Numerical Investigation of Flow-Induced Noise Generation at the Nozzle End of Jet Engines

Direct Numerical Simulation of a Square-Notched Trailing Edge for Jet-Noise Reduction

“…At the inflow of the upper boundary layer, the flow is disturbed with the Tollmien-Schlichting (TS) wave (1, 0) with the fundamental frequency ω 0 and an amplitude ofû max = 0.005, being the same as for the two-dimensional simulation, performed earlier. 2 The TS wave generates higher harmonics in the upper boundary layer, driving the rollup of spanwise vortices (Kelvin-Helmholtz instability) and the subsequent vortex pairing behind the splitter plate. An additional oblique wave (1, 1) with a small amplitude ofû max = 0.0005 is intended to provide a more realistic inflow disturbance than a purely two-dimensional forcing.…”

“…With an amplitude of the driving TS wave ofv ≈ 2 • 10 −3 , shown in figure 12, the generated higher harmonic modes (2, 0), (3, 0) reach an amplitude ofv ≈ 3 • 10 −4 andv ≈ 2 • 10 −5 , respectively. According to the forcing at the inflow, only low-amplitude oblique disturbances (2,1) and (3,1) are generated in the upper boundary layer. Behind the splitter plate, the growth of two-dimensional disturbances (h, 0) is only weakly affected by the engrailed trailing edge.…”

“…In order to evaluate the effect of the modified trailing edge, the emitted sound is compared with a twodimensional simulation with the same flow parameters, performed earlier. 2 The acoustic field, visualized by the dilatation ∇ u, is given for the two cases in figures 15 and 16 for the two-dimensional simulation and the engrailed trailing edge, respectively. In both cases, no reflections from the boundaries are visible.…”

“…This corresponds to the positions of vortex pairing. 2 The emitted sound for the engrailed trailing edge is mainly high-frequency noise with short wavelengths.…”

“…7 Nevertheless two main sources can be determined at x ≈ 150 and x ≈ 220, corresponding to the positions of vortex pairing. 2 The emitted sound for the engrailed trailing edge is mainly highfrequency noise with short wavelengths as shown in figure 16. The main sources are located at x ≈ 140 and x ≈ 200 which is equivalent to the pairing of the allocations of the small-scale structures.…”