Optimized Aerodynamic Design of Aggressive Intermediate Turbine Duct With Strut Fairings Using Genetic Algorithms

Due to demands from industry on improved efficiency, reduced CO2 and NOx and decreased noise levels, the trend of future aero engines show that turbofan engines are designed with higher by-pass ratio. Two-spool and three-spool turbofan engines are designed with an intermediate turbine duct that connects the high-pressure turbine to the low-pressure turbine in the two-spool engine and two intermediate turbine ducts from HPT to intermediate pressure turbine (IPT) and IPT to LPT in the three-spool engines. The design of agressive intermediate turbine ducts (high radial offset for a short axial length) for these engines enables the possibility to increase the energy efficiency of the aero engine. The flow and heat transfer in a turbine duct is very complex. The flow has large secondary structures and is sensitive to flow separation, which is difficult to predict with numerical methods. Limited information is available in open literature that can be used for validation of numerical methods. This paper presents an experimental study of the heat transfer in an aggressive intermediate turbine duct. The aim of this study is to measure the of a surface temperature distribution and convection heat transfer coefficient with very high resolution and precision on a loaded guide vane which is located inside the intermediate turbine duct. Furthermore, the experimental results are compared to CFD carried out with ANSYS CFX. This experiment was carried out in a state-of-the-art large-scale low-speed turbine facility at Chalmers University of Technology. The duct configuration investigated represents a modern counter rotating turbine design, with a flow turning structural vane. The facility includes a turbine stage which provides realistic inlet conditions into the duct and operates at realistic flow Reynolds number based on the ITD vane chord length. The measurements were performed by using an infrared camera. The results shows that the heat transfer coefficient predicted in the computations close to the shroud is not well predicted. There can also be seen areas where there is flow transition and boundary layer transition.

In order to improve the efficiency, ultra-high bypass ratio engine attracts more and more attention because of its huge advantage, which has larger diameter low pressure turbine (LPT). This trend will lead to aggressive (high diffusion) intermediate turbine duct (ITD) design. It is necessary to guide the flow leaving high pressure turbine (HPT) to LPT at a larger diameter without any severe loss generating separation or flow disturbances. In this paper, eight ITDs with upstream swirl vanes and downstream LPT nozzle are investigated with the aid of numerical method. These models are modified from a unique ITD prototype, which comes from a real engine. Key parameters like area ratio, inlet height, and non-dimensional length of the ITDs are kept unchanged, while the rising angle (radial offset) is the only changed parameter which ranges from 8 degrees to 45 degrees. In this paper, the effects of rising angle (RA) on ITD, as well as nearby turbines, will be analyzed in detail. According to the investigation results, RA could be as large as 40 degrees in such model of this paper to escape separation; When RA increases, local inlet flow field of LPT nozzle appears to be with apparent variation; while a positive result is that outlet flow field could be kept almost unchanged through modifying blade profile. On the other hand, it seems optimistic that the overall total pressure loss could be kept nearly equivalent among different RA cases. And a valuable conclusion is that outer wall curvature is more important for pressure loss, which advises a clear direction for optimizing ITD.

Intermediate turbine ducts are used in modern multi-spool jet engines to connect the high pressure turbine with the low-pressure turbine. The trend towards turbofan engines with larger by-pass ratios requires the radial off-set between the high-pressure and low-pressure turbines to increase with a corresponding increase in radial off-set for the intermediate turbine ducts. Other improvements of the ducts is to make them shorter and more diffusing but this strive towards more aggressive design increases the risk for separation. This paper deals with an experimental investigation of the time-averaged mean flow field and turbulence development in an aggressive intermediate turbine duct (downstream a rotating turbine stage) using a 5-hole probe and 2-component hot-wire anemometry. In addition the duct endwall static pressure distribution is discussed. The investigation revealed the complex flow structure development within the duct, where co-rotating vortices emanating from the break-up of the tip gap shear-layer dominates the flow pattern.

With the improvement of requirement, design and manufacture technology, aero-engines for the future are characterized by further reduction in fuel consumption, cost, but increment in propulsion efficiency, which leads to ultra-high bypass ratio. The intermediate turbine duct (ITD), which connects the high pressure turbine (HPT) with the low pressure turbine (LPT), has a critical impact on the overall performances of such future engines. Therefore, it becomes more and more urgent to master the design technique of aggressive, even super-aggressive ITDs. Over the last years, a lot of research works about the flow mechanism in the diffuser ducts were carried out. Many achievements were reported, but further investigation should be performed. With the aid of numerical method, this paper focuses on the change of performance and flow field of ITD, as well as nearby turbines, brought by rising angle (RA). Eight ITDs with the same area ratio and length, but different RAs ranges from 8 degrees to 45 degrees, are compared. According to the investigation, flow field, especially outlet Ma of swirl blade is influenced by RA under potential effect, which is advisable for designers to modify HPT rotor blades after changing ITD. In addition to that, low velocity area moves towards upstream until the first bend as RA increases, while pressure loss distribution at S2 stream surface shows that hub boundary layer is more sensitive to RA, and casing layer keeps almost constant. On the other hand, the overall total pressure loss could keep nearly equivalent among different RA cases, which implies the importance of optimization.

In the present investigation the distribution of mean velocity, static pressure and total pressure are experimentally studied on a C-shape diffuser of 40° angle of turn with an area ratio of 1.284 and centerline length was chosen as three times of inlet diameter. The experimental results then were numerically validated with the help of Fluent and then a series of parametric investigations are conducted with same centre line length and inlet diameter but with different area ratios varying from 1.25 to 2.0 and angle of turn 30° to 75°. The measurements were taken at Reynolds number 2.25 × 105 based on inlet diameter and mass average inlet velocity. Predicted results of coefficient of mass averaged static pressure recovery (48%) and coefficient of mass averaged total pressure loss (12%) are in good agreement with the experimental results of coefficient of mass averaged static pressure recovery (45%) and coefficient of mass averaged total pressure loss (11%) respectively. Standard k-e model in fluent solver was chosen for validation. From the parametric investigation it is observed that for the increase in area ratio from1.25 to 2.0, static pressure recovery increases sharply but with the increase of angle of turn pressure recovery decreases steadily. The coefficient of total pressure loss almost remains constant with the change in area ratio and angle of turn for similar inlet conditions.

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation P. K. Sinha, A. N. Mullick, B. Halder, B. Majumdar; Flow Investigation through Annular Curved Diffusing Duct. AIP Conf. Proc. 26 October 2010; 1298 (1): 80–90. https://doi.org/10.1063/1.3516429 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

This article proposes a passive flow control method for arranging bionic microstructures on the surface of fan blade based on the structural characteristics of shark shield scales. The mechanisms of drag reduction through bionic microstructure were analyzed by numerical simulation at a Mach number of 0.5 and angles of attack from −6° to 9°. The bionic microstructure effectively increases the binding ability of wall to the fluid and the viscous force. This resulted in a decrease in the velocity gradient within the boundary layer and an increase in the viscous sublayer's thickness, so the wall shear stress on the suction surface was diminished and the position of the separation point on the blade surface was delayed by 7.7% of the axial chord length in comparison with that of the smooth blades. The turbulent intensity in the fluid domain on the suction side was reduced by 17.2% within the cascade passage. The total pressure loss coefficients were decreased, respectively, by 14.3%, 17.9%, and 29.1% at angles of attack of 0°, 6°, and −9° compared to the smooth blades. The frictional drag was reduced by the bionic microstructure effectively, thereby enhancing the pressure expansion capability of the cascade. The static pressure coefficient was increased by 5.4% at the angle of attack of 0° and the angle of attack corresponding to the peak point varies from 3° to 6°. The cascade has a wider application range for the angle of attack.

In this paper, results of CFD analysis of boundary layer flow control in a few representative turbine exhaust diffuser geometries are discussed. The simplest of the above configurations was subjected to rig tests with a few of the parameters simulated to produce realistic turbine exhaust diffuser flow. These rig tests provided matching and validation of the CFD results obtained for the same configuration. The diffuser designs were attempted to create strong diffusion field ahead of the struts, in a controlled manner. On the other hand in some of the configurations, an externally induced casing injection system was introduced to control the diffusing flow field behind the struts. In a separate design attempt, the struts and the rear hub were merged in to a smooth blended body in an attempt to reduce the overall diffuser losses and to maximise diffuser pressure recovery. Both these attempts showed mixed results. The studies were carried out at a Reynolds number of 7.7 × 105 based on the diffuser inlet hydraulic diameter. The performance of the diffusers was assessed in terms of total pressure loss and static pressure coefficient across the diffuser. Significant performance benefits were observed using boundary layer control through casing injection as well as through endwall design modifications. In the best performance configuration, the static pressure at the diffuser exit improved by about 16 % and the total pressure losses reduced by about 30% as compared to the baseline configuration at the same axial location.

Learning Classifier Systems (LCS) evolve IF-THEN rules for classification and control tasks. The earliest Michigan-style LCS used a panmictic Genetic Algorithm (GA) (in which all rules compete for selection) but newer ones tend to use a niche GA (in which only a certain subset of rules compete for selection at any one time). The niche GA was thought to be advantageous in all learning tasks, but recent research suggests it has difficulties when the rules composing the solution overlap. Furthermore, the niche GA's effects are implicit, making it difficult study, and fixed, which prevents tuning its performance. Given these issues, we set out on a long-term project to reevaluate the niche GA. This work is our starting point and in it we address the implicit and unquantified effects of the niche GA by building a mathematical model of the probability of rule selection. This model reveals a number of insights into the components of rule fitness, particularly the bonus for rule generality and penalty for overlaps, both previously unquantified. These theoretical results are our primary contribution. However, to demonstrate one way to apply this theory, we then introduce a new variant of the UCS algorithm, which uses a hybrid panmictic/niche GA. Preliminary results suggest, unexpectedly, that the niche GA may have even more drawbacks than previously thought.

The potential of UAVs to serve as an alternative solution for performing inspection and surveillance is of greater interest when considering lower workforce and operating costs. Coanda effect-based UAV is one of the options. However, the present knowledge on this type of UAV is yet fully explored, such as the profile of the curved surface to harness the utmost lift force augmentation. This paper presents an experimental evaluation of the static lift force due to the changes in the curved surface tilting profile angle subjected to the Coanda jet flow. Two test models (axisymmetric 2D half-hemispherical curved surfaces) are considered in this study; semi-circular surface (Rx/Ry = 1) and semi-ellipse surface (Rx/Ry = 2). The static lift force is quantified through static pressure measurement from 13 pressure tapping points located at the centerline of the test models that are connected to a manometer. From the acquired measurements, the static pressure coefficient and lift coefficient distributions are plotted. The result has shown that altering the tilting angle of the test models has yielded additional static lift, up to about 30%; due to the translation of the concentrated pressure region on the curved surface. It was also shown that the semi-circular surface provides a higher lift output compared to the semi-ellipse surface.

To analyze the effect of dsfferent impeller type on inner flow in impeller, two low-specific-speed high-speed com- plex impellers with eight blades are investigated whose types are closed and semi-open. Using the Spalart-Allmaras turbu- lence model and the Reynolds-Averaged Navier-Storkes equa- tions, the three-dimensional turbulent flow fields in impellers are analyzed numerically. And the experimental studies on the centrifugal pump are carried out. The simulation results show that there all exists back flow region in impellers, the back flow region is few and the relative flow in clearance is alone the circumferential orientation in the half-open impeller, the static pressure in impellers rises gradually from blade inlet to outlet whose contours are almost alone the circumferential orientation, the static pressure of blade tip is bigger than that of blade root in the same radius of the blade in half-open impeller, and the static pressure coefficient at outlet of closed impeller is larger. The experimental results show that the efficiency of the half-open impeller is higher and the back flow has important influence on the performance of pump.

This study compares the numerical analyzes of two commercial computational fluid dynamics (CFD) software programs: Ansys® CFX 14.5, based on the finite volume method (FVM); and Altair® AcuSolve 13.0, based on the finite element method (FEM). For this purpose, the flow around a circular cylinder inserted into the test section of a low speed wind tunnel was simulated. The same turbulence model, κ–ω SST (shear stress transport), was used in both software, and the numerical results were compared with experimental results. Results of velocity, pressure, static pressure coefficient and skin friction coefficient are presented. A mesh test was carried out to evaluate the mesh convergence and the numerical uncertainties, which indicated greater uncertainties and sensitivity of FVM to the mesh quality. The average computing time for the FEM method was ten times greater than for FVM. Numerical results of both codes showed a good agreement with experimental results and with the literature.

Earlier research demonstrated that a car following a cyclist can provide an aerodynamic benefit to this cyclist. This effect could be large enough to potentially influence the outcome of individual time trials. This incited the International Cycling Union (UCI) in 2023 to raise the minimum distance from 10 to 25 m. However, this previous research work did not consider the bicycles typically mounted on the roof of a team car. Indeed, some teams have mounted up to ten bicycles on the roof, possibly in an attempt to optimise the aerodynamic benefit by their team car, even in individual time trials. This study employs CFD simulations validated by wind tunnel measurements to assess the benefit provided by different rooftop bicycle configurations. It is shown that the extra benefits are substantial and extend up to a distance of at least 25 m between cyclist and car, which could trigger new rules by the UCI. This study also shows that the cyclist drag reduction by a following car and for any car-cyclist separation distance d, can be estimated by the static pressure coefficient at position d in front of the isolated car, which can be obtained by a single CFD simulation.

This paper presents a crowding niche cellular genetic algorithm (referred to NCGA) aiming at solving the problems of local convergence and non-uniform population distribution in traditional genetic algorithm. The selecting operation in traditional genetic algorithm is improved by bringing in the concept of neighbors of cellular genetic algorithm, and the population distribution is greatly enhanced by introducing crowding niche mechanism, which betters the ability of global searching and helps to avoid the population local convergence. Meanwhile, the paper describes the crowding niche cellular genetic algorithm in details and compares it with simple genetic algorithm （SGA） and simple niche genetic algorithm （NGA）; the comparison results reveal that, NCGA outperforms the other two algorithms in terms of convergence rate and population diversity.

We propose a new framework of computing-inspired multifocal cancer detection procedure (MCDP). Under the rubric of MCDP, the tumor foci to be detected are regarded as solutions of the objective function, the tissue region around the cancer areas represents the parameter space, and the nanorobots loaded with contrast medium molecules for cancer detection correspond to the optimization agents. The process that the nanorobots detect tumors by swimming in the high-risk tissue region can be regarded as the process that the agents search for the solutions of an objective function in the parameter space with some constraints. For multimodal optimization (MMO) aiming to locate multiple optimal solutions in a single simulation run, the niche technology has been widely used. Specifically, the niche genetic algorithm (NGA) has been shown to be particularly effective in solving MMO. It can be used to identify the global optima of multiple hump functions in a running, effectively keep the diversity of the population, and prematurely avoid the genetic algorithm. Learning from the optimization procedure of NGA, we propose the NGA-inspired MCDP in order to locate the tumor targets efficiently while taking into account realistic in vivo propagation and controlling of nanorobots, which is different from the use scenario of the standard NGA. To improve the performance of the MCDP, we also modify the crossover operator of the original NGA from crossing within a population to crossing between two populations. Finally, we present comprehensive numerical examples to demonstrate the effectiveness of the NGA-inspired MCDP when the biological objective function is associated with the blood flow velocity profile caused by tumor-induced angiogenesis.