Row Of Ribs Research Articles

Conjugate heat transfer investigation of impingement cooling for ribbed internal passage of a turbine vane

In this study, the effect of internal cooling configuration on overall cooling effectiveness of gas turbine vane is investigated using conjugate heat transfer approach. The C3X turbine vane with internal cooling and a turbine vane leading edge model with combined impingement and film cooling scheme are used as primary cases. An impingement cooling configuration is designed in order to enhance cooling effectiveness on the leading edge of the internally cooled C3X vane. In an attempt to further improvement, two rows of ribs are added on regions where impingement jets do not cover. In the leading edge model, the effect of modification for internal cooling channel and within film cooling holes are investigated by adding different rib configurations in those regions. The SST model is adopted for turbulence modeling in fluid zones. In the C3X vane, overall cooling effectiveness is generally enhanced using impingement cooling configuration. Furthermore, span wise distribution of overall cooling effectiveness becomes uniform in the leading edge of the vane. In the leading edge model, it is found that overall cooling effectiveness is varied due to the change in distribution of coolant flow in internal cooling channel and on external surface of the vane by adding ribs in internal cooling channel. The case with ribs perpendicular to the internal channel cross flow provides higher overall effectiveness. The results also indicate that cooling performance of the film cooled vane is sensitive to the location of ribs installed within film holes. The interaction between coolant flow and hot gas flow and its contribution in cooling performance of the vane are elaborately discussed for the leading edge model.

Coherent structures in a compressible turbulent plane jet

Coherent structures represented by proper orthogonal decomposition (POD) modes from large-eddy simulation of a compressible plane jet are analyzed. The leading POD modes of the fluctuating velocity components u′, v′, and w′, and the pressure fluctuation p′ are considered. Spatial and temporal features of these modes are analyzed by the modes and the spectra of the temporal coefficients, respectively. Interactions between leading modes of u′, v′, and w′ and the relationship between the modes of u′, v′, and w′ and of the p′ are discussed. The results show that the leading mode of u′ is in the shape of longitudinal stripes, and the mode is dominated by the jet column frequency Stc. For spanwise fluctuation w′, the leading modes are a pair of modes in the shape of a train of ridges along streamwise, and they are dominated by the fundamental frequency St0. The leading modes for v′ are a pair of modes in a row of ribs. For the dominant frequencies of the v′ modes, suppression of subharmonic frequency at St0/2 and formation of sideband frequencies around (St0 ± Stc)/2 are observed. These spatiotemporal features suggest the mode of v′ is modulated by the modes of u′ and w′. Both the leading modes of p′ and of v′ are in the shape of puffs outside the averaged shear layer. These puff modes are related as an oscillation system, which is confirmed by the spectral-POD modes.

COMPARISON OF SUB-GRID-SCALE MODELS BASED ON PREDICTION OF COHERENT STRUCTURES IN PLANE TURBULENT JETS

A compressible plane jet at Mach 0.9 is numerically studied by large-eddy simulation. The governing equations are discretized by fourth-order spatial and third-order temporal schemes. Five sub-grid-scale (SGS) models, namely, the standard Smagorinsky model (SM), the coherent structure kinetic model (CKM) and the selective mixed-scale model (SMSM), the localized dynamic Smagorinsky model (LDSM), and the coherent-structure Smagorinsky model (CSM), are employed for closure of the sub-grid scale (SGS) terms, respectively, and compared. Proper orthogonal decomposition (POD) method is applied to extract the leading modes of the fluctuating velocity components, i.e., \begin{document}$u'$\end{document} in the streamwise, \begin{document}$v'$\end{document} in the lateral and \begin{document}$w'$\end{document} in the spanwise. The averaged flow fields, dissipation, the instantaneous vortical structures and the coherent structures represented by the leading POD modes, are compared. The leading POD modes of \begin{document}$u'$\end{document} are two longitudinal stripes with fracted contours in the turbulent region, representing the multi-scaled flow and the decay of fluctuation strength. The leading modes of \begin{document}$v'$\end{document} are a row of ribs with the lateral size growing along the streamwise, while the modes of \begin{document}$\left( {u', v'} \right)$\end{document} are in a circular flow pattern around the ends of the ribs. The circular pattern penetrates both the jet flow and the peripheral flow, representing the flow entrainment. The leading modes of \begin{document}$w'$\end{document} are a train of ridges along streamwise. Their positive and negative values represent the spanwise stretching pattern of the coherent structures. In comparison of these five SGS models, the instantaneous multi-scale vortical flow is not effectively predicted by the SM and the CKM, as the small vortical scale is smeared. The POD modes are found to be sensitive to the sub-grid dissipation, since the valley regions of the mode of \begin{document}$u'$\end{document} coincide with the peak dissipation regions predicted by the CKM. The circular flow pattern is also not clearly predicted by the CKM. Neither the ridge pattern of the mode of \begin{document}$w'$\end{document} is predicted by the SM. On the other hand, the multi-scales turbulent flow and the flow patterns of POD modes are well predicted by the CSM, the SMSM, and the LDSM, in which the CSM is computationally more efficient.

Modeling of thermal and gas dynamic processes in additive shell and tube heat exchangers

As part of a gas microturbine engine development, a number of new heat exchanger flow channels, which are produced by using additive technologies, are considered. Geometric three-dimensional models of several heat exchanger elements (with internal, external and combined finning – 3 and 6 rows of ribs, spade spiral of three sizes) are created. Also a mathematical modeling of heat carriers in their flow channels is carried out, taking into account heat transfer through the walls. The analysis of calculated thermohydraulic parameters, namely the heat power and pressure losses, is realized. The spade shape of the heat exchanger element allows intensifying heat exchange (comparable to a 3-fin pipe). It has lower hydraulic resistance compared to 6-fin pipes. It has been found that the change in a standard size of spade spiral pipes does not affect their heat exchange characteristics. The disadvantage of pipes with internal fins is a rapid increase of hydraulic resistance during the operation due to a deposition of microturbine exhaust gases soot.

Mechanical Stresses Induced by Compression in Castings of the Load-carrying Grate

Abstract The main aim of this study was to examine the compression-induced state of stress arising in castings of the guide grates during operation in pusher-type furnaces for heat treatment. The effect of grate compression is caused by its forced movement in the furnace. The introduction of flexible segments to the grate structure changes in a significant way the stress distribution, mainly by decreasing its value, and consequently considerably extends the lifetime of the grates. The stress distribution was examined in the grates with flexible segments arranged crosswise (normal to the direction of the grate compression) and lengthwise (following the direction of force). A regression equation was derived to describe the relationship between the stress level in a row of ribs in the grate and the number of flexible segments of a lengthwise orientation placed in this row. It was found that, regardless of the distribution of the flexible segments in a row, the stress values were similar in all the ribs included in this row, and in a given row of the ribs/flexible segments a similar state of stress prevailed, irrespective of the position of this row in the whole structure of the grate and of the number of the ribs/flexible segments introduced therein. Parts of the grate responsible for the stress transfer were indicated and also parts which play the role of an element bonding the structure.

Heat transfer enhancement of natural convection with ribs

Natural convection heat transfer is found in many industrial applications such as nuclear technologies, electronic circuit board cooling, solar panel cooling and many other fields. When natural convection heat transfer coefficients are insufficient, passive heat transfer enhancement devices (called ribs/fins) are often used. In this paper, the effect of periodic patterns of protrusions (ribs) on the free-convection heat transfer of a vertical plate, with a uniform heat flux rate boundary condition, is experimentally investigated. The convective fluid is air. Two-dimensional, high resolution heat transfer measurements are performed by using infrared thermography and the heated thin foil technique. Experiments are performed on two types of ribs pattern topology: single or two staggered rows of ribs inclined at different angles and single or two-staggered rows of V-ribs.

DNS of velocity and thermal fields in turbulent channel flow with transverse-rib roughness

A detailed knowledge of both velocity and thermal fields in wall turbulence disturbed by a row of ribs on the wall is important for clarifying the chief factors of fluid and thermal dynamics related to the control of heat transfer. In this study, in order to elucidate the effects of roughness on the statistical quantities in the velocity and thermal fields, direct numerical simulations (DNS) of heat transfer in turbulent channel flows with transverse-rib roughness have been performed by varying their spacing, width and height, in which the turbulent heat transfer with k-type and d-type roughness walls are simulated. It is found that since turbulent mixing is promoted by arranging ribs, the distributions of mean velocity and temperature become markedly asymmetric. Systematic variations of secondary flow patterns between ribs are clearly identified. The best heat transfer performance is found to be obtained with the k-type roughness.

Direct Numerical Simulations of Turbulent Velocity and Thermal Fields in a Channel with Transverse-Rib Roughness.

A detailed knowledge of both velocity and thermal fields in wall turbulence disturbed by a row of ribs on the wall is important for clarifying the chief factors of fluid and thermal dynamics related to the control of heat transfer. In this study, in order to elucidate the effects of roughness on the statistical quantities in the velocity and thermal fields, direct numerical simulations (DNS) of heat transfer in turbulent channel flows with transverse-rib roughness are performed by varying their interval, width and height, in which the turbulent heat transfer with k-type and d-type roughness walls are simulated. It is found that since turbulent mixing is promoted by arranging ribs, the distributions of mean velocity and temperature become asymmetric markedly. And the systematic variations of secondary flow patterns between ribs are clearly identified. With the k-type roughness, the best heat transfer performance is found to be obtained.

Revision of the monogenean family Gotocotylidae (Polyopisthocotylea)

We revise the diagnosis of the Gotocotylidae Yamaguti, and acceptGotocotyla Ishii and CathucotyleLebedev as valid genera. We synonymise PseudomicrocotyleSandarsand Swakopella Lebedev & Parukhin withGotocotyla. The number of nominal species in the familyis reduced from ten to four, and six new species are described from newmaterial. Members of Gotocoty lahave asymmetrical clampswith a single row of internal ribs, and those ofCathucotyle have more or less symmetrical clamps withtwo rows of ribs. Members of both genera can be distinguished from congenersby the morphology of clamp sclerites and/or spines of the male copulatoryorgan, and the number of vaginae (0–2). The following species arerecognised: Gotocotyla acanthura (Parona & Perugia),G.africanensis, sp. nov.,G.bivaginalis (Ramalingam),G.elegatis (Meserve), G.heapae,sp. nov., G.niphonii, sp. nov.,G.queenslandici, sp. nov.,Cathucotyle cathuaui Lebedev,C.filipinensis, sp. nov.andC.sinensis, sp.nov.Gotocotyla acanthura as recognised here may be aspecies complex, but we could not distinguish the morphologies of individualsfrom different hosts and localities. There is strong evidence that larvae andyoung juveniles of G.acanthura infect intermediate hostsfor short periods (mostly pelagic fishes, belonging to at least eight orders),until eaten by the final host.

Ultrastructure of the protonephridial system of regenerating Stenostomum sp. (Plathelminthes, Catenulida)

The ultrastructure of the flame bulbs, protonephridial capillaries and duct of fully developed and regenerating Stenostomum sp. is described. Flame bulbs are formed by a single cell whose nucleus is located basally or laterally to the weir. The weir is formed by a single row of transverse ribs connected by a thin ‘membrane’, apparently of extracellular matrix. Internal leptotriches arise from the proximal cytoplasm and extend in a (usually) single row along the weir and into the lumen of the distal cytoplasmic tube. Many or all leptotriches do not fuse with the distal cytoplasm. Two cilia are each anchored in the proximal cytoplasm by a cross-striated vertical and lateral rootlet, the latter bent forward and extending for some distance into one of the two cytoplasmic cords along the weir. Each cord contains the lateral rootlet in its proximal part, as well as many microtubules. The distal cytoplasmic tube contains two (longitudinal) junctions, i.e. lines of contact between cell processes of the same, terminal cell. Occasionally, more than two junctions were seen, apparently due to branches of the terminal cell in contact with each other. Flame bulbs join capillaries lined by several canal cells type I, containing few or no microvilli but lateral flames. Such capillaries join a duct (or ducts?) lined by canal cells type II with many long microvilli. The large protonephridial duct is lined by numerous cells with lateral flames and many long microvilli. In regenerating tissue (10.5 hours after cutting) some flame bulbs were ‘free’, i.e. not connected to capillaries, and some capillaries openly communicated with the surrounding intercellular space. In the presence of a single row of ribs in the weir, of internal leptotriches, and of vertical and lateral ciliary rootlets, the flame bulb of Stenostomum sp. resembles that of other Plathelminthes much more closely than hitherto thought. The species differs from non-catenulid plathelminths mainly in the large number of glandular cells lining the large protonephridial ducts, in the transverse orientation of the ribs in the weir and in the presence of only two cilia in the flame.