Gas Turbine Combustor Simulator Research Articles

Parallelization of a Transient Method of Lines Navier–Stokes Code

Parallel implementation of a serial code, namely method of lines (MOL) solution for momentum equations (MOLS4ME), previously developed for the solution of transient Navier–Stokes equations for incompressible separated internal flows in regular and complex geometries, is described. *E-mail: ceme@metu.edu.tr The serial code was parallelized by using a domain decomposition strategy with overlapped boundary at the interfaces for information exchange between the sub-domains. A parallel virtual machine (PVM) and dual-processor personal computer (PC) connected over a switch are employed as the message passing software and the parallel computing platform, respectively. Performance of the parallelization strategy was first tested on a transient 1-D laminar pipe flow problem for MOL, explicit and implicit finite difference methods. Assessment of the performance of the parallel code (PARMOLS4ME) was then tested by applying it to two test cases; (i) laminar pipe flow with sudden expansion and (ii) turbulent flow in a gas turbine combustor simulator (GTCS) and comparing the results of serial and parallel codes. Comparisons show that the flow fields predicted by parallel codes agree well with those of serial codes at considerably lower execution times. Effects of load balancing are also investigated and it is seen that the load balancing has a significant effect on the execution time of the parallel code.

The method of lines solution of discrete ordinates method for radiative heat transfer in cylindrical enclosures

A radiation code based on method of lines solution of discrete ordinates method for radiative heat transfer in axisymmetric cylindrical enclosures containing absorbing–emitting medium was developed and tested for predictive accuracy by applying it to (i) test problems with black and grey walls (ii) a gas turbine combustor simulator enclosing a non-homogeneous absorbing–emitting medium and benchmarking its steady-state predictions against exact solutions and measurements. Comparisons show that it provides accurate solutions for radiative heat fluxes and can be used with confidence in conjunction with CFD codes based on the same approach.

A robust and accurate algorithm of the β-pdf integration and its application to turbulent methane–air diffusion combustion in a gas turbine combustor simulator

The β-pdf has been widely assumed for the probability distribution of the mixture fraction in many turbulent mixing and turbulent non-premixed combustion models in the literature. The numerical integration of the β-pdf often encounters the singularity difficulties and only few publications have addressed this issue. An efficient, accurate and robust numerical treatment of the β-pdf integration was proposed. The present treatment of the β-pdf integration was implemented into a flamelet model to calculate turbulent methane–air combustion in a model gas turbine combustor. Numerical results obtained using the present β-pdf integration method and those based on the properties of the beta and gamma functions were compared to illustrate the accuracy of the present method. Effect of assuming the β-pdf to the mass-weighted pdf and unweighted pdf of the mixture fraction on the calculated density field was also investigated.

Experimental Investigation of Limit-Cycle Oscillations in an Unstable Gas Turbine Combustor

This paper describes an experimental investigation of the characteristics of limit cycle oscillations in an unstable gas turbine combustor simulator. This investigation was performed to improve the current understanding of the nonlinear processes controlling these oscillations. Such an understanding is needed in order to predict instability amplitudes, to aid in correlating data, and to develop and optimize active control methodologies. The paper first describes an analysis of the statistical and temporal features of the limit cycle pressure oscillations, and discusses the role of system nonlinearities upon these oscillations. Next, it discusses the important role that the combustor inlet velocity plays in determining the amplitude of the limit cycle oscillations. The paper also presents data illustrating the characteristics of the combustor's transition from stable to unstable operation, and shows that these characteristics can be used to predict the occurrence of nonlinear phenomenon (e.g., hysteresis) that are often observed in unstable combustors. Finally, it is shown that inherent noise in the system can strongly affect the limit cycles, and may even be responsible for causing the combustor to become unstable under nominally stable conditions. The paper concludes with a discussion of the implications of these results on the current understanding of self-excited, combustion driven oscillations in lean, premixed gas turbine combustors.

Studies on free stream turbulence as related to gas turbine heat transfer. A review of authors' past work and future implications.

A review of the past work done on free stream turbulence (FST) as applied to gas turbine heat transfer and its implications for future studies are presented. It is a comprehensive approach to the results of many individual studies in order to derive the general conclusions that could be inferred from all rather than discussing the results of each individual study. Three experimental and four modeling studies are reviewed. The first study was on prediction of heat transfer for film cooled gas turbine blades. An injection model was devised and used along with a 2-D low Reynolds number k-epsilon model of turbulence for the calculations. Reasonable predictions of heat transfer coefficients were obtained for turbulence intensity levels up to 7%. Following this modeling study a series of experimental studies were undertaken. The objective of these studies was to gain a fundamental understanding of mechanisms through which FST augments the surface heat transfer. Experiments were carried out in the boundary layer and in the free stream downstream of a gas turbine combustor simulator, which produced initial FST levels of 25.7% and large length scales (About 5-10 cm for a boundary layer 4-5 cm thick). This result showed that one possible mechanism through which FST caused an increase in heat transfer is by increasing the number of ejection events. In a number of modeling studies several well-known k-epsilon models were compared for their predictive capability of heat transfer and skin friction coefficients under moderate and high FST. Two data sets, one with moderate levels of FST (about 7%) and one with high levels of FST (about 25%) were used for this purpose. Although the models did fine in their predictions of cases with no FST (baseline cases) they failed one by one as FST levels were increased. Under high FST (25.7% initial intensity) predictions of Stanton number were between 35-100% in error compared to the measured values. Later a new additional production term indicating the interaction between the turbulent kinetic energy (TKE) and mean velocity gradients was introduced into the TKE equation. The predicted results of skin friction coefficient and Stanton number were excellent both in moderate and high FST cases. In fact these model also gave good predictions of TKE profiles whereas earlier unmodified models did not predict the correct TKE profiles even under moderate turbulence intensities. Although this new production term seems to achieve the purpose, it is the authors' belief that it is diffusion term of the TKE equation, which needs to be modified in order to fit the physical events in high FST boundary layer flows. The results of these studies are currently being used to come up with new diffusion model for the TKE equation.

Performance of discrete ordinates method in a gas turbine combustor simulator

Abstract Predictive accuracy of discrete ordinates method (DOM) was assessed by applying it to the prediction of incident radiative fluxes on the walls of a gas turbine combustor simulator (GTCS), and comparing its predictions with measurements. Input data utilized for the DOM were measured gas concentration and temperature profiles and inner wall temperatures of the GTCS which is a cylindrical enclosure containing a turbulent diffusion flame of propane and air. Effects of order of approximation (S4 and S6) and using uniform and non-uniform gas absorption coefficients for the non-homogeneous medium on the accuracy of the predicted heat fluxes were also investigated. Comparisons show that S4 approximation is adequate for the prediction of incident wall heat fluxes and that the use of an absorption coefficient profile based on measured gas concentrations and temperatures improves the accuracy significantly.