Numerical Simulation of Single-Stream Jets from a Serrated Nozzle

Abstract

Hybrid large-eddy type simulations for cold jet flows from a serrated nozzle are performed at an acoustic Mach number Ma ac = 0.9 and Re = 1.03 × 10 6 . Since the solver being used tends towards having dissipative qualities, the subgrid scale (SGS) model is omitted, giving a numerical type LES (NLES) or implicit LES (ILES) reminiscent procedure. To overcome near wall streak resolution problems a near wall RANS (Reynolds averaged Navier-Stokes) model is smoothly blended to the LES making a hybrid RANS-ILES. The geometric complexity of the serrated nozzle is fully considered without simplification or emulation. An improved but still modest hexahedral multi-block grid with circa 20 million grid points (with respect to 12.5 million in Xia et al., Int J Heat Fluid Flow 30:1067-1079) is used. Despite the modest grid size, encouraging and improved results are obtained. Directly resolved mean and second-order fluctuating quantities along the jet centerline and in the jet shear layer compare favorably with measurements. The radiated far-field sound predicted using the Ffowcs Williams and Hawkings (FW-H) surface integral method shows good agreement with the measurements in directivity and sound spectra.

Parabolized stability analysis of jets from serrated nozzles

“…However, the LES predicts a somewhat thicker shear layer in the chevron tip plane, especially near the nozzle exit. Xia & Tucker (2012) demonstrated favorable agreement of the far-field sound predictions (using a Ffowcs-Williams Hawkings solver) with measured values for the SMC006 nozzle case computed using the same numerical setup.…”

“…The original calculation (Xia et al 2009) was performed on a 12.5 million cell mesh. Following the subsequent success in simulating the SMC006 chevron case on a 20 million cell mesh (Xia & Tucker 2012), the SMC001 case was also rerun on a mesh having 20 million cells. The simulation time step was 5 × 10 −4 D/U j , and it was run for a flow time duration of 200D/U j beyond the initial transients.…”

“…Following Gudmundsson & Colonius (2011), the pressure data is filtered with proper orthogonal decomposition (POD) to extract the coherent wavepackets existing in the turbulence, which are then used to validate the stability results. Another novel comparison pursued here is with an LES database of the same serrated jet (Xia et al 2009;Xia & Tucker 2012). The pressure component of this data (extracted in a cylindrical domain containing the jet plume) is also POD-filtered to identify the wavepacket structure within the shear layer.…”

Far-field Noise Prediction of Round and Serrated Jets with Increasingly Refined Grids

“…The desire to more reliably predict the noise reduction available to individual jet engine designs has led to the increasingly popular use of Large-Eddy Simulation. For example, Xia et al 1,2 recently made attempts to predict far-field noise radiated from chevron nozzles, Uzun and Hussuni 3 showed high frequency spectra of a chevron jet, while Shur et al 4,5 and Mendez et al 6 explored a generic approach for emulating complex nozzle jets.…”

Turbulent jet characteristics for axisymmetric and serrated nozzles

“…For example, Xia et al [38,37] recently made attempts to predict far-field noise radiated from chevron nozzles, Uzun and Hussuni [34] showed high frequency spectra of a chevron jet, while Shur et al [25,24] explored a generic approach for emulating complex nozzle jets. In order to understand noise generation (reduction) mechanisms and to potentially improve prediction, the turbulent characteristics of the jet flow, especially for complex nozzle geometry, need to be explored in contrast to a baseline axisymmetric nozzle.…”