Comparison of RANS and DES Modeling Against Measurements of Leading Edge Film Cooling on a First-Stage Vane

The performance of a showerhead arrangement of film cooling in the leading edge region of a first stage nozzle guide vane was experimentally and numerically evaluated. A six-vane linear cascade was tested at an isentropic exit Mach number of Ma2s = 0.42, with a high inlet turbulence intensity level of 9%. The showerhead cooling scheme consists of four staggered rows of cylindrical holes evenly distributed around the stagnation line, angled at 45° towards the tip. The blowing ratios tested are BR = 2.0, 3.0 and 4.0. Adiabatic film cooling effectiveness distributions on the vane surface around the leading edge region were measured by means of Thermochromic Liquid Crystals technique. Since the experimental contours of adiabatic effectiveness showed that there is no periodicity across the span, the CFD calculations were conducted by simulating the whole vane. Within the RANS framework, the very widely used Realizable k-ε (Rke) and the Shear Stress Transport k-ω (SST) turbulence models were chosen for simulating the effect of the BR on the surface distribution of adiabatic effectiveness. The turbulence model which provided the most accurate steady prediction, i.e. Rke, was selected for running Detached Eddy Simulation at the intermediate value of BR = 3. Fluctuations of the local temperature were computed by DES, due to the vortex structures within the shear layers between the main flow and the coolant jets. Moreover, mixing was enhanced both in the wall-normal and spanwise direction, compared to RANS modeling. DES roughly halved the prediction error of laterally averaged film cooling effectiveness on the suction side of the leading edge. However, neither DES nor RANS provided the expected decay of effectiveness progressing downstream along the pressure side, with 15% overestimation of ηav at s/C =0.2.

Turbine Blade Platform Film Cooling With Simulated Swirl Purge Flow and Slashface Leakage Conditions

The combined effects of inlet purge flow and the slashface leakage flow on the film cooling effectiveness of a turbine blade platform were studied using the pressure sensitive paint (PSP) technique. Detailed film cooling effectiveness distributions on the endwall were obtained and analyzed. The inlet purge flow was generated by a row of equally-spaced cylindrical injection holes inside a single-tooth generic stator-rotor seal. In addition to the traditional 90 degree (radial outward) injection for the inlet purge flow, injection at a 45 degree angle was adopted to create a circumferential/azimuthal velocity component toward the suction side of the blades, which created a swirl ratio (SR) of 0.6. Discrete cylindrical film cooling holes were arranged to achieve an improved coverage on the endwall. Backward injection was attempted by placing backward injection holes near the pressure side leading edge portion. Slashface leakage flow was simulated by equally-spaced cylindrical injection holes inside a slot. Experiments were done in a five-blade linear cascade with an average turbulence intensity of 10.5%. The inlet and exit Mach numbers were 0.26 and 0.43, respectively. The inlet and exit mainstream Reynolds numbers based on the axial chord length of the blade were 475,000 and 720,000, respectively. The coolant-to-mainstream mass flow ratios (MFR) were varied from 0.5%, 0.75%, to 1% for the inlet purge flow. For the endwall film cooling holes and slashface leakage flow, blowing ratios (M) of 0.5, 1.0, and 1.5 were examined. Coolant-to-mainstream density ratios (DR) that range from 1.0 (close to low temperature experiments) to 1.5 (intermediate DR) and 2.0 (close to engine conditions) were also examined. The results provide the gas turbine engine designers a better insight into improved film cooling hole configurations as well as various parametric effects on endwall film cooling when the inlet (swirl) purge flow and slashface leakage flow were incorporated.

Film Cooling Investigation of a Slot-Based Diffusion Hole

This paper presents a new configuration of discrete film hole, i.e., the slot-based diffusion hole. Retaining the similar diffusion features to a traditional diffusion hole, the slot-based diffusion hole transforms the cross section of circle for the traditional diffusion hole to a flattened rectangle with respect to the equivalent cross-sectional area. Consequently, the exit width of the new hole is effectively enlarged. To verify the film cooling effectiveness, a low speed flat plate experimental facility incorporated with Pressure Sensitive Paint (PSP) measurement technique was employed to obtain the adiabatic film cooling effectiveness. The experiments were performed with hole pitch to diameter ratio p/D=6 and density ratio DR=1.38. The blowing ratio was varied from M=0.5 to M=2.5. A fan-shaped hole and two slot-based diffusion holes were tested and compared. Three-dimensional numerical simulation was employed to analyze the flow field in detail. The experimental results showed that the area averaged effectiveness of two slot-based diffusion holes is significantly higher than that of the fan-shaped hole when the blowing ratio exceeds 1.0. The slot-based diffusion hole demonstrates the great advantage over the fan-shaped hole at hole exit and maintains this to far downstream. The numerical results showed that the ends shape of the flattened rectangular cross section has large influences on film distribution patterns and downstream vortex structures. The semi-circle and straight line ends shapes lead to a bi-peak and a single-peak effectiveness pattern, respectively. The optimal ends shape can regulate the vortex structures and improve the film cooling effectiveness further.

Investigation of Steady and Unsteady Film-Cooling Using Immersed Mesh Blocks With New Conservative Interface Scheme

Advanced development of high pressure turbines requires accurate predictions of film cooling flow. However, the length scales inherent to film cooling flows produce a large disparity compared to those of the mainstream flow field. To address this computational modelling challenge, an immersed mesh block (IMB) methodology has been initiated (Lad and He, 2011) which uses the much refined mesh around cooling holes to be mapped into the base mesh which tends to be much coarser for blade aerodynamic designs. Both the base mesh flow field and that of the IMB are solved simultaneously. By employing a simultaneous two-way coupling, the flow physics in and around cooling holes is able to interact with the mainstream, hence the length scales of both types of flow, as well as their interactions, are appropriately captured and resolved. The present work is aimed to develop a new numerical scheme for enforcing conservation at the interfacing boundary between the immersed cooling block and the base mesh, as well as, carry out a systematic validation and application of the IMB method for some well-established film-cooling experimental configurations (cylindrical and fan-shaped holes) at different blowing ratios. During the validation process, the mesh counts/resolution requirements for consistent cooling predictions for design analyses are established. The method is then applied to a transonic HPT stage. Its steady and unsteady flows are investigated. The results consistently demonstrate the effectiveness and applicability of the conservative IMB method, and indicate, for the first time, some interesting and relevant unsteady film-cooling behaviour.

Combined Effects of Freestream Pressure Gradient and Density Ratio on the Film Cooling Effectiveness of Round and Shaped Holes on a Flat Plate

The combined effects of a favorable, mainstream pressure gradient and coolant-to-mainstream density ratio have been investigated. Detailed film cooling effectiveness distributions have been obtained on a flat plate with either cylindrical (θ = 30°) or laidback, fan-shaped holes (θ = 30°, β = γ = 10°) using the pressure sensitive paint (PSP) technique. In a low speed wind tunnel, both non-accelerating and accelerating flows were considered while the density ratio varied from 1–4. In addition, the effect of blowing ratio was considered, with this ratio varying from 0.5 to 1.5. The film produced by the shaped hole outperformed the round hole under the presence of a favorable pressure gradient for all blowing and density ratios. At the lowest blowing ratio, in the absence of freestream acceleration, the round holes outperformed the shaped holes. However, as the blowing ratio increases, the shaped holes prevent lift-off of the coolant and offer enhanced protection. The effectiveness afforded by both the cylindrical and shaped holes, with and without freestream acceleration, increased with density ratio.

Accuracy of Superposition Predictions of Film Cooling Effectiveness on a Flat Plate With Double Rows of Holes

Multi-row film cooling is widely used on both suction side and pressure side of turbine vane, and the coolant behavior is considerable for engine design. Main work of this paper is to find out the accuracy of superposition predictions. Experiments were conducted on flat plates with double rows of cooling holes. The method of stable infrared measurement technique was used to measure surface temperature. Four factors, including hole shape, hole arrangement, row-to-row spacing and blowing ratio were simulated. Numerical simulation using commercial software ANSYS Fluent was also performed to observe the flow structure and film cooling mechanisms between each row. Result showed that the blowing ratio within the range of 0.5 to 2 has an obvious influence on the accuracy of superposition prediction. At low blowing ratio, results obtained by superposition method agreed well with the experimental data while the increase of blowing ratio caused a decrease in accuracy. Another significant factor is hole arrangement, results obtained by superposition prediction was nearly the same as experimental values on staggered arrangement plates while it was much higher on in-line arrangement plates. For different hole shapes, the accuracy of superposition prediction on converging-expanding holes was better than cylinder holes and compound angle holes. For both two hole spacing in this paper, prediction results show good agreement with the experiment results.

Novel Designs of Turbine Blades for Additive Manufacturing

Improving engine performance requires creating new materials and improving design and manufacturing. Additive Manufacturing (AM) is advancing rapidly and allows us to produce details of complex shapes that cannot be produced by traditional methods. The goal of this study was to demonstrate the possibility of using AM for the manufacture of turbine blades with a complex geometry, including those with advanced cooling systems, which cannot be manufactured by conventional methods. This paper presents the results of the design and calculations of high-pressure turbine (HPT) cooled blades, as well as a low-pressure turbine (LPT) uncooled blade that was designed using topology optimization (TO). Several blades were manufactured using AM. 3D tomography test results for those blades confirm the possibility of AM application in production of blades with complex geometry.

Turbine Blade Life Prediction Using Fluid-Thermal-Structural Interaction Simulation

In this study a fluid-thermal-structural simulation is performed to investigate cyclic stress-strain behavior and fatigue life of a gas turbine blade. The Hysteresis loop characteristic of the blade is presented under the coupled influence of various loading conditions, aerodynamic, thermal and static centrifugal loadings. Based on the predicted loading behavior, an energy-based method was used to analyze the fatigue and cumulative damage properties of the blade. The predicted hysteresis loop under aerodynamic load was purely of elastic nature and as such tends to assume a Masing behavior at the stable condition. The case for a combined thermal and aeromechanical loading showed a non-Masing behavior, but rather a temperature-dependent material softening behavior. The fatigue life was also estimated based on the energy density approach using the predicted thermal-structural predicted cyclic loops.

Dependence of Film Cooling Effectiveness on 3D Printed Cooling Holes

Film Cooling Effectiveness is closely dependent on the geometry of the hole emitting the cooling film. These holes are sometimes quite expensive to machine by traditional methods so 3D printed test pieces have the potential to greatly reduce the cost of film cooling experiments. What is unknown is the degree to which parameters like layer resolution and the choice among 3D printing technologies influence the results of a film cooling test. A new flat-plate film cooling facility employing oxygen sensitive paint (OSP) verified by gas sampling and the mass transfer analogy and measurements both by gas sampling and OSP is verified by comparing measurements by both gas sampling and OSP. The same facility is then used to characterize the film cooling effectiveness of a diffuser shaped film cooling hole geometry. These diffuser holes are then produced by a variety of additive manufacturing technologies with different build layer thicknesses. Technologies used include Fused Deposition Modeling (FDM), Stereo Lithography Apparatus (SLA) and PolyJet with build layer thicknesses ranging from 0.001D (25 μm) to 0.12D (300 μm). These are compared with an aluminum coupon manufactured by traditional machining methods. The objective is to determine if cheaper manufacturing techniques afford usable and reliable results. Tests are carried out at mainstream flow Mach number of 0.30 and blowing ratios (BRs) from 1.0 to 3.5. The coolant gas used is CO2 yielding a density ratio of 1.5. Surface quality is characterized by an Optical Microscope that measures surface roughness. Test coupons with rougher surface topology generally showed delayed blow off and higher film cooling effectiveness at high blowing ratios compared to the geometries with lower measured surface roughness. At the present scale, none of the additively manufactured parts consistently matched the traditionally machined part, indicating that caution should be exercised in employing additively manufactured test pieces in film cooling work.