Row Of Film Cooling Holes Research Articles

An experimental study of the effects of different transverse trenches on deposition on a turbine vane with film-cooling at high temperature

Turbine vanes may be subjected to particle deposition, which usually has negative effect on the aerodynamical and heat transferring performances of vanes. If a vane has film-cooling configuration, particle deposition may also block film-cooling holes. Therefore, it is of interest to reduce the harm of particle deposition on vanes. In this paper, an experiment is designed to investigate the effects of different transverse trenches on the deposition on a turbine vane. The mainstream temperature is high and comparable to that of typical turbines and the particles are sands. These transverse trenches are arranged along the rows of film-cooling holes. It is found from the tests that the transverse trenches could reduce total deposition mass and make the deposition distribution on the pressure surface more uniform. Based on the deposition on the suction surface, the deposition reduction effectiveness of the trenches is also analyzed and corrected. In general, deeper trenches could reduce more deposition near the film-cooling holes. The temperature reduction on the pressure surface due to the transverse trenches is also detected and deeper trenches results in lower temperature. The results in this paper are similar to those by the tests at low temperatures. The results may be helpful for the design to reduce the harm of sand deposition on vanes.

Multi-Objective Optimization of a Row of Film Cooling Holes Using an Evolutionary Algorithm and Surrogate Modeling

Multi-objective shape optimization of a row of laidback fan-shaped film cooling holes has been performed using a hybrid multi-objective evolutionary approach in order to achieve an acceptable compromise between two competing objectives: the enhancement of film cooling effectiveness and the reduction of aerodynamic loss. In order to perform comprehensive optimization of a film cooling hole shape, the injection angle of the hole, lateral expansion angle of the diffuser, forward expansion angle of the hole, and pitch-to-hole diameter ratio are chosen as design variables. Forty experimental designs within the design spaces are selected using the Latin hypercube sampling method. The response surface approximation method is used to construct the surrogate using objective function values calculated at the experimental points using Reynolds-averaged Navier-Stokes analysis. The shear stress transport turbulence model is used as a turbulence closure. The optimization results are processed using the Pareto-optimal method. The Pareto-optimal solutions are obtained using a combination of a evolutionary algorithm and a local search method. The optimum designs are grouped using the k-means clustering technique, and the three optimal points selected in the Pareto-optimal solutions are evaluated by numerical analysis. The optimum designs give enhanced objective function values compared to the experimental designs.

Simulations of Multiphase Particle Deposition on Endwall Film-Cooling Holes in Transverse Trenches

Integrated gasification combined cycle (IGCC) power plants allow for increased efficiency and reduced emissions as compared to pulverized coal plants. A concern with IGCCs is that impurities in the fuel from the gasification of coal can deposit on turbine components reducing the performance of sophisticated film-cooling geometries. Studies have shown that recessing a row of film-cooling holes in a transverse trench can improve cooling performance; however, the question remains as to whether or not these improvements exist in severe environments such as when particle deposition occurs. Dynamic simulations of deposition were completed using wax injection in a large-scale vane cascade with endwall film cooling. Endwall cooling effectiveness was quantified in two specific endwall locations using trenches with depths of 0.4D, 0.8D, and 1.2D, where D is the diameter of a film-cooling hole. The effects of trench depth, momentum flux ratio, and particle phase on adiabatic effectiveness were quantified using infrared thermography. Results showed that the 0.8D trench outperformed other geometries with and without deposition on the surface. Deposition of particles reduced the cooling effectiveness by as much as 15% at I = 0.23 with the trenched holes as compared to 30% for holes that were not placed in a transverse trench.

Film-Cooling Flowfields With Trenched Holes on an Endwall

The leading edge region along the endwall of a stator vane experiences high heat transfer rates resulting from the formation of horseshoe vortices. Typical gas turbine endwall designs include a leakage slot at the combustor-turbine interface as well as film-cooling holes. Past studies have documented the formation of a horseshoe vortex at the leading edge of a vane, but few studies have documented the flowfield in the presence of an interface slot and film-cooling jets. In this paper, a series of flowfield measurements is evaluated at the leading edge with configurations including a baseline with neither film-cooling holes nor an upstream slot, a row of film-cooling holes and an interface slot, and a row of film-cooling holes in a trench and an interface slot. The results indicated the formation of a second vortex present for the case with film-cooling holes and a slot relative to the baseline study. In addition, turbulence intensity levels as high as 50% were measured at the leading edge with film-cooling holes and a slot compared with the 30% measured for the baseline study. A trench was shown to provide improved overall cooling relative to the no trench configuration as more of the coolant stayed attached to the endwall surface with the trench.

Increasing Adiabatic Film-Cooling Effectiveness by Using an Upstream Ramp

A new design concept is presented to increase the adiabatic effectiveness of film cooling from a row of film-cooling holes. Instead of shaping the geometry of each hole; placing tabs, struts, or vortex generators in each hole; or creating a trench about a row of holes, this study proposes a geometry modification upstream of the holes to modify the approaching boundary-layer flow and its interaction with the film-cooling jets. Computations, based on the ensemble-averaged Navier–Stokes equations closed by the realizable k‐ε turbulence model, were used to examine the usefulness of making the surface just upstream of a row of film-cooling holes into a ramp with a backward-facing step. The effects of the following parameters were investigated: angle of the ramp (8.5deg, 10deg, 14deg), distance between the backward-facing step and the row of film-cooling holes (0.5D,D), blowing ratio (0.36, 0.49, 0.56, 0.98), and “sharpness” of the ramp at the corners. Results obtained show that an upstream ramp with a backward-facing step can greatly increase surface adiabatic effectiveness. The laterally averaged adiabatic effectiveness with a ramp can be two or more times higher than without the ramp by increasing upstream and lateral spreading of the coolant.

Film Cooling Effectiveness on the Leading Edge Region of a Rotating Turbine Blade With Two Rows of Film Cooling Holes Using Pressure Sensitive Paint

Detailed film cooling effectiveness distributions are measured on the leading edge of a rotating gas turbine blade with two rows (pressure-side row and suction-side row from the stagnation line) of holes aligned to the radial axis using the pressure sensitive paint (PSP) technique. Film cooling effectiveness distributions are obtained by comparing the difference of the measured oxygen concentration distributions with air and nitrogen as film cooling gas respectively and by applying the mass transfer analogy. Measurements are conducted on the first-stage rotor blade of a three-stage axial turbine at 2400rpm (positive off-design), 2550rpm (design), and 3000rpm (negative off-design), respectively. The effect of three blowing ratios is also studied. The blade Reynolds number based on the axial chord length and the exit velocity is 200,000 and the total to exit pressure ratio was 1.12 for the first-stage rotor blade. The corresponding rotor blade inlet and outlet Mach numbers are 0.1 and 0.3, respectively. The film cooling effectiveness distributions are presented along with discussions on the influence of rotational speed (off design incidence angle), blowing ratio, and upstream nozzle wakes around the leading edge region. Results show that rotation has a significant impact on the leading edge film cooling distributions with the average film cooling effectiveness in the leading edge region decreasing with an increase in the rotational speed (negative incidence angle).

Film Cooling From a Single Row of Holes Oriented in Spanwise/Normal Planes

Experimental results are presented that describe the development and structure of flow downstream of a single row of film-cooling holes inclined at 30 deg from the test surface in spanwise/normal planes. With this configuration, holes are spaced 6d apart in the spanwise direction in a single row. Results are presented for a ratio of injectant density to free-stream density near 1.0, and injection blowing ratios from 0.5 to 1.5. Compared to results measured downstream of simple angle (streamwise) oriented holes, spanwise-averaged adiabatic effectiveness values are significantly higher for the same spanwise hole spacing, normalized streamwise location x/d, and blowing ratio m when m = 1.0 and 1.5 for x/d < 80. The injectant from the spanwise/normal holes is also less likely to lift off of the test surface than injectant from simple angle holes. This is because lateral components of momentum keep higher concentrations of injectant in closer proximity to the surface. As a result, local adiabatic effectiveness values show significantly greater spanwise variations and higher local maxima at locations immediately downstream of the holes. Spanwise-averaged iso-energetic Stanton number ratios range between 1.07 and 1.26, which are significantly higher than values measured downstream of two other injection configurations (one of which is simple angle, streamwise holes) when compared at the same x/d and blowing ratio.

Film Cooling from Two Staggered Rows of Compound Angle Holes at High Blowing Ratios

Experimental results are presented which describe the development and structure of flow downstream of two staggered rows of film‐cooling holes with compound angle orientations at high blowing ratios. These film cooling configurations are important because they are frequently employed on the first stage of rotating blades of operating gas turbine engines. With this configuration, holes are spaced 3d apart in the spanwise direction, with inclination angles of 24 degrees, and angles of orientation of 50.5 degrees. Blowing ratios range from 0.5 to 4.0 and the ratio of injectant to freestream density is near 1.0. Results show that spanwise averaged adiabatic effectiveness, spanwise‐averaged iso‐energetic Stanton number ratios, surveys of streamwise mean velocity, and surveys of injectant distributions change by important amounts as the blowing ratio increases. This is due to injectant lift‐off from the test surface just downstream of the holes which becomes more pronounced as blowing ratio increases.

Measured Coolant Distributions Downstream of Single and Double Rows of Film Cooling Holes

A mass-transfer technique has been used to investigate experimentally the distribution of coolant from two rows of holes with independently varied blowing rates. Both staggered and in-line configurations were investigated for two injection angles and a range of row spacings. Detailed concentration distributions measured at and above the surface are presented and a possible mechanism to account for the large differences in behavior between staggered and in-line configurations is discussed.

Discussion: “Measured Coolant Distributions Downstream of Single and Double Rows of Film Cooling Holes” (Afejuku, W. O., Hay, N., and Lampard, D., 1983, ASME J. Eng. Power, 105, pp. 172–177)

Discussion: “Measured Coolant Distributions Downstream of Single and Double Rows of Film Cooling Holes” (Afejuku, W. O., Hay, N., and Lampard, D., 1983, ASME J. Eng. Power, 105, pp. 172–177)

Closure to “Discussion of ‘Measured Coolant Distributions Downstream of Single and Double Rows of Film Cooling Holes’” (1983, ASME J. Eng. Power, 105, p. 177)

Closure to “Discussion of ‘Measured Coolant Distributions Downstream of Single and Double Rows of Film Cooling Holes’” (1983, ASME J. Eng. Power, 105, p. 177)