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Improvement of Airfoils Aerodynamic Efficiency by Thermal Camber Phenomenon at Low Reynolds Number

Improvement of Airfoils Aerodynamic Efficiency by Thermal Camber Phenomenon at Low Reynolds Number

ABSTRACT: In this research, viscous, laminar and steady flow around symmetric and non-symmetric airfoils is simulated at Low Reynolds Number (LRN). Navier-Stokes (N-S) equations are discretized by Finite Volume Method (FVM) and are solved by the SIMPLE algorithm in an open source software, namely OpenFOAM. The main objective of this paper is the introduction of the thermal camber phenomenon. This phenomenon is used to improve the aerodynamic performance. Hence, a symmetric airfoil, like NACA0012, with thermal camber is compared with the airfoils with the physical camber, including NACA2412 and NACA4412, to specify which camber type has more effects on the aerodynamic efficiency. Furthermore, various temperatures are tested in order to find the optimum condition. After validation, results indicated that cooling upper surface and heating lower surface, namely thermal camber, generate lift force and improve aerodynamic performance for symmetric airfoils at a 0° Angle of Attack (AOA). These improvements are more than the airfoils with physical camber. Also, when this method is applied to the NACA2412 and NACA4412 airfoils, lift to drag coefficient ratio will increase more than the condition with only cooling or heating the surfaces.
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Low Reynolds Number Fowler Flap Design

Low Reynolds Number Fowler Flap Design

In 1992 at NASA, Florian R. Menter presented the two-equation turbulence model 𝑘-𝜔 SST (Shear Stress Transport) which was designed to produce results comparable to the existing 𝑘-𝜔 model developed by Wilcox in 1988 [19], without its strong dependence on freestream values [20]. For this, the model is identical to the 𝑘-𝜔 model in the inner 50% of the boundary layer and gradually changes to the 𝑘-𝜖 model towards the boundary layer edge, with the additional ability to account for the transport of the principal shear stress in boundary layers with adverse pressure gradients. It was shown that the results obtained with the 𝑘-𝜔 SST model are in fact independent from the freestream values and agree with experimental data for flows with adverse pressure gradient boundary layers. The usage of a 𝑘-𝜔 formulation in the inner part of the boundary layer also gives the 𝑘-𝜔 SST model the capability to be used in low Reynolds number flows without the addition of damping functions, unlike the standard 𝑘-𝜖 turbulence model.
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COMPUTATIONAL FLUID DYNAMICS OF WINDTURBINE BLADE AT VARIOUS ANGLES OF ATTACK AND LOW REYNOLDS NUMBER

COMPUTATIONAL FLUID DYNAMICS OF WINDTURBINE BLADE AT VARIOUS ANGLES OF ATTACK AND LOW REYNOLDS NUMBER

Aerodynamic studies are quite mature for flows with Reynolds number greater than 10 6 . However, there are not many analytical or numerical or experimental studies available for flows at very low Reynolds numbers. Consideration of 2D geometries, i.e., airfoils, for such studies seems to be a good starting point to improve our understanding of low Reynolds number flows. Some experimental studies are reported in [1, 2, 3]. Numerical studies, for analysis as well as for design and experimental validations of airfoils at ultralow Reynolds number are presented in [4, 5].
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Low Reynolds Number Propeller Performance Measurement in Wind Tunnel Test Rig

Low Reynolds Number Propeller Performance Measurement in Wind Tunnel Test Rig

Any new aircraft design have to meet speci c performance requirements. To achieve this ob- jective, it is necessary that each part of the aircraft be as ef cient and serviceable as possible while taking into consideration such factors as weight and volume. Propeller selection is a key factor to achieve a good propulsion system, which makes the availability of the propeller performance data a critical issue to reach a successful design. Experimental work on propeller performance was abundant before WWII [1, 2] and a database of propeller performance char- acteristics got established. That was the golden age of propeller driven aircraft. After WWII, the widespread of jet propulsion limited the use of propellers to light aircraft. However, in re- cent times, the small Unmanned Aerial Vehicles (UAV) advent has triggered the interest in the Low Reynolds Number (LRN) wing and propeller aerodynamics. LRN effects can decrease the performance of propellers and the ability of the available numerical methods to predict that performance. To deal with this, JBLADE [3] software is being developed, as an open-source pro- peller design code, using a modi ed [4] Blade Element Momentum (BEM) theory which accounts for three dimensional ow equilibrium. The software is coupled with XFOIL [5] for its suitability in predicting LRN airfoil performance [6]. JBLADE will be used to design different propellers as well as to estimate their off-design performance. To improve the prediction capability of JBLADE, accurate LRN propeller performance data is needed.
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Cross and clover shaped orifice jets analysis at low Reynolds number

Cross and clover shaped orifice jets analysis at low Reynolds number

The role played by the Kelvin-Helmholtz (K-H) azimuthal rings and the streamwise vortices in the entrainment process in the near field of a round free orifice jet have been qualita- tively and quantitatively analysed in our previous investigations, for a Reynolds number of 800 [21, 22] and 3600 [20], respectively. A strong correlation between the entrainment rate and the K-H vortex dynamics was found for both flow regimes. The K-H ring controls the sign of the ra- dial velocity and the entrainment is mainly produced in the upstream part of the K-H ring as well as in the braid region where the streamwise vortices appear. In the downstream part of the K-H ring, the flow expands from the jet core to the surrounding. Hence, the K-H ring passing gener- ates periodical compression/depression cycles in the round jet, which are believed to contribute to ambient air engulfment towards the jet core, but at the same time opposes the induction when the ring is approaching at a given axial position (i. e. in the downstream part of the ring). In our previous studies the dynamics of the round jet have been considered as a reference in the investi- gation of lobed jets (cross-shaped and daisy-shaped) having the same exit diameter and initial volume flow rate. It was found that large streamwise structures generated by the lip of the lobed diffuser are present. For the lobed jet, entrainment and expansion coexist in a practically un- changed manner in the presence or not of a K-H structure. The lobed orifice geometry intro- duces a transverse shear in the lobe troughs, like the one generated by a triangular tabs in a square jet [23], conducting to a breakdown of the K-H structures into ring segments. Streamwise structures continuously develop in the lobe troughs, at the resulting discontinuity regions, and control the ambient air entrainment. In this case the entrainment rate is less affected by the dy- namics of the K-H structure and achieves higher levels that in the reference round jet.
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Numerical Prediction of Closed Contra-Rotating Disc Flows

Numerical Prediction of Closed Contra-Rotating Disc Flows

with measurements. As a next step, the model has been applied to the computations of rotor-stator [12-13] and rotating cavity flows [15]. Comparison of predictions with calculations of the low-Reynolds number k-ε model (hereafter referred to as the k-ε model) of Morse, [10] and measurements indicated that both turbulence models are sufficiently effective to mimic the complex flow conditions (e.g. recirculation, impingement and rotation), however, the second moment closure is more effective when the anisotropic behaviour of the turbulence field influences the mean flow behaviour.
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Braz. J. Chem. Eng.  vol.34 número2

Braz. J. Chem. Eng. vol.34 número2

The momentum characteristics of an unconined laminar low of shear-thinning luids over a pair of cylinders in a side-by-side arrangement have been studied numerically over wide ranges of conditions as: 0.1 ≤ Re ≤ 100, 0.2 ≤ n ≤ 1.8 by varying gap ratios (G = 1.2, 1.7, 2, 2.5 and 4). The results reported here include the efect of Reynolds number (Re) and gap ratio (G) on the low patterns, friction, pressure and total drag coeicients, lift coeicient and surface pressure coeicients for Newtonian and shear- thinning luid low. Reynolds number, power-law index and gap ratio signiicantly afect the streamline as well as the surface pressure coeicient of both the cylinders. From the analysis of results, it is also noted that at low Re, the total drag coeicient (C D ) of shear-thinning luid is higher than that of the Newtonian and shear-thickening luids. However, as the value of Re (especially above Re =10) increases, the C D of shear-thinning luid reduces and becomes less than that of Newtonian luid. This behavior is attributed to the characteristic of shear-thinning luid by virtue of which it ofers less resistance to low compared to a Newtonian luid with increased agitation above a critical value of Re. The variation of lift coeicient (C L ) with Re divides the entire steady low range into three diferent sub- ranges. In the low and high Re range, the lift coeicient remains almost independent of Re; in the medium Reynolds number range it shows a strong dependency on Re. Power law index (n) has a strong inluence on the lift coeicient in both the low and medium Re range, whereas the efect of n becomes signiicantly weak on C L in the high Re regime. On the basis of this study, for a speciic luid, the low and gap ratio can be optimized to ensure the safety and stability of the components in industrial operations.
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The kinematics of swimming and relocation jumps in copepod nauplii.

The kinematics of swimming and relocation jumps in copepod nauplii.

Both protists and nauplii swim in a low Reynolds number, viscous world. Protists typically swim by beating flagella or by metachronal waves of cilia, and the kinematics and hydrodynam- ics of protist swimming are rather well described and understood [4–9]. The swimming in protists is typically smooth because of the high beat frequencies [10] and/or because they possess flagella with helical beat patterns that, similar to a propeller, yields nearly time-invariant propulsion force [5–7,11]. Most protists swim in a helical pattern, both because of the propulsion asymmetry imposed by the arrangement of the flagella/cilia [5–6], but also because any asymmetry at low Reynolds numbers will cause rotation that may lead to a helical swimming path [12–13]. Copepod nauplii are bilaterally symmetrical crustaceans with an exoskeleton onto which the muscular apparatus attaches [14] and they swim or jump by means of appendages in a way fundamen- tally different from protists. Both nauplii and copepodites may display three basic modes of motile behavior: 1) motionless sinking, 2) swimming by vibrating and rotating the feeding appendages at a high frequency, or 3) swimming-by-jumping, which is conducted by alternating power and recovery strokes of the appendages [15–
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Critical Reynolds number in bifurcations / Numero de Reynolds Critico em Bifurcações

Critical Reynolds number in bifurcations / Numero de Reynolds Critico em Bifurcações

Amado, F. P., Corradi, V. H., 2020.“Qualitative analysis of the region of flow development in the entrance of bifurcations”, to be published In the Proceedings of the 18th Brazilian Congress of Thermal Sciences and Engineering - ENCIT2020, November 16-20, Bento Gonçalves, RS, Brazil Amado, F. P., Corradi, V. H., Vegara, P. F. H., Mazzarela, N. G. S., Da Silva, W. A., 2019b. “Influence of Low Reynolds Number in the region of flow development In bifurcations”. In the Proceedings of the 25th ABCM International Congress of Mechanical Engineering - COBEM2019, October 20-25, Uberlândia, MG, Brazil;
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Bifurcation phenomena in viscoelastic flows through a symmetric 1: 4 expansion

Bifurcation phenomena in viscoelastic flows through a symmetric 1: 4 expansion

with “benchmark” creeping flow calculations of Alves et al. [23] shows agreement of better than 0.5%. Additionally, excel- lent agreement is obtained with the correlations of Scott et al. [24] in their range of validity (say 20 ≤ Re ≤ 37). For low Reynolds number, a comparison can also be performed against the results for the 4:1:4 constriction geometry of Cartalos and Piau [25], Szabo et al. [26] and Rothstein and McKinley [27]. These authors have studied experimentally [25,27] and numeri- cally [26] the viscoelastic flow of Boger fluids in axisymmetric contraction/expansions, with particular emphasis placed on the flow upstream of the first contraction. For low Deborah numbers the results are almost independent of whether the flow is non- Newtonian or not, and whether it occurs in a contraction or an expansion; in that situation [27] measured a vortex length and the coordinates of the vortex central position which compares very well with our predictions at De = 1.
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Braz. J. Chem. Eng.  vol.34 número1

Braz. J. Chem. Eng. vol.34 número1

Figure 5 shows the drag-reducing performance of 0-150 ppm CTAC solutions in the smooth and grooved channels at 20 °C. It can be seen that there is no drag-reducing effect in the entire range of ex- perimental Reynolds number for the grooves without surfactant. However, Bechert et al. (1997) obtained the drag-reduction effect when s + was smaller than 27 with almost the same shape and dimensionless size of grooves (riblet) by using a precise measure- ment. There is a discrepancy between his results and ours. Detailed analysis shows that the discrepancy may mainly be caused by different smoothness of the grooved surfaces. In their study, the riblet surfaces were relatively smooth by using the plastic riblet film (Bechert et al., 1997). However, the grooved surfaces used in the present study are manufactured directly by a milling machine. The small size of the grooves makes it impossible to completely remove some small burr structures and some accidental ma- chining errors may occur during the machining pro- cess, resulting in a relatively poor smoothness of the grooved surface (seen from Figure 2). So the friction factor is larger than that obtained by Bechert et al. (1997) under the same conditions, resulting in the disappearance of the drag-reducing phenomenon at low Reynolds numbers in the present study. Never- theless, in practical industrial pipeline transportation, the pipeline system constructed mainly from steel pipes will undergo corrosion as time goes by and be subject to deposition of fouling on its surface, and finally leading to development of roughness. Thus the less-smooth grooved surfaces used in this study are more approximate to the conditions of industrial grooved pipes after long-term use, and therefore the present results can be a guidance for the practical application of grooved pipe.
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Hagen number versus Bejan number

Hagen number versus Bejan number

Prof. Holger Martin rose an interesting question: “Is Hagen number defined in literature as Hg = =(DP/L)/(l 3 /rv 2 ) (see, for example: H. Martin, Chapter A2-Dimensionless numbers, in: VDI- -Gesellschaft Verfahrenstechnik und Chemieingenieurwesen (GVC), Editor, VDI Heat Atlas, Second Edition, Springer-Verlag Berlin Heidelberg, 2010, pp. 11-13), identical with Bejan number defined in paper published in Thermal Science, as Be = (DPL 2 /rv 2 )”?

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Genetic analysis for water use efficiency traits, yield and yield attributes  in groundnut  (Arachis hypogaea L.)

Genetic analysis for water use efficiency traits, yield and yield attributes in groundnut (Arachis hypogaea L.)

Groundnut is an important oilseed crop grown in India and is largely cultivated in dry lands. Drought is the most important factor limiting the yield potential of the rain-fed crop. Although high yield potential is the target of most crop breeding programs, it might not be compatible with superior drought resistance. On the other hand, high yield potential can contribute to yield in moderate stress environments. Recent research breakthroughs have revived interest in targeted drought resistance breeding and use of new genomic tools to enhance crop water use efficieny. However, with the fast progress in genomics, a better understanding of the gene functions and physiological mechanism for drought tolerance will be essential for the progress of genetic enhancement of crop for water use efficieny. Crop physiologists have identified a number of traits that would help the breeder in development and identification of moisture stress tolerant genotypes with high yield potential (Basu et al.,2004) The present study is aimed at evaluating the genetic parameters for water use efficiency traits, yield and yield attributes for efficient selection in segregating generations. Material and methods
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J. Braz. Soc. Mech. Sci. & Eng.  vol.28 número2

J. Braz. Soc. Mech. Sci. & Eng. vol.28 número2

because the velocity fluctuations become better defined, and it reaches a maximum of 0.75. A high coherence between the velocity fluctuations at different locations indicates that these fluctuations are associated with the same (global) flow phenomenon. The phase and coherence measurements were repeated for rows 5, 7 and 9 at a higher velocity of 33 m/s (Re = 39600) in order to verify this very organized flow behavior. The results are given in Fig. 6(b). All the characteristics of the previous low Re case are evident also in this case, indicating that the same flow structure exists at high Reynolds numbers. Additionally, a significant enhancement is observed in the coherence level at this velocity, reaching a maximum of 0.98 in comparison with a level of 0.75 in the low velocity case. Both cases are clearly away from the range of acoustic resonance (Oengoeren & Ziada, 1998). Thus, this globally organized flow cannot be attributed to a coupling with acoustic standing waves, but rather to a fluid dynamic mechanism that gains in strength as the Reynolds number is increased. The impingement of the shed vortices on the downstream cylinders may well be the source of the fluid dynamic mechanism that enhances this global mode of vortex shedding (Rockwell & Naudascher, 1979).
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Experimental investigation of convective heat transfer enhancement using alumina/water and copper oxide/water nanofluids

Experimental investigation of convective heat transfer enhancement using alumina/water and copper oxide/water nanofluids

The ongoing energy crisis motivated the researchers to develop more eicient heat transfer devices with higher efectiveness. Advancement in the development of smaller and compact equipments, which works at a much faster rate, requires large amount of heat to be handled. The higher performance devices generate large amounts of heat due to its smaller size, hence heat lux increases drastically. So cooling remains as a signiicant challenge in the modern engineering applications such as manufacturing, transportation, and microelectronics. Due to this downsizing of the equipment and increase in the heat lux, the traditional cooling involving natural convection or fan based cooling reaches to its critical point. Hence the rapid heat removal technique needs to be implemented so as to have better performance of the sys- tem, under normal operating condition. A number of ways which include – extended surface, mini channels, bales are provided so as to withdraw the heat, but still more enhancements in the heating and cooling process are in great demand due to compacting of the process heat exchanger. This leads to the development of the innovative cooling process apart from the conventional ways. The conventional heat removal process is accelerated by enhancing the
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Flow Simulations with Ultra-Low Reynolds Numbers over Rigid and Flexible Airfoils Subject to Heaving and Flapping Motions

Flow Simulations with Ultra-Low Reynolds Numbers over Rigid and Flexible Airfoils Subject to Heaving and Flapping Motions

The fundamental parameter of unsteady analysis is the Strouhal number, defined as St  2 f f h a / U . Taylor et al. (2003) and Triantafyllou et al. (1993) performed a study of wing frequencies and amplitudes, and cruise speeds across a range of birds, in-sects, fishes and cetaceans, to determine Strouhal numbers in “cruising” flight. They found that 75% of the 42 species considered, fall within a narrow range of 0.19  St  0.41 Guerrero (2008). There-fore, a similar range of Strouhal numbers in this work has been selected. The Reynolds number based on the airfoil chord was chosen to be equal to R e  1100. Which is a representative number of flight regime of insects, small birds and MAVs.
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Carlos Maria Reynolds de Souza Parreira do Amaral

Carlos Maria Reynolds de Souza Parreira do Amaral

Num aspecto de desenvolvimento teórico, foi apresentado uma metodologia onde através da refinação de malha é possível estimar um valor aproximado para a largura d[r]

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Aerodynamics and percolation: unfolding laminar separation bubble on Airfoils

Aerodynamics and percolation: unfolding laminar separation bubble on Airfoils

The idea is quite reasonable in the sense that transition from laminar to turbulent flow (hereafter referred to as transition) can be described via the so-called spatiotemporal intermittency [2,3]. Since Pomeau’s work, several simula- tions have supported his conjecture; however, only in the last few years has it been possible to provide experimental evidence [4] because of the novel possibilities of extracting accurate measurements from a turbulent flow with sufficient spatial and temporal resolution. Recent studies approached transition from different angles by means of low-order models [5 –7] and sophisticated simulations [8 –11] , as well as experiments [12 –14] . They concordantly indicate non- equilibrium phase transition occurring in basic shear flows, i.e., pipe, channel, and Couette flows. While investigating
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Estud. Econ.  vol.40 número1

Estud. Econ. vol.40 número1

the private university tuition, V is the voucher that can be used either in private or public university, and the utility function u has the usual properties. The university tuition can be seen as the cost per student in terms of units of consumption. The first term within the parenthesis in the above problem indicates the public univer- sity option, which may be available to the family. 5 At t = 0, the family receives its wage net of taxes, may have to pay the public university tuition and may receive vouchers to pay the child's education. It consumes and sends its child to a public university. At t = 1, the child becomes either a worker with high or low level of human capital, based on the quality of the public university, and earns his wage. The second term indicates the private university option, which is available to all families who have enough resources to pay the tuition. 6,7 The difference with res- pect to the first option is that the probability of the child becoming an individual with high level of human capital is now based on the quality of the private univer- sity. The last term within the parenthesis is the option of not sending the child to university at all. The family pays taxes and the child becomes a worker with low level of human capital.
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Braz. J. Chem. Eng.  vol.31 número1

Braz. J. Chem. Eng. vol.31 número1

Abstract - The continuous stirred tank reactor (CSTR) is a widely used equipment in chemical related industries. The flow behaviour of fluid inside the reactor may either change from dispersion to ideal or ideal to dispersion mixing state. It is studied using the computational fluid dynamics (CFD) simulation software ANSYS Fluent. The mixing behaviour is predicted in terms of age distribution function, I ( ). θ For the CSTR without impeller and baffles, I ( ) θ is found by the tracer injection method. It is measured and predicted by the impeller swept volume method for the CSTR in the presence of impeller and baffles. The predicted results are found to be in good agreement with the literature experimental data. Effect of rpm of the impeller, Reynolds number and viscosity of the process fluid on the mixing characteristics has been investigated.
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