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1 – 10 of 119Mohamed Arif Raj Mohamed, Rajesh Yadav and Ugur Guven
This paper aims to achieve an optimum flow separation control over the airfoil using a passive flow control method by introducing a bio-inspired nose near the leading edge of the…
Abstract
Purpose
This paper aims to achieve an optimum flow separation control over the airfoil using a passive flow control method by introducing a bio-inspired nose near the leading edge of the National Advisory Committee for Aeronautics (NACA) 4 and 6 series airfoil. In addition, to find the optimised leading edge nose design for NACA 4 and 6 series airfoils for flow separation control.
Design/methodology/approach
Different bio-inspired noses that are inspired by the cetacean species have been analysed for different NACA 4 and 6 series airfoils. Bio-inspired nose with different nose length, nose depth and nose circle diameter have been analysed on airfoils with different thicknesses, camber and camber locations to understand the aerodynamic flow properties such as vortex formation, flow separation, aerodynamic efficiency and moment.
Findings
The porpoise nose design that has a leading edge with depth = 2.25% of chord, length = 0.75% of chord and nose diameter = 2% of chord, delays the flow separation and improves the aerodynamic efficiency. Average increments of 5.5% to 6° in the lift values and decrements in parasitic drag (without affecting the pitching moment) for all the NACA 4 and 6 series airfoils were observed irrespective of airfoil geometry such as different thicknesses, camber and camber location.
Research limitations/implications
The two-dimensional computational analysis is done for different NACA 4 and 6 series airfoils at low subsonic speed.
Practical implications
This design improves aerodynamic performance and increases the structural strength of the aircraft wing compared to other conventional high lift devices and flow control devices. This universal leading edge flow control device can be adapted to aircraft wings incorporated with any NACA 4 and 6 series airfoil.
Social implications
The results would be of significant interest in the fields of aircraft design and wind turbine design, lowering the cost of energy and air travel for social benefits.
Originality/value
Different bio-inspired nose designs that are inspired by the cetacean species have been analysed for NACA 4 and 6 series airfoils and universal optimum nose design (porpoise airfoil) is found for NACA 4 and 6 series airfoils.
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Nikhil Kalkote, Ashutosh Kumar, Ashwani Assam and Vinayak Eswaran
The purpose of this paper is to study the predictability of the recently proposed length scale-based two-equation k-kL model for external aerodynamic flows such as those also…
Abstract
Purpose
The purpose of this paper is to study the predictability of the recently proposed length scale-based two-equation k-kL model for external aerodynamic flows such as those also encountered in the high-lift devices.
Design/methodology/approach
The two-equation k-kL model solves the transport equations of turbulent kinetic energy (TKE) and the product of TKE and the integral length scale to obtain the effect of turbulence on the mean flow field. In theory, the use of governing equation for length scale (kL) along with the TKE promises applicability in a wide range of applications in both free-shear and wall-bounded flows with eddy-resolving capability.
Findings
The model is implemented in the in-house unstructured grid computational fluid dynamics solver to investigate its performance for airfoils in difficult-to-predict situations, including stalling and separation. The numerical findings show the good capability of the model in handling the complex flow physics in the external aerodynamic computations.
Originality/value
The model performance is studied for stationary turbulent external aerodynamic flows, using five different airfoils, including two multi-element airfoils in high-lift configurations which, in the knowledge of the authors, have not been simulated with k-kL model until now.
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Jorge Lucas Krenchiglova, Luís Orlando Emerich dos Santos, Diogo Nardelli Siebert and Paulo Cesar Philippi
The main purpose of this paper was to investigate Lattice Boltzmann (LB) models for the bulk incompressible flow past immersed bodies and to find the set of boundary conditions…
Abstract
Purpose
The main purpose of this paper was to investigate Lattice Boltzmann (LB) models for the bulk incompressible flow past immersed bodies and to find the set of boundary conditions (BCs) that can be considered suitable for modeling the borders of the numerical simulation domain in such a way as to avoid any effect of these BC on the flow trail that is formed behind the body.
Design/methodology/approach
Three different models of the Lattice Boltzmann equation (LBE) and six different sets of BCs are tested. In addition to the classical LBE based on the Bhatnagar–Gross–Krook (BGK) single relaxation time collision model, a moments-based model and a model with two relaxation times were investigated.
Findings
The flow pattern and its macroscopic effects on the aerodynamic coefficients appear to be very dependent on the set of BC models used for the borders of the numerical domain. The imposition of pressure at the exit results in pressure perturbations, giving rise to sound waves that propagate back into the simulation domain, producing perturbations on the upwind flow. In the same way, the free-slip BC for the lateral bords appears to affect the trail of vortices behind the body in this range of Reynolds number (Re = 1,000).
Originality/value
The paper investigates incompressible flow past immersed bodies and presents the set of BCs that can be considered suitable for modeling the borders of the numerical simulation domain in such a way as to avoid any effect of these BCs on the flow trail that is formed behind the body.
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Mao-Lin Shi, Liye Lv and Lizhang Xu
Extreme support vector regression (ESVR) has been widely used in the design, analysis and optimization of engineering systems of its fast training speed and good computational…
Abstract
Purpose
Extreme support vector regression (ESVR) has been widely used in the design, analysis and optimization of engineering systems of its fast training speed and good computational ability. However, the ESVR model is only able to utilize one-fidelity information of engineering system. To solve this issue, this paper extends extreme support vector regression (ESVR) to a multi-fidelity surrogate (MFS) model which can make use of a few expensive but higher-fidelity (HF) samples and a lot of inaccurate but cheap low-fidelity (LF) samples, named ESVR-MFS.
Design/methodology/approach
In the ESVR-MFS model, a kernel matrix is designed to evaluate the relationship between the HF and LF samples. The root mean square error of HF samples is used as the training error metric, and the optimal hyper-parameters of the kernel matrix are obtained through a heuristic algorithm.
Findings
A number of numerical problems and three engineering problems are used to compare the ESVR-MFS model with the single-fidelity ESVR model and two benchmark MFS models. The results show that the ESVR-MFS model exhibits competitive performance in both numerical cases and practical cases tested in this work.
Practical implications
The proposed approach exhibits great capability for practical multi-fidelity engineering design problems.
Originality/value
A MFS model is proposed based on ESVR, which can make full use of the advantages of both HF data and LF data to achieve optimal results at same or lower cost.
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Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States…
Abstract
Under this heading are published regularly abstracts of all Reports and Memoranda of the Aeronautical Research Council, Reports and Technical Memoranda of the United States National Advisory Committee for Aeronautics and publications of other similar Research Bodies as issued
Farid Shahmiri, Maryam Sargolzehi and Mohammad Ali Shahi Ashtiani
The effects of rotor blade design variables and their mutual interactions on aerodynamic efficiency of helicopters are investigated. The aerodynamic efficiency is defined based on…
Abstract
Purpose
The effects of rotor blade design variables and their mutual interactions on aerodynamic efficiency of helicopters are investigated. The aerodynamic efficiency is defined based on figure of merit (FM) and lift-to-drag responses developed for hover and forward flight, respectively.
Design/methodology/approach
The approach is to couple a general flight dynamic simulation code, previously validated in the time domain, with design of experiment (DOE) required for the response surface development. DOE includes I-optimality criteria to preselect the data and improve data acquisition process. Desirability approach is also implemented for a better understanding of the optimum rotor blade planform in both hover and forward flight.
Findings
The resulting system provides a systematic manner to examine the rotor blade design variables and their interactions, thus reducing the time and cost of designing rotor blades. The obtained results show that the blade taper ratio of 0.3, the point of taper initiation of about 0.64 R within a SC1095R8 airfoil satisfy the maximum FM of 0.73 and the maximum lift-to-drag ratio of about 5.5 in hover and forward flight.
Practical implications
The work shows the practical possibility to implement the proposed optimization process that can be used for the advanced rotor blade design.
Originality/value
The work presents the rapid and reliable optimization process efficiently used for designing advanced rotor blades in hover and forward flight.
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W.J. Cox, J.N. Siddall and T.E. Stephenson
FOR some years there has been proceeding, under the auspices of the National Research Council of Canada, an investigation of the control and stability characteristics of tailless…
Abstract
FOR some years there has been proceeding, under the auspices of the National Research Council of Canada, an investigation of the control and stability characteristics of tailless aircraft. Because of the difficulties inherent in other methods of investigation, the work is being done in flight, using a glider.
Siva Marimuthu and Dhavamani Chinnathambi
Since the inception of aerospace engineering, reducing drag is of eternal importance. Over the years, researchers have been trying to improve the aerodynamics of National Advisory…
Abstract
Purpose
Since the inception of aerospace engineering, reducing drag is of eternal importance. Over the years, researchers have been trying to improve the aerodynamics of National Advisory Committee for Aeronautics (NACA) aerofoils in many ways. It is proved that smooth-surfaced NACA 0012 aerofoil produces more drag in compressible flow. Recent research on shark-skin pattern warrants a feasible solution to many fluid-engineering problems. Several attempts were made by many researchers to implement the idea of shark skin in the form of coatings, texture and more. However, those ideas are at greater risk when it comes to wing maintenance. The purpose of this paper is to implement a relatively larger biomimetic pattern which would make way for easy maintenance of patterned wings with improved performance.
Design/methodology/approach
In this paper, two biomimetic aerofoils are designed by optimizing the surface pattern of shark skin and are tested at different angles of attack in the computational flow domain.
Findings
The results of the biomimetic aerofoils prove that viscous and total drag can be reduced up to 33.08% and 3.68%, respectively, at high subsonic speed when validated against a NACA 0012 aerofoil. With the ample effectiveness of patched shark-skin pattern, biomimetic aerofoil generates as high as 10.42% lift than NACA 0012.
Originality/value
In this study, a feasible shark-skin pattern is constructed for NACA 0012 in a transonic flow regime. Computational results achieved using the theoretical model agree with experimental data.
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Rajesh Sahu and B.S.V. Patnaik
The purpose of this paper is to achieve high‐performance aerofoils that enable delayed stall conditions and achieve high lift to drag ratios.
Abstract
Purpose
The purpose of this paper is to achieve high‐performance aerofoils that enable delayed stall conditions and achieve high lift to drag ratios.
Design/methodology/approach
The unsteady Reynolds averaged Navier‐Stokes equations are employed in conjunction with a shear stress transport (κ‐ω) turbulence model. A control equation is designed and implemented to determine the temporal response of the actuator. A rotating element, in the form of an actuator disc, is embedded on the leading edge of NACA 0012 aerofoil, to inject momentum into the wake region. The actuator disc is rotated at different angular speeds, for angles of attack (α) between 00 and 240.
Findings
Phenomena such as flow separation, wake vortices, delayed stall, wake control, etc. are numerically investigated by means of streamlines, streaklines, isobars, etc. Streamwise and cross‐stream forces on the aerofoil are obtained. The influence of momentum injection parameter (ξ) on the fluid flow patterns, and hence on the forces acting on the streamlined body are determined. A synchronization‐based coupling scheme is designed and implemented to achieve annihilation of wake vortices. A delayed stall angle resulted with an attendant increase in maximum lift coefficient. Due to delay and/or prevention of separation, drag coefficient is also reduced considerably, resulting in a high‐performance lifting surface.
Research limitations/implications
The practicality of momentum injection principle requires both wide ranging and intensive further studies to move forward beyond the proof of concept stage.
Practical implications
Determination of forces and moments on an aerofoil is of vital interest in aero‐dynamic design. Perhaps, runways of the future can be shorter and/or more pay load can be carried by an aircraft, for the same stall speed.
Originality/value
The paper describes how a synchronization‐based coupling scheme is designed and implemented along with the RANS solver. Furthermore, it is tested to verify the dynamic adaptability of the wake vortex annihilation for NACA 0012 aerofoils.
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The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability…
Abstract
Purpose
The purpose of this paper is to investigate airfoil’s tonal noise reduction mechanism when deploying surface irregularities, such as surface waviness by means of spatial stability analyses.
Design/methodology/approach
Flow field calculations over smooth and wavy-surface NACA 0012 airfoils at 2° angle of attack and at Reynolds number of 200,000 are performed using the large eddy simulation (LES) approach. Three geometrical configurations are considered: a smooth NACA 0012 airfoil, wavy surface on the suction side (SS) and wavy surface on the pressure side (PS). The spatial stability analyses using the LES-generated flow fields are conducted and validated against the Orr-Sommerfeld stability analysis for the smooth airfoil configuration.
Findings
The spatial stability analyses show that inclusion of the wavy-type modification on the SS of the airfoil does not lead to altering of the acoustic feedback loop mechanism, with respect to the mechanism observed for the smooth airfoil configuration. In contrast, applying the surface modifications to the airfoil PS leads to a significant reduction of the amplification range of disturbances in the vicinity of the trailing edge for the frequency of the acoustic feedback loop mechanism.
Practical implications
The spatial analyses using, for example, LES-generated flow fields can be widely used to determine acoustic sources and associated distributions of amplifications for a wide range of applications in the aeroacoustics.
Originality/value
The spatial stability analysis approach based on flow fields computed a priori using the LES method has been introduced, validated and used to determine behaviour of the acoustic feedback loop when accurate reconstruction of geometry effects is required.
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