Jet engine test facilities, often called test cells or testbeds, are highly specialized facilities where manufacturers, airlines, maintenance providers, or defense organizations run jet engines on the ground before certification, delivery or return to service.

These facilities are built to measure thrust, vibration, temperature, pressure and noise while keeping workers and nearby communities safe and undisturbed. Modern cells use sophisticated instrumentation to capture precise performance data, and carefully designed inlet and exhaust systems to recreate flight-like conditions. Acoustic treatment of the building itself and the inlet/exhaust is required to reduce disturbance to surrounding communities.

Exhaust Systems

The most difficult area to design is the exhaust, due to the high flows and high temperature exhaust gases which must be controlled and directed out of the building. A key principle behind the design of exhaust systems is entrainment. In simple terms, as the engine’s fast exhaust jet stream moves into the exhaust ducting (typically referred to as the detuner or augmentor), it pulls in surrounding “secondary” air.

That induced airflow mixes with the hot jet plume, cooling and slowing it before it reaches downstream structures (i.e. bends or silencing elements). The amount of induced air can strongly affect stability, temperature management and the accuracy of test results.

Engineers rely on entrainment to protect the exhaust system (and hence the longevity of the test cell), improve ventilation, and control pressure conditions inside the test cell. As newer engines grow larger and hotter, facility designers must pay even closer attention to these kinds of airflow physics that begin with one fast jet and the air it draws along with it.

Cullum Design

Cullum has a long history of understanding how to control jet exhaust flows. Starting with the first ever exhaust detuner (patented 1949), entrainment has been a cornerstone of our design philosophy.