V072 is a computer program that predicts the noise generated by the interaction between the rotor-blade wake (fan wake) and the stator vanes of a turbofan engine. The program is a combination of subroutines from prior NASA programs, with many added features.

Limits on aircraft noise near airports are becoming more stringent. Noise associated with fans is a significant portion of the noise that emanates from modern turbofan engines. In order to reduce noise from fan stages, engineers rely on accurate computer programs to predict noise from new blading and duct designs. V072 is useful because it quickly predicts inlet and aft sound-pressure and power levels.

In V072, the computation of noise is divided into two parts: a rotor-wake calculation and the stator-noise-response calculation. First, V072 uses a semiempirical mathematical model of a wake to calculate the characteristics of the rotor wake at the leading edge of the stator. The fan stage is modeled as a constant-area annulus with the rotor blades and stator vanes represented as twisted flat plates. Empirical rotor-wake profiles are superimposed on a two-dimensional, analytically calculated mean flow. The wake model can be augmented by simple tip- and hub-vortex models. Wake harmonic magnitudes and amplitudes are then calculated at the leading edge of the stator.

The results from the wake-model calculation are then automatically fed as input to an analytical noise-prediction routine. More specifically, the unsteady flow predicted in the wake-model calculation is used to calculate the total harmonic power levels propagating upstream and downstream in the engine duct. The noise-prediction routine calculates inlet and aft sound-pressure and power levels for the blade-passage-frequency tones and their harmonics, along with complex radial mode amplitudes. The code can calculate the noise from either a fan-wake/outlet-guide-vane interaction or a fan-wake/core-stator interaction.

Although V072 is based partly on many simplifying assumptions about the fan geometry and the flow through the fan stage, V072 is nevertheless a useful software tool for designing to minimize fan noise. (The simplifications incorporated in the code make it unsuitable for analyzing cases that involve transonic or supersonic fan-tip speeds.) This program runs quickly on modern Unix workstations, making it possible to predict noise for many new designs in a timely manner, and thereby reducing the number of experiments needed to prove noise-reduction concepts.

This program was written by David Topol and Douglas C. Mathews of United Technologies for Glenn Research Center. For further information on this code, please visit the following web site: http://www.grc.nasa.gov/WWW/5900/5940.

Inquiries concerning rights for the commercial use of this invention should be addressed to

NASA Glenn Research Center
Commercial Technology Office
Attn: Steve Fedor
Mail Stop 4 —8
21000 Brookpark Road
Ohio 44135.

Refer to LEW-17065.