Numerical Investigation of Adiabatic Film Cooling Effectiveness over a Flat Plate Model with Cylindrical Holes

Film cooling is one of the cooling techniques used in gas turbines to protect the blades from high temperature. The efficiency of gas turbine can be increased by increasing the inlet gas temperature. The present study aims at numerical investigation of adiabatic film cooling effectiveness over the cylindrical hole exit flat plate test model. The hole inclination angle of 20° with stream wise direction is considered. The test model has 35 film cooling holes arranged in two rows in a staggered configuration with the coolant hole length to diameter ratio of 5.4 and pitch to diameter ratio of 4. During the experimental analysis, the adiabatic film cooling effectiveness is found at five different blowing ratios in the range of 0.5 to 2.5 with the coolant to mainstream density ratio at 1.6. The laterally averaged film cooling effectiveness is calculated along the stream wise direction at these blowing ratios. The realizable k-epsilon turbulence model with enhanced wall function is used to solve the flow field. The CFD obtained results are validated with the experimental results at a blowing ratio of 1.0. Further, the CFD analysis is done for other blowing ratios in the range of 0.5 to 4.0 at density ratios of 1.6, 1.8 and 2.0. From the CFD results, the laterally averaged film cooling effectiveness is found to be increasing with the increase in blowing ratio up to 1.5 immediately downstream of the coolant holes. For the blowing ratios of 2.0 to 4, the adiabatic film cooling effectiveness is less immediately downstream of coolant holes up to x/d=15 and then increases with increase in the blowing ratios considered

Experimental investigation of adiabatic film cooling effectiveness over a circular, fan and laidback fan shaped hole flat plate test models

The experimental investigation of adiabatic film cooling effectiveness is carried out on a flat plates with 4:1 scaled up hole geometries, similar to that of typical turbine nozzle guide vane film cooling holes. Under this study, three flat plate models are considered with the two rows of holes having circular, fan and laidback fan shapes arranged in a staggered manner. These flat plate models are generated using solid works design software and fabricated using low thermal conductivity nylon based material using RPT technique. The mass flow results indicated the average nominal coefficient of discharge for the cooling holes as 0.71, for all these three models based on the inlet hole area and length of the holes. The laterally averaged adiabatic film cooling effectiveness is found along the stream wise direction at a density ratio of 1.62 by varying the blowing ratio in the range of 0.5 to 2.5. The surface temperatures of the test models are captured using the infrared camera, to evaluate the film cooling effectiveness. The experimentally evaluated results shows that, there is no increase in cooling effectiveness for the blowing ratio of 2.0 to 2.5 in the stream wise direction up to the X/d of 25 and there is a marginal increase above the X/d of 25 in the cases of these type of two row circular and Fan shaped hole models. Where as in the Laidback fan shaped hole model, the increase in cooling effectiveness is found significant up to the blowing ratio of 2.5 in the considered range. From the comparative results of adiabatic film cooling effectiveness of these three models, the laidback fan shaped hole model shows the higher film cooling effectiveness than the circular and fan shaped holes model at all the considered blowing ratios

Parametric studies on gas turbine labyrinth seal for the secondary air flow optimization at static and rotating conditions

Various studies have been carried out related to the labyrinth seals and reported in the open literature using the different seal arrangements at the stator-rotor seal cavity region. In the present study, numerical analysis has been carried out for the static and rotational effects of labyrinth seals at various flow and geometrical, parametric conditions for the optimized leak flow using straight and steeped seal configurations. And, an experimental data has been generated for the straight through seals, and the numerical data of the same case is validated with the experimental data. The k-omega SST turbulence model is considered with 5% turbulence intensity for the CFD analysis. At a particular seal clearance, as the number of teeth increases the leakage flow is found to be decreased. The leak flow is found to be lower with the stepped labyrinth seals in comparison to the straight through seals. The leak flow amount is found to be lower at a rotational condition in comparison to the stationary condition. From the overall results, it is observed that the stepped seal with a lower clearance at a compressor bleed air temperature and rotational conditions have shown better performance with the lower leak air mass flow

Experimental investigation of overall cooling effectiveness on combustion chamber liner with and without impingement holes

The gas turbine combustor liner which is subjected to high temperature requires efficient cooling. In earlier days concept of slot film cooling is utilized in the combustion liners and in modern combustors multiple row film cooling (effusion cooling) is mainly used. This study aims at the experimental investigation of overall film cooling effectiveness of an effusion plate with and without impingement holes at the backside. The experiments are done at different blowing ratios and the surface temperature measurements are taken using infrared thermography. The effusion and impingement holes are arranged in staggered manner on two parallel plates and each effusion hole is surrounded by four impingement holes. Effusion holes are drilled at an angle of 27° and the impingement plate is kept at a distance of 6D away from the effusion plate. The experiments are done on the effusion plate with and without impingement plate at the backside. The results show, increase in cooling effectiveness as the blowing ratio increases. The comparative results shows that at a particular blowing ratio the overall cooling effectiveness is higher for effusion plate with impingement holes at the backside due to the higher convective heat transfer coefficients produced by the impinging jets at the cold side of the effusion plate