 engine, a commercial off-the-shelf (CoTS) engine and KTJ-3200 engine. The estimation of the present windmilling model fits very well with test results of three different engines within an error band of ±1.2% for various atmosphere conditions depending on flight speed, altitudes and temperature. The difference between the present model and KTJ-3200 test data for engine mass flow rate is less than ±1% regardless of the flight speed and the altitude. Additionally, the present model is compared with loss modeling windmilling estimation methods described in literature. The comparison at sea level static condition for different flight speed fits well with literature and the difference is less than ±2.5%. The agreement between the present model, loss method, test data of Microturbo TRI 60 and the CoTS engine is very good for most of the ranges investigated.