An Experimental Study of Turbine Vane Film Cooling Using Endoscope-Based PSP Technique in a Single-Passage Wind Tunnel

Limited optical access has been a challenge in gas-turbine related researches since the small blade pitch makes it difficult to arrange the camera at a proper viewing angle. In this paper, the application of an endoscopic system in a single-passage wind tunnel is presented. The film cooling effectiveness over the turbine vane’s pressure side with two types of holes was measured using the pressure-sensitive paint (PSP) technique. With the 7-7-7 shaped hole serving as the baseline, the sister shaped hole was compared side-by-side to examine its cooling performance at exit Ma = 0.84. Carbon dioxide (i.e., DR = 1.53) as coolant was discharged into the flow passage through two rows of holes (i.e., 4D spacing between holes and 1.5D spacing between rows) with blowing ratio (M) varied from 0.6 to 2.0. Through the implementation of the homography algorithm, the distorted coolant traces were recovered from the cambered surface. It was found that the film cooling effectiveness of both holes was greatly influenced by the blowing ratio. The sister shaped hole exhibited a relatively high effectiveness distribution at low M but its effectiveness decreased at high M due to the coolant jet detachment. In contrast, the 7-7-7 shaped hole demonstrated significantly higher effectiveness at high M, which can be attributed to the lower momentum flux ratio results of its larger exit area. The endoscope-based PSP technique and the obtained adiabatic effectiveness results may lay the foundation for other investigations and support other CFD studies in the gas turbine community.

The required aerodynamic simulation fidelity to usefully support a gas turbine Digital Twin for manufacturing

With the imminent digitalisation of the manufacturing processes of gas turbine components, a large volume of geometric data of as-manufactured parts is being generated. This geometric data can be used in aerodynamic simulations to predict component performance. Both the cost and accuracy of these simulations increase with their fidelity. To efficiently exploit Digital Twin technology, one must therefore understand how realistic the aerodynamic simulations need to be to give useful performance predictions. This paper considers this issue for a sample of scrapped high-pressure turbine rotor blades from a civil aero engine. The measured geometric data was used to build aerodynamic models of varying degrees of realism, ranging from quasi-three-dimensional blade sections for an Euler solver to three-dimensional, multi-passage and multi-stage Reynolds-Averaged-Navier-Stokes models. The flow near the tip of these shrouded blades is sensitive to manufacturing variability and can switch between two quasi-stable horseshoe vortex modes. In general, capacity and exit flow angle can be adequately predicted by three-dimensional, single-passage calculations: averaging single-passage calculations gives a good prediction of the multi-passage behaviour. For efficiency and stage loading, the approach of averaging single-passage calculations is less accurate as the multi-passage behaviour requires an accurate prediction of the horseshoe vortex modes.

Averaging for High Fidelity Modeling—Toward Large Eddy Simulations in Multi-Passage Multi-Row Configurations

A major challenge in high-fidelity turbomachinery flow computations is the need for high resolution in a very large domain of multiple blade-passages and multiple blade rows. Scale-resolving turbulent solutions are prohibitively costly. The question is, what will it take to get high-fidelity solutions if we are only after time-mean flows for aerothermal performance? A novel two-scale approach is adopted to address the issue by coupling between a local fine-mesh domain in a single-passage and a global coarse-mesh multi-passage domain. This is achieved by harnessing the extra product terms generated when averaging a nonlinear process in time, as well as in space. As such a space-time averaging is purposely applied in either a direct mode or an inverse one in the two domains respectively. The source terms in a compact form (one scalar for one equation) are conveniently obtained to enable the interaction between the single-passage fine-mesh and the multi-passage coarse-mesh solutions. The converged solution for this two-scale coupled system should meet two seemingly conflicting requirements: an otherwise poorly conditioned local fine-mesh domain is now subject to a right environment/flow conditions, and an otherwise poorly resolved global coarse-mesh domain is now effectively subject to high resolution. In this paper, the concepts, the formulations of the framework methodology, and the implementation methods will be described. The validity and feasibility of the approach for efficient scale-resolving high- fidelity turbomachinery flow simulations will be illustrated by several computational examples of practical interest.

Style in Narrative

Style has often been understood both too broadly and too narrowly. In consequence, it has not defined a psychologically coherent area of study. In the opening chapter, Hogan first defines style so as to make possible a systematic theoretical account through cognitive and affective science. This definition stresses that style varies by both scope and level—thus, the range of text or texts that may share a style (from a single passage to an historical period) and the components of a work that might involve a shared style (including story, narration, and verbalization). Hogan illustrates the main points of this chapter by reference to several works, prominently Woolf’s Mrs. Dalloway. Subsequent chapters in the first part focus on under-researched aspects of literary style. The second chapter explores the level of story construction for the scope of an authorial canon, treating Shakespeare. The third turns to verbal narration in a single work, Faulkner’s As I Lay Dying. Part two, on film style, begins with another theoretical chapter. It turns, in chapter five, to the perceptual interface in the genre of “painterly” films, examining works by Rodriguez, Mehta, Rohmer, and Husain. The sixth chapter treats the level of plot in the postwar films of Ozu. The remaining film chapter turns to visual narration in a single work, Lu’s Nanjing! Nanjing! The third part addresses theoretical and interpretive issues bearing on style in graphic fiction, with a focus on Spiegelman’s Maus. An Afterword touches briefly on implications of stylistic analysis for political critique.

Literary Style

Style has often been understood both too broadly and too narrowly. In consequence, it has not defined a psychologically coherent area of study. In this chapter, Hogan first defines style so as to make possible a consistent and systematic theoretical account of the topic in relation to cognitive and affective science. This definition stresses that style varies by both scope and level—thus, the range of text or texts that may share a style (from a single passage to a historical period) and the components of a work that might involve a shared style (including story, narration, and verbalization). This chapter also addresses a second question—what purposes are served by style? There are three key functions of style: 1) the shaping of story understanding, 2) the communication of thematic concerns (i.e., concerns that extend beyond the work to values in the world), and 3) the arousal and modulation of emotion. Hogan illustrates the main points of this chapter by reference to literary works, prominently Woolf’s Mrs. Dalloway.

Visuality in Esoteric Buddhism – Awakened with a Single Glance?

In the year 806 CE the Japanese monk Kūkai returned from a journey to China and brought a large amount of visual artefacts with him. Commentators have wondered since what role these visual media play in Kūkai’s Buddhist thought. It has been speculated that the art works show that Kūkai values visual media higher when it comes to transmitting the teaching of the Buddha. Proponents of this view usually refer to a single passage from Kūkai’s writings to warrant their interpretation. By analysing the respective passage in detail and showing how it connects to Kūkai’s other writings, this article argues that Kūkai did not prefer the visual to the verbal in transmitting the dharma. Mandalas certainly play an important role in Kūkai’s thought, but their role differs from what these modern interpreters suppose: first, when Kūkai speaks about ‘mandalas’ he often does not refer to paintings, but to the structure of reality or to ritual procedures. Second, mandala paintings have an ambiguous role in esoteric ritual, because they were added rather late in the development of esoteric ritual. For Kūkai they serve primarily as storyboards for ritual performance. Third, the first glance at a mandala is an important moment during esoteric initiations, but it is only the beginning of a rigorous training. Moreover, the crucial moment in esoteric ritual is the union of the practitioner with the deity; glancing at the mandala has no role to play in this mystic union. Fourth, mandala paintings can be used, according to Kūkai, to reveal the deeper structure of texts, but in this role they are not superior to the written medium but rather play a helping role. Fifth, Kūkai believes that texts as well as paintings can be misleading whenever they are taken as representations of a rigid structure of reality. In Kūkai’s eyes, the visual cannot, therefore, solve the problem how the Buddha can transmit his dharma.

On the Development of a Synchronized Harmonic Balance Method for Multiple Frequencies and its Application to LPT Flows

The aim of this paper is to describe the development and application of a multi-frequency harmonic balance solver for GPUs, particularly suitable for the simulation of periodic unsteadiness in nonlinear turbomachinery flows comprised of a few dominant frequencies, with an unsteady multistage coupling that bolsters the flow continuity across the rotor/stator interface. The formulation is addressed with the time-domain reinterpretation, where several non-equidistant time instants conveniently selected are solved simultaneously. The set of required frequencies in each row is driven into the governing equations with the help of almost-periodic Fourier transforms for time derivatives and time shifted boundary conditions. The spatial repetitiveness inside each row can be exploited to perform single-passage simulations and the relative circumferential positioning of the rotors or stators and the different blade or vane counts is tackled by means of adding fictitious frequencies referring to non-adjacent rows therefore taking into account clocking and indexing effects. Existing multistage row coupling techniques of harmonic methods rely on the use of non-reflecting boundary conditions, based on linearizations, or time interpolation, which may lead to Runge phenomenon with the resulting numerical instabilities and non-preserving flux exchange. Different sets of time instants might be selected in each row but the interpolation in space and time across their interfaces gives rise to robustness issues due to this phenomenon. The so-called synchronized approach, developed in this work, consist of having the same time instances among the whole ensemble of rows, ensuring that flux transfer at sliding planes is applied more robustly. The combination of a set of shared non-equidistant time instances plus the use of unequal frequencies (real and fictitious) may spoil the Fourier transforms conditioning but this can be dramatically improved with the help of oversampling and instants selection optimization. The resulting multistage coupling naturally addresses typical numerical issues such as flow that might reverse locally across the row interfaces by means of not using boundary conditions but a local flux conservation scheme in the sliding planes. Some examples will be given to illustrate the ability of this new approach to preserve accuracy and robustness while resolving them. A brief analysis of results for a fan stage and a LPT multi-row case is presented to demonstrate the correctness of the method, assessing the impact in the modeling accuracy of the present approach compared with a time-domain conventional analysis. Regarding the computational performance, the speedup compared to a full annulus time-domain unsteady simulation is a factor of order 30 combining the use of single-passage rows and time spectral accuracy.