Volume 38, Issue 2

The purpose of this paper is to present a novel turbine balancing using Ant Colony Optimization method. Results are compared against well known optimization methods available at open literature. With the new approach, turbine blade set can be separated in to two blade sets as heavy and light blades. This approach makes possible the application of Ant Colony Optimization methodology. ACO methodology is compared with Steepest Descent and Exchange Heuristic methods using nine different initial blade placements. And results are presented. Performance of the three evaluated methods is affected by the initial blade placement. Exchange Heuristics method was quick and provided good results in most of the cases. Ant colony optimization was able find better results than the Steepest Descent method. The approach of separating blades into two sets decreased the solution time of Steepest Descent algorithm. Ant colony optimization method can be used for turbine blade assembly and balancing for aircraft gas turbine applications. This approach is used for the first time in this area and not seen at the open literature.

Conjugate heat transfer analysis is carried out in a cascade domain for a nozzle guide vane. The nozzle guide vane is internally cooled by jet impingement cooling, and the external surface is cooled by film cooling. A computational study was carried out with three different materials, having conductivity values of 0.0048, 0.2 and 1.1 W/m.K. Distribution of local surface temperature along the leading edge, pressure and suction surface is reported. The leading edge region showed the maximum increase in internal surface temperature as the conductivity increased among the different regions of the vane internal surface. However, the pressure and suction surfaces showed relatively less increase in the surface temperature distribution. In order to validate the computational result, the obtained temperature data were compared with experimentally obtained surface temperature data. The flow phenomena like jet lift-off and self-induced cross-flow affect the local temperature distribution differently in the three materials. For a constant mainstream and coolant flow, the surface temperature gradient is higher for the lower conductivity material, and the gradient decreases as conductivity increases. Hence, a material with higher conductivity is desired in a combined impingement and film cooled nozzle guide vane, to increase the durability of the vane.

Humpback whales possess bumpy tubercles on the leading edge of their flippers. Due to these leading edge tubercles, whales are able to produce high degree of maneuverability. Inspired by the flippers, this paper applies sinusoidal-like tubercles to the leading edge of blades in an annular compressor cascade, and presents a numerical investigation to explore the effects of tubercles with the aim of controlling the corner separation and reducing losses. Steady 3D RANS simulations are performed to investigate the aerodynamic performance and behavior of the corner separation in compressor cascades with and without leading edge tubercles. A crucial geometry parameter of the tubercles, wavelength, is varied to obtain different configurations. Results show that a smaller wavelength (more wave number) corresponds to a larger loss reduction and the maximum loss reduction reaches to 46.0%. Also, it is found that leading edge tubercles result in a stall delay and the maximum stall angle improvement reaches to 28.1%. Flow visualizations show that leading edge tubercles could induce the formation of counter-rotating streamwise vortices. The interaction between the streamwise vortices and corner separation is thought to be the primary flow mechanism generated by leading edge tubercles in an annular compressor cascade.

Due to the epistemic uncertainty, it is difficult for the experts to give precise parameter values in Risk Priority Number (RPN) evaluations. To overcome this drawback, a hybrid method is proposed by integrating the concepts of fuzzy set theory, weight analysis and similarity value measure of fuzzy numbers. The analysis process is divided into two phases to identify the hazard source. The first phase uses fuzzy Fault Tree Analysis (FTA) and Failure Mode and Effect Analysis (FMEA), then the main potential failure modes can be determined. The importance analysis of basic events can be calculated using fuzzy set theory and weight analysis. In the second phase, the multiple failure modes and component correlations are modelled using the Fuzzy Risk Priority Number (FRPN) evaluation and the Similarity Measure Value Method (SMVM). The proposed method has been applied to the risk analysis of a satellite propulsion system to show the effectiveness and applicability.

The process of rotor speed variation under tiltrotor cruise state has been studied, and the integrated variable speed control method of tiltrotor based on two-speed gearbox is proposed. Firstly, a nonlinear model predictive controller (NMPC) based on state variable model of the component-level model of the turboshaft engine is designed. Then based on the integrated engine model, the two-speed dual path tiltrotor driveline comprehensive simulation model was developed by utilizing gear kinematics theory, blade element analysis and the theory of classical mechanics. Finally, both a Parallel Shift Control (PSC) strategy and a Sequential Shift Control (SSC) strategy in tiltrotor cruise state were analyzed and compared with conventional PID controller. It is shown that the rotors’ speed can synchronously vary by 50 percent under the PSC strategy in tiltrotor cruise state. Meanwhile, disengaging the engine in turn by freewheel clutches can reduce the rotors’ speed from 190 rpm to 102.5 rpm along the specified path under the SSC strategy. The overshoot and droop amount of the power turbine speed can be reduced to less than 1.5 % with the steady error no more than 0.2 % through NMPC, which realizes the fast response control of the turboshaft engine.

Exergy efficiencies of the gas turbine become an important issue in recent years and by the way conducted studies regarding to this subject shows that the highest exergy destruction is observed in the combustor and afterburner modules. Therefore it is beneficial to perform analyses that are specific to the combustor exergy efficiency. This study includes the energy ηcc$\left( {{\eta _{cc}}} \right)$ and exergy efficiencies ηex$\left( {{\eta _{ex}}} \right)$ (thermo-efficiencies) of a tubular combustor for different inlet conditions. Both of the first law and second law efficiencies have been performed on the experimental data and efficiency trends are investigated for changing aerodynamic conditions. Combustor tests have been conducted in an atmospheric test rig and combustor air inlet temperatureT03$\left( {{T_{03}}} \right)$, air mass flow rate m˙a$\left( {{{\dot m}_a}} \right)$ and fuel mass flow rate m˙f$\left( {{{\dot m}_f}} \right)$ have been set for the pre-defined conditions. Moreover, exhaust gas emissions were measured by using a gas analyzer system. In the study, highest energy and exergy efficiencies have been obtained at minimum aerodynamic loading condition as 99.0 % and 70.2 % respectively. Moreover efficiencies have the lowest value as 92.7 % and 54.0 % at the maximum aerodynamic loading condition. To summarize, this study aims to show the energy and exergy trends by changing inlet conditions of a tubular combustor in the atmospheric test rig.

The acoustic and flow characteristics of a jet with elliptical throat is studied at different levels of nozzle expansion ratio. In this study, we have taken two types of CD nozzle configuration (circular and elliptical throat) and it is studied for various NPR ratios of 2, 3, 4 and 6. In addition, the acoustic characteristic of the jet flow is also measured for respective NPRs. Measurements of acoustic data are done using microphones placed at 30, 60 and 90 degrees to imprison the effects of screech tone. At NPR 2, 3 and 4, the jet with elliptical throat witnesses superior mixing and shorter core length compared to the circular throat. Its surprising to see both the configurations provides the identical oscillation at NPR 2, 3 and 4, however the efficiency of jet mixing is larger in elliptical throat jet. As the nozzle pressure ratio increased from 2 to 3 and 3 to 4, the potential core length of the jet reduces marginally about 5 to 10 % for every NPR until nozzle pressure ratio of 5. At NPR 2 and 3, the centerline pitot pressure profile shows, the decay of jet from the elliptical throat is healthier than a circular jet. At various levels of nozzle expansion, shock cell shows an appreciable change with an increase in NPR. Introduction of the elliptical throat on circular modifies the structure of shock cell which significantly changes the magnitude of screech tone due to the weakening of shock waves.

Numerical simulation was performed to investigate adiabatic film cooling effectiveness of cooling holes over thermal barrier coated superalloy substrate. Divergent, convergent-divergent and curved configuration of cooling holes were compared with the inclined cylindrical hole configuration. The coolant flow was strongly attached with the surface for 35º inclination. The film cooling effectiveness at different blowing ratios of 0.4, 0.8 and 1.2 was analysed. The study was carried out using realizable k-ϵ (RKE) model. The curved hole configuration provided enhanced cooling effectiveness even at 0.8 blowing ratio in comparison with other cases. The presence of curvature reduced the coolant velocity thereby preventing the detachment of jet from the surface and forming a very strong longitudinal film. The coolant jet starts detaching from the surface for blowing ratio higher than 1.2; the high momentum of the film cooling jet causes a lift off the surface. At 1.2 blowing ratio, a greater spread of coolant flow along the test surface was observed. Better film cooling effectiveness was evident at 0.8 and 1.2 blowing ratios. At 0.8, the enhancement in the overall film cooling effectiveness of divergent, convergent-divergent and curved hole configuration was about 14 %, 50 % and 59 %, respectively.

The theory of steady-state laminar jet spray flames is developed in the limit of small Stokes number. The spray is modeled using the sectional approach. A similarity solution is suggested, and it is shown that for typical operating conditions the leading order small Stokes number solution suffices for determining lift-off and blow-out features of the flames. The latter are demonstrated to be strongly dependent on spray properties, in contrast to the Schmidt number dependence only which was predicted by classical laminar jet gaseous flame theory. The strong influence of the ambient oxygen content and the liquid fuel’s evaporation coefficient on flame characteristics, blow-out and lift-off are established.