Effect Of Dimples Research Articles

CFD Analysis of Controlling the Airflow over Airfoils using Dimples: Technical Note

The main objective of this work is to improve the aerodynamic characteristics and manoeuvrability of the aircraft. The reduction in drag and stall phenomena will automatically enhance the aerodynamic characteristics. This project is an effort to enhance the aerodynamic characteristics of airfoil by introducing surface modifications in the form of dimples. The shape of the dimples we selected is circular shaped dimple. We placed 12 dimples in both the surfaces in appropriate places so that they could delay the boundary layer formation. The dimple generally creates turbulence by creating vortices which in turn delays the boundary layer formation. With the effects of dimple, pressure drag gets reduced and also the acoustic effects get reduced. This project includes the computational analysis of dimple effect on aircraft wing using NACA 0018 symmetric airfoil with uniform cross section throughout the length of airfoil. Subsonic flows are considered for this analysis. The analyses were done under the inlet velocities of 30m/s and 60m/s at different angle of attack such as 0, 5, 10 and 15 degrees. The models were designed using CATIA V5 and simulated using ANSYS CFX software.

Numerical simulation of the effects of passive flow control techniques on hydrodynamic performance improvement of the hydrofoil

Efficient hydrofoil design is a massive challenge for the current turbine blade designers. Flow separation on the suction side of the hydrofoil reduces the hydrodynamic performance of the current turbine. In this paper, the combined effects of dimple with vortex generators and dimple with tubes on S1210 hydrofoil is numerically studied and compared with baseline hydrofoil. The lift coefficient values increased at a higher angle of attack, and the stall angle is delayed from 10° to 12°. Maximum glide ratio increments are 132% and 144% at an angle of attack of 12° for outward dimple with tubes and outward dimple with vortex generators respectively. The findings will be helpful to design a stronger blade profile for the current turbine.

Heat Transfer Enhancement from a Heated Plate with Hemispherical Convex Dimples by Forced Convection Along with a Cross Flow Jet Impingement

In the present study, heat transfer from a small three dimensional rectangular channel due to turbulent jet impinging from a nozzle normal to the main flow at the inlet has been investigated. Hemispherical convex dimples are attached to the bottom plate from where heat transfer calculations are to be performed. Numerical simulations were performed using the finite volume method with SST <i>k</i>– ω turbulence model. The duct and nozzle Reynolds number are varied in the range of <i>10000 ≤</i> Re<i>D ≤ 50000</i> and <i>6000 ≤</i> Re<i>d ≤ 12000</i>, respectively. Different nozzle positions (<i>X/D = 10.57</i>, <i>12.88</i>, <i>15.19</i>) along the axial direction of the rectangular duct have been considered. It has been found that higher heat transfer is observed at <i>X/D = 10.57</i> as compared to the other positions. The heat transfer enhancements with and without cross-flow effects have also been compared. It has been shown that the heat transfer rate with cross-flow is found to be much higher than that without cross-flow. Also, the effect of dimples on the heated surface on heat transfer was investigated. The heat transfer is found to be greater in the presence of a dimpled surface than a plane surface.

Geometric Effects of Shallow Dimples in Turbulent Channel Flows at $$Re_{\tau }\approx 180$$: A Vorticity Transport Perspective

Shallow dimples have shown a great potential to reduce turbulent drag in several experiments. However, the mechanism underlying their effects on turbulence dynamics remains a subject of deliberation. In this numerical study, a vorticity transport perspective is adopted to elucidate the geometric effects of shallow dimples on the turbulence dynamics in a fully-developed turbulent channel flow. The geometric modifications considered in the present direct numerical simulation at a bulk Reynolds number of 2800 include changing the planform design and modulating the streamwise wall slope. The planform design had a significant impact on the mean flow topology and the drag property. Out of the five planform designs, diamond (shape) dimples produced the highest amount of total drag reduction of $$\approx 7\%$$, whereas symmetric circular dimples caused the greatest increase in total drag by $$\approx 6\%$$. Results revealed that geometric modifications of shallow dimples mainly affect the vorticity redistribution process that predominates in the inner region of a turbulent boundary layer, and in turn the generation of Reynolds stress. The drag property of a dimpled surface was found to scale with the velocity–vorticity correlation term representing the physical process of vorticity stretching and reorientation. The occurrence of flow separation near the leading edge of the dimple altered the vorticity dispersion process in the outer region, thereby modifying the generation of Reynolds stress in the bulk flow. On the other hand, the vortex dispersion process in the inner layer can be altered by modulating the streamwise wall slope. Accordingly, the vorticity redistribution process was modified but the near-wall generation of Reynolds stress was unaffected. Thus, only the form drag varied with the streamwise wall slope, while the viscous drag remained largely the same.

Numerical Study on Effect of Dimples on Tribo-Characteristics in Non-Newtonian Thermal Elastohydrodynamic Lubrication Point Contacts With Different Mechanical and Thermal Properties

Abstract The transient behavior of tribo-characteristics caused by micro-dimples on point contact surfaces with different mechanical and thermal properties was investigated based on non-Newtonian thermal elastohydrodynamic lubrication (EHL) analysis. The dimples were assumed to exist on both contact surfaces and the surface shapes of the contact bodies were evaluated separately. It is pointed out that surface texturing due to the micro-dimples is not necessarily beneficial in EHL contacts under fully flooded conditions since the micro-dimples provide a high pressure and a thin minimum film thickness as compared with the case of contacts with smooth surfaces, although the friction coefficient of surfaces with micro-dimples is always lower than that of the smooth surfaces. In order to obtain relatively good tribo-characteristics, the velocity of the surface with low thermal conductivity should be faster than that with high thermal conductivity, and the wavelengths of micro-dimples in the direction of motion on both surfaces should be different.

A Study on Flow Characteristics with Dimple in Rectangular Flow Channel

In order to improve the performance of the heat exchanger, it is important to enhance the heat transfer coefficient at the wall surface. It has been reported that the dimples are used in the heat exchanger to increase the cross-sectional area and agitate the fluid motion for enhancing the heat transfer coefficient. There are many experimental studies on effects of multiple dimples on flow characteristics. However, there are few experimental reports which comparing the turbulent-flow characteristics on dimple shapes. Regarding the turbulent-flow characteristics which are exerted a single elliptical dimple, three-dimensional flow and Reynolds stress measured by a particle image velocimetry experiments. Furthermore, in order to explore the effect of installation angle of dimple on heat transfer, it investigated the difference in the characteristics of the flow field on dimple which installed different angle and the factors that improve the heat transfer performance and the flow agitation performance.

Thermo-elasto-hydrodynamic analysis of triangular textured mechanical face seals

A 3D thermo-elasto-hydrodynamic (TEHD) model is presented to study the effects of triangular dimples on the loadcarrying capacity, leakage and friction of a mechanical seal operated under mixed or full film lubrication conditions. The model is solved by the finite element method (FEM), which takes into account the effects of the Jakobsson-Floberg-Olsson (JFO) cavitation boundary condition, surface roughness, elastic-plastic contact, thermo-elastic deformation, and the temperature-viscosity relation. The numerical results of the TEHD model are quite different from those of the hydrodynamic (HD) and thermo-hydrodynamic (THD) models, especially at high speeds. In order to obtain the optimum shape and distribution of the triangular dimples, a comparative study is conducted to investigate different distributions of equilateral triangles and isosceles right triangles. The results show that a surface textured mechanical seal with isosceles right triangular dimples has the most significant hydrodynamic and pumping effects which, in turn, are beneficial to sealing face opening behavior and leakage limitation. The theoretical results are in good agreement with the experimental ones, and offer new guidance for the future design and development of high-speed mechanical seals for aviation piston pumps.

Developing Experimental of Dimple Effect Applied on Flat Plate against Fluid Flow

Dimple is a concave commonly seen on a golf ball. These concaves turn out to have an effect on the movement of the golf ball so as to help the golf ball fly further. From the advantages of golf balls, whether the cavity can help to reduce the friction of the hull with the water surface. This study aims to determine the effect of dimple on flat plate with different types of flow (laminar, transition, and turbulent) and how it affects the coefficient of friction (Cf). In addition, with the difference in the ratio of the concavity (Rc) how it affects the coefficient of friction (Cf). From these influences later we can know how the optimal dimple design on the hull of the ship. The simulation method will be done with Numeca Fine Open. This software can simulate the complicated shape dimple well than any other software. The result of the analysis will be known to decrease the coefficient of friction (Cf) during laminar flow, transition, and turbulent. With a growing influence when turbulent flow. In addition, the greater the ratio of the concentration will decrease the coefficient of friction greater than the small-scale ratio .

Improving the wear resistance of PTFE-based friction material used in ultrasonic motors by laser surface texturing

Abstract For improving wear resistance of PTFE-based material and performances of ultrasonic motors, 1-Dimple and 3-Dimple textures were fabricated on stator surface based on observations of transfer material. The worn surface and wear debris were observed to investigate the effect of textures on wear behavior. Meanwhile, performances of the motor were tested. The wear rate of PTFE material sliding against 3-Dimple stator decreased by 52.5%, the average speed of the motor was improved by 20.6%, and the maximum efficiency of 3-Dimple stator reached 32.7%. The beneficial effect of dimples was to make the contact surface discontinuous, thereby reducing the adhesion force between stator and PTFE material, which prevented severe adhesive wear of PTFE-based material and improved the motor performances.

Effects of dimples’ arrangement style of rough surface and jet geometry on impinging jet heat transfer

The enhancement of heat transfer from the impinging jets can be reason of tens of parameters. In earlier studies, researchers have done numerous experiments or numerical runs to show the effect of each parameter individually. However, in recent decade some new methodologies, such as Design of Experiment (DoE) and Analysis of Variance (ANOVA) have been used to achieve more comparative parameter analysis and to optimize the number of experiments (or numerical runs). In this study, DoE and ANOVA methods are applied to an experimental impinging jet study. The jet geometry and roughness of impingement plate are the main considered parameters of this study. Beside them, effects of jet-to-surface distance (H) and radial distance (r) on the target surface are analyzed. The data runs are performed for a constant jet Reynolds number 20,000. The Taguchi DoE method is applied to the study in order to design the experiments. Totally 18 experiments are run base on the orthogonal array of L18 (16) (33), and effects of each design parameter on heat transfer is found out by ANOVA. As a result, it is concluded that, the highest effect on Nusselt number is observed to be the radial distance (88%), while surface roughness has the effect in percentage of 8%. The contribution of jet geometry and jet-to-surface distance are much lower, as being 3% and 1%, respectively.

Investigation of deposition and self-cleaning mechanism during particulate fouling on dimpled surfaces

Structuring of surfaces increases the efficiency of heat exchangers, but influences the deposition of particles suspended in the fluid. It is assumed, that spherical dimples suppress the deposition of particles or even induce a permanent cleaning of the occupied surface. In this study the self-cleaning mechanism of dimpled surfaces in heat exchangers is investigated to describe the influencing factors and mechanisms of particulate fouling. To get a detailed insight into fundamental deposition mechanisms, experiments on different dimpled surfaces have been carried out. According to conditions of industriell problems, e.g. cooling water fouling using river or sea water, concentrations of particles (spherical glas, dp,50 = 3 μm) of c = 2 g/l to c = 10 g/l were used. Influences of enforced turbulence due to structuring of surface with dimples or increasing fluid velocity were investigated and visualialized with μPIV technique. Furthermore, different test durations and number as well as the geometry of the dimples were considered and evaluated with specially developed analytical methods. In extension of preceding studies on the effect of a single dimple the influencing parameters were quantified and the effect of multiple dimples in a row were investigated experimentally. A repeatable fouling pattern was observed for the different structured surfaces. The quantitative results show that the surface coverage is generally decreased downstream of the dimples. Therefore, the results confirm earlier findings suggesting an advantage of dimpled surfaces against other surface structures with respect to thermo-hydraulic efficiency as well as reduced fouling propensit. Thus, this study has shown the occurrence of self-cleaning mechanisms of the surface downstream of the dimple and provides the possibility to estimate values for the reduction of particulate depositions on dimpled surfaces. All results presented were obtained by analyzing the surface around the dimple.

Effect of additives on a surface textured piston ring–cylinder liner system

ABSTRACTLaser texturing of the surface is a known approach to improve the tribological performance of mechanical systems. Many studies focused on optimising surface texture parameters for the piston-ring cylinder liner (PRCL) system. However, little attention is given to explore the effect of the textured surface on additive film formation. In the present work, the effect of a laser textured surface on the formation of additives tribochemical films and its impact on the tribological performance of PRCL system is studied. Commercially available steel piston ring and grey cast iron cylinder liner are used as samples to carry out the experiments using linear reciprocating tribometer. Experiments are carried out at 75 N load, 0.1 Hz frequency and 80°C temperature, using polyalphaolefin as base oil mixed with different additives. It is found that dimples are interfering in the formation of tribo-chemical films. However, the hydrodynamic effect of dimples is contributing to the improvement of lubrication performance even in the presence of additives.

A Numerical and Experimental Investigation of Dimple Effects on Heat Transfer Enhancement with Impinging Jets

This research was aimed at studying the numerical and experimental characteristics of the air flow impinging on a dimpled surface. Heat transfer enhancement between a hot surface and the air is supposed to be obtained from a dimple effect. In the experiment, 15 types of test plate were investigated at different distances between the jet and test plate (B), dimple diameter (d) and dimple distance (Er and Eθ). The testing fluid was air presented in an impinging jet flowing at Re = 1500 to 14,600. A comparison of the heat transfer coefficient was performed between the jet impingement on the dimpled surface and the flat plate. The velocity vector and the temperature contour showed the different air flow characteristics from different test plates. The highest thermal enhancement factor (TEF) was observed under the conditions of B = 2 d, d = 1 cm, Er= 2 d, Eθ = 1.5 d and Re = 1500. This TEF was obtained from the dimpled surface and was 5.5 times higher than that observed in the flat plate.

Edge-area form removal of two-process surfaces with valley excluding method approach

This paper analyses the influence of edge-area form removal on surface texture parameters (from ISO 25178 standard). The study focused on assessing the effect of near-edge dimples on surface texture analysis. Areal form removal was performed by means of digital filtering methods (regular Gaussian filter, robust Gaussian regression filter, median filter and/or other algorithms). For minimisation of dimples distortion the valley digital excluding method (VDEM) with standard deviation determination procedure was applied to measure plateau-honed cylinder liner surfaces (more than 20 measured and/or 20 with digitally added dimples surfaces were studied). The measurements were performed with a stylus instrument, Talyscan 150, or a white light interferometer, Talysurf CCI Lite. It was assumed that application of VDEMwith further application of proposed digital filtering algorithms caused the decrease in dimples distortion with accordance to regular Gaussian regression and/or robust Gaussian regression filtering methods. It was also found that the near-edge dimples were more vulnerable to distortion than the centre-located oil pockets.

Investigation on effect of square dimples on NACA0012 airfoil with various Reynolds numbers

ABSTRACT In this present investigation, we extend our previous research (Booma Devi, P., and Dilip A. Shah. 2018. “Effect of Square Dimples on the Temperature Distribution and Heat Transfer Coefficient of NACA0012 Airfoil.” International Journal of Ambient Energy ISSN0143-0750 (Print) 2162-8246 (Online). doi:10.1080/01430750.2017.1399450) and we consider the square dimples over the upper surface of the NACA 0012 wing whereas the Reynolds number range extended to the order of 106 say (4.00 × 106, 4.25 × 106 and 4.50 × 106) for different ranges of upper surface temperatures and lower surface temperatures on the airfoils. Coefficient of drag, coefficient of lift and coefficient of skin friction are evaluated during this investigation for various angles of attacks and it is found that the same size dimples failed to provide a desired effect in the higher Reynolds number.

Flow and Heat Transfer in the Tree-Like Branching Microchannel with/without Dimples.

This work displays a numerical and experimental investigation on the flow and heat transfer in tree-like branching microchannels and studies the effects of dimples on the heat transfer enhancement. The numerical approach is certified by a smooth branching microchannel experiment. The verification result shows that the SSG turbulence model can provide a reasonable prediction. Thus, further research on the convective heat transfer in dimpled branching microchannels is conducted with the SSG turbulence model. The results indicate that the dimples can significantly improve the averaged heat transfer performance of branching microchannels, and the heat transfer increment of the branch segment increases with the increase in the branching level. However, the flow dead zones in some dimples at bifurcations and bends suppress the turbulent flow and heat transfer. Furthermore, the Nu number ratio (Nua/Nus) and thermal enhancement factor (η) both monotonously decrease as the Re number increases, while the friction factor ratio (fa/fs) changes nonlinearly. The entropy generation rates of and in all dimpled cases are lower than those in the smooth case, and the dimpled case with the streamwise spacing to diameter ratio s/D = 3 obtains the lowest value of augmentation entropy generation (Ns) under the high Re number conditions. Nua/Nus, fa/fs, and η decline with the increase in the streamwise spacing to diameter ratio (s/D) from 3 to 9; therefore, the dimpled case with s/D = 3 shows the best overall thermal performance.

Analyzing the Effect of Dimples on Wind Turbine Efficiency Using CFD

Analyzing the Effect of Dimples on Wind Turbine Efficiency Using CFD

Effect of square dimples on the temperature distribution and heat transfer coefficient of an NACA0012 airfoil

ABSTRACTThe thermal boundary layer is the barrier for convective heat transfer, since the temperature within the thermal boundary layer is lower than the free stream temperature; therefore, it is preferable to maintain a small thermal boundary layer thickness (δt). Among the various categories of dimples like square, rectangle and triangle we considered square dimples for the upper surface of the NACA0012 wing throughout the span. The dimples increase the coefficient of lift due to delayed flow separation. The skin friction coefficient improvement reduces the δh which in turn reduces the (δt), therefore the rate of heat transfer is increased and surface temperature distribution becomes smooth. Dimples also act as fins, reducing the upper surface temperature to lower than the lower surface, which in turn increases the lift particularly in low-speed and micro-scale airfoils [Kim, Jongmin, Zvi Rusak, and Nikhil Koratkar. 2003. ‘Small-Scale Airfoil Aerodynamic Efficiency Improvement by Surface Temperature and Heat Transfer.’ AIAA Journal 41 (11): 2105–2113].

A Study on effects of dimple on flow and heat transfer characteristics

A Study on effects of dimple on flow and heat transfer characteristics

FORCED CONVECTION BASED HEAT TRANSFER ANALYSIS OF SPHERICAL DIMPLE AND PROTRUSION SURFACE IN TURBULENT FLOW

An experimental and numerical investigation is performed to study the effect of dimple and protrusion geometry on the heat transfer enhancement and the friction factor of surfaces with dimples and protrusions subjected to turbulent flow. The parameters used to compare the spherical dimples and protrusions are Nusselt Number, friction factor, and flow pattern. These parameters are obtained for a Reynolds number of 10500-60900. The spherical dimple results showed the greater heat transfer, which is about 6.97% higher and pressure loss which is 5.07% lower than the spherical protrusion. The realistic heat transfer augmentation capabilities of channels with dimples and protrusions can be studied from the experimental results. The comparison is made with respect to the smooth rectangular channel under the same flow and thermal boundary conditions. The numerical analysis is performed which shows the different vortex flow structures of the spherical dimples and protrusions channel.