The modern gas turbine is widely applied in the aviation propulsion and power generation. The rim seal is usually designed at the periphery of the wheel-space and prevented the hot gas ingestion in modern gas turbines. The high sealing effectiveness of rim seal can improve the aerodynamic performance of gas turbines and avoid of the disc overheating. Effect of outer fin axial gap of radial rim seal on the sealing effectiveness and fluid dynamics was numerically investigated in this work. The sealing effectiveness and fluid dynamics of radial rim seal with three different outer fin axial gaps was conducted at different coolant flow rates using three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and SST turbulent model solutions. The accuracy of the presented numerical approach for the prediction of the sealing performance of the turbine rim seal was demonstrated. The obtained results show that the sealing effectiveness of radial rim seal increases with increase of coolant flow rate at the fixed axial outer fin gap. The sealing effectiveness increases with decrease of the axial outer fin gap at the fixed coolant flow rate. Furthermore, at the fixed coolant flow rate, the hot gas ingestion increases with the increase of the axial outer fin gap. This flow behavior intensifies the interaction between the hot gas and coolant flow at the clearance of radial rim seal. The preswirl coefficient in the wheel-space cavity is also illustrated to analyze the flow dynamics of radial rim seal at different axial outer fin gaps.
In order to make better use of the hidden information value in the Deep Web, get fast and accurate access to the embedded entity data, this paper presented a method for extracting entity data from Deep Web precisely, designed a entity extraction system, which will extract data from Deep Web automatically. Firstly, designed a web crawler based on the characteristics of Deep Web, take advantage of the web crawler to get resources from Internet; Secondly, the pretreatment of web resources, normalize the pages which are non-standard; Finally, locate and extract the entity data from Deep Web accurately, in this paper, based on the hierarchy and layout features in DOM tree, combined XPath with RegExp to locate entity data, then stored the extracted entity attributes and attribute values. Experiments show that, using this method can locate and extract the entity data from Deep Web quickly and efficiently, and achieved a higher accuracy.
Abstract Effects of SDBD and DBD-VGs plasma actuations on film cooling performance of a plain wall were numerically investigated based on the RANS solutions and linearized body force model. With a user defined function (UDF), the plasma actuation forces were implemented into the momentum equations as the source terms in the commercial CFD solver ANSYS Fluent. With the experiment data and referenced numerical results, reliabilities of the linearized body force model and numerical methods were validated. At a range of dimensionless actuation strengths and frequencies, the film cooling effectiveness on the wall surface and flow structure development in the near-wall regions were analyzed and compared with the plasma-off case. The results show that both SDBD and DBD-VGs plasma actuations are beneficial for reducing the development of kidney vortex pair downstream of the cooling hole, thus significantly improving the film cooling effect on the wall surface. With SDBD plasma actuation, the streamwise velocity gradient in near-wall region is increased compared with the plasma-off case, resulting in delayed coolant flow lifting-off downstream of the cooling hole. However, with DBD-VGs plasma actuation, the development of anti-kidney vortex pair is intensified, which in turn weakens the development of kidney vortex pair and widens the coolant coverage on the wall surface along lateral direction. As the actuation strength and frequency increase, the film cooling effectiveness on the wall surface is enhanced along both streamwise and lateral directions. Compared with the plasma-off case, the area-averaged film cooling effectiveness for DBD-VGs plasma actuation case is increased by 331% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 30, whereas for SDBD plasma actuation case the area-averaged film cooling effectiveness is only increased by 42.8% at dimensionless actuation frequency of 2.5 and dimensionless actuation strength of 60. With the same actuation parameters, compared against the SDBD case, a higher film cooling effectiveness is achieved on wall surface for the DBD-VGs plasma actuation case, and the coolant coverage along the lateral direction is significantly improved by DBD-VGs plasma actuation.
Abstract As gas turbine inlet temperature continuously increases, blade trailing edge suffers an extremely high thermal load due to the thin structure and constraint of internal convective cooling arrangements. To overcome these difficulties, pressure-side cutback, which is strengthened with multiple internal structures and land extensions, is widely used in blades to protect trailing edge from high thermal stresses. Due to the geometrical complexity and strong interactions between coolant flow and mainstream, sophisticated heat transfer and flow patterns exist in the cutback region, which presents a great challenge for the trailing edge cutback design. To understand the heat transfer and aerodynamic performance in blade with trailing edge cutback, CFD method has become an efficient tool which provides deep insights into the flow mechanisms and heat transfer characteristics in the detailed region. To accurately resolve the flow and heat transfer performance in a turbine blade with trailing edge cutback, structured grids are preferred because of higher resolution in flow/heat transfer prediction than unstructured grids, especially in boundary layers. However, for a blade with landed trailing edge cutback, few researchers tried to employ structured grids to predict aero-thermal performance due to the geometrical complexity. In this paper, the Background-Grid Based Mapping (BGBM) method proposed in Part I of this study was adopted to generate multi-block structured grids for a gas turbine vane with landed trailing edge cutback. With the coordinate transformation strategies, multi-block structured grids for the vane with landed trailing edge cutback were generated conveniently. With the generated structured grids, flow and heat transfer performance in vane were investigated using RANS (Reynolds-Averaged Navier-Stokes) equations solutions combined with transitional turbulence model. Effects of land extensions on the heat transfer and aerodynamic performance were analyzed, as well as the effects of inflow turbulence intensity, mainstream Reynolds number and ejection rate. The results show that heat transfer coefficients on vane surface, total pressure loss coefficient and energy loss coefficient in vane are all increased with the increase of inflow turbulence intensity. However, heat transfer coefficients on cutback and trailing edge surface are not sensitive to inflow turbulence intensity. At the same inflow turbulence intensity, the aerodynamic loss in vane is decreased with increasing the Reynolds number of mainstream. The increase of ejection rate significantly increases the heat transfer coefficients on cutback surface. Compared with the vane without land extensions, heat transfer coefficients and pressure coefficients on vane surface are reduced and the heat transfer coefficients on cutback surface are increased for the vane with land extensions. In the case of Re = 2.0 × 106, the area-averaged heat transfer coefficient on landed cutback is 14.46% higher than the cutback without lands. Compared with the experimental data, predictions with structured grids based on BGBM method are more agreeable than those with unstructured grids.
Abstract The helical-labyrinth seal (HLS) can reduce rub between labyrinth teeth and rotor during the rotor vibration because the helical teeth on the stator and steps (or teeth) on the rotor are staggered in some positions. The helical-labyrinth seal with the bristle pack named as the helical-labyrinth-brush seal (HLBS) has excellent sealing performance, but the study on the leakage flow characteristics of the HLBS is not available. This paper, using computational fluid dynamic (CFD) analysis technology based on a porous medium model, investigates the leakage flow characteristics of two types of HLBSs (bristle pack installed upstream or downstream of helical-labyrinth tooth named as HLBS-U and HLBS-D, respectively) at various pressure ratios (1–1.3) and rotational speeds (0–10,000 r/min, surface speeds range from 0 to 209 m/s). The radial clearance cb between the rotor and the bristle pack ranges from 0 mm to 1.0 mm, and the radial clearance ct between the labyrinth teeth and the steps on the rotor is 1.6 mm. In parallel, the leakage flow characteristics of the HLBS-D with the constant cb of 1.0 mm are experimentally measured at the pressure ratio up to 1.3 and rotational speed up to 2000 r/min (surface speed 42 m/s). The CFD-derived leakage flow rate (represented as effective clearance) and static cavity pressure agree well with the experimental data in the whole range of test conditions. The shaft rotation eliminates the leakage hysteresis effect of the HLBS-D. Compared with the HLBS-D, the effective clearance of HLBS-U is less sensitive to rotational speed changes. The effective clearance of the HLBS-U is smaller than that of the HLBS-D in the case of cb = 0.5 mm and rotational speed n < 10,000 r/min, and the case of cb = 1.0 mm. However, for the case of cb = 0.5 mm and n = 10,000 r/min, and the case of cb ≤ 0.1 mm, the situation is opposite. The brush seal sections of the HLBS-U and the HLBS-D offer over 55% and 65% total static pressure drop in the case of cb = 1.0 mm, respectively. The brush seal sections of two HLBSs bear almost the same static pressure drop of the over 97% total static pressure drop as cb equals to 0.1 mm. What is more, the HLBS-U has lower turbulent kinetic energy upstream of the bristle pack than the HLBS-D does, which means that the intensity of the bristles flutter of the HLBS-U is lower.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)