This document describes a method to correct engine thrust, measured in an indoor test cell, for the aerodynamic effects caused by the secondary airflow induced in the test cell by the engine operating in an enclosed environment in close proximity to an exhaust duct. While it is not recommended to be used to replace test cell correlation, it does provide a means to verify an existing thrust correlation factor.
Rationale: For accurate, indoor ground-level testing of jet engines, the influence of the test cell on the thrust produced by the engine must be established. The "true" gross thrust may be derived from the measured scale force, if the aerodynamic conditions inside the test cell are known. The "test cell effect" may also be quantified using correlation factors determined from comparison of test data taken from indoor facilities, and reference outdoor, or "free-air" test stands.
In this report, the influence of the test cell on engine performance is described. The forces measured in a particular indoor test cell are derived. The results show that if all the aerodynamic forces have been accounted for, the corrected thrust in an indoor cell is the "true" gross thrust. As this paper is a derivation from first principles, there will never be a requirement to revise this document.