Supersonic Jet Noise Reduction Using Fluidics, Mechanical Chevrons and Fluidically Enhanced Chevrons

2010 ◽  
Author(s):  
David Munday ◽  
Nick Heeb ◽  
Ephraim Gutmark ◽  
Junhui Liu ◽  
K. Kailasanath
Keyword(s):  
Near Field ◽  
Supersonic Jet ◽  
Acoustic Emissions ◽  
Nozzle Geometry ◽  
Axial Position ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Nozzle Geometries ◽  
The Impact

This paper presents observations and simulations of the impact of several technologies on modifying the flow field and acoustic emissions from supersonic jets from nozzles typical of those used on military aircraft. The flowfield is measured experimentally by shadowgraph and particle image velocimetry (PIV). The acoustics are characterized by near and far-field microphone measurements. The flow and near-field pressures are simulated by monotonically integrated large-eddy simulation (MILES). Use of unstructured grids allows accurate modeling of the nozzle geometry. The nozzle geometries used in this research are representative of practical engine nozzles. The emphasis of the work is on “off-design” or non-ideally expanded flow conditions. The technologies applied to these nozzles include chevrons, fluidic injection and fluidically enhanced chevrons. The fluidic injection geometry and fluidic enhancement geometry follow the approach found successful for subsonic jets by Alkislar, Krothapalli & Butler [1] employing jets pitched 60° into the flow, impinging on the shear layer just past the tips of the chevrons, or in the same axial position when injection is without chevrons.

Supersonic Jet Noise Reduction Technologies for Gas Turbine Engines

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
David Munday ◽  
Nick Heeb ◽  
Ephraim Gutmark ◽  
Junhui Liu ◽  
K. Kailasanath
Keyword(s):  
Flow Field ◽  
Near Field ◽  
Supersonic Jet ◽  
Acoustic Emissions ◽  
Nozzle Geometry ◽  
Axial Position ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy ◽  
The Impact

This paper presents observations and simulations of the impact of several technologies on modifying the flow-field and acoustic emissions from supersonic jets from nozzles typical of those used on military aircraft. The flow-field is measured experimentally by shadowgraph and particle image velocimetry. The acoustics are characterized by near- and far-field microphone measurements. The flow- and near-field pressures are simulated by a monotonically integrated large eddy simulation. Use of unstructured grids allows accurate modeling of the nozzle geometry. The emphasis of the work is on “off-design” or nonideally expanded flow conditions. The technologies applied to these nozzles include chevrons, fluidic injection, and fluidically enhanced chevrons. The fluidic injection geometry and the fluidic enhancement geometry follow the approach found successful for subsonic jets by employing jets pitched 60 deg into the flow, impinging on the shear layer just past the tips of the chevrons or in the same axial position when injection is without chevrons.

Impact of Mechanical Chevrons on Supersonic Jet Flow and Noise

2009 ◽  
Author(s):  
K. Kailasanath ◽  
Junhui Liu ◽  
Ephraim Gutmark ◽  
David Munday ◽  
Steven Martens
Keyword(s):  
Flow Field ◽  
Large Scale ◽  
Near Field ◽  
Supersonic Jet ◽  
Initial Step ◽  
Nozzle Geometry ◽  
Jet Flows ◽  
Flow Conditions ◽  
Nozzle Geometries ◽  
The Impact

In this paper, we present observations on the impact of mechanical chevrons on modifying the flow field and noise emanated by supersonic jet flows. These observations are derived from both a monotonically integrated large-eddy simulation (MILES) approach to simulate the near fields of supersonic jet flows and laboratory experiments. The nozzle geometries used in this research are representative of practical engine nozzles. A finite-element flow solver using unstructured grids allows us to model the nozzle geometry accurately and the MILES approach directly computes the large-scale turbulent flow structures. The emphasis of the work is on “off-design” or non-ideally expanded flow conditions. LES for several total pressure ratios under non-ideally expanded flow conditions were simulated and compared to experimental data. The agreement between the predictions and the measurements on the flow field and near-field acoustics is good. After this initial step on validating the computational methodology, the impact of mechanical chevrons on modifying the flow field and hence the near-field acoustics is being investigated. This paper presents the results to date and further details will be presented at the meeting.

Large Eddy Simulations of Static and Rotating Ribbed Channels in Adiabatic and Isothermal Conditions

2017 ◽  
Author(s):  
Thomas Grosnickel ◽  
Florent Duchaine ◽  
Laurent Y. M. Gicquel ◽  
Charlie Koupper
Keyword(s):  
Flow Direction ◽  
Secondary Flows ◽  
Flow Topology ◽  
Time Resolved ◽  
Piv Measurements ◽  
Eddy Simulation ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Rib Turbulators ◽  
The Impact

In an attempt to better understand spatially developing rotating cooling flows, the present study focuses on a computational investigation of a straight, rotating rib roughened cooling channel initially numerically studied by Fransen et al. [1]. The configuration consists of a squared channel equipped with 8 rib turbulators placed with an angle of 90 degrees with respect to the flow direction. The rib pitch-to-height (p/h) ratio is 10 and the height-to-hydraulic diameter (h/Dh) ratio is 0.1. The simulations are based on a case where time resolved two-dimensional Particle Image Velocimetry (PIV) measurements have been performed at the Von Karman Institute (VKI) in a near gas turbine operating condition: the Reynolds number (Re) and the rotation number (Ro) are around 15000 and ± 0.38 respectively. Adiabatic as well as anisothermal conditions have been investigated to evaluate the impact of the wall temperature on the flow, especially in the rotating configurations. Static as well as both positive and negative rotating channels are compared with experimental data. In each case, either an adiabatic or an isothermal wall boundary condition can be computed. In this work, Large Eddy Simulation (LES) results show that the high fidelity CFD model manages very well the turbulence increase (decrease) around the rib in destabilizing (stabilizing) rotation of the ribbed channels. Thanks to the full spatial and temporal description produced by LES, the spatial development of secondary flows are found to be at the origine of observed differences with experimental measurements. Finally, the model is also able to reproduce the differences induced by buoyancy on the flow topology in the near rib region and resulting from an anisothermal flow in rotation.

scholarly journals Exploration of the impact of nearby sources on urban atmospheric inversions using large eddy simulation

Elem Sci Anth ◽  
2017 ◽  
Vol 5 ◽  
Author(s):  
Brian J. Gaudet ◽  
Thomas Lauvaux ◽  
Aijun Deng ◽  
Kenneth J. Davis
Keyword(s):  
Large Eddy Simulation ◽  
Mesoscale Model ◽  
Near Field ◽  
Turbulent Transport ◽  
Analytical Models ◽  
Source Inversion ◽  
Mesoscale Models ◽  
Eddy Simulation ◽  
Large Eddy ◽  
The Impact

The Indianapolis Flux Experiment (INFLUX) aims to quantify and improve the effectiveness of inferring greenhouse gas (GHG) source strengths from downstream concentration measurements in urban environments. Mesoscale models such as the Weather Research and Forecasting (WRF) model can provide realistic depictions of planetary boundary layer (PBL) structure and flow fields at horizontal grid lengths (Δx) down to a few km. Nevertheless, a number of potential sources of error exist in the use of mesoscale models for urban inversions, including accurate representation of the dispersion of GHGs by turbulence close to a point source. Here we evaluate the predictive skill of a 1-km chemistry-adapted WRF (WRF-Chem) simulation of daytime CO2 transport from an Indianapolis power plant for a single INFLUX case (28 September 2013). We compare the simulated plume release on domains at different resolutions, as well as on a domain run in large eddy simulation (LES) mode, enabling us to study the impact of both spatial resolution and parameterization of PBL turbulence on the transport of CO2. Sensitivity tests demonstrate that much of the difference between 1-km mesoscale and 111-m LES plumes, including substantially lower maximum concentrations in the mesoscale simulation, is due to the different horizontal resolutions. However, resolution is insufficient to account for the slower rate of ascent of the LES plume with downwind distance, which results in much higher surface concentrations for the LES plume in the near-field but a near absence of tracer aloft. Physics sensitivity experiments and theoretical analytical models demonstrate that this effect is an inherent problem with the parameterization of turbulent transport in the mesoscale PBL scheme. A simple transformation is proposed that may be applied to mesoscale model concentration footprints to correct for their near-field biases. Implications for longer-term source inversion are discussed.

Wake-Airfoil Interaction as Broadband Noise Source: A Large-Eddy Simulation Study

2005 ◽  
Vol 4 (1-2) ◽  
pp. 93-115 ◽  
Author(s):  
Jérôme Boudet ◽  
Nathalie Grosjean ◽  
Marc C. Jacob
Keyword(s):  
Large Eddy Simulation ◽  
Particle Image ◽  
Broadband Noise ◽  
Far Field ◽  
Acoustic Analogy ◽  
Eddy Simulation ◽  
Naca0012 Airfoil ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Proper Orthogonal

A large-eddy simulation is carried out on a rod-airfoil configuration and compared to an accompanying experiment as well as to a RANS computation. A NACA0012 airfoil (chord c = 0.1 m) is located one chord downstream of a circular rod (diameter d = c/10, Red = 48 000). The computed interaction of the resulting sub-critical vortex street with the airfoil is assessed using averaged quantities, aerodynamic spectra and proper orthogonal decomposition (POD) of the instantaneous flow fields. Snapshots of the flow field are compared to particle image velocimetry (PIV) data. The acoustic far field is predicted using the Ffowcs Williams & Hawkings acoustic analogy, and compared to the experimental far field spectra. The large-eddy simulation is shown to accurately represent the deterministic pattern of the vortex shedding that is described by POD modes 1 & 2 and the resulting tonal noise also compares favourably to measurements. Furthermore higher order POD modes that are found in the PIV data are well predicted by the computation. The broadband content of the aerodynamic and the acoustic fields is consequently well predicted over a large range of frequencies ([0 kHz; 10 kHz]).

Describing the Mechanism of Instability Suppression Using a Central Pilot Flame With Coupled Experiments and Simulations

2021 ◽  
Author(s):  
Jihang Li ◽  
Hyunguk Kwon ◽  
Drue Seksinsky ◽  
Daniel Doleiden ◽  
Jacqueline O’Connor ◽  
...  
Keyword(s):  
Gas Turbines ◽  
Equivalence Ratio ◽  
Vortex Breakdown ◽  
Eddy Simulation ◽  
Breakdown Region ◽  
Large Eddy ◽  
Rate Oscillations ◽  
Combustion Oscillation ◽  
The Stability ◽  
The Impact

Abstract Pilot flames are commonly used to extend combustor operability limits and suppress combustion oscillations in low-emissions gas turbines. Combustion oscillations, a coupling between heat release rate oscillations and combustor acoustics, can arise at the operability limits of low-emissions combustors where the flame is more susceptible to perturbations. While the use of pilot flames is common in land-based gas turbine combustors, the mechanism by which they suppress instability is still unclear. In this study, we consider the impact of a central jet pilot on the stability of a swirl-stabilized flame in a variable-length, single-nozzle combustor. Previously, the pilot flame was found to suppress the instability for a range of equivalence ratios and combustor lengths. We hypothesize that combustion oscillation suppression by the pilot occurs because the pilot provides hot gases to the vortex breakdown region of the flow that recirculate and improve the static, and hence dynamic, stability of the main flame. This hypothesis is based on a series of experimental results that show that pilot efficacy is a strong function of pilot equivalence ratio but not pilot flow rate, which would indicate that the temperature of the pilot gases as well as the combustion intensity of the pilot flame play more of a role in oscillation stabilization than the length of the pilot flame relative to the main flame. Further, the pilot flame efficacy increases with pilot flame equivalence ratio until it matches the main flame equivalence ratio; at pilot equivalence ratios greater than the main equivalence ratio, the pilot flame efficacy does not change significantly with pilot equivalence ratio. To understand these results, we use large-eddy simulation to provide a detailed analysis of the flow in the region of the pilot flame and the transport of radical species in the region between the main flame and pilot flame. The simulation, using a flamelet/progress variable-based chemistry tabulation approach and standard eddy viscosity/diffusivity turbulence closure models, provides detailed information that is inaccessible through experimental measurements.

A Method of Measuring Turbulent Flow Structures With Particle Image Velocimetry and Incorporating Into Boundary Conditions of Large Eddy Simulations

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Puxuan Li ◽  
Steve J. Eckels ◽  
Garrett W. Mann ◽  
Ning Zhang
Keyword(s):  
Particle Image Velocimetry ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Particle Image ◽  
Advantages And Disadvantages ◽  
Eddy Simulation ◽  
Piv Measurement ◽  
Image Velocimetry ◽  
Large Eddy ◽  
Inlet Conditions

The setup of inlet conditions for a large eddy simulation (LES) is a complex and important problem. Normally, there are two methods to generate the inlet conditions for LES, i.e., synthesized turbulence methods and precursor simulation methods. This study presents a new method for determining inlet boundary conditions of LES using particle image velocimetry (PIV). LES shows sensitivity to inlet boundary conditions in the developing region, and this effect can even extend into the fully developed region of the flow. Two kinds of boundary conditions generated from PIV data, i.e., steady spatial distributed inlet (SSDI) and unsteady spatial distributed inlet (USDI), are studied. PIV provides valuable field measurement, but special care is needed to estimate turbulent kinetic energy and turbulent dissipation rate for SSDI. Correlation coefficients are used to analyze the autocorrelation of the PIV data. Different boundary conditions have different influences on LES, and their advantages and disadvantages for turbulence prediction and static pressure prediction are discussed in the paper. Two kinds of LES with different subgrid turbulence models are evaluated: namely dynamic Smagorinsky–Lilly model (Lilly model) and wall modeled large eddy simulation (WMLES model). The performances of these models for flow prediction in a square duct are presented. Furthermore, the LES results are compared with PIV measurement results and Reynolds-stress model (RSM) results at a downstream location for validation.

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