Umesh Paliath

Prediction of Jet Noise From Circular Beveled Nozzles

In this paper, simulations are performed of flow-induced noise from circular beveled jet nozzles. The Detached-Eddy Simulation (DES) approach is used to simulate both the jet nozzle internal and external flows as well as the jet plume. This methodology allows the turbulence model to transition from an unsteady Reynolds Averaged NavierStokes (URANS) method for attached boundary layers to a Large-Eddy Simulation (LES) in separated regions. A cylindrical coordinate system is used, with the centerline of the jet nozzle coinciding with the coordinate system’s polar axis. The one equation SpalartAllmaras turbulence model is used to describe the evolution of the turbulent eddy viscosity. An explicit 4th order Runge-Kutta time marching scheme is used. To avoid the use of a full turbulent grid in the nozzle, simple wall functions are used. The far-field sound is evaluated using the Ffowcs Williams-Hawkings permeable surface acoustic analogy. The computational domain is divided into at least two blocks, with the nozzle being along part of the boundary of the inner and outer blocks. A rigid cylindrical boundary, with finite thickness, is used to represent the jet exhaust nozzle. A nozzle with uniform inlet flow of M = 0.9, for both unheated and heated jets is considered. The grid distribution is uniform in the axial and azimuthal directions. The grid is clustered in the radial direction near the lip line of the jet. It is observed that the thrust axis deviates from the geometric centerline at an angle of 8.5 degrees. This is in reasonable agreement with experimental flow measurements. Flow characteristics such as the variation of the mean velocity and turbulent intensity in the radial, axial and azimuthal directions are described. The Ffowcs Williams-Hawkings calculations are performed using the code PSU-WOPWOP developed at Penn State. For these calculations, the surface chosen for the beveled nozzle case is a conical surface at r = 6D and length x = 25D, with a cone angle equal to the deflection angle of the thrust axis. The predictions capture the peak noise levels above and below the bevel as well as the crossover in the spectra at lower polar angles to the jet exit and the shielding effect at higher angles. Noise characteristics for the beveled nozzle are compared with experimental measurements. In addition, the effect of, and need for, artificial excitation to stimulate the development of a turbulent jet mixing layer are studied. Finally, the choice of acoustic data surface for the Ffowcs Williams-Hawkings permeable surface method, as well as whether it should be closed or open at the downstream end are considered.

Prediction of Jet Noise From Rectangular Nozzles

In this paper, numerical simulations are performed to study the phenomenon of flowinduced noise from rectangular jet. In addition, simulations are performed with the addition of forward flight as well as forward flight at an angle of attack. The Detached Eddy Simulation (DES) approach is used to simulate both the jet nozzle internal and external flows as well as the jet plume. This methodology allows the turbulence model to transition from an unsteady Reynolds Averaged Navier-Stokes (URANS) method for attached boundary layers to a Large Eddy Simulation (LES) in separated regions. Thus it is ideally suited to jet flow simulations when the nozzle is included. The radiated noise is calculated using a permeable surface Ffowcs Williams - Hawkings surface integral method. Simulations of a turbulent jet flow from a rectangular nozzle with an aspect ratio of 3 have been carried out. Simulations for both unheated and heated cases are included. The eects of forward flight and jet angle of attack on the radiated noise are also examined. Comparisons are made with available experimental data or empirical databases.

Open Rotor Designs for Low Noise and High Efficiency

Building upon the successes of the UDF® program in the 1980’s, open rotor designs for high flight speed efficiency and low community noise have been developed at GE in collaboration with NASA and the FAA. Targeting a narrow body aircraft with 0.78 cruise Mach number, the cost-share program leveraged computational fluid dynamics (CFD), computational aero-acoustics (CAA), and rig scale testing to generate designs that achieved significant noise reductions well beyond what was attained in the 1980’s while substantially retaining cruise performance. This paper presents overall propeller net efficiency and acoustic assessments of GE’s modern open rotor designs based on measured rig data and the progression of the technology from the 1980’s through the present. Also discussed are the effects of aft rotor clipping, inter-rotor spacing, and disk loading. This paper shows how the two-phase design and scale model wind tunnel test program allowed for test results of the first design phase to feed back into the second design phase, resulting in 2–3% improvement in overall propeller net efficiency than the best efficiency design of the 1980’s while nominally achieving 15–17 EPNdB noise margin to Chapter 4 (when projected to full scale for a prescribed aircraft trajectory and installation). Accounting for trades and near term advancements, such a propulsion system is projected to meet the goal of 26% fuel burn reduction relative to CFM56-7B powered narrow body aircraft.Copyright

Large Eddy Simulation for Jets from Chevron and Dual Flow Nozzles

Large eddy simulations based on high-order finite d ifference schemes have been carried out for jet flows from a NASA ARN2 circular and a SMC001 chevron nozzle at acoustic Mach 0.9. Simulations have also been carried out fo r a bypass ratio 5 dual-flow nozzle at a typical take-off condition. Implicit LES approach i s applied, wherein high-order numerical filters are used in place of SGS models. Far field noise spectra are computed from near field flow solutions with the use of the FWH method. Numerical experiments are conducted to explore the sensitivity of the predicted flow and a coustic field to grid size. Good agreement with experiment data is achieved for both flow and acoustic predictions at moderate grid sizes. It is shown that the first-principles based implicit LES approach can capture the effect of chevron geometry on the far-field acoustics. The predicted noise reduction trend is in good agreement with the experimental data. The LES approach has also been demonstrated for a dual flow realistic engine configuration

Multiple Pure Tone Noise Prediction and Comparison with Static Engine Test Measurements

This paper presents an integrated numerical procedure to predict the generation, in-duct propagation, and radiation of multiple pure tone (MPT) noise of aircraft engines. Reynoldsaveraged Navier-Stokes (RANS) computational fluid dynamics (CFD) simulations using part-annulus grids have been performed to resolve the non-uniform shock signature just upstream of the fan blades. A linear superposition method is then used to reconstruct the full-annulus pressure field using the part-annulus CFD results and the as-manufactured blade stagger angles measured by a coordinate-measuring machine. In order to account for the nonlinear propagation of the shock waves inside the nacelle, a one-dimensional model has been employed to simulate the propagation of MPT from upstream of the fan leading edge to the nacelle lip. For far-field propagation, a commercially available software ACTRAN/TM is used to linearly propagate the acoustic modes to far-field microphone locations. The entire analysis process has been applied to predict MPT noise of a typical high bypass ratio engine at operating conditions when the relative tip Mach number of the fan is transonic. Comparisons against static engine test measurement are made for in-duct, near-field, and far-field sound pressure levels. Good agreement has been observed between predictions and measured data.

Multiple Pure Tone Noise Prediction for Acoustically Treated Aircraft Engines

A multiple pure tone noise prediction approach for acoustically treated aero-engine inlets is described. It consists of three steps that account for noise source generation, nonlinear acoustic propagation with lined walls inside the nacelle, and linear acoustic propagation outside the engine. The predictions are compared with static test measurements for a typical high bypass ratio engine at inlet nacelle unsteady pressure transducer, near-field microphone array, and far-field microphone array locations.

Fine-Scale Turbulent Noise Predictions from Non-Axisymmetric Jets

In this work a model for fine-scale turbulent noise predictions from non-axisymmetric, heated and unheated jets is developed. This model, called GENO, improves upon the previous noise prediction methods JeNo and MGBK by including the effects of mean flow refraction from non-circular geometry, as well as a more complete model for the self, shear, and enthalpy noise sources. The Greens function for non-axisymmetric flows is determined by solving the Lilley-Goldstein equation in terms of coupled azimuthal modes. Additionally, the noise source model evaluates the fourth order velocity correlation tensor I ijkl for the general case and the relationship between non-zero components is found. This is combined with an empirical noise source model for heated jets. Acoustic results using GENO are shown for aspect ratio 2:1 and 4:1 rectangular jets, under unheated (SP7) and heated (SP46) conditions, and the comparisons agree favorably with experimental data.

Numerical simulation of jet noise from different jet nozzle geometries

This paper describes the numerical simulation of flow‐induced noise from jets with different nozzle geometries. The nozzles considered include axisymmetric and nonaxisymmetric nozzles, such as circular and rectangular. Also the study is extended to examine the differences between noise radiated from nozzles with planar exists and those with nonplanar exist, such as beveled nozzles. The detached‐eddy simulation (DES) approach is used to simulate both the jet nozzle internal and external flows as well as the jet plume. This methodology allows the turbulence model to transition from an unsteady Reynolds averaged Navier‐Stokes (URANS) method for attached boundary layers to a large‐eddy simulation (LES) in separated regions. Thus, it is ideally suited to jet flow simulations when the nozzle is included. Both cylindrical polar and Cartesian coordinate systems are used as the basis for grid generation. The one equation Spalart‐Allmaras turbulence model is used to describe the evo! lution of the turbulent eddy vi...