This work presents a numerical investigation of the combined effects of thermal barrier coating (TBC) with mainstream turbulence intensity (Tu) on a modified vane of the real film-cooled nozzle guide vane (NGV) reported by Timko (NASA CR-168289). Using a 3D conjugate heat transfer (CHT) analysis, the NGVs with and without TBC are simulated at three Tus (Tu = 3.3%, 10% and 20%). The overall cooling effectiveness, TBC effectiveness and heat transfer coefficient are analyzed and discussed. The results indicate the following three interesting phenomena: (1) TBC on the pressure side (PS) is more effective than that on the suction side (SS) due to a fewer number of film holes on the SS; (2) for all three Tus, the variation trends of the overall cooling effectiveness are similar, and TBC plays the positive and negative roles in heat flux at the same time, and significantly increases the overall cooling effectiveness in regions cooled ineffectively by cooling air; (3) when Tu increases, the TBC effect is more significant, for example, at the highest Tu (Tu = 20%) the overall cooling effectiveness can increase as much as 24% in the film cooling ineffective regions, but near the trailing edge (TE) and the exits and downstream of film holes on the SS, this phenomenon is slight.

The high-speed-train pantograph is a complex structure that consists of different rod-shaped and rectangular surfaces. Flow phenomena around the pantograph are complicated and can cause a large proportion of aerodynamic noise, which is one of the main aerodynamic noise sources of a high-speed train. Therefore, better understanding of aerodynamic noise characteristics is needed. In this study, the large eddy simulation (LES) coupled with the acoustic finite element method (FEM) is applied to analyze aerodynamic noise characteristics of a high-speed train with a pantograph installed on different configurations of the roof base, i.e. flush and sunken surfaces. Numerical results are presented in terms of acoustic pressure spectra and distributions of aerodynamic noise in near-field and far-field regions under up- and down-pantograph as well as flushed and sunken pantograph base conditions. The results show that the pantograph with the sunken base configuration provides better aerodynamic noise performances when compared to that with the flush base configuration. The noise induced by the down-pantograph is higher than that by the up-pantograph under the same condition under the pantograph shape and opening direction selected in this paper. The results also indicate that, in general, the directivity of the noise induced by the down-pantograph with sunken base configuration is slighter than that with the flush configuration. However, for the up-pantograph, the directivity is close to each other in Y-Z or X-Z plane whether it is under flush or sunken roof base condition. However, the sunken installation is still conducive to the noise environment on both sides of the track.

Abstract:The aim of this paper is to numerically investigate cooling performances of a non-film-cooled turbine vane coated with a thermal barrier coating (TBC) at two turbulence intensities (Tu = 8.3% and 16.6%). Computational fluid dynamics (CFD) with conjugate heat transfer (CHT) analysis is used to predict the surface heat transfer coefficient, overall and TBC effectiveness, as well as internal and average temperatures under a condition of a NASA report provided by Hylton et al. [NASA CR-168015]. The following interesting phenomena are observed: (1) At each Tu, the TBC slightly dampens the heat transfer coefficient in general, and results in the quantitative increment of overall cooling effectiveness about 16-20%, but about 8% at the trailing edge (TE). (2) The protective ability of the TBC increases with Tu in many regions, that is, the leading edge (LE) and its neighborhoods on the suction side (SS), as well as the region from the LE to the front of the TE on the pressure side (PS), because the TBC causes the lower enhancement of the heat transfer coefficient in general at the higher Tu. (3) Considering the internal and average temperatures of the vane coated with two different TBCs, although the vane with the lower thermal conductivity protects more effectively, its role in the TE region reduces more significantly. (4) For both TBCs, the increment of Tu has a relatively small effect on the reduction of the average temperature of the vane.

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Since the theoretical aeroelasticity for flapping-wing aerodynamics was introduced in the 1920s, the effects of flexibility on aeroelasticity have been paid more attention to aerodynamic design. In recent years, the trait of the wing flexibility is applied for small-scale wings of biomimetic flyers including micro air vehicles and mini unmanned aerial vehicles. Until now, the aerodynamic performance and great agility of these flyers, which are beneficially used for military missions and other civilian applications, have been improved through surrogate flapping wings with the favorable effects of the flexibility. As per the aeroelasticity principle for the forward flying, the chordwise flexibility of an elastic flapping wing can generate thrust and lift redistributions, whereas the spanwise flexibility can result in variations of the angle of attack and the shift of phase along the wingspan direction. Consequently, all vortices generated by the flapping wing i.e. (1) leading-edge vortices, (2) tip vortices, and (3) trailing-edge vortices are blended supportively, thereby improving the aerodynamic performance and agility. Hence, the growth of research and development of the aerodynamic performance and agility for these flyers under the influence of flexible wings increases through experimental and computational studies dynamically and rapidly. This review aims to highlight the important role of the flexibility in the recent progress in wing aerodynamics of these flyers through several wing models done by famous groups of experts in this field. In addition, this review includes the acoustics of the wings under the flexibility effects which is considered as a new key for better flyer design and improvement. A comprehensive understanding of the integrated aerodynamics and acoustics under the wing flexibility is, therefore, needed.

This is a numerical study of thermal barrier coating (TBC) and turbulence on leading edge (LE) cooling of a guide vane. Numerical results were carried out using 3D CFD with conjugate heat transfer analysis. Important phenomena were revealed. (1) TBC is effective in the LE region especially when free stream turbulence (Tu) increases. (2) At each Tu, TBC near the hub of the vane provides the most effective protection and at the highest Tu, TBC improves overall cooling effectiveness there by about 25%. (3) Near the exits of film hole, TBC may have negative effect, because of heat transfer impedance from the solid structure into the mixing fluid between mainstream and cooling air emitted from film holes.

Revisiting the clap-and-fling mechanism in small wasp Encarsia formosa using quantitative measurements of the wing motion

The thermal efficiency of gas turbine engines increases with turbine inlet temperature (TIT) directly. However, the TIT is limited by the allowable temperature of current blade materials. Film cooling technique is an effective method to maintain turbine vane working smoothly under high TIT conditions. The adiabatic film effectiveness has been widely employed to understand film cooling mechanism. Therefore, the prediction of the adiabatic effectiveness of gas turbine engines under real operating conditions is essential. The showerhead film cooled turbine vane reported by L. P. Timko (NASA CR-168289) is adopted in the present study. There are two rows of film holes on the leading edge, three rows on the pressure side, and two rows on the suction side. All holes are cylindrical, which are placed at an angle of 45 degrees to the vane surface in the span-wise direction. This numerical investigation discusses the influences of free stream turbulence intensity on the adiabatic film effectiveness in the vane leading edge region and its vicinity. Five two-equation turbulence models based on Reynolds Averaged Navier-Stokes (RANS) are employed to predict the adiabatic film effectiveness under real operating conditions at a blowing ratio (BR) of 1.41 and three free stream turbulence intensities (Tu=3.3, 10, and 20%). The adiabatic film effectiveness on the vane surface at 8, 52.5, and 89% span in an x/C range between −0.4 and 0.4 is presented. Obviously, the numerical results predicted by all five models show that on the suction side, the increasing free stream turbulence intensity can reduce film effectiveness except at 8% span. On the pressure side, the RNG k-ε, Realizable k-ε and SST k-ω models predict the same trend of the adiabatic film effectiveness, especially the RNG k-ε and SST k-ω models. Those three models predict that the locally adiabatic film effectiveness (especially near film holes) can be improved when turbulence intensity increases. However, at a span of 89% within the x/C range between −0.4 and −0.2, all k-ε models and SST k-ω model predict that the increase of turbulence intensity can reduce the adiabatic film effectiveness. In addition, the film effectiveness contours show a significant variation of film effectiveness predicted by the five turbulence models on the leading edge when turbulence intensity increases. For the near-pressure side, all models except the Standard k-ω model predict that the high turbulence intensity can reduce the film spreading from film holes dramatically.