Pierre Gajan

Experimental and Numerical Studies of Dilution Systems for Low-Emission Combustors

Numerical and experimental investigations of eight isothermal jets in crossflow (eight-JICF) issuing radially in a round pipe are presented to assess advanced numerical approaches in industry-like configurations. The simulations are performed with large-eddy simulations (LES). Numerical issues such as grid resolution and physical issues such as injection of turbulence in the crossflow are addressed in this work. Detailed analyses of the LES predictions and comparisons with data underline the potential of the approach for industry-like configurations. Unsteady and averaged LES solutions of eight-JICF picture most of the single JICF features. The counter-rotating vortex pair, the wake vortices, and the shear-layer vortices are clearly identified in the experiment and by LES. Spectral analysis of the LES predictions reveals proper physical behavior of the different structures and good energy content distribution. Characteristic Strouhal numbers are within experimental scatter

Investigation of Spray Behavior Downstream of an Aeroengine Injector with Acoustic Excitation

DO1: 10.251411.22394 An experiment was developed to reproduce the effects on fuel spray behavior of large pressure and velocity fluctuations observed in a gas turbine with combustion instability phenomena. A spray produced by an air-blast atomizer was injected into a chamber closed on both sides by sonic nozzles. The pressure and velocity fluctuations were created by periodic modification of the downstream nozzle area using a cogged wheel. Phase-averaged techniques were used to monitor the air velocity field and spray pattern oscillations during the excitation cycle. The results revealed the existence of low Mach number traveling waves inside the chamber. Convection velocities of these waves were determined. The spray exhibited a droplet density wave formed mainly with smaller droplet sizes. An analysis based on experimental observations and numerical calculations showed that this wave has two origins. The first is linked to the atomization process and the second to the transport of droplets by the oscillating airflow. The existence of this wave plays an important role in the pressure and heat release coupling that is at the origin of the combustion instabilities.

Experimental Application of an Active Control Loop on Backward-Facing Step Flow.

Experimental results are presented on the active control of a backward-facing step flow revealing some features observed in combustion chambers. These experiments were performed under nonreactive conditions, and the effect of the pressure fluctuations induced by the unsteady heat release was simulated by an external acoustic excitation produced by two loudspeakers placed far downstream from the step. This excitation signal was delivered by a generator or by a hot-wire probe placed in the shear layer. The latter configuration reproduces some aspects of the actual coupling that have been observed with combustion instabilities. This preexcited flow was then controlled using six synthetic jets located on the vertical side of the step. The control loop uses an recursive least-mean-square autoadaptive algorithm applied to a signal from either a microphone or a hot-wire probe placed downstream of the step edge. The influence of the external acoustic excitation on the flow organization and the effect of the control loop are described

Full Coverage Film Cooling: Comparison Of Experimental And Numerical Data.

[Abstract] An experimental study is carried out on a cooling film issuing from a multiperforated wall of a simplified combustor. The objectives of this work are to achieve a better understanding of the dynamics of the film and to construct a database on a simplified geometry in order to test numerical models. RANS calculations using a multiperforation injection model are performed and compared to experimental results. This approach delivers promising results although some weaknesses appear very close to the wall in the recovery region.

Planar droplet sizing: Application to a spray of Jet A1 kerosene

This work is conducted in cooperation between ONERA and SAFRAN AIRCRAFT ENGINES (Safran Group). The authors gratefully acknowledge the ANRT (Association Nationale de la Recherche et de la Technologie) which supports part of the PhD

Fuel Vapor Concentration Measurements by Laser Induced Fluorescence and Infra-Red Extinction: An Investigation on a Monodisperse Droplet Stream

The vapor mole fraction field around a stream of monodisperse acetone droplets is investigated by Planar Laser Induced Fluorescence (PLIF) and Infra-Red Extinction (IRE). The PLIF works develop an interface positioning method based on the Lorenz-Mie Theory and on geometrical optics, which can be applied to the images despite the blooming effect caused by the liquid phase. Quantitative results obtained at two different injection temperatures concur with the numerical predictions. IRE results — taken at a high repetition rate on the same configuration — are presented. The dynamical behavior, possibilities and constraints of the employed techniques are discussed and an outlook to following investigations is given. This paper presents some PLIF and IRE basics, a description of the test rigs, the post processing of the obtained data and a comparison of the results to a simplified numerical calculation. Finally a discussion of the results and suggestions for improvements are proposed.Copyright

Validation and benefits of a homogeneous effusion cooling model for combustor RANS simulations

[Abstract] An extensive numerical study is carried out on a cooling film issuing from a multiperforated wall of a simplified combustor. The objective of this work is to validate the use of a homogeneous effusion cooling model against both experiments and detailed numerical simulations. An experimental database on representative configurations has been used. The model validated in this study is suitable for RANS calculations. Then the model has been used in typical real combustor simulations. This approach delivers promising results although some weaknesses concerning film thickness and turbulence appear.