Manufacturers of jet engines
regularly require research in two areas. The first area entails the
noise produced by the engines, with the intention of making them as
silent as possible. The second area involves the engines’ efficiency,
which must be as high as possible for every new type. Two main set-ups
are used for simulating the flight conditions under which engines are
tested: isolated from the aircraft (primarily to test acoustics), or
fully installed on the wing or fuselage.
The majority of present-generation
jet aircraft feature engine nacelles with integrated thrust reversers.
This equipment has a positive effect on brake wear and the landing
path. Inevitably, the use of reversers causes interaction with the jet
engines themselves and the control elements of the aircraft. Testing is
therefore indispensable in the development and finalization of thrust
reverser designs. Even in a wind tunnel, simulating the effects of
thrust reverse is an extremely complex issue.
DNW has been using the simulation technology known as Turbofan Propulsion Simulator (TPS) in combination with balance measurements
to test the performance of installed engines for over 20 years. Testing
is not only performed in low-speed wind tunnels, but also in DNW’s
transonic wind tunnel HST in Amsterdam. Testing an engine and its
nacelle on a full model with TPS, requires a fairly large wind tunnel.
If the test matrix comprises asymmetrical configurations, full-model
testing is essential. Half-model testing is more appropriate for cruise
conditions when TPS is combined with a high Reynolds number.
The balances in DNW’s simulations
with TPS can measure effects of less than 0.2 %. This makes DNW’s
largest wind tunnel very attractive for powered testing. To calculate
the aircraft performance, these accurate balance measurements have to
be corrected for the TPS thrust. This is the reason why the powered
nacelles have to be accurately calibrated in isolation, which ensures
reliable measurements. Calibration is performed in the Engine
Calibration Facility (ECF) – a large tank with a diameter of 3 m and a
length of 6 m. Special software tools help compare the data from the
calibration process in the ECF with the data collected in the actual
wind tunnel tests conducted with TPS.