Aerodynamic Heat Transfer Research Articles

Effects of varying non-axisymmetric contours of the turbine endwall on aerodynamics and heat transfer Aspects:A sensitivity analysis study

Non-axisymmetric endwall contouring of gas turbines has been widely employed as an effective way to improve the aerodynamic performance or heat transfer features. Though efforts have been exerted by previous investigators to generate improved contoured endwall designs, better understandings of the physics behind the phenomenon that non-axisymmetric contoured endwall configurations change the aerodynamic or heat transfer performances are still in demand. In this study, a global sensitivity analysis (GSA) methodology is used to determine shape changes at which locations on the endwall have the most significant impact on the aerodynamic or endwall heat transfer performances. Then, typical non-axisymmetric contoured endwall cases found by a multi-objective optimization approach are studied to understand further why shape changes in such locations impact the passage aero-thermal aspects so much. The results show that the most prominent areas for the passage aerodynamic performance are at the passage mid-pitch from the passage forepart to the aft part by impacting the stream-wise acceleration features. The locations at the passage's aft part influence the heat transfer features most due to high velocity, thus large heat transfer coefficient values there.

Adjoint-assisted Pareto front tracing in aerodynamic and conjugate heat transfer shape optimization

In this paper, a prediction-correction algorithm, built on the method proposed in [1], uses the adjoint method to trace the Pareto front. The method is initialized by a point on the Pareto front obtained by considering one of the objectives only. During the prediction and correction steps, different systems of equations are derived and solved by treating the Karush-Kuhn-Tucker (KKT) optimality conditions in two different ways. The computation of second derivatives of the objective functions (Hessian matrix) which appear in the equations solved to update the design variables is avoided. Instead, two approaches are used: (a) the computation of Hessian-vector products driving a Krylov subspace solver and (b) the approximations of the Hessian via Quasi-Newton methods. Three different variants of the prediction-correction method are developed, applied to 2D aerodynamic shape optimization problems with geometrical constraints and compared in terms of computational cost. It is shown that the inclusion of the prediction step in the algorithm and the use of Quasi-Newton methods with Hessian approximations in both steps has the lowest computational cost. This method is, then, used to compute the Pareto front in a 3D conjugate heat transfer shape optimization problem, with the total pressure losses and max. solid temperature as the two contradicting objectives.

Effect of grid displacement models on sensitivity derivatives computed by the continuous adjoint method in aerodynamic and conjugate heat transfer shape optimization

ABSTRACT For aerodynamic and conjugate heat transfer problems, the work reported in this article investigated the effect of the grid displacement model on the derivatives of an objective function with respect to the design variables. A comparison was made in the first step of the study between reference sensitivity derivatives computed by finite differences and different grid displacement models (volumetric B-splines, Laplace partial differential equations, Delaunay graphs and inverse distance weighting). Then, a continuous adjoint method including the adjoint to the Laplace grid displacement model was used to recompute sensitivity derivatives. To shed more light and to support the authors' findings, an alternative continuous adjoint method for computing the objective function gradient in terms of the field integrals of grid sensitivities was also formulated and programmed. Finally, the effect of an inconsistent differentiation of the grid displacement model on the optimized solution was investigated. The choice of the grid displacement model did not affect the sensitivity derivatives in any of the cases examined.

Hypersonic Flow Past Over an Elliptic Nose Cone Configurations: International Conference on Recent Trends in Artificial Intelligence, IOT, Smart Cities & Applications (ICAISC-2020)

The present work provides a detailed study of the hypersonic flow over elliptical nose cones at a Mach number of 5.8, numerically. The main focus of the paper is to determine parameters of the nose cones which provide minimum aerodynamic drag and heating. The conjugate heat transfer method is used to examine aerodynamic heat transfer between gas and surface accommodations for different fineness ratios at zero angle of attack. It is observed that for higher fineness ratio provide minimum drag. It also shows the detailed comparison of the flow/shock features in the vicinity of the elliptical nose cones for different fineness ratios in order to determine its influence on aerodynamic drag and heating. It is also noticed that the aerodynamic heating is almost same for all fineness ratios. In general, the present study reveals that at higher fineness ratios are preferred for achieving aerodynamic characteristics in hypervelocity vehicles.

Computational investigations into heat transfer over a double wedge in hypersonic flows

Recently developed OpenFOAM application hy2FOAM is employed to predict the aerodynamic heat transfer numerically and compared with the experimental data from the University of Illinois. Mach 7 nitrogen flow at 2.1 MJ/kg stagnation enthalpy, and Mach 7 nitrogen and air flows at 8 MJ/kg stagnation enthalpy over a double wedge geometry have been reproduced numerically assuming chemical and thermal non-equilibrium. Good agreement of mean heat transfer profiles has been observed, although none of the simulations achieved a steady-state. The reattachment heat transfer peak in the high enthalpy air case showed an improved agreement with the experimental data, which is due to the non-equilibrium in the flow field.

PERFORMANCE ENHANCEMENT OF AIRCRAFT ENGINE AXIAL FLOW TURBINE USING THEORETICAL, EXPERIMENTAL AND NUMERICAL APPROACHES – A REVIEW

Axial flow turbine is widely used in gas turbines for expansion of hot gases, emerging from the combustion chamber. The turbine expands the flow and generates power to drive the compressor and fan. The designing needs to accommodate high speeds and altitudes, as well as reduce losses in order to improve stage efficiency and overall efficiency. Some of the problems are tip leakage flow, high thermal loads on the blades, airfoil erosion, etc. Using public domain literature, a comprehensive review was carried out to get detailed understanding of the working and new techniques used to overcome losses of axial flow turbine. The present paper is a summary of literature of axial flow turbine over the span of three decades. The review covers Theoretical, Experimental and Numerical approaches, used in the literature for research on secondary flows, tip leakage losses, heat transfer coefficients, etc. This paper uses three broad classifications, namely aerodynamic performance, heat transfer and blade tip. This paper aims to aid researchers to understand the advancements in the field of aircraft engine axial flow turbines.

The design of thermal management system for hypersonic launch vehicles based on active cooling networks

In this paper, a design method of thermal management system (TMS) for hypersonic vehicles is developed. The system consists of a passive thermal protection system (TPS) and an active cooling network (ACN) with coolant of kerosene. In most previous studies, the passive TPS and ACN are always designed separately and thus leads to over-conservative results that deviating from real engineering conditions. A coupled design method is developed in present work, and the process includes calculation of aerodynamic heat, determination of passive TPS concept distribution, computation of TPS and ACN scales, and iterative design. The coupled design is realized based on two keys, the active cooling is coupled in aerodynamic heating and heat transfer in TPS by an equivalent thermal equilibrium model, and the overall capacity of active cooling is indicated by an equivalent heat transfer coefficient. The model and the coefficient act as the rationale and the equivalent parameter of the whole process, respectively. The TMS of a reusable launch vehicle is established under a typical trajectory. The influences of equivalent heat transfer coefficient on aerodynamic heating, passive TPS and ACN are studied. The results show that the weight of passive TPS decreases, while the coolant mass flow rate increases with the enhancement of active cooling.

An integrated algorithm for hypersonic fluid–thermal–structural analysis of aerodynamically heated cylindrical leading edge

The accurate and efficient prediction of the fluid–thermal–structural performance of thermal protection systems on hypersonic vehicles to protect against severe aerodynamic heating is attracting increasing worldwide attention. In this paper, a new integrated fluid-structural-thermal investigation based on the finite volume method is proposed to study the thermal behavior of aerodynamically heated cylinder leading edges in hypersonic flows. A unified integral equation system is developed based on the governing equations for the physical processes of aerodynamic heating and structural heat transfer, which is resolved by using an up-wind finite volume method and a new two-thermal-resistance model in one integrated, vectorized computer program. To demonstrate its capability and reliability, applications for steady/unsteady fluid–thermal–structural analysis are demonstrated on aerodynamically heated cylinder leading edges at Ma 6.47. The results show that the steady maximum temperature of the cylinder can reach approximately 648 K at the stagnation point, and the unsteady results are in good agreement with the experimental data and related references. Compared with the partitioned approach, the integrated method shows better computational stability with relatively small sensitivity to mesh scale and time step, reducing the computation time for the same unsteady case by approximately 50%. The present study indicates that the integrated approach has potential for significant improvements and efficiency in predicting long-endurance fluid-structural-thermal problems of hypersonic vehicles.

Numerical analysis of the aerodynamic performance & heat transfer of a transonic turbine with a partial squealer tip

The purpose of this study is to evaluate thermal load and aerodynamic performance by applying different shapes of tips depending on the velocity region in a transonic turbine where subsonic and supersonic regions coexist. The RS1S, which is the transonic turbine of SNECMA, is used. To understand the tendencies, geometries A, B and C were created by varying the length of the pressure surface rim and the suction surface rim, and they were compared with a flat tip, squealer tip, pressure surface rim and suction surface rim. RANS computational analysis was performed using the commercial code ANSYS CFX 18.0, and aerodynamic performance was evaluated by using the mass-averaged total pressure loss coefficient at the 133% Cax and the mass flow rate of tip leakage. Thermal load was also evaluated by using the area-averaged heat transfer coefficient at the tip. Although the mass flow rate of leakage was smallest with the squealer tip, geometry C, the 75% rim of the pressure surface and the suction surface showed the lowest total pressure loss coefficient, which was 6.5% lower than that of the flat tip. In addition, when only the suction surface rim was applied, the area-averaged heat transfer coefficient was 10% lower than that of the flat tip.

Effect of turbulence models' choice on the aero-thermal flow numerical validations within a ribbed trailing edge geometry

In this paper, the commercial ANSYS Fluent software was used to achieve a numerical survey of the effect of five (05) turbulence models’ formulation on the aero-thermal computational fluid dynamics validation of two 30:1 scaled models reproducing an original internal ribbed trailing edge prototype. Tests were conducted for stationary and rotation conditions, for Re = 10,000–40,000 and Ro = 0–0.23. Particle image velocimetry and thermochromic liquid crystal experimental data were employed to check the consistence computational fluid dynamics results qualitatively and quantitatively, aerodynamically and thermally, for various working conditions. Numerical predictions revealed that the choice of the turbulence model affects the accuracy of results. Concerning the shear stress transport k-w model, limiters defined in the eddy viscosity formulation induce a surplus estimation of the turbulence kinetic energy ( k) which leads to noticeable discrepancies in terms of velocity profiles and recirculation zones. Also, numerical calculations confirmed former experimental assumptions concerning origins of the aerodynamic structures and heat transfer's features, especially, those related to the increase of the cooling temperature balance efficiency, the appearance/disappearance of the horseshoe structures within the trailing edge region and velocities/boundary layers’ profile variations. The obtained results assist the understanding and the forecast of the flow field behavior, throughout the design process, by the assessment of the aerodynamic and thermal performances within the considered blade's cooling system.

Performance of Partial and Cavity Type Squealer Tip of a HP Turbine Blade in a Linear Cascade

Three-dimensional highly complex flow structure in tip gap between blade tip and casing leads to inefficient turbine performance due to aerothermal loss. Interaction between leakage vortex and secondary flow structures is the substantial source of that loss. Different types of squealer tip geometries were tried in the past, in order to improve turbine efficiency. The current research deals with comparison of partial and cavity type squealer tip concepts for higher aerothermal performance. Effects of squealer tip have been examined comprehensively for an unshrouded HP turbine blade tip geometry in a linear cascade. In the present paper, flow structure through the tip gap was comprehensively investigated by computational fluid dynamic (CFD) methods. Numerical calculations were obtained by solving three-dimensional, incompressible, steady, and turbulent form of the Reynolds-averaged Navier-Stokes (RANS) equations using a general purpose and three-dimensional viscous flow solver. The two-equation turbulence model, shear stress transport (SST), has been used. The tip profile belonging to the Pennsylvania State University Axial Flow Turbine Research Facility (AFTRF) was used to create an extruded solid model of the axial turbine blade. For identifying optimal dimensions of squealer rim in terms of squealer height and squealer width, our previous studies about aerothermal investigation of cavity type squealer tip were utilized. In order to obtain the mesh, an effective parametric generation has been utilized using a multizone structured mesh. Numerical calculations indicate that partial and cavity squealer designs can be effective to reduce the aerodynamic loss and heat transfer to the blade tip. Future efforts will include novel squealer shapes for higher aerothermal performance.

Quantifying Model Discrepancy in Time-Dependent, Coupled Analyses

Model discrepancy in coupled, time-dependent analyses is addressed with emphasis on aerothermoelastic response prediction for hypersonic aircraft. Time-dependent temperature data from historic hypersonic wind-tunnel experiments are used to calibrate both aerodynamic heating and heat transfer model errors and improve prediction confidence of coupled aerothermal predictions through time. Three different model discrepancy resolutions are considered (global, stepwise, and partitioned) for model error calibration, and appropriate model discrepancy forms in the presence of evolving coupled physics are also discussed. The three model discrepancy resolutions are compared using the model reliability metric, where the partitioned model discrepancy approach is observed to yield higher prediction confidence in both nonlinear and extrapolation regions.

Shape memory alloy-based mechanism for aeronautical application: Theory, optimization and experiment

Efforts to create efficient and lighter aeronautical structures are defining morphing systems especially those associated with smart materials. In this regard, three simple mechanisms using shape memory alloy (SMA) wires are investigated to generate torque that could be used for flap actuation. The devices consist of an SMA wire biased by a linear spring in the following configurations: concurrent, collinear, and in parallel attached to a pulley. The design of such mechanisms are modeled, optimized, and experimentally verified. The model for the flap consists of two rigid bodies, one fixed and the other rotating, with a single actuator connected to each body. Aerodynamic loading and heat transfer analysis are also considered. The model utilizes the thermomechanical properties for an SMA wire experimentally characterized via improved inverse problem techniques. A multiobjective genetic optimization is implemented to find designs for the three configurations that minimize power consumption and maximize flap deflection magnitude. Overall, as design complexity (i.e., number of degrees of freedom) increases, the power to achieve a certain flap deflection decreases. The maximum deflection for all three mechanisms is sufficient for typical aircraft operations. Finally, numerical results were verified via an experimental apparatus, where similar performance to the model was achieved.

Heat and mass transfer processes at high-temperature media during combustion of low-grade pulverized coal

Abstract. The article is devoted to the complex research processes of heat and mass transfer occurring in the real conditions of solid fuel (coal) combustion. Development of technological processes with economic and ecological advantages are the main purpose for many researches in thermal physics and technical physics. The complex processes of heat and mass transfer in the presence of combustion are non-stationary, strongly non-isothermal with a constant change in the physical and chemical state of the environment. It greatly complicates their experimental study. In this case, studying of heat and mass transfer in high-reacting media with simulation of physical and chemical processes occur during combustion of pulverized coal is important for the solution of modern power engineering industry and ecology problems. In this regard, a comprehensive study of heat and mass transfer processes at high-temperature media observed. Investigations based on the achievements of modern physics by using numerical methods for 3D modeling. Numerical experiments are conducted to describe and study aerodynamic characteristics, heat and mass transfer processes during the burning of pulverized Kazakhstan low-grade coal. The results obtained are of great practical importance, since they allow us to develop recommendations for the improvement and design of new combustion chambers and burners, and also can be useful in optimizing the whole process of burning fossil fuels. G M T Английский Испанский Итальянский Казахский Китайский Трад Китайский Упр Корейский Русский Турецкий Французский Английский Испанский Итальянский Казахский Китайский Трад Китайский Упр Корейский Русский Турецкий Французский Звуковая функция ограничена 200 символами Настройки : История : Обратная связь : Donate Закрыть

An aerothermal study of the influence of squealer width and height near a HP turbine blade

Highly three-dimensional and complex flow structure within the tip gap of an axial flow turbine is a substantial source of aerodynamic loss and heat transfer due to the interaction between the tip leakage vortex, secondary flows and the main passage flow. Most contemporary shroudless high pressure (HP) turbine designs employ squealer tips for durability, structural, aerodynamic design and heat transfer reasons. The present research deals with the influence of squealer width and height on the aerothermal performance of a HP turbine blade. In this study, four different squealer heights and seven squealer width values are investigated using a computational approach for an axial turbine blade depicting an E3 “Energy Efficient Engine” design. The specific HP turbine airfoil under investigation is identical to the rotor tip profile of the Axial Flow Turbine Research Facility (AFTRF) of the Pennsylvania State University. Numerical calculations are performed by solving the three-dimensional, steady and turbulent form of the Reynolds-Averaged Navier-Stokes (RANS) equations. A two-equation turbulence model, Shear Stress Transport (SST) k-ω is used in the present set of calculations. The current numerical predictions show a very good agreement with the extensive aerodynamic measurements obtained in the nozzle guide vane passages of AFTRF. The results indicate that determining proper squealer width and height is crucial to obtain better aerothermal performance in the form of reduced aerodynamic loss and heat transfer to the tip platform. Extensive numerical analysis within the tip gap reveals that increasing squealer height and reducing squealer width increases cavity volume leading to enlarged vortical structures near the pressure side and suction side of the cavity. Because of this enhanced vortical activity in the tip cavity, a blockage to the incoming pass-over flow is introduced and as a result tip leakage mass flow rate is reduced. While the tip leakage flow rate tends to decrease with increased height and reduced width, there is a strong effect from the squealer width and height combination due to the presence of complex interactions in the tip gap region. From a heat transfer point of view, decreasing squealer width and increasing squealer height noticeably reduces the overall Nu‾ on the blade tip platform. Nu‾ on the cavity floor, blade tip and squealer side walls are reduced depending on the increasing height and decreasing width values.

Investigation into aerodynamic and heat transfer of annular channel with inner and outer surface of the shape truncated cone and swirling fluid flow

We have carried out Investigation into aerodynamic and convective heat transfer of the annular channel. Inner or outer surface of annular channel has shape of blunt-nosed cone tapering to outlet end. Truncated cone connects to a cyclone swirling flow generator. Asymmetric and unsteady flow from the swirling generator in the shape of periodic process gives rise to the formation of secondary flows of the type Taylor-Görtler vortices. These vortices occupy the whole space of the annular channel, with the axes, which coincide with the motion direction of the major stream. Contraction of cross-sectional area of channel (in both cases 52%) causes a marked increase in total velocity of flow, primarily due to its axial component and promotes a more intensive vortex generation. Vortex structures have a significant influence on both average heat transfer and surface distribution. At cross-sections of the annular channel we observe similarity of curves describing distribution of total velocity about wall and heat flux density on the surface. The coordinates of maximum and minimum values of velocity and heat flux coincide. At the average cross-section channel of maximum value of heat transfer is greater than minimum of about by a factor of 2.7 times for outer heat transfer surface and about by a factor of 1.7 times for inner heat transfer surface. Taper channel has a much higher influence on heat transfer of the inner surface than the outer surface and manifests itself at lower values of dimensionless axial coordinate. For the investigated taper cone geometry of the annular channel the heat transfer coefficient of inner surface increases at the outlet section and exceeds value in comparison with straight-line section by 91 … 98%. Heat transfer of the outer cylinder in the same section increases only by 5 … 11%. The increase in average heat transfer over the surfaces is 36% and 4% respectively.

Study on the Temperature Field of Hypersonic Vehicle Structure with Aerothermoelasticity Deformation

The malfunction of thermal protection system (TPS) caused by aerodynamic heating is a latent trouble to aircraft structure safety. Accurately predicting the structure temperature field is quite important for the TPS design of hypersonic vehicle. Since Thornton’s work [14] in 1988, the coupled method of aerodynamic heating and heat transfer has developed rapidly. However, little attention has been paid to the influence of structural deformation on aerodynamic heating and structural temperature field. In the flight, especially the longendurance flight, the structural deformation, caused by the aerodynamic heating and temperature rise, has a direct impact on the aerodynamic heating and structural temperature field. Thus the coupled interaction cannot be neglected. In this paper, based on the method of static aerothermoelasticity, considering the influence of aerothermoelasticity deformation, the aerodynamic heating and heat transfer coupled results of hypersonic vehicle wing model were calculated. The results show that, for the low-curvature region, such as fuselage or centersection wing, structure deformation has little effect on temperature field. However, for the stagnation region with high curvature, the coupled effect is not negligible. Thus, it is quite important for the structure temperature prediction to take into account the effect of elastic deformation. This work has laid a solid foundation for improving the prediction accuracy of the temperature distribution of aircraft structures and the evaluation capacity of structural performance.

Nonlinear unsteady streaks engendered by the interaction of free-stream vorticity with a compressible boundary layer

The nonlinear response of a compressible boundary layer to unsteady free-stream vortical fluctuations of the convected-gust type is investigated theoretically and numerically. The free-stream Mach number is assumed to be of $O(1)$ and the effects of compressibility, including aerodynamic heating and heat transfer at the wall, are taken into account. Attention is focused on low-frequency perturbations, which induce strong streamwise-elongated components of the boundary-layer disturbances, known as streaks or Klebanoff modes. The amplitude of the disturbances is intense enough for nonlinear interactions to occur within the boundary layer. The generation and nonlinear evolution of the streaks, which acquire an $O(1)$ magnitude, are described on a self-consistent and first-principle basis using the mathematical framework of the nonlinear unsteady compressible boundary-region equations, which are derived herein for the first time. The free-stream flow is studied by including the boundary-layer displacement effect and the solution is matched asymptotically with the boundary-layer flow. The nonlinear interactions inside the boundary layer drive an unsteady two-dimensional flow of acoustic nature in the outer inviscid region through the displacement effect. A close analogy with the flow over a thin oscillating airfoil is exploited to find analytical solutions. This analogy has been widely employed to investigate steady flows over boundary layers, but is considered herein for the first time for unsteady boundary layers. In the subsonic regime the perturbation is felt from the plate in all directions, while at supersonic speeds the disturbance only propagates within the dihedron defined by the Mach line. Numerical computations are performed for carefully chosen parameters that characterize three practical applications: turbomachinery systems, supersonic flight conditions and wind tunnel experiments. The results show that nonlinearity plays a marked stabilizing role on the velocity and temperature streaks, and this is found to be the case for low-disturbance environments such as flight conditions. Increasing the free-stream Mach number inhibits the kinematic fluctuations but enhances the thermal streaks, relative to the free-stream velocity and temperature respectively, and the overall effect of nonlinearity becomes weaker. An abrupt deviation of the nonlinear solution from the linear one is observed in the case pertaining to a supersonic wind tunnel. Large-amplitude thermal streaks and the strong abrupt stabilizing effect of nonlinearity are two new features of supersonic flows. The present study provides an accurate signature of nonlinear streaks in compressible boundary layers, which is indispensable for the secondary instability analysis of unsteady streaky boundary-layer flows.

Efficiently modelling urban heat storage: an interface conduction scheme in an urban land surface model (aTEB v2.0)

Abstract. Intercomparison studies of models simulating the partitioning of energy over urban land surfaces have shown that the heat storage term is often poorly represented. In this study, two implicit discrete schemes representing heat conduction through urban materials are compared. We show that a well-established method of representing conduction systematically underestimates the magnitude of heat storage compared with exact solutions of one-dimensional heat transfer. We propose an alternative method of similar complexity that is better able to match exact solutions at typically employed resolutions. The proposed interface conduction scheme is implemented in an urban land surface model and its impact assessed over a 15-month observation period for a site in Melbourne, Australia, resulting in improved overall model performance for a variety of common material parameter choices and aerodynamic heat transfer parameterisations. The proposed scheme has the potential to benefit land surface models where computational constraints require a high level of discretisation in time and space, for example at neighbourhood/city scales, and where realistic material properties are preferred, for example in studies investigating impacts of urban planning changes.

Secondary flow and heat transfer coefficient distributions in the developing flow region of ribbed turbine blade cooling passages

This paper reports an experimental and numerical study of the development and coupling of aerodynamic flows and heat transfer within a model ribbed internal cooling passage to provide insight into the development of secondary flows. Static instrumentation was installed at the end of a long smooth passage and used to measure local flow features in a series of experiments where ribs were incrementally added upstream. This improves test turnaround time and allows higher-resolution heat transfer coefficient distributions to be captured, using a hybrid transient liquid crystal technique. A composite heat transfer coefficient distribution for a 12-rib-pitch passage is reported: notably the behaviour is dominated by the development of the secondary flow in the passage throughout. Both the aerodynamic and heat transfer test data were compared to numerical simulations developed using a commercial computational fluid dynamics solver. By conducting a number of simulations it was possible to interrogate the validity of the underlying assumptions of the experimental strategy; their validity is discussed. The results capture the developing size and strength of the vortical structures in secondary flow. The local flow field was shown to be strongly coupled to the enhancement of heat transfer coefficient. Comparison of the experimental and numerical data generally shows excellent agreement in the level of heat transfer coefficient predicted, though the numerical simulations fail to capture some local enhancement on both the ribbed and smooth surfaces. Where this was the case, the coupled flow and heat transfer measurements were able to identify missing velocity field characteristics.