Location Of Maximum Thickness Research Articles

Effects of body shape on hydrodynamic interactions in a dense diamond fish school

To examine the effect that body shape plays in the interactions between fish in a dense fish school, fish-like undulating foils are numerically studied in a high-density diamond school. Shape parameters of leading edge radius, boattail angle, and maximum thickness location along the body are independently varied to control the body shape. A traveling wave is prescribed to the body, and the flow around the school is solved using an immersed boundary method-based incompressible Navier–Stokes flow solver. Our findings indicate that body shape does play a significant role in the performance of the school and varies school efficiency and thrust productions by as much as 7% and 40%, respectively, and changes the efficiency in individual swimmers within the school by up to 25%. The leading edge radius drives the scale of the anterior body suction experienced throughout the school. A rounder leading edge generates more suction but consequently consumes more power. Changes to the location of the maximum thickness along the foil significantly impact the wall effect in the school by changing the shape of the “wall.” A maximum thickness that occurs at or in front of the closest point of interaction between the body and tail is favored. Finally, changes to the boattail angle manipulate the shape of the active channels in the school altering vortex–body interactions and the wall effect. A large boattail angle leads to a pinching that prohibits significant flow in the channels, reducing performance.

Numerical Investigation of the Interaction of a Circumferential Groove Casing Treatment and Near-Tip Modifications for a Highly Loaded Low-Speed Rotor Under the Influence of Double Leakage

Abstract Eckel et al. (2023, “Numerical Investigation of Near-Tip Modifications for a Highly Loaded Low-Speed Rotor Under the Influence of Double Leakage,” ASME J. Turbomach., 145(4), p. 041003) proposed using a convex-profiled pressure side region close to the tip, known as belly, as an effective method of extending the operating range of low-speed axial compressor rotors. In the literature, circumferential grooves are another well-described technique for improving the stable working range of a compressor rotor. No research has been conducted to date to determine which modification is more effective and how they interact when used together. This paper numerically investigates the influence of circumferential casing grooves and near-tip modifications on the flow field in the tip region of a highly loaded, low-speed axial compressor rotor. The simulated rotor consists of a hybrid blade configuration with a tandem profile in the mid-span region and single blade profiles near the endwalls. The single blade profile close to the tip features three different convex-profiled elements, which differ in their respective thicknesses. The aim of the numerical analysis is to explain the interaction of the secondary flow phenomena when applying the circumferential grooves and the belly geometries. For this purpose, eight different axial positions of the circumferential groove are investigated for each of the three belly configurations. These are arranged in 10% increments from −7% to 63% along the axial rotor tip chord. The potential of the concept is evaluated by a numerical investigation in the 1.5-stage setup with an inlet guide vane and tandem stator. It is shown that a circumferential groove can further increase the operating range for all belly configurations when positioned axially correctly. In this respect, equalization of the near-casing deceleration in the circumferential direction leads to an extension of the stall margin with both modifications. Concentrated regions of low-momentum fluid with a large extent in the radial direction should be avoided consequently. A tip vortex stability factor is introduced to quantitatively evaluate this effect. The operating range can thus already be estimated in a first approximation at the design point. In general, the groove and belly should be positioned where the tip leakage vortex meets the pressure side of the adjacent blade. If the groove is used together with the belly, the leading edge of the former should be situated at the location of maximum thickness of the near-tip modification. The effects of the circumferential groove and the belly are then superimposed. If using only one modification, the belly appears better suited for ensuring an extension of the operating range while maintaining high efficiencies.

Numerical Study of Geometrical Properties of Full-Span Tubercle Leading Edge Wing at Post-Stall Condition

In order to upsurge the maneuverability of micro aerial vehicles, a tubercle leading edge inspired by the whale flipper was applied as a passive stall control method. Although this method could be useful to control stall phenomena, the effect of geometrical properties on the flow physic should be investigated to reach the root of them. According to preceding research, the effect of some parameters on the tubercle leading edge wing is a hot topic among researchers. The aim of this research is to explore the effects of sectional wing geometries like amplitude, wavelength, thickness, maximum thickness location, and camber on the aerodynamic feature of full-span tubercle leading edge wing, particularly at 22 degree in post-stall circumstances. The results present that by reducing the amplitude about 2.5%c, the lift coefficient upsurges by about 3.5%; instead, the drag coefficient reduces about 6%. On the other hand, by decreasing the wavelength from 46.2%c to 11.7%c, the drag coefficient and the lift coefficient decrease by about 15% and 19%, respectively. Furthermore, as the thickness rises from 10.55%c to 18.14%c, the lift and drag coefficient goes down about 9.4% and 2.9%, respectively. Furthermore, by increasing the camber from 2.56%c to 3.34%c, the lift to drag ratio goes down by about 1.06%. Finally, by raising the last design variable (maximum thickness location) from 0.26c to 0.51c, the lift to drag ratio increases about 13.7%.

Research on optimization of structural parameters for airfoil fin PCHE based on machine learning

The thermal hydraulic performance of the printed circuit heat exchanger (PCHE) is critical to the efficiency of the supercritical carbon dioxide (S-CO2) Brayton cycle. Therefore, in this paper, four parameters (maximum thickness, maximum thickness location, transverse pitch and staggered pitch of the airfoil fin) were selected to carry out optimization research on the airfoil PCHE combined with CFD simulations, machine learning and optimization algorithms. Firstly, the simulation of the airfoil PCHE with different channel configurations was carried out to analyze the effects of four parameters on its performance. Then, the thermal hydraulic parameters were trained and predicted using the ANN model, from which correlations integrating the structural and arrangement parameters of the airfoil PCHE were obtained. Finally, the sequential quadratic programming (SQP) algorithm and non-dominated sorting genetic algorithm II (NSGA-II) were used to carry out the optimization studies of PCHE, respectively. The results showed that increasing the value of the maximum thickness location can improve the comprehensive performance of PCHE. After optimization, the performance coefficient ηh was improved by about 6.2 % compared to the basic structure when Re = 45000.

Uncertainty quantification of wind turbine airfoil aerodynamics with geometric uncertainty

An artificial neural network based reduced order model (ROM) is developed to predict the load coefficients and performance of wind turbine airfoils. The model is trained using a representative database of 972 wind turbine airfoil shapes generated by perturbing the design parameters in each of 12 baseline airfoils defining commercially relevant modern wind turbines. The predictions from our ROM show excellent agreement with the CFD data, with a 99th percentile maximum errors of 0.03 in lift-coefficient, 2 in lift-to-drag ratio and 0.002 in pitching moment coefficient. A Monte-Carlo based uncertainty quantification (UQ) and global sensitivity analysis (GSA) framework is developed using this computationally economical ROM. Using UQ, we observed the stall behavior to be very sensitive to geometric uncertainty, with more than 10% deviation in lift coefficient associated to 5% deviation in geometric features. Sobol’s analysis is used to identify the most influencing geometric feature for the stall behavior to be concentrated at the maximum thickness location on the airfoil suction surface.

Maximum Thickness Location Selection of High Subsonic Axial Compressor Airfoils and Its Effect on Aerodynamic Performance

Solidity and camber angle are key parameters with a primary effect on airfoil diffusion. Maximum thickness location has a considerable impact on blade loading distribution. This paper investigates correlations of maximum thickness location, solidity, and camber angle with airfoil performance to choose maximum thickness location quickly for compressor airfoils with different diffusion. The effects of maximum thickness location, solidity, and camber angle on incidence characteristics are discussed based on abundant two-dimensional cascade cases computed through numerical methods. Models of minimum loss incidence, total pressure loss coefficient, diffusion factor, and static pressure rise coefficient are established to describe correlations quantitatively. Based on models, dependence maps of total pressure loss coefficient, diffusion factor, and static pressure rise coefficient are drawn and total loss variation brought by maximum thickness location is analyzed. The study shows that the preferred selection of maximum thickness location can be the most forward one with no serious shock loss. Then, the choice maps of optimal maximum thickness location on different design conditions are presented. The optimal maximum thickness locates at 20–35% chord length. Finally, a database of optimal cases which can meet different loading requirements is provided as a tool for designers to choose geometrical parameters.

Coupling optimization of casing groove and blade profile for a radial turbine

In order to suppress the tip leakage loss and increase the isentropic efficiency in a radial turbine with low aspect ratio blade, a new coupling flow control technology including casing groove and NACA blade profile is proposed and optimized numerically. The coupling effects of casing groove size LS, groove number Numslot, maximum thickness location of profile MLT and leading parameter of profile LP on isentropic efficiency of a radial turbine are obtained with Design of Experiment (DOE) and response surface model. A genetic optimization is achieved and the coupling flow control mechanism is revealed. Complex variation of isentropic efficiency is observed with the coupling effect of groove size and groove number, and maximum isentropic efficiency variation of 0.6% is obtained with the increase of LS when Numslot is 3. The coupling effect between LS and LP, is also significantly influenced by groove number. The lower limit of LP for maximum isentropic efficiency is decreased from 7 to 3 with the increase of groove number. The optimization result illustrates that the isentropic efficiency can be increased by 0.9% at design point when the LS, Numslot, MLT and LP are 0.8 mm, 2, 0.1, and 0.8 respectively. A maximum isentropic efficiency increment of 2.0% is also found when total pressure ratio is 2.1. The optimal casing groove forms a flow opposite to the tip leakage flow to suppress the impact range of the secondary flow near suction surface. At the same time, the optimal NACA profile also decreases the tip leakage velocity near trailing, suppresses the tip leakage vortex generation, and reduces the trailing edge loss.

The Effect of Aspect Ratio on Wall Pressure Fluctuations at a Wing-Plate Junction

AbstractMeasurements of the wall pressure fluctuations near a wing-plate junction were made for wings with three different aspect ratios (AR) of 0.2, 0.5, and 1.0 at several angles of attack. The chord-based Reynolds number for each wing was 274,000. The results show that the wall pressure fluctuations are a function of wing AR for cases where AR≤ 1.0. For each wing, the pressure fluctuations are highest upstream of the wing leading-edge due to three-dimensional flow separation; wings with AR = 1.0 and 0.5 show comparable levels, while those with AR = 0.2 show lower fluctuation levels over a wide frequency range. Downstream of the leading-edge, the pressure fluctuations decay rapidly on both sides of the wing until the maximum thickness location after which little variation is observed. The pressure fluctuations downstream of the leading-edge on the suction-side were observed to be comparable for AR = 0.2 and 0.5, while those for AR = 1.0 were higher in magnitude. On the pressure-side, the pressure fluctuations near the leading-edge are a weak function of AR; however, those further downstream remain independent of AR. The pressure fluctuations aft of the wing on the suction-side are more coherent for lower ARs and show higher convection velocity, possibly due to an interaction between the tip and the junction flows for lower ARs.

Aero-Structural study on the blade thickness effects in an automotive turbocharger turbine in transonic conditions

Turbine blade thickness is limited by blockage and trailing edge losses, and are damaged due to high aerodynamic loadings. Safe turbine blade design needs a comprehensive knowledge of the exciting forces. This work investigates a mixed flow turbocharger turbine to study the effects of blade thickness distribution on the aero-structural performance. Three-dimensional flow field of the turbine was calculated using a CFD model in ANSYS CFX V.17. The blade structural responses are determined using an FEA model in ANSYS static structural module. Validation is performed by reference to experimental data carried out in Imperial College London on a dual turbocharger turbine. The results are presented to describe how and why the turbine aerodynamic and structural behavior varies with thickness under transonic conditions. On higher spans shock is more distributed to the passage but it has lower intensity. Thicker leading edge leads to more drop in Mach number through the bow shock. Higher distance of maximum thickness location from the leading edge caused the smaller separation bubble on the suction surface. DOI: http://dx.doi.org/10.5755/j01.mech.25.2.22151

Epiretinal membrane profile on spectral domain optical coherence tomography in patients with uveitis.

Purpose:To study the epiretinal membrane (ERM) profile on the spectral-domain optical coherence tomography (SDOCT) in eyes with uveitis.Methods:In this prospective observational study, macula of uveitic eyes were evaluated by SDOCT (Cirrus, model 5000) for ERM. ERM was quantified (in microns) and were followed up along with the best-corrected visual acuity (BCVA) and treatment profile for 1 year. ERM morphology (focal, global, or mixed) and characteristics (thickness at fovea, maximum thickness, and location of maximum thickness in relation to fovea) were documented. Changes in altered foveal contour, cystoid macular edema (CME), and central foveal thickness were also noted. BCVA was noted when the inflammation subsided and it was correlated to specific ERM characteristics. SDOCT characteristics were compared in three treatment groups (no oral steroids, oral steroids with, and without immunomodulators).Results:Thirty-four eyes of 25 patients were evaluated. Mean logMAR BCVA decreased from 0.25 to 0.35 (P = 0.005). Foveal involvement with ERM (P = 0.011), lost foveal contour (P = 0.043), and ellipsoid layer disruption (P = 0.017) were associated significantly with reduced BCVA. Focal attachment of ERM was more commonly associated with CME (P = 0.03). Median ERM thickness showed significant increase (P < 0.001). Significant ERM progression from parafoveal to foveal (P = 0.02), significant progression of the thickest area of ERM closer to fovea (P = 0.0006) indicated a strong tendency of foveal involvement and this was correlated with worse BCVA (P = 0.009, r = −0.44) Oral steroids/immunomodulators showed no significant benefit on ERM progression.Conclusion:ERM progression in uveitis has a tendency to involve the fovea and is associated with significant vision loss, particularly in foveal ERM, focal attachment, and IS-OS disruption. Oral steroids and immunomodulators have no role in halting progression.

Improving the propulsion speed of a heaving wing through artificial evolution of shape.

Aeronautical studies have shown that subtle changes in aerofoil shape substantially alter aerodynamic forces during fixed-wing flight. The link between shape and performance for flapping locomotion involves distinct mechanisms associated with the complex flows and unsteady motions of an air- or hydro-foil. Here, we use an evolutionary scheme to modify the cross-sectional shape and iteratively improve the speed of three-dimensional printed heaving foils in forward flight. In this algorithmic-experimental method, 'genes' are mathematical parameters that define the shape, 'breeding' is the combination of genes from parent wings to form a daughter, and a wing's measured speed is its 'fitness' that dictates its likelihood of breeding. Repeated over many generations, this process automatically discovers a fastest foil whose cross-section resembles a slender teardrop. We conduct an analysis that uses the larger population to identify what features of this shape are most critical, implicating slenderness, location of maximum thickness and fore-aft asymmetries in edge sharpness or bluntness. This analysis also reveals a tendency towards extremely thin and cusp-like trailing edges. These findings demonstrate artificial evolution in laboratory experiments as a successful strategy for tailoring shape to improve propulsive performance. Such a method could be used in related optimization problems, such as tuning kinematics or flexibility for flapping propulsion, and for flow-structure interactions more generally.

Experimental studies on the thickness of upward flame over poly(methyl methacrylate) slabs

SummaryExperiments were performed to investigate the flame thickness of the upward flame on the poly(methyl methacrylate) slabs with width of 100‐400 mm. The results indicated that the flame thickness exhibited an increase first and then decrease trend in the upright orientation, and the maximum thickness location was approximately equal to the pyrolysis front location. The thickness of the flame along the lateral side of slab was less than that of the interior flame. The flame maximum thickness as a function of pyrolysis height and width was obtained, which showed the maximum thickness provided a power law increase with the pyrolysis height and width. Furthermore, the maximum thickness exhibited a power law increase with the total heat release rate as well. Based on the obtained flame thickness, the radiation heat flux at the pyrolysis height was estimated by using a simplified model. Comparison with the calculated convective heat flux revealed approximated pyrolysis heights for upward flame transition from convective heat flux controlled to radiation heat flux controlled.

Lift distribution based design of two-dimensional sections

A lift distribution based section design method has been proposed. Through Newton-Raphson iterations, the section geometry is efficiently designed to meet the requirements for total lift and lift distribution. The effect of fluid viscosity on total lift is taken into account by coupling Reynolds-averaged Navier-Stokes (RANS) simulation with the potential-flow based design procedure. The present method avoids the difficulty of assigning velocity or pressure distributions on section surfaces. As the loading and thickness distributions are expressed in parametric forms, it is easy to ensure that the designed geometry is continuous and smooth. The effects of lift and thickness distributions on cavitation bucket are numerically investigated. A shift of lift loading towards the aft part of section tends to decrease the margin of back cavitation, while the width of cavitation bucket can be kept almost unchanged. To have a wider cavitation bucket, one can increase the leading edge radius, move properly the location of maximum thickness towards the leading edge, or decrease the curvature at the location of maximum thickness.

Aerodynamic Analysis of Trailing Edge Enlarged Wind Turbine Airfoils

The aerodynamic performance of blunt trailing edge airfoils generated from the DU- 91-W2-250, DU-97-W-300 and DU-96-W-350 airfoils by enlarging the thickness of trailing edge symmetrically from the location of maximum thickness to chord to the trailing edge were analyzed by using CFD and RFOIL methods at a chord Reynolds number of 3 × 106. The goal of this study is to analyze the aerodynamic performance of blunt trailing edge airfoils with different thicknesses of trailing edge and maximum thicknesses to chord. The steady results calculated by the fully turbulent k-ω SST, transitional k-ω SST model and RFOIL all show that with the increase of thickness of trailing edge, the linear region of lift is extended and the maximum lift also increases, the increase rate and amount of lift become limited gradually at low angles of attack, while the drag increases dramatically. For thicker airfoils with larger maximum thickness to chord length, the increment of lift is larger than that of relatively thinner airfoils when the thickness of blunt trailing edge is increased from 5% to 10% chord length. But too large lift can cause abrupt stall which is profitless for power output. The transient characteristics of blunt trailing edge airfoils are caused by blunt body vortices at low angles of attack, and by the combined effect of separation and blunt body vortices at large angles of attack. With the increase of thickness of blunt trailing edge, the vibration amplitudes of lift and drag curves increase. The transient calculations over-predict the lift at large angles of attack and drag at all angles of attack than the steady calculations which is likely to be caused by the artificial restriction of the flow in two dimensions.

Computational investigations of blunt trailing‐edge and twist modifications to the inboard region of the NREL 5 MW rotor

ABSTRACTThe effects of twist and section shape modifications in the inboard region on the aerodynamic characteristics of the NREL 5 MW rotor have been examined using a Reynolds‐averaged Navier–Stokes method OVERFLOW2. The baseline rotor blade was modified by increasing the trailing‐edge thickness over the inboard region by modifying the sections’ thickness distribution aft of the maximum thickness location. Results when compared with the baseline rotor show that a modest increase of trailing‐edge thickness to 10–20%c increased power capture by 1%. Further increases in trailing‐edge thickness decrease in effectiveness to the point of reducing power capture when thicknesses reach 40%c. Increasing trailing‐edge thicknesses also leads to an increase in thrust, but this load is concentrated in the inboard region, resulting in a small increase in root bending moments. The blunt trailing‐edge concept greatly reduces the spanwise extent of inboard flow separation evident in the baseline NREL 5 MW rotor. The low‐pressure region aft of the trailing edge, created by the geometry, acts to reduce the spanwise spreading of the inboard separation. Rotors with modified twist distributions over the inboard 35%R of span are also compared. Inboard twist angles are varied from + 6° to − 6° from the baseline twist schedule. Increasing inboard blade twist reduces overall rotor power capture but reduces thrust at a faster rate. Power capture remains constant with decreasing inboard geometry twist, whereas thrust increases approximately linearly by 0.75% for a decrease in thrust of 6°. Copyright © 2012 John Wiley &amp; Sons, Ltd.

Wind Tunnel Experiment for Low Wind Speed Wind Turbine Blade

Environment and green energy awareness are two main factors why this study has been carried out. This research is focused on aerodynamics study for airfoil structure modification based on NACA 0044 and NACA 0063 by using wind tunnel experiment. Aerodynamic characteristics such as lift coefficient, CL, drag coefficient, CD, lift to drag ratio and cell relative velocity has been investigated in this study. CFD simulation has been carried out at the early stage of the investigation (for NACA 0044 and NACA 0063), and a new airfoil profile had been created (0044-63) by modified the chord length and the location of maximum thickness of the airfoil by using the modified NACA Four-Digit Series. Wind tunnel experiment has been take place for three different wind speeds from 25m/s, 35m/s and 45m/s at various angles of attack from 0oto 40owith 5oincremental for the respective airfoil. The results show that the modified 0044-63 produced the better lift coefficient and this airfoil has been fabricated and tested in the wind tunnel experiment in order to validate the CFD result. This paper reports the result of aerodynamics characteristics for respective new airfoil and it shows that at angle of attack between 5oto 15o, this airfoil produced good lift to drag ratio value. Also, by modified the location of maximum thickness 30% to the trailing edge give the increment of lift to drag ratio produced approximately 15% and at the same time, give insignificant changes to the drag coefficient value.

캐비테이션 감소를 위한 혼타의 형상 연구

This paper studies on the rudder shapes for the suppression of the cavitation around a horn-type rudder. To improve the problems due to cavitation, there have been several studies. However, these some studies are recognized as incomplete ways to suppress the rudder cavitation. In this study, the section shapes to suppress the cavitation phenomena are determined by moving the location of maximum thickness for reducing the curvature variation and changing the radius of leading edge. Also, in the pintle part, the curvature radius of the inlet outlet edge of rudder plate is changed. During the design of rudder shape, two-dimensional numerical simulations are firstly performed because those offer some advantages with that cavitation phenomena becomes predictable for a short time, and then the three-dimensional numerical simulations are performed to confirm the determination. The time mean distribution of the propeller slipstream is imposed on the inlet boundary condition. As some results, this paper shows the effects reducing the range of the occurrence of cavitation, and suggests the references on the design of a horn-type rudder for the suppression of cavitation phenomena.

Influence of Thickness Variation on the Flapping Performance of Symmetric NACA Airfoils in Plunging Motion

In order to investigate the impact of airfoil thickness on flapping performance, the unsteady flow fields of a family of airfoils from an NACA0002 airfoil to an NACA0020 airfoil in a pure plunging motion and a series of altered NACA0012 airfoils in a pure plunging motion were simulated using computational fluid dynamics techniques. The “class function/shape function transformation“ parametric method was employed to decide the coordinates of these altered NACA0012 airfoils. Under specified plunging kinematics, it is observed that the increase of an airfoil thickness can reduce the leading edge vortex (LEV) in strength and delay the LEV shedding. The increase of the maximum thickness can enhance the time-averaged thrust coefficient and the propulsive efficiency without lift reduction. As the maximum thickness location moves towards the leading edge, the airfoil obtains a larger time-averaged thrust coefficient and a higher propulsive efficiency without changing the lift coefficient.

On the mean characteristics of the juncture vortex in cross-flow planes

Juncture flow of wings with leading edge sweep angles of 0°, ±15°, ±30°, and ±45° mounted on a flat plate for a turbulent approach boundary layer was investigated using laser Doppler velocimetry (LDV) in a subsonic wind tunnel. Time-averaged measurements in the cross-flow planes indicated incompletely formed vortical structures. Additionally, in the cross-flow plane at the airfoil maximum thickness location, measured velocity directions were inconsistent with vortex rotation. Complex motion of the juncture vortex system in the cross-flow direction was observed during flow visualization of the configuration in a water tunnel, suggesting masking of the mean vortex structure by the global motion of the structures. The mean vortex signature with correct rotational direction was ‘frozen’ by subtracting a constant cross-flow velocity component from the LDV mean measurements. Vorticity contours in the cross-flow planes were calculated using a finite differencing scheme on the measured data. Good comparison of vortex core estimated locations between the ‘frozen’ vortex and from vorticity contours was observed. Another artefact of the measurements was asymmetry in the vertical velocities, which is attributed to motion of the vortex core towards the flat plate in the maximum thickness plane and away from it in the 80 per cent chord plane. The horizontal location of the vortex core was observed to be influenced by wing sweep; however, the vertical location was insensitive to this parameter.

Design optimization of low-speed axial flow fan blade with three-dimensional RANS analysis

This work presents a numerical optimization procedure for a low-speed axial flow fan blade with polynomial response surface approximation model. Reynolds-averaged Navier-Stokes equations with SST turbulence model are discretized by finite volume approximations and solved on hexahedral grids for flow analyses. The blade profile as well as stacking line is modified to enhance blade total efficiency, i.e., the objective function. The design variables of blade lean, maximum thickness and location of maximum thickness are selected, and a design of experiments technique produces design points where flow analyses are performed to obtain values of the objective function. A gradient-based search algorithm is used to find the optimal design in the design space from the constructed response surface model for the objective function. As a main result, the efficiency is increased effectively by the present optimization procedure. And, it is also shown that the modification of blade lean is more effective to improve the efficiency rather than modifying blade profile.