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The study aims to focus on rotation effects on a ribbed channel of gas turbine blades for internal cooling. The combination and interaction between secondary flows generated by angled rib geometry and Coriolis forces in the rotating channel are studied numerically.

A radially outward flow passage as an internal cooling test model with and without ribs is used to perform the investigation. Aspect ratio of the passage is 1:1. Square ribs with e/Dh = 0.1, p/e = 10 and four various rib angles of 90°, 75°, 60° and 45° are configured on both the leading and trailing surfaces along the rotating duct. The study covers a Reynolds number of 10,000 and Rotation number in the range of 0-0.15.

Nusselt numbers in the ribbed duct are 2.5 to 3.5 times those of a smooth square duct, depending on the Rotation number and rib angle. The maximum value is attained for the 45° ribbed surface. The synergy angle between the velocity and temperature gradients is improved by the angled rib secondary flows and Coriolis vortex. The decrease of the synergy angle is 8.9, 13.4, 12.1 and 10.1 per cent for the 90°, 75°, 60° and 45° ribbed channels with rotation, respectively. Secondary flow intensity is increased by rotation in the 90° and 75° ribbed ducts and is decreased in 45° and 60° ribbed cases for which the rib-induced secondary flow dominates.

The primary motivation behind this work is to investigate the possibility of heat transfer enhancement by vortex flow with developing turbulence in the view point of the field synergy principle and secondary flow intensity.

To investigate the effect of aspect ratio on the quantitative analogy between developing laminar flows in orthogonally rotating straight ducts and stationary curved ducts

A fractional step method is used to obtain the numerical solution of the governing equations by decoupling the solution of the momentum equations from the solution of the continuity equation. In order to clarify the similarity of the two flows, dimensionless parameters K_LR and Rossby number, Ro, in a rotating straight duct were used as a set corresponding to Dean number, K_LC, and curvature ratio, λ, in a stationary curved duct.

Under the condition that the aspect ratio was larger than one and that the magnitude of Ro or λ was large enough to satisfy the “asymptotic invariance property” the quantitative analogy between the two flows was established clearly.

As the aspect ratio decreased below one, the difference between the secondary flow intensities of these two flows increased, and therefore, the analogy between the two flows was not as evident as that for the larger aspect ratios.

Based on this methodology, the characteristics of the developing flow in orthogonally rotating ducts of higher aspect ratio can be predicted by considering the flow in stationary curved ducts, and vice versa.

The results obtained in this study will suggest an optimal criterion for the application of this approach to the flow similarity analysis in rectangular ducts with arbitrary aspect ratios.

In a boundary layer ingestion (BLI) propulsion system, the fan operates continuously under distorted inflow conditions, leading to an increment of aerodynamic loss and in turn impacting the potential fuel burn reduction of the aircraft. Usually, in the preliminary design stage of a BLI propulsion system, it is essential to assess the impact of fuselage boundary layer fluids on fan aerodynamic performances under various flight conditions. However, the hub region flow loss is one of the major loss sources in a fan and would greatly influence the fan performances. Moreover, the inflow distortion also results in a complex and highly nonlinear mapping relation between loss and local physical parameters. It will diminish the prediction accuracy of the commonly used low-fidelity computational approaches which often incorporate traditional physics-based loss models, reducing the reliability of these approaches in evaluating fan performances. Meanwhile, the high-fidelity full-annulus unsteady Reynolds-averaged Navier–Stokes (URANS) approach, even though it can give rather accurate loss predictions, is extremely time-consuming. This study aims to develop a fast and accurate hub loss prediction method for a BLI fan under distorted inflow conditions.

This paper develops a data-driven hub loss prediction method for a BLI fan under distorted inflows. To improve the prediction accuracy and applicability, physical understandings of hub flow features are integrated into the modeling process. Then, the key physical parameters related to flow loss are screened by conducting a sensitivity analysis of influencing parameters. Next, a quasi-steady assumption of flow is made to generate a training sample database, reducing the computational time by acquiring one single sample from the highly time-consuming full-annulus URANS approach to a cost-efficient single-blade-passage approach. Finally, a radial basis function neural network is used to establish a surrogate model that correlates the input parameters and the output loss.

The data-driven hub loss model shows higher prediction accuracy than the traditional physics-based loss models. It can accurately capture the circumferentially and radially nonuniform variation trends of the losses and the associated absolute magnitudes in a BLI fan under different blade load, inlet distortion intensity and rotating speed conditions. Compared with the high-fidelity full-annulus URANS results, the averaged relative prediction errors of the data-driven hub loss model are kept less than 10%.

The originality of this paper lies in developing a new method for predicting flow loss in a BLI fan rotor blade hub region. This method offers higher prediction accuracy than the traditional loss models and lower computational time cost than the full-annulus URANS approach, which could realize fast evaluations of fan aerodynamic performances and provide technical support for designing high-performance BLI fans.

This study aims to propose the increase of heat dissipation requirements of modern electronic equipment and the fast development of micro-scale manufacturing technologies. The heat transfer mechanism is studied in-depth, especially for its pattern of secondary flow caused by the repeated inversion of centrifugal force. Effects of η on the frictional pressure drop and average Nusselt number are studied and the performance of such microchannel heat sink with various bend amplitudes is comprehensively evaluated. These results can provide important insight into the optimal design of this novel design configuration for microelectronics cooling.

A three-dimensional model based on the finite volume approach and SIMPLEC algorithm is performed to test an innovative serpentine microchannel, which behaves differently from conventional serpentine microchannel due to the significant effect of centrifugal force inversion.

The effect of centrifugal force significantly influences the flow and thermal fields which are responsible for the enhancement in heat transfer coefficient. The number, size and intensity of vortices increase with increasing Re, and the vortices are reformed at every change of the geometry in a periodic fashion. The serpentine microchannel studies more effectively at larger bend amplitude. Pressure fluctuations and temperature variation are greater with increasing bend amplitude.

Several techniques have been developed to augment single-phase convective heat transfer in channels. One technique is to use a serpentine channel that enhances the heat transfer due to flow mixing and periodic interruption of thermal boundary layers. This technique has been applied to micro-heat exchangers, thermal regenerators and mini/microreactors.

The optimal design of this novel design configuration for microelectronics cooling can be attained. It will become an effective cooling technology for solving the increasing of heat dissipation requirements of modern electronic equipment.

The flow and heat transfer characteristics are first presented for the circular serpentine microchannel made up of alternate U-bends without interposed straight segments. The present study first examines the effect of such centrifugal force inversion on velocity contour, pressure distribution and temperature distribution. The patterns of secondary flow along the flow passage caused by the repeated inversion of centrifugal force are further studied in depth. The effect of bend amplitude on the flow and heat transfer is explored and the performance of such microchannel heat sink has been comprehensively evaluated.

The aim of this paper is to investigate the convective heat transfer in swirl tubes, which are obtained by roto‐translating a circular section eccentric with respect to the rotation axis. The geometry is numerically investigated with the aim of evaluating the convective heat transfer enhancement effect due to the secondary flow induced by the centrifugal force.

The governing equations, i.e. continuity, momentum and energy equations, are integrated numerically within Comsol Multiphysics^® environment, under the assumption of incompressible Newtonian and constant properties fluid and of periodically fully developed laminar flow for what concerns both the hydrodynamic and the thermal problem under the uniform wall heat flux thermal boundary condition.

The heat transfer performance of the geometry is discussed in relation to the flow pattern. In particular, the numerical results show that two different stable flow regimes may exist, according to the ratio of the Reynolds number to the dimensionless helix pitch. The Nusselt number augmentation becomes significant for high Prandtl number fluids when a critical Re/P* value, corresponding to the onset of the centrifugal forces induced secondary flow, is reached.

The geometry here investigated represents an interesting solution to enhance the convective heat transfer in situations in which the flow, although disturbed, persists in the laminar regime. This type of enhanced tubes shows then interesting heat transfer performances (which becomes particularly significant for high Prandtl number values) by thus suggesting convenient applications also for highly viscous fluids which are often treated under the laminar flow regime.

This article aims to study numerically three dimensional developing incompressible flow and heat transfer in a fixed curved pipe.

A projection algorithm based on the second order finite difference method is used for discretizing governing equations written in the toroidal coordinate system.

The effects of curvature and governing non‐dimensional parameters consisting of Reynolds, Prandtl, and Dean numbers on the flow field, entrance length, and heat transfer are studied in detail. The numerical results indicate that the entrance length depends only on the Reynolds number for the curvature ratios greater than 1/7 and therefore, Dean number is not a pertinent parameter in this range.

For heat transfer analysis, two different thermal boundary conditions, i.e. constant wall temperature and constant heat flux at the wall are implemented. The results are calculated for the Dean numbers in the range of 76‐522 and for the two prandtl numbers of 0.5 and 1.

The results can be used in designing heat exchangers, piping systems, and cooling of gas turbine blades.

The numerical results obtained here concentrate on the detailed investigation of flow and temperature field at the entrance region by a quantitative analysis of hydrodynamic and thermal entrance length. The effects of different thermal boundary conditions and different inlet profiles on the flow and temperature fields are studied in the circular curved pipe for the first time.

This study aims to provide an insight into the relationship between design parameters and thermal performance of plate fin heat sinks (PFHSs) incorporating longitudinal vortex generators (VGs) inside a PFHS channel.

A computational fluid dynamics model of a delta winglet pair VG mounted inside a PFHS geometry is detailed, and the model is validated by comparison with experimental data. The validated model is used to perform a virtual design of experiments study of the heat sink with bottom plate and vertical plate mounted VGs. Data from this study is used to regress a response surface enabling the influence of each of the assessed design variables on thermal performance and flow resistance to be determined.

The results of this study show that the thermal hydraulic performances of a PFHS with bottom plate mounted VG and vertical plate fin mounted VG are, respectively, 1.12 and 1.17 times higher than the baseline PFHS. Further, the performance variation of the heat sink with VG, relative to delta winglet’s arrangement (common flow up and common flow down), trailing edge gap length and Reynolds number were also evaluated and reported.

For the first time, performance characteristics of delta winglet VGs mounted inside the PFHS are evaluated against different design variables and a polynomial regression model is developed. The developed regression model and computed results can be used to design high performance PFHSs mounted with delta winglet VGs.

The purpose of this study is to suppress secondary flows and improve aerodynamic performance of a centrifugal impeller.

A multi-objective optimisation design system was described. The optimization design system was composed of a three-dimensional (3D) inverse design, multi-objective optimisation and computational fluid dynamics (CFD) analysis. First, the control parameter ΔCp for the secondary flows was derived and selected as the optimisation objective. Then, aimed at minimising ΔCp, a 3D inverse design for impellers with different blade loading distributions and blade lean angles was completed and multi-objective optimisation was conducted. Lastly, the improvement in the distribution of secondary flows and aerodynamic performance of the optimal impeller was demonstrated by CFD analysis.

The study derived the control parameter ΔCp for the secondary flows. ΔCp can indicate the distribution of secondary flows both near the blade pressure and suction surfaces. As ΔCp decreased, secondary flows decreased. The blade loading distribution with fore maximum blade loading at the shroud and aft maximum blade loading at the hub, coupled with a small negative blade lean angle, could help suppress secondary flows and improve aerodynamic efficiency.

A direct control method on internal flow field characteristic-secondary flows by optimisation design was proposed for a centrifugal impeller. The impeller optimisation design process saves time by avoiding substantial CFD sample calculations.

This paper aims to investigate the influences of dimple location on the heat transfer performance of a pin fin-dimpled channel with upright/curved/inclined pin fins under stationary and rotating conditions.

Numerical methods based on a realizable k-ε turbulent model are used to conduct this study. Three kinds of pin fins (upright, curved, inclined) and three dimple locations (front, middle, behind) are studied for Ro varying from 0 to 0.5.

On the whole, pin fin plays a dominated role in heat transfer performance compared to dimple. The heading path and interaction of the longitudinal secondary flow and jet-like flow critically affect heat transfer performance. The formation, development and impingement of jet-like flow and longitudinal secondary flow are significantly affected by dimple locations. Dimple at behind position shows the poorest heat transfer enhancement.

This study is an extend of another previous study in which an innovative curved pin fin is proposed. The originality of this paper is to evaluate the heat transfer performance for the combined cooling structure of dimple and pin fin, which will provide original and useful application and experience for turbine blade design.

The purpose of this paper is to numerically study the influence of wall conduction on the heat transfer of supercritical n-decane in the active regenerative cooling channels.

A horizontally placed rectangular pipe with a solid zone and another one without a solid zone were used. A drastic variation of thermo-physical properties was emphatically addressed. After the verification of mesh and turbulence models comparing with the experimental results, a mesh number of 4.5 M and the low Reynolds number SST k-ω turbulence model were chosen. The solution of the governing equations and the acquisition of the numerical results were executed by the commercial software FLUENT 2020 R1.

The numerical results indicate that there is a heat transfer deterioration (HTD) potential for the upper wall, lower wall and sidewall with the decrease of mass flux. Due to wall conduction, the distribution of the fluid temperature at spanwise-normal planes becomes uniform and this feature also takes advantage of the relatively uniform transverse velocity. For the streamwise-normal planes, the low fluid temperature appears close to the upper wall at the region near the sidewall and vice versa for the region near the centre. Undoubtedly, the secondary flow at the cross-section plays a crucial role in this process and the relatively cool mainstream is affected by the vortices.

This study warns that the wall conduction must be considered in the practical design and thermal optimization due to the sensibility of thermo-physical properties to the heat flux. The secondary flow caused by the buoyancy force (gravity) plays a significant role in the supercritical heat transfer and mixed convection heat transfer should be further studied.