Effect of Nozzle-exit Flow Conditions on the Flow and Acoustic Properties of Imperfectly Expanded Supersonic Jets

Abstract

The impact of the turbulence level at the nozzle exit on the jet flow and far-field noise level has been investigated using large-eddy simulations (LES) and the Ffowcs Williams & Hawkings (FW-H) surface integral method. The jet exit flow condition is slightly underexpanded. Both the random perturbations inside the nozzle and the nozzle surface roughness are used to increase the turbulence level. Increasing the turbulence level at the nozzle exit increases the shear-layer spreading, reduces the screech intensity and also decreases slightly the far-field noise level. The LES predictions of the shock-cell structures and the jet core lengths agree well with the measurement data. In addition, the impact of grid resolution used in both the jet flow and the near-field acoustic propagation region has also been investigated. It is found that the grid resolution used in the shear layer impacts the numerical predictions more than those used in the other regions. Adding an adequate amount of turbulence level at the nozzle exit greatly improves the predictions using a coarser grid resolution in the shear layer. Furthermore, the far-field noise predictions agrees well with measurement data, and the contribution from the end cap is found small, but it is sensitive to the mesh size used in the integration.

Efficient Supersonic Jet Noise Simulations Using JENRE

“…The predicted shock-cell structures and jet core length agree well with experimental data as shown in Figure 3. The importance of using realistic nozzle-exit flow conditions has been highlighted by this study and more details are available elsewhere [14]. Another key computational study conducted recently involves the effect of installation geometry.…”

“…Typical results for the projected far field with one-such choice for the near-field surface is shown in Figure 1 and is in excellent agreement with experimental data. The impact of the choice of near field control surface and the end cap is discussed in detail elsewhere [14]. A comparison of the computed overall sound pressure level is shown in Figure 2.…”

“…The flow structure and acoustics of these conic convergent-divergent nozzles have been presented elsewhere [13] in detail and will not be repeated here. In more recent work, our simulations have been extended to include the effects of inflow turbulence [14] and jet heating [10], since realistic operating conditions involve hot turbulent, exhaust jets. The results from the simulations of heated jets are in agreement with observations made in the literature.…”

Jet Noise Simulations for Complex Nozzle Geometries

“…2) has the least axial variation of this product beyond x/D = 10.0. Liu et al [29] used a similar criterion in selecting the integral surface that has minimum contribution from hydrodynamic pressure fluctuations. Also, the sampling bin size in the farfield computation using the FWH method was closely matched to that of the experimental bandwidth value of 25.63 Hz.…”

Validating a Monotonically-Integrated Large Eddy Simulation Code for Subsonic Jet Acoustics

“…A number examples of the application of unstructured LES codes to the problem of supersonic jet noise can also be found in the literature, e.g., the work done by researchers associated with Cascade Technologies [22][23][24][25][26] and the Naval Research Laboratory (NRL). [27][28][29][30][31][32][33] Comparably little work has been done to validate the effectiveness of unstructured LES codes at simulating the acoustics of subsonic jets. While not needed to capture the geometry of the simple nozzles considered in this paper, the flexibility provided by unstructured meshes allows users to use small cell sizes in localized areas of the flow without affecting the mesh downstream, unlike structured meshes.…”