Direct Numerical Simulation of Pulsating Jet Mixing

ABSTRACT In lean premixed combustors, the fuel/air ratio oscillation can cause a serious problem since it can produce pressure and heat release fluctuations, and further, combustion instability if it is well phased with them. In order to design a system where such air/fuel ratio fluctuation is well suppressed, it is important to understand the mixing process and its interaction with the flow structures inside a premixer. In this study, the flow-field of a pulsating jet and the mixing of the jet with the co-flow are examined using direct numerical simulation. The effects of the frequency and amplitude of the imposed pulsation on the flow structures and mixing process are investigated in detail. It is found that the modulation amplitude has a favorable effect on mixing, but the dependency on frequency is more complicated

A CRITICAL EVALUATION OF TURBULENCE MODELING IN A MODEL COMBUSTOR

ABSTRACT Based on the previous benchmark studies on combustion, scalar transfer and radiation models, a critical evaluation of turbulence models in a propane-air diffusion flame combustor with interior and exterior conjugate heat transfers has been performed. Results obtained from six turbulence models are presented and compared in detail with a comprehensive database obtained from a series of experimental measurements. It is found that the Reynolds stress model (RSM), a second moment closure, is superior over the five popular eddyviscosity two-equation models. Although the main flow patterns are captured by all six turbulence models, only the RSM is able to successfully predict the lengths of both recirculation zones and give fairly accurate predictions for mean velocity, temperature, CO 2 and CO mole fractions, as well as turbulence kinetic energy in the combustor chamber. In addition, the realizable k-ε (Rk-ε) model illustrates better performance than four other two-equation models and can provide comparable results to those from the RSM for the configuration and operating conditions considered in the present study

Assessment of Combustor Working Environments

In order to assess the remaining life of gas turbine critical components, it is vital to accurately define the aerothermodynamic working environments and service histories. As a part of a major multidisciplinary collaboration program, a benchmark modeling on a practical gas turbine combustor is successfully carried out, and the two-phase, steady, turbulent, compressible, reacting flow fields at both cruise and takeoff are obtained. The results show the complicated flow features inside the combustor. The airflow over each flow element of the combustor can or liner is not evenly distributed, and considerable variations, ±25%, around the average values, are observed. It is more important to note that the temperatures at the combustor can and cooling wiggle strips vary significantly, which can significantly affect fatigue life of engine critical components. The present study suggests that to develop an adequate aerothermodynamics tool, it is necessary to carry out a further systematic study, including validation of numerical results, simulations at typical engine operating conditions, and development of simple correlations between engine operating conditions and component working environments. As an ultimate goal, the cost and time of gas turbine engine fleet management must be significantly reduced

Assessment of scavenge efficiency for a helicopter particle separation system

The effectiveness of a typical helicopter particle separation system has been numerically assessed at practical operating conditions and sand environments for various scenarios. The particle separation mechanism and its limitation are revealed by the flow characteristics and particle trajectories in the flow-field. The separation-by-inertia concept is effective for removing large particles, but problematic for small particles of diameter (d) 64 36\u3bcm. The particle size, shape factor, and rebound characteristics exert substantial effects on particle scavenge efficiency. On the other hand, the effects of gravity, particle inlet velocity, inlet mass distribution, and engine operating conditions on scavenge efficiency are minor or limited for the configurations and operating conditions considered in the present study. In addition, a few suggestions for further investigation on engine particle separation systems are included. Copyright \ua9 2011 by Her Majesty the Queen in Right of Canada. Copyright \ua9 2011 by ASME.Peer reviewed: YesNRC publication: Ye