Investigations on the interaction between the front and aft purge flow and the downstream vane of 1.5-stage turbine

The present work reports the influence of the 1.5-stage turbine flow field by the front and aft rim seal flow. The interaction between the front and aft purge flow and the mainstream of a 1.5-stage turbine was numerically simulated, and the influence of the front and aft purge flow on the downstream vane was analyzed separately. The results show that the front purge flow is distributed at the higher radius of second vane inlet, which changes the position of the blade hub secondary flows, and the aft purge flow is distributed at the low radius. The purge flow at different locations in the aft cavity exit forms shear induced vortex, pressure and suction side legs of the egress, which converges with the suction and pressure side legs of the horse vortex to form vane hub passage vortex. The increased purge flow rate in both the front and aft cavities significantly increases the sealing effectiveness of the rim seal, but also causes a reduction in turbine efficiency. The combined effect of the front and aft purge flow reduces the turbine efficiency of the end-wall structure by 0.3619, 0.9062, 1.5004, 2.0188 and 2.509% at IR = 0, IR = 0.5%, IR = 0.9%, IR = 1.3% and IR = 1.7%.

Flow quality improvement of the wind tunnel testing for a highly-loaded compressor cascade at high incidence

To obtain reliable and accurate experimental data in cascade testing, the influencing factors and the improving method of the flow quality of a highly-loaded compressor cascade under high incidence were investigated through a series of numerical simulations and experiments. The numerical method was validated by experimental data and agreed well at both incidence angles of 0° and 6°. Under the original upper end wall, both experimental and numerical results indicated an unsatisfactory flow quality of the cascade with an obvious nonuniformity of inlet Mach number, and the incidence of the central blade is 3.6° larger than the theoretical value. Using a small curved upper wall can reduce the severe flow separation on the upper wall and achieve a maximum improvement in flow quality under the critical installation angle, where the incidence deviation of the central blade was reduced to 2.1°. Using the combination of adjustable tailboards and a small curved upper end wall can further improve the cascade flow quality. Under the optimal angle of the tailboards, both the inflow uniformity and the outflow periodicity of the three middle blade passages the test requirements, and the incidence deviation of the central blade is reduced to 0.2°.

Cooling holes with different structures effects on coolant cross flow and heat transfer at the outlet of the combustion chamber

The major effects of cylindrical and row trenched cooling holes with angles of alpha=30, beta=0, alpha=40, beta=0 and alpha=50, beta=0 at BR=3.18 on the effectiveness of film cooling near the combustor end wall surface is an important subject to study in detail. In the current study, researchers used a FLUENT package 16/11 to simulate a 3-D model of a Pratt and Whitney gas turbine engine. In this research, RNG turbulence model K-ε model was used to analyze the flow behavior on the passage ways of internal cooling. In the combustor simulator, the dilution jets and cooling flow staggered in the streamwise direction and aligned in the spanwise direction as well. In comparison with the baseline case of cooling holes, the application of trenched hole near the end wall surface increased the effectiveness of film cooling up to 100% for different trench cases.

Numerical Investigations on Effect of Inflow Parameters on Development of Secondary Flow Field for Linear LP Turbine Cascade

End wall flows contribute the most crucial role in loss generation for axial flow turbine and compressor blades. These losses lead to modify the blade loading and overall performance in terms of stable operating range. Present study aimed to determine the end wall flow streams in a low speed low pressure linear turbine cascade vane using numerical approach. The study includes two sections. The first section includes an attempt to understand different secondary flow streams available at end wall. Location of generation of horseshoe vortex streams and subsequent vortex patterns are identified in the section. The selection of suitable turbulence model among SST (Shear Stress Transport) k–ω and SST γ–θ to identify end wall flow streams is studied in prior in the section. The steady state numerical study is performed using Reynolds Averaged Navier-Stoke’s Equations closed by SST γ–θ turbulence model. The computational results are validated with experimental results available in the literature and are found to be in good agreement. The study is extended for different inflow conditions in later section. The second section includes effect of flow incidence and turbulence intensity on the end wall secondary flow field. Inflow incidences considered for the study are −20°, −10°, 0° (design incidence), +10° and +20°. The inlet turbulence intensities are varied by 1% and 10% for each case. The results revealed different secondary flow patterns at an end wall and found the change in behavior with an inflow conditions. SST γ–θ turbulence model with lower turbulence intensity is more suitable to identify such flow behavior.

Optimization study on the influence of little blades’ spatial position on a compressor cascade performance

To reveal the importance of little blades’ spatial position to improve the cascade performance at different condition, the pitchwise and axial direction of the little blades on the end-wall are adopted as the optimization variables to complete a double-objective optimization. Meanwhile, the three-dimensional flow field characteristics of the cascade with and without little blades are analyzed comparatively. The study found that as the optimal solutions are obtained at the three bigger incidences (3°, 5°, and 7°), the optimal position is always close to the leading edge of blade and far away from the blade suction surface, and the more intuitive design suggestions are given in this article. Moreover, at the near design conditions (−1°, 0°, and 1°), little blades increase the total pressure loss and reduce the static pressure, which are considered unsuitable for improving the cascade performance. If the stable operation range are the main performance indicators, the optimization of the little blades’ spatial position should be completed at the near stall condition (7° incidence). If the conditions with mid-range incidences (2°< i <5°) are the main performance index, the parameter optimization of little blades should be achieved at 5°. Based on the further flow field analysis of the optimization results obtained at 3°, 5°, and 7° incidences (named Opt_Act3, Opt_Act5, and Opt_Act7), the induced vortices resist the effect of axial reverse pressure gradient and pass through the blade passage, which is the main reason for the total pressure loss reduction. Appropriate spatial position of little blades not only strengthens the capability to prevent the low-energy fluids accumulating in the corner region near the end-wall, but exhibits sufficient advantage to weaken the boundary layer.

Large-Eddy Simulation of Cavitating Tip Leakage Vortex Structures and Dynamics around a NACA0009 Hydrofoil

The tip leakage vortex (TLV) has aroused great concern for turbomachine performance, stability and noise generation as well as cavitation erosion. To better understand structures and dynamics of the TLV, large-eddy simulation (LES) is coupled with a homogeneous cavitation model to simulate the cavitation flow around a NACA0009 hydrofoil with a given clearance. The numerical results are validated by comparisons with experimental measurements. The results demonstrate that the present LES can well predict the mean behavior of the TLV. By visualizing the mean streamlines and mean streamwise vorticity, it shows that the TLV dominates the end-wall vortex structures, and that the generation and evolution of the other vortices are found to be closely related to the development of the TLV. In addition, as the TLV moves downstream, it undergoes an interesting progression, i.e., the vortex core radius keeps increasing and the axial velocity of vortex center experiences a conversion from jet-like profile to wake-like profile.