The present paper reports on the numerical simulation of flow dynamics in a model gas-turbine combustor by large eddy simulation in order to evaluate the effect of coherent flow structures on the local fluctuations of gas temperature and local concentrations of NO and CO. The simulations were performed for a generic swirler, based on the design by Turbomeca, for a Reynolds number of 15,000 at normal and elevated inlet temperature and pressure (up to 500 K and 3.4 atm). The simulation data were validated based on the velocity measurements by stereoscopic particle image velocimetry. In order to reveal coherent flow structures, the velocity snapshots were processed by the proper orthogonal method. The temporal coefficients of the decomposition were used to evaluate the conditional sampled spatial distributions of the temperature and species concentration. It is shown that the coherent fluctuations of temperature can locally reach up to 200 K with the fluctuations of NO up to 20%. Thus, the results demonstrate that coherent flow structures in a lean swirl combustor can sufficiently contribute to NOx emission.

The present paper compares the flow structure and flame dynamics during combustion of methane and syngas in a model gas-turbine swirl burner. The burner is based on a design by Turbomeca. The fuel is supplied through injection holes between the swirler blades to provide well-premixed combustion, or fed as a central jet from the swirler’s centerbody to increase flame stability via a pilot flame. The measurements of flow structure and flame front are performed by using the stereo particle image velocimetry and OH planar laser-induced fluorescence methods. The measurements are performed for the atmospheric pressure without preheating and for 2 atm with the air preheated up to 500 K. The flow Reynolds numbers for the non-reacting flows at these two conditions are 1.5 × 10³ and 1.0 × 10³, respectively. The flame dynamics are analyzed based on a high-speed OH* chemiluminescence imaging. It is found that the flame dynamics at elevated conditions are related with frequent events of flame lift-off and global extinction, followed by re-ignition. The analysis of flow structure via the proper orthogonal decomposition reveals the presence of two different types of coherent flow fluctuations, namely, longitudinal and transverse instability modes. The same procedure is applied to the chemiluminescence images for visualization of bulk movement of the flame front and similar spatial structures are observed. Thus, the longitudinal and transverse instability modes are found in all cases, but for the syngas at the elevated pressure and temperature the longitudinal mode is related to strong thermoacoustic fluctuations. Therefore, the present study demonstrates that a lean syngas flame can become unstable at elevated pressure and temperature conditions due to a greater flame propagation speed, which results in periodic events of flame flash-back, extinction and re-ignition. The reported data is also useful for the validation of numerical simulation codes for syngas flames.

Swirling flows often occur in nature and industrial applications. With an increase in swirl intensity, such rotating flows are known to become unstable and undergo a sudden breakdown of the vortex core, resulting in unsteady flow dynamics with intensive pressure fluctuations. In particular, swirling flows are organized in combustion chambers to stabilize the flame around the central recirculation zone, formed due to the vortex core breakdown. However, the impact of large-scale vortex structures, including the precessing vortex core and secondary helical vortices, on unsteady combustion regimes is still unclear. The present paper demonstrates experimentally that for the swirling flow of a model swirl combustor, the injection of a central jet may be used to alter the configuration of coherent flow structures, including helical vortices. In particular, the asymmetric hydrodynamics mode, associated with the precessing vortex core, is suppressed, whereas the symmetrical one becomes dominant. This effect demonstrates the importance of central jet injection to control the dominant mode of flow instability for the design of swirl combustors.

Flame impingement heat transfer is implemented in many industrial applications. The laminar premixed Bunsen flame, impinging on a flat cold surface, represents a basic model for the validation of computational fluid dynamics (CFD) codes, used for the simulation of industrial processes. Meanwhile, as the present paper demonstrates, some features of basic flame configurations are not well-reviewed. The present paper reports on the direct numerical simulation of the thermofluidic field in a laminar premixed impinging Bunsen flame in comparison with advanced optical measurements. The results reveal the phenomenon of the central recirculation zone formation between the tip of the Bunsen flame cone and the cold surface. Cooled combustion products concentrate inside this zone, resulting in reduced heat transfer near the flow axis. All three tested chemical kinetic mechanisms (GRI-Mech 3.0, SanDiego, RMech1) provide reasonable predictions of the observed phenomenon, which explain previous experimental observations on the reduced heat transfer at the central axis of impinging flames. Moreover, the most detailed mechanism, GRI-Mech 3.0, predicts an elevated concentration of NO_X pollutants caused by the mentioned phenomenon.

A brief overview of the designs of low-emission gas turbine-type combustion chambers is given using the example of aircraft propulsion systems. The most promising technology that helps reduce emissions of harmful substances is the combustion of a lean premixed fuel-air mixture, but its use is limited by nonstationary phenomena that have a significant impact on flame stabilization and lead to the occurrence of thermoacoustic resonance. Currently, this technology is implemented for high-power engines by only two companies: General Electric and Rolls-Royce. Work on creating a high-thrust engine in Russia is being carried out at AO UEC-Aviadvigatel within the framework of the PD-35 program. The problems of developing low-emission combustion chambers for gas pumping units are successfully solved at AO UEC-Aviadvigatel together with the Baranov Central Institute of Aviation Motor Development (GTU-16P). One of the key areas of energy development is also the development of high-power gas turbines of the classes GTE-65, GTE-170 (PAO Power Machines), GTD-110M (ODK Saturn), and here it is necessary to solve the same problems as for gas turbine engines. The most pressing problems are predicting the occurrence of thermoacoustic self-oscillations of gas in combustion chambers and controlling them using feedback both in nominal modes and in low-power modes. A review of technologies using low-emission combustion chambers is presented, and the current state of experimental studies of the flow structure and transfer processes in model combustion chambers is considered. Examples of advanced experimental stands that simulate flow and combustion in gas turbine-type combustion chambers are given and the necessary operating parameters and the technical solutions used are indicated that allow efficient measurements using modern optical diagnostic methods.

This paper reports on experimental study of the flow in a model combustion chamber using planar optical methods. The flow was organized by model GT-premixer produced by JSC “EUC-Aviadvigatel”, Perm, Russia. The measurements were carried out in a cold flow without combustion at elevated pressure of 2 atm and air flow rate up to 0.5 kg/s. Acetone vapor was seeded to the flow as a tracer of model fuel. The distributions of local concentration were measured using planar laser-induced fluorescence approach. To measure velocity fields by particle image velocimetry technique, water-glycerol particles were introduced to the air flow. Two series of experiments were accomplished for design and off-design conditions. The pressure drop at the GT-premixer was the same for these two cases. The results for off-design conditions show that fuel concentration distribution drastically depends on the scheme of fuel supply.