AIAA R-146-2020: Sub-Scale Thrust Test Rigs

Aerospace engineers rely on testing to understand how engines and nozzle systems perform and to make sure their measurements are accurate. A nozzle plays an important role in propulsion by directing and accelerating exhaust gases to help produce thrust. Because airflow and thrust measurements can affect how a propulsion system’s performance is evaluated, having a reliable test setup is essential. For sub-scale testing, AIAA R-146-2020, Dual Flow Reference Nozzles for Verification of Sub-Scale Thrust and Airflow Test Rigs: Dual Separate Flow Reference (DSFR) and Dual Mixed Flow Reference (DMFR) provides recommended practices for using two types of reference nozzles to help verify the performance of thrust and airflow test rigs.

What Is Sub-Scale Propulsion Testing?

Sub-scale propulsion testing is a way for engineers to evaluate smaller versions of propulsion systems, such as rocket motors, jet engines, and exhaust nozzles, before moving to full-scale testing. Using smaller test hardware can help engineers evaluate designs, validate performance models, and identify potential issues while reducing the cost and risks associated with full-scale testing.

Because accurate measurements are essential when evaluating sub-scale propulsion systems, the test rig itself must also be reliable. AIAA R-146-2020 provides recommended practices for reference nozzles used to verify thrust and airflow test rigs that measure sub-scale exhaust nozzle system performance.

What Is AIAA R-146-2020?

AIAA R-146-2020 provides recommended specifications for defining reference nozzle aerodynamic loft lines (aero-lines) and key features, including flow conditioning, instrumentation, operational procedures, and data reduction methods. These recommended practices are intended to support the use of reference nozzles to verify thrust rigs that measure sub-scale exhaust nozzle system performance.

DSFR and DMFR Reference Nozzles

The recommended practice defines two types of reference nozzles:

Dual Separate Flow Reference (DSFR): A configuration in which the two flows remain separate as they move through the reference nozzle system.
Dual Mixed Flow Reference (DMFR): A configuration in which the two flows are mixed before exiting through the nozzle.

Both reference nozzles are intended to support the verification of sub-scale thrust and airflow test rigs. Additionally, each represents a different flow configuration and provides a distinct reference for evaluating test-rig performance.

The Importance of Nozzle Testing in Aerospace

Testing nozzle performance is an important part of aerospace research because engineers need to understand how nozzles behave under different operating conditions. NASA’s Nozzle Acoustic Test Rig (NATR), for example, uses scale models of aircraft engine nozzles to study jet noise and evaluate new nozzle designs before they are tested on full-scale engines. The facility can simulate different engine flow conditions while microphones measure noise produced by the exhaust. By using sub-scale models, researchers can evaluate nozzle concepts more efficiently than through full-scale engine testing.

Accurate results from sub-scale testing depend on reliable test equipment and consistent verification methods. AIAA R-146-2020 addresses this need by providing recommended practices for reference nozzles used to verify sub-scale thrust and airflow test rigs.