Randal G. McKinney

Application of an Advanced CFD-Based Analysis System to the PW6000 Combustor to Optimize Exit Temperature Distribution: Part I — Description and Validation of the Analysis Tool

This paper is the first of two parts that describes an advanced CFD-based analysis system, developed at Pratt & Whitney, which has been used to optimize the PW6000 combustor exit temperature distribution. It utilizes a CFD calculation through the entire combustor domain to predict temperature distribution at the combustor exit. In this part, all components of the analysis system are presented, including the CAD and grid generation approach used to represent the complex combustor geometry, the core CFD solver, the Lagrangian fuel spray model, and the combustion model. In addition, the predictive capability of the system is established by comparing calculated exit temperature profiles to full annular rig test data for three aircraft gas turbine engine combustors: PW4090, PW4098, and a low-emissions technology development combustor. Comparisons of combustor airflow distribution and pressure drop are also presented to verify the accuracy of the tool. The paper demonstrates that the CFD-based analysis system is capable of calculating exit temperature distribution for a range of combustor configurations, and thus can be utilized as a predictive design tool. Part II demonstrates this predictive capability by applying the analysis tool to optimize the PW6000 combustor exit temperature distribution for turbine durability and life. Copyright

Application of an Advanced CFD-Based Analysis System to the PW6000 Combustor to Optimize Exit Temperature Distribution: Part II — Comparison of Predictions to Full Annular Rig Test Data

Pratt & Whitney is developing a 107 kN (24,000 pound) thrust PW6000 engine for the 100-seat aircraft market. The combustor for this engine has been designed by combining the TALON emissions concept demonstrated on the PW4000 engine family with an advanced CFD-based analysis system to optimize the combustor exit temperature distribution. The design objective is to provide a low cost highly reliable engine, which produces low emissions.This paper is the second of two parts, which describe an advanced CFD-based analysis system used to optimize the combustor exit temperature distribution for turbine life. The analysis system applied the identical Allstar solver, which is described and validated in part I, to the PW6000 combustor. All calculations in this paper were completely predictive in nature. The effect of dilution hole pattern changes on the exit temperature profile was determined by solving the flowfield from the prediffuser inlet to the combustor exit. Results from the study were used to understand the physical processes taking place inside the prediffuser and combustor that impact the exit temperature profile and from this understanding a hole pattern configuration was identified. Full annular rig measurements of the pressure drop and airflow distribution throughout the model along with exit temperature profile measurements agreed very well with CFD predictions. A second target exit temperature profile was defined based upon engine testing and the analysis tool demonstrated the ability to define a second dilution hole pattern that met the target profile to optimize turbine life. An annular rig test again confirmed the CFD predictions.Parametric studies were also performed on the prediffuser inlet pressure profile to predict how the turbine inlet temperature profile would change. These studies were used to desensitize the combustor temperature profile to prediffuser inlet profile changes that may occur over the life of the engine. The predictive capability of this CFD-based analysis tool has significantly reduced experimental development costs and has optimized the combustor exit temperature profile to meet PW6000 design objectives.Copyright

Pratt and Whitney Gas Turbine Combustor Design Using ANSYS Fluent and User Defined Functions

This paper summarizes work conducted at Pratt & Whitney to incorporate ANSYS Fluent into the computational fluid dynamics-based combustor design process. As a first step, turbulence, combustion and spray models that already exist and have been validated in the Pratt & Whitney legacy computational fluid dynamics (CFD) solver ALLSTAR were converted into user defined functions (UDFs) for usage with the core ANSYS Fluent solver. In this manner, a baseline solver was established that allowed a systematic testing of the ANSYS Fluent native models. The baseline solver was validated against computational results as well as experimental data obtained for (i) liquid jet in cross-flow (LJICF), (ii) ambient spray injector tests and (iii) Pratt & Whitney next generation product family configurations. These test cases established a thorough evaluation of ANSYS Fluent with UDFs on a spectrum of simple to complex geometries and flow physics relevant to the conditions encountered in aeroengine combustors. Results show that Fluent produces calculated results obtained by ALLSTAR with similar level of agreement to the experiments. Furthermore, Fluent provides better convergence compared to the legacy ALLSTAR solver with a similar computational resource requirement. The ANSYS Fluent native spray break-up models were also tested for the liquid jet in cross flow configuration, demonstrating the importance of modeling the stripping and primary break-up regime of a spray jet. This capability is currently available only via the use of UDFs.Copyright

Large Eddy Simulation Based Flame Transition Modeling in a Lean Premixed Swirl Combustor

This paper assesses two widely used large eddy simulation (LES) sub-grid scale combustion models, the thickened flame model (TFM) and the flamelet generated manifolds model (FGM), that are available in the commercial software ANSYS/Fluent, against an experimental study of a swirling and lean premixed combustor from the literature [1]. The experimental study demonstrated the sensitivity of the flame stabilization mechanism to different equivalence ratios. In particular, a change from an equivalence ratio of 0.55 to 0.65 resulted in a transition from a flame burning only in the inner shear layer, to a flame burning both at the inner and outer shear. First, the current paper assesses the ability of TFM and FGM to capture this transition process. Then, comparisons are made between the computationally and experimentally obtained axial velocity profiles at several locations downstream of the swirler exit to further investigate the accuracy of the models. It is observed that both of the models can predict the correct flame transition behavior while providing good agreement with the experimentally obtained velocity profiles.

Characterizing Particulate Matter Emissions From Aircraft Engines

Research in the areas of particulate matter (PM) emissions impacts on both climate and human health are currently very active, however there are a large number of variables and response times. As a better understanding of the contribution of aviation PM emissions is developed, new aircraft engines will need to be designed for reduced PM emissions. In order to do this, measurement methods for different PM metrics like mass, number, size distribution, volatile precursors and composition need to be developed followed by measurements for existing engines to assess their environmental impact. Relevant literature will be reviewed to show that it is necessary to control emissions of nanometer-size particles from a total “number count” as well as a “mass” perspective. Several activities to develop a measurement method and evaluate its effectiveness will be discussed. The results are being used to develop standard measurement methods for aircraft PM emissions which will allow the design of lower emission combustors.Copyright