The Effect of Spray Initial Conditions on Heat Release and Emissions in LDI CFD Calculations

This paper describes the time-filtered Navier-Stokes (TFNS) approach capable of capturing unsteady flow structures important for turbulent mixing in the combustion chamber and two different subgrid models used to emulate the major processes occurring in the turbulence-chemistry interaction. These two subgrid models are termed as LEM-like model and EUPDF-like model, respectively. Two-phase turbulent combustion in a singleelement lean-direct-injection (LDI) combustor is calculated by employing the TFNS/LEMlike approach as well as the TFNS/EUPDF-like approach. Results obtained from the TFNS approach employing these two different subgrid models are compared with each other, along with the experimental data, followed by more detailed comparison between the results of an updated calculation using the TFNS/LEM-like model and the experimental data. Acronym CFD= computational fluid dynamics DNS = direct numerical simulation LES = large-eddy simulation RANS = Reynolds-averaged Navier-Stokes approach URANS = unsteady RANS TFNS = time-filtered Navier-Stokes approach SGS = subgrid scale SFC = subfilter component FCP = filtering-control parameter LEM = linear-eddy mixing EUPDF = Eulerian probability density function LDI = lean-direct injection VBB = vortex-breakdown bubble PVC = precession vortex core IntroductionTogether with rig testing and diagnostics, combustion CFD is now a major tool for combustion technology development. It is being used to complement, and sometimes to substitute the rig test. This leads to reduced costs, deepened insight, and improved foresight. Nevertheless, high-fidelity simulation of liquid combustion in practical engineering devices remains an elusive target in spite of significant advances in combustion modeling and simulation over the past decade. The main difficulty lies in the fact that combustion operates at the intersection of fluid dynamics, fuel chemistry, and multi-phase physics. Consequently, in addition to high-fidelity models for turbulence, chemical kinetics, and liquid fuel atomization and transport, models for accurately accounting for their interactions also are required. Furthermore, these intricate physical and chemical phenomena are present throughout a broad range of time scales and length scales in engineering devices.Some of these modeling and simulation issues are discussed in the next section, followed by a description of the TFNS formulation for two-phase flow and the subfilter closure models in Section 3. In Section 4, we describe the estimation of the filtered, chemical-reaction source terms via two different subgrid models of turbulence-chemistry 1 Research Aerospace Engineer, Combustion Branch, Associate Fellow AIAA. 2 Research Aerospace Engineer, Combustion Branch, Member AIAA.

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“…Ref. 26) is employed for the chemical reactions. The computational domain consists of approximately 862,000 hexahedral elements.…”

Section: Experimental and Computational Setupmentioning

confidence: 99%

On The TFNS Sub-Grid Models for Liquid-Fueled Turbulent Combustion

Liu

Wey²

2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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“…A generalized wall function model was applied to resolve near-wall turbulence [21]. The flow solver code base has been extensively validated against a number of experimental datasets for single and multipoint LDI configurations with non-reacting and chemically reacting flows [16,20,[22][23][24][25][26][27][28]. In a recent study [28], EINO x comparisons were made between several experimental and simulated LDI configurations at 17 different combinations of pressure drop, temperature, fuel-air ratio and with various fuel staging options.…”

Section: High-fidelity Combustor Modelingmentioning

confidence: 99%

Parametric Modeling Investigation of a Radially-Staged Low-Emission Aviation Combustor

Heath

2016

54th AIAA Aerospace Sciences Meeting

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Aviation gas-turbine combustion demands high efficiency, wide operability and minimal trace gas emissions. Performance critical design parameters include injector geometry, combustor layout, fuel-air mixing and engine cycle conditions. The present investigation explores these factors and their impact on a radially staged low-emission aviation combustor sized for a next-generation 24,000-lbf-thrust engine. By coupling multi-fidelity computational tools, a design exploration was performed using a parameterized annular combustor sector at projected 100% takeoff power conditions. Design objectives included nitrogen oxide emission indices and overall combustor pressure loss. From the design space, an optimal configuration was selected and simulated at 7.1, 30 and 85% part-power operation, corresponding to landing-takeoff cycle idle, approach and climb segments. All results were obtained by solution of the steady-state Reynolds-averaged Navier-Stokes equations. Species concentrations were solved directly using a reduced 19-step reaction mechanism for Jet-A. Turbulence closure was obtained using a nonlinear κ-ε model. This research demonstrates revolutionary combustor design exploration enabled by multi-fidelity physics-based simulation. Nomenclature A 3 = inlet combustor cross sectional area, m 2

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“…The NCC has been extensively validated against a number of experimental datasets including low speed chemically reacting flows. 7,19,[21][22][23] All computations were executed on a high performance compute cluster, using 400 Intel Xeon cores operating at 2.93-GHz. Wall-times were on the order of 36 to 48 hours per sector design, neglecting data transfer and queuing overhead.…”

Section: High-order Modelingmentioning

confidence: 99%

“…For stability, NCC computations were conducted using a staged approach, similar to that described in Ref. 21. Injector designs were first analyzed to quasi steady-state without reacting chemistry or liquid spray.…”

Section: High-order Modelingmentioning

confidence: 99%

Characterization of Swirl-Venturi Lean Direct Injection Designs for Aviation Gas Turbine Combustion

Heath

2014

Journal of Propulsion and Power

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Injector geometry, physical mixing, chemical processes, and engine cycle conditions together govern performance, operability and emission characteristics of aviation gasturbine combustion systems. The present investigation explores swirl-venturi lean direct injection combustor fundamentals, characterizing the influence of key geometric injector parameters on reacting flow physics and emission production trends. In this computational study, a design space exploration was performed using a parameterized swirl-venturi lean direct injector model. From the parametric geometry, 20 three-element lean direct injection combustor sectors were produced and simulated using steady-state, Reynolds-averaged Navier-Stokes reacting computations. Species concentrations were solved directly using a reduced 18-step reaction mechanism for Jet-A. Turbulence closure was obtained using a nonlinear κ-ε model. Results demonstrate sensitivities of the geometric perturbations on axially averaged flow field responses. Output variables include axial velocity, turbulent kinetic energy, static temperature, fuel patternation and minor species mass fractions. Significant trends have been reduced to surrogate model approximations, intended to guide future injector design trade studies and advance aviation gas-turbine combustion research.

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The Effect of Spray Initial Conditions on Heat Release and Emissions in LDI CFD Calculations

Cited by 21 publications

References 6 publications

On The TFNS Sub-Grid Models for Liquid-Fueled Turbulent Combustion

On The TFNS Sub-Grid Models for Liquid-Fueled Turbulent Combustion

Parametric Modeling Investigation of a Radially-Staged Low-Emission Aviation Combustor

Characterization of Swirl-Venturi Lean Direct Injection Designs for Aviation Gas Turbine Combustion

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