On the acoustic response of a generic gas turbine fuel injector passage

A current trend in the design of modern aero engines is the transition towards leaner combustion as a solution to satisfy increasingly stringent emission regulations. Lean combustion systems are often more susceptible to thermoacoustic instability and the fuel injector can play a critical role. This paper presents an analytical study on the unsteady air flow through a generic injector passage in response to incident acoustic waves. The injector passage is represented by a simplified geometry which comprises the main geometrical passage features. The unsteady flow through the passage is obtained by combining the elemental solutions for different parts of the passage. This enables the transfer impedance of the injector passage to be determined and the effects of different design parameters on the sensitivity of the air flow to acoustic perturbations to be examined. The convective wave associated with the unsteady swirl vane wakes is also visited and compared with the results from the numerical simulations obtained in previous works. In addition to helping derive design practices for injector passages from the perspective of thermoacoustic instability, the current analysis can also be applied as a preliminary design tool to assess the acoustic characteristics for an injector passage of the axial swirler type

An efficient method to reproduce the effects of acoustic forcing on gas turbine fuel injectors in incompressible simulations

Previous studies have highlighted the importance of both air mass flow rate and swirl fluctuations on the unsteady heat release of a swirl stabilised gas turbine combustor. The ability of a simulation to correctly resolve the heat release fluctuations or the flame transfer function (FTF), important for thermoacoustic analysis, is therefore dependent on the ability of the method to correctly include both the swirl number and mass flow rate fluctuations which emerge from the multiple air passages of a typical lean-burn fuel injector. The fuel injector used in this study is industry representative and has a much more complicated geometry than typical premixed, lab-scale burners and the interaction between each flow passage must be captured correctly. This paper compares compressible, acoustically forced, CFD (computational fluid dynamics) simulations with incompressible, mass flow rate forced simulations. Incompressible mass flow rate forcing of the injector, which is an attractive method due to larger timesteps, reduced computational cost and flexibility of choice of combustion model, is shown to be incapable of reproducing the swirl and mass flow fluctuations of the air passages given by the compressible simulation as well as the downstream flow development. This would have significant consequences for any FTF calculated by this method. However, accurate incompressible simulations are shown to be possible through use of a truncated domain with appropriate boundary conditions using data extracted from a donor compressible simulation. A new model is introduced based on the Proper Orthogonal Decomposition and Fourier Series (PODFS) that alleviates several weaknesses of the strong recycling method. The simulation using this method is seen to be significantly computationally cheaper than the compressible simulations. This suggests a methodology where a non-reacting compressible simulation is used to generate PODFS based boundary conditions which can be used in cheaper incompressible reacting FTF calculations. In an industrial context, this improved computational efficiency allows for greater exploration of the design space and improved combustor design

Primers used in this study.

<p>Primers used in this study.</p

Effect of Ku80 expression on cell cycle distribution under hyperthermia.

<p>786-O-shKu80 and 786-O-scramble cells were subjected to 42°C for the indicated amount of time. Then the cell cycle distribution was measured immediately after hyperthermia. Images showing flow cytometric analysis of cell cycle distribution.</p

RNAi sequences used in this study.

<p>RNAi sequences used in this study.</p

Hyperthermia induces apoptosis in 786-O cells.

<p>Cells were exposed to 37°C and 42°C for the indicated amount of time. Apoptotic cells were measured by flow cytometry immediately after heat treatment. <b>A:</b> Images showing flow cytometric analysis of apoptosis. <b>B:</b> The histogram shows the result from A (%). *P<0.05 compared to control. Results are representative of three independent experiments.</p

Effect of Ku80 expression on heat-sensitivity under hyperthermia.

<p>786-O-shKu80 and 786-O-scramble cells were subjected to 42°C for the indicated amount of time. Survival fractions were measured by colony formation assay after hyperthermia. <b>A:</b> Images showing colony formation assay. <b>B:</b> The histogram shows the result from A (%). *P<0.05 compared to control. Each date point is the mean of three independent experiments.</p

Response of 786-O-shKu80 and 786-O-scramble cells to hyperthermia.

<p>Cells were exposed to 42°C for the indicated amount of time. Apoptotic cells were measured by flow cytometry immediately after hyperthermia. <b>A:</b> Images showing flow cytometric analysis of apoptosis. <b>B:</b> The histogram shows the result from A (%). *P<0.05 compared to control. Each date point is the mean of three independent experiments.</p

Ku expression was detected in 786-O cells exposed to 37°C or 42°C for the indicated amount of time.

<p><b>A</b> and <b>B:</b> Ku70 and Ku80 mRNA expression was analysed by RT-PCR. <b>C</b> and <b>D:</b> Ku70 and Ku80 protein expression was detected by Western blot. *P<0.05 compared to control.</p

Cell cycle detection in 786-O-scramble at 42°C for the indicated amount of time.

<p>Cell cycle detection in 786-O-scramble at 42°C for the indicated amount of time.</p