Somashekar V. and Immanuel Selwynraj A.
The heatwave effects over an airfoil have a greater influence in the aerodynamic efficiency. The purpose of this study is to investigate the effects of heatwave upon the low…
Abstract
Purpose
The heatwave effects over an airfoil have a greater influence in the aerodynamic efficiency. The purpose of this study is to investigate the effects of heatwave upon the low Reynolds number airfoil aerodynamic performance.
Design/methodology/approach
In this research, the heatwave effects on micro-aerial vehicles’ wing operation are also demonstrated both numerically and experimentally, at the Chord-based Reynolds number Rec = 2 × 105, and under the influence of various environmental temperatures, i.e. 27ºC (room temperature), 40ºC and 50ºC for various flying conditions. A numerical investigation of the low Reynolds number flows with the thermal effect around the unmanned aerial vehicle is presented using the k–ɛ turbulent model. Besides that, the low Reynolds number-based wind tunnel experimental setup is developed to determine the effects of a heatwave over an airfoil. Then, the numerical simulations and wind tunnel experiments are conducted.
Findings
The numerical and wind tunnel’s experimental investigations have been performed on a 2D airfoil under a heatwave environment, i.e. 27ºC, 40ºC and 50ºC for different flight conditions. The numerical and experimental results revealed that the heatwave effect and aerodynamic performance are validated with experimental results. The lift and drag coefficients for both numerical and experimental results show very good correlation at Reynolds number 2 × 105.
Practical implications
The consequences of the increasing temperatures to varying degrees will also be experienced by all commercial aircraft. That is why some great findings are presented here, which are highly relevant for the current and future airline operations. However, sooner than later, the aviation industry should also begin to consider the rising effects of temperature on aircraft operations to develop the loss-reducing adaptable plans.
Originality/value
From the numerical and wind tunnel experimental results, the recorded maximum lift coefficients are observed to be 2.42, 2.39 and 2.36 for 27ºC (room temperature), 40ºC and 50ºC, respectively, at 16° angle of attack, numerically. Similarly, the recorded maximum lift coefficients are observed to be 2.410, 2.382 and 2.354 for 27ºC (room temperature), 40ºC and 50ºC, respectively, at 16° angle of attack, experimentally. The heatwave effects over an airfoil have a greater influence in the aerodynamic efficiency.
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Francisco-Javier Granados-Ortiz, Joaquin Ortega-Casanova and Choi-Hong Lai
Impinging jets have been widely studied, and the addition of swirl has been found to be beneficial to heat transfer. As there is no literature on Reynolds-averaged Navier Stokes…
Abstract
Purpose
Impinging jets have been widely studied, and the addition of swirl has been found to be beneficial to heat transfer. As there is no literature on Reynolds-averaged Navier Stokes equations (RANS) nor experimental data of swirling jet flows generated by a rotating pipe, the purpose of this study is to fill such gap by providing results on the performance of this type of design.
Design/methodology/approach
As the flow has a different behaviour at different parts of the design, the same turbulent model cannot be used for the full domain. To overcome this complexity, the simulation is split into two coupled stages. This is an alternative to use the costly Reynold stress model (RSM) for the rotating pipe simulation and the SST k-ω model for the impingement.
Findings
The addition of swirl by means of a rotating pipe with a swirl intensity ranging from 0 up to 0.5 affects the velocity profiles, but has no remarkable effect on the spreading angle. The heat transfer is increased with respect to a non-swirling flow only at short nozzle-to-plate distances H/D < 6, where H is the distance and D is the diameter of the pipe. For the impinging zone, the highest average heat transfer is achieved at H/D = 5 with swirl intensity S = 0.5. This is the highest swirl studied in this work.
Research limitations/implications
High-fidelity simulations or experimental analysis may provide reliable data for higher swirl intensities, which are not covered in this work.
Practical implications
This two-step approach and the data provided is of interest to other related investigations (e.g. using arrays of jets or other surfaces than flat plates).
Originality/value
This paper is the first of its kind RANS simulation of the heat transfer from a flat plate to a swirling impinging jet flow issuing from a rotating pipe. An extensive study of these computational fluid dynamics (CFD) simulations has been carried out with the emphasis of splitting the large domain into two parts to facilitate the use of different turbulent models and periodic boundary conditions for the flow confined in the pipe.
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Carolina P. Naveira-Cotta, Jian Su, Paulo Lucena Kreppel Paes, Philippe R. Egmont, Rodrigo P.M. Moreira, Gabriel Caetano G.R. da Silva and André Sampaio Monteiro
The purpose of this paper is to investigate the impact of semi-circular zigzag-channel printed circuit heat exchanger (PCHE) design parameters on heat transfer and pressure drop…
Abstract
Purpose
The purpose of this paper is to investigate the impact of semi-circular zigzag-channel printed circuit heat exchanger (PCHE) design parameters on heat transfer and pressure drop of flows under high Reynolds numbers and provide new thermal-hydraulic correlations relevant to conditions encountered in natural gas processing plants.
Design/methodology/approach
The correlations were developed using three-dimensional steady-state computational fluid dynamics simulations with varying semicircular channel diameter (from 1 to 5 mm), zigzag angle (from 15° to 45°) and Reynolds number (from 40,000 to 100,000). The simulation results were validated by comparison with experimental results and existing correlations.
Findings
The results revealed that the thermal-hydraulic performance was mostly affected by the zigzag angle, followed by the ratio of the zigzag channel length to the hydraulic diameter. Overall, smaller zigzag angles favored heat transfer intensification while keeping reasonably low pressure drops.
Originality/value
This study is, to date, the only one providing thermal-hydraulic correlations for PCHEs with zigzag channels under high Reynolds numbers. Besides, the broad range of parameters considered makes the proposed correlations valuable PCHE design tools.
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William D. York, D. Keith Walters and James H. Leylek
The purpose of this paper is to present a new eddy‐viscosity formulation designed to exhibit a correct response to streamline curvature and flow rotation. The formulation is…
Abstract
Purpose
The purpose of this paper is to present a new eddy‐viscosity formulation designed to exhibit a correct response to streamline curvature and flow rotation. The formulation is implemented into a linear k‐ ε turbulence model with a two‐layer near‐wall treatment in a commercial computational fluid dynamics (CFD) solver.
Design/methodology/approach
A simple, robust formula is developed for the eddy‐viscosity that is curvature/rotation sensitive and also satisfies realizability and invariance principles. The new model is tested on several two‐ and three‐dimensional problems, including rotating channel flow, U‐bend flow and internally cooled turbine airfoil conjugate heat transfer. Predictions are compared to those with popular eddy‐viscosity models.
Findings
Converged solutions to a variety of turbulent flow problems are obtained with no additional computational expense over existing two‐equation models. In all cases, results with the new model are superior to two other popular k‐ ε model variants, especially for regions in which rapid rotation or strong streamline curvature exists.
Research limitations/implications
The approach adopted here for linear eddy‐viscosity models may be extended in a straightforward manner to non‐linear eddy‐viscosity or explicit algebraic stress models.
Practical implications
The new model is a simple “plug‐in” formula that contains important physics not included in most linear eddy‐viscosity models and is easy to implement in most flow solvers.
Originality/value
The present model for curved and rotating flows is developed without the need for second derivatives of velocity in the formulation, which are known to present difficulties with unstructured meshes.
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Robert G. Reynolds, Xiangdong Che and Mostafa Ali
The purpose of this paper is to investigate the performance of cultural algorithms (CAs) over a complete range of optimization problem complexities, from fixed to chaotic and…
Abstract
Purpose
The purpose of this paper is to investigate the performance of cultural algorithms (CAs) over a complete range of optimization problem complexities, from fixed to chaotic and specifically observing whether there is a given homogeneous agent topology within a culture which can dominate across all complexities.
Design/methodology/approach
In order to apply the CA overall complexity classes it was necessary to generalize on its co‐evolutionary nature to keep the variation in the population across all complexities. First, previous CA approaches were reviewed. Based on this the existing implementation was extended to produce a more general one that could be applied across all complexity classes. As a result a new version of the cultural algorithms toolkit, CAT 2.0, was produced, which supported a variety of co‐evolutionary features at both the knowledge and population levels. The system was applied to the solution of a 150 randomly generated problems ranging from simple to chaotic complexity classes.
Findings
No homogeneous social fabric tested was dominant over all categories of problem complexity; as the complexity of problems increased so did the complexity of the social fabric that was need to deal with it efficiently. A social fabric that was good for fixed problems might be less adequate for periodic problems, and chaotic ones.
Originality/value
The paper presents experimental evidence that social structure of a cultural system can be related to the frequency and complexity type of the problems that presented to a cultural system.
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Yujun Wang, Qiang Li, Shuo Zhang, Xinhao Tang, Weiwei Xu and Zhenbo Wang
The loading mechanism of textures considering turbulence has not been fully covered. This paper aims to investigate the effect of turbulence on the textured loading capacity under…
Abstract
Purpose
The loading mechanism of textures considering turbulence has not been fully covered. This paper aims to investigate the effect of turbulence on the textured loading capacity under water lubrication and to analyze the causes of the turbulence effect.
Design/methodology/approach
Computational fluid dynamic models with different textured shapes are established after validation. The transition shear stress transport (SST) model, which is suitable for predicting the transition process of fluid from laminar state to turbulent state, is adopted in the present study. To illustrate the effect of turbulence, the loading capacity of textures predicted by transition SST model and laminar model is compared.
Findings
The loading capacity is higher after considering turbulence because more lubricant enters into textures and the flow rate of lubricant to textured outlet increases. There exists an optimal textured depth ratio and density for loading capacity and the change of flow state would not affect the optimal values. The degree of fluid blockage at textured outlet has a dominant influence on loading capacity. As the textured shape changes to triangle or ellipse from rectangle, the vortices at the textured bottom move forward and the blockage at a textured outlet is enhanced, which makes loading capacity improved under the action of blocking effect.
Originality/value
The enhancement of the blocking effect is found to be crucial to the improvement of textured loading capacity after considering turbulence. Present research provides references to understand the loading mechanism of textures under turbulent conditions.
Peer review
The peer review history for this article is available at: https://publons.com/publon/10.1108/ILT-04-2020-0149/
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Antonio Memmolo, Matteo Bernardini and Sergio Pirozzoli
This paper aims to show results of numerical simulations of transonic flow around a supercritical airfoil at chord Reynolds number Rec = 3 × 106, with the aim of elucidating the…
Abstract
Purpose
This paper aims to show results of numerical simulations of transonic flow around a supercritical airfoil at chord Reynolds number Rec = 3 × 106, with the aim of elucidating the mechanisms responsible for large-scale shock oscillations, namely, transonic buffet.
Design/methodology/approach
Unsteady Reynolds-averaged Navier–Stokes simulations and detached-eddy simulations provide a preliminary buffet map, while a high fidelity implicit large-eddy simulation with an upstream laminar boundary layer is used to ascertain the physical feasibility of the various buffet mechanisms. Numerical experiments with unsteady RANS highlight the role of waves travelling on pressure side in the buffet mechanism. Estimates of the propagation velocities of coherent disturbances and of acoustic waves are obtained, to check the validity of popular mechanisms based on acoustic feedback from the trailing edge.
Findings
Unsteady RANS numerical experiments demonstrate that the pressure side of the airfoil plays a marginal role in the buffet mechanism. Implicit LES data show that the only plausible self-sustaining mechanism involves waves scattered from the trailing edge and penetrating the sonic region from above the suction side shock. An interesting side result of this study is that buffet appears to be more intense in the case that the boundary layer state upstream of the shock is turbulent, rather than laminar.
Originality/value
The results of the study will be of interest to any researcher involved with transonic buffet.
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Katherine J Reynolds, John C Turner and S.Alexander Haslam
Within social and organizational psychology and the other social sciences the concept of identity is now widely embraced. Two theories that are increasingly being applied to help…
Abstract
Within social and organizational psychology and the other social sciences the concept of identity is now widely embraced. Two theories that are increasingly being applied to help make sense of group and organizational identification are social identity theory and self-categorization theory (Tajfel, 1978; Turner, 1982; Turner, Hogg, Oakes, Reicher & Wetherell, 1987). These theories, jointly referred to as the social identity perspective, recognise that people’s individual characteristics and their group memberships play a significant role in shaping attitudes, values, beliefs, and behavior. Given this focus, interest in these theories mirrors the growing popularity of group-based management techniques applied to topics such as group decision-making, team building, group performance, organizational culture and organizational change.
Guohua Zhang, Xueting Liu, Bengt Ake Sundén and Gongnan Xie
This study aims to clarify the mechanism of film hole location at the span-wise direction of an internal cooling channel with crescent ribs on the adiabatic film cooling…
Abstract
Purpose
This study aims to clarify the mechanism of film hole location at the span-wise direction of an internal cooling channel with crescent ribs on the adiabatic film cooling performance, three configurations are designed to observe the effects of the distance between the center of the ellipse and the side wall(Case 1, l = w/2, Case 2, l = w/3 and for Case 3, l = w/4).
Design/methodology/approach
Numerical simulations are conducted under two blowing ratios (i.e. 0.5 and 1) and a fixed cross-flow Reynolds number (Rec = 100,000) with a verified turbulence model.
Findings
It is shown that at low blowing ratio, reducing the distance increases the film cooling effectiveness but keeps the trend of the effectiveness unchanged, while at high blowing ratio, the characteristic is a little bit different in the range of 0 = x/D =10.
Research limitations/implications
These features could be explained by the fact that shrinking the distance between the hole and side wall induces a much smaller reserved region and vortex downstream the ribs and a lower resistance for cooling air entering the film hole. Furthermore, the spiral flow inside the hole is impaired.
Originality/value
As a result, the kidney-shaped vortices originating from the jet flow are weakened, and the target surface can be well covered, resulting in an enhancement of the adiabatic film cooling performance.