Momentum Characteristics Research Articles

Numerical modeling of the momentum and thermal characteristics of air flow in the intercooler connection hose

This paper presents a numerical investigation on the momentum and thermal characteristics of an intercooler connection hose that is in use in the 1.3 SDE 75 CV type FIAT engine. Computational analyses are carried out with ANSYS FLUENT v.12.0.1, where both stationary and vibrating scenarios are handled. The work is structured in accordance with the “Subsystem Functional Description for Charge Air Hoses Fiat 225 Euro 5” FIAT standard, where the air mass flow rate, temperature, and gage pressure at the hose inlet are identified as $$ {\mathop m\limits^ \cdot }$$ = 0.085 kg/s, T in = 90°C, and P in = 130 kPa, respectively. In the stationary case, it is determined that the pressure loss value in the air domain of the hose is ΔP K = 1.50 kPa; moreover, the corresponding data for the temperature drop is ΔT = 0.80°C. Vibration is characterized by employing simple harmonic motion at the engine side of the hose. The fluid–solid interaction methodology showed that pressure loss values grow due to vibration; moreover, the impact of vibration came out to generate diverse fluctuation schemes at different sections of the hose.

Turbulent Flow Properties Around a Staggered Wind Farm

The fundamental properties of turbulent flow around a perfectly staggered wind farm are investigated in a wind tunnel. The wind farm consisted of a series of 10 rows by 2–3 columns of miniature wind turbines spaced 5 and 4 rotor diameters in the streamwise and spanwise directions respectively. It was placed in a boundary-layer flow developed over a smooth surface under thermally neutral conditions. Cross-wire anemometry was used to obtain high resolution measurements of streamwise and vertical velocity components at various locations within and above the wind farm. The results show that the staggered configuration is more efficient in terms of momentum transfer from the background flow to the turbines compared to the case of an aligned wind turbine array under similar turbine separations in the streamwise and spanwise directions. This leads to improved power output of the overall wind farm. A simplified analysis suggests that the difference in power output between the two configurations is on the order of 10%. The maximum levels of turbulence intensity in the staggered wind farm were found to be very similar to that observed in the wake of a single wind turbine, differing substantially with that observed in an aligned configuration with similar spacing. The dramatic changes in momentum and turbulence characteristics in the two configurations show the importance of turbine layout in engineering design. Lateral homogenization of the turbulence statistics above the wind farm allows for the development of simple parametrizations for the adjustment of flow properties, similar to the case of a surface roughness transition. The development of an internal boundary layer was observed at the upper edge of the wind farm within which the flow statistics are affected by the superposition of the ambient flow and the flow disturbance induced by the wind turbines. The adjustment of the flow in this layer is much slower in the staggered situation (with respect to its aligned counterpart), implying a change in the momentum/power available at turbine locations. Additionally, power spectra of the streamwise and vertical velocity components indicate that the signature of each turbine-tip vortex structure persists to locations deep within the wind farm.

Flow of power-law fluids past an equilateral triangular cylinder: Momentum and heat transfer characteristics

Extensive numerical simulations for the 2-D laminar flow of power-law fluids over an equilateral triangular cylinder are performed to elucidate the role of power-law index (0.2 ≤ n ≤ 1.8) on the critical Reynolds number denoting the onset of flow separation and of vortex shedding. Results are presented for both orientations of the triangular cylinder, namely, its apex facing in the upstream and the downstream directions. For shear-thinning fluids, the onset of wake formation and vortex shedding both are seen to be delayed than that in Newtonian and shear-thickening fluids. After delineating the limits of the steady flow regime, the effects of the Reynolds and Prandtl numbers and the power-law index on drag phenomena and heat transfer characteristics of triangular cylinder for shear-thinning fluids have been studied in the steady flow regime. The results reported herein embrace the following ranges of conditions: 0.2 ≤ n ≤ 1; 1 ≤ Re ≤ 30 and 1 ≤ Pr ≤ 100. Detailed results on isotherm contours, local Nusselt number and its surface-averaged values are presented. Finally, the present numerical values of the critical Reynolds numbers and Nusselt number have been correlated using simple forms which are convenient for interpolating the present results for the intermediate values of the governing parameters in a new application.

Momentum and heat transfer characteristics of a semi-circular cylinder immersed in power-law fluids in the steady flow regime

The continuity, momentum and energy equations describing the flow and heat transfer of power-law fluids over a semi-circular cylinder have been solved numerically in the two-dimensional steady flow regime. The influence of the Reynolds number ( Re), Prandtl number ( Pr) and power-law index ( n) on the local and global flow and heat characteristics have been studied over wide ranges of conditions as follows: 0.01 ⩽ Re ⩽ 30, 1 ⩽ Pr ⩽ 100 and 0.2 ⩽ n ⩽ 1.8. The variation of drag coefficient and Nusselt number with the Reynolds number, Prandtl number and power-law index is shown over the aforementioned ranges of conditions. In addition, streamline and isotherm profiles along with the recirculation length and distribution of pressure coefficient and Nusselt number over the surface of the semi-circular cylinder are also presented to gain further insights into the nature of the underlying kinematics. The wake size (recirculation length) shows almost linear dependence on the Reynolds number ( Re ⩾ 1) for all values of power-law index studied herein. The drag values show the classical inverse variation with the Reynolds number, especially for shear-thinning fluids at low Reynolds numbers. The point of maximum pressure coefficient is found slightly displaced from the front stagnation point for highly shear-thinning fluids, whereas for shear-thickening and Newtonian fluids, it coincides with the front stagnation point. For fixed values of the Prandtl number and Reynolds number, the rate of heat transfer decreases with the gradual increase in power-law index; this effect is particularly striking at high Prandtl numbers due to the thinning of the thermal boundary layer. Conversely, as expected, shear-thinning behavior facilitates heat transfer and shear-thickening impedes it. The effect of power-law index on both momentum and heat-transfer characteristics is seen to be appreciable at low Reynolds numbers and it gradually diminishes with the increasing Reynolds number.

Effect of power-law fluid behavior on momentum and heat transfer characteristics of an inclined square cylinder in steady flow regime

The governing equations describing the momentum and heat transfer phenomena of power-law non-Newtonian fluids over a heated square cylinder at 45° of incidence in the two-dimensional (2-D) steady flow regime are solved numerically. Extensive results on the detailed structure of the flow and temperature fields as well as on the gross engineering parameters are presented over the following ranges of conditions: 0.2 ⩽ n ⩽ 1; 0.1 ⩽ Re ⩽ 40 and 0.7 ⩽ Pr ⩽ 100. At low Reynolds numbers, the flow remains attached to the surface of the cylinder. This seems to occur for all values of power-law index, at least up to about Re = 1. On the other hand, twin standing vortices were seen to form at Re = 10 for all values of power-law index considered herein. The influence of the Reynolds number and power-law index is delineated on the detailed structure of the flow field (streamlines), wake characteristics and surface pressure distribution as well as on the value of drag coefficients. Similarly, the effect of Prandtl number is studied on forced convective heat transfer for the two commonly encountered boundary conditions, namely, constant temperature or constant heat flux prescribed on the surface of the cylinder. Using the computed numerical results, simple heat transfer correlations are obtained in terms of the Nusselt number as a function of the pertinent governing parameters thereby enabling the prediction of the rate of heat transfer between the fluid and the immersed cylinder. In addition, variation of the local Nusselt number on the surface of the inclined of square cylinder and representative isotherm plots are also presented to elucidate the effect of Reynolds number, Prandtl number and power-law index on the heat transfer phenomenon.

Homotopy analysis method for the heat transfer in a asymmetric porous channel with an expanding or contracting wall

The flow of a viscous incompressible fluid between two parallel plates due to the normal motion of the porous upper plate is investigated and an analysis is made to determine the heat and mass transfer. The unsteady Navier–Stokes equations are reduced to a generalization of the Proudman–Johnson equation retaining the effect of wall motion using a suitable similarity transformation. The analytical solution for stream function and heat transfer characteristics are obtained by employing homotopy analysis method. The effects of various physical parameters like expansion ratio, Prandtl number, Reynolds number on various momentum and heat transfer characteristics are discussed in detail.

Accruals and Momentum

We establish a robust link between momentum and accruals. Momentum profitability is mostly concentrated in firms with high accruals. Cross-sectional characteristics of momentum previously documented do not subsume the effect of accruals on momentum. Loser stocks with high accruals experience significant decreases in industry-adjusted sales growth and the largest amount of income-decreasing special items in subsequent years. Most of momentum profit among high-accrual firms is attributable to the high discretionary accrual group. Our findings indicate that due to the joint force of earnings overestimation and earnings manipulation, the downward payoff of loser stocks with high accruals largely drives the accrual-based momentum profit.

Oil Risk Exposure: The Case of the U.S. Oil and Gas Sector

We estimate oil price risk exposures of the U.S. oil and gas sector using the Fama-French-Carhart's four-factor asset pricing model augmented with oil price and interest rate factors. Results show that the market, book-to-market, and size factors, as well as momentum characteristics of stocks and changes in oil prices are significant determinants of returns for the sector. Oil price risk exposures of U.S. oil and gas companies in the oil and gas sector are generally positive and significant. Our study also finds that oil price risk exposures vary considerably over time, and across firms and industry subsectors.

Characteristics of Momentum and Heat Transfer over Semiarid Grasslands with Different Grazing Intensities in Inner Mongolia, China

The drag coefficient (C d) and heat transfer coefficient (C h) with the bulk transfer scheme are usually used to calculate the momentum and heat fluxes in meteorological models.The aerodynamic roughness length (z 0m) and thermal roughness length (z 0h) are two crucial parameters for bulk transfer equations.To improve the meteorological models,the seasonal and interannual variations of z 0m,z 0h,coefficient kB 1,C d,and C h were investigated based on eddy covariance data over different grazed semiarid grasslands of Inner Mongolia during the growing seasons (May to September) from 2005 to 2008.For an ungrazed Leymus chinensis grassland (ungrazed since 1979),z 0m and z 0h had significant seasonal and interannual variations.z 0m was affected by the amount and distribution of rainfall.kB 1 exhibited a relatively negative variation compared with z 0h,which indicates that the seasonal variation of z 0h cannot be described by kB 1.To parameterize z 0m and z 0h,the linear regressions between ln(z 0m),ln(z 0h),and the leaf area index (LAI) were performed with R 2 =0.71 and 0.83.The monthly average kB 1 was found to decrease linearly with LAI.The four-year averaged values of C d and C h were 4.5×10 3 and 3.9×10 3,respectively.The monthly average C d only varied by 8% while the variation of C h was 18%,which reflects the different impacts of dead vegetation on momentum and heat transfer at this natural grassland.Moreover,with the removal of vegetation cover,grazing intensities reduced z 0m,z 0h,C d,and C h.

The Importance of Accounting Information in Portfolio Optimization

We study the economic importance of accounting information as defined by the value that a sophisticated investor can extract from publicly available financial statements when optimizing a portfolio of U.S. equities. Our approach applies the elegant new parametric portfolio policy method of Brandt, Santa-Clara, and Valkanov (2009) to three simple and firm-specific annual accounting characteristics-accruals, change in earnings, and asset growth. We find that the set of optimal portfolio weights generated by accounting characteristics yield an out-of-sample, pre-transact ions-costs annual information ratio of 1.9 as compared to 1.5 for the standard price-based characteristics of firm size, book-to-market, and momentum. We also find that the delevered hedge portion of the accounting-based optimal portfolio was especially valuable during the severe bear market of 2008 because unlike many hedge finds it delivered a hedged return in 2008 of 12 percent versus only 3 percent for price-based strategies and −38 percent for the value-weighted market.

Investigation of Swirling Flows in Mixing Chambers

This investigation analyzed the three‐dimensional momentum and mass transfer characteristics arising from multiple inlets and a single outlet in micromixing chamber. The chamber consists of a right square prism, an octagonal prism, or a cylinder. Numerical results which were presented in terms of velocity vector plots and concentration distributions indicated that the swirling flows inside the chamber dominate the mixing index. Particle trajectories were utilized to demonstrate the rotational and extensional local flows which produce steady stirring, and the configuration of colored particles at the outlet section expressed at different Re represented the mixing performance qualitatively. The combination of the Taylor dispersion and the vorticity was first introduced and made the mixing successful. The effects of various geometric parameters and Reynolds numbers on the mixing characteristics were investigated. An optimal design of the cylindrical chamber with 4 inlets can be found. At larger Reynolds number, Re > 15, more inertia caused the powerful swirling flows in the chamber, and more damping effect on diffusion was diminished, which then increased the mixing performance.

Flow over and forced convection heat transfer in Newtonian fluids from a semi-circular cylinder

Momentum and heat transfer characteristics of a semi-circular cylinder immersed in unconfined flowing Newtonian fluids have been investigated numerically. The governing equations, namely, continuity, Navier–Stokes and energy, have been solved in the steady flow regime over wide ranges of the Reynolds number (0.01 ⩽ Re ⩽ 39.5) and Prandtl number ( Pr ⩽ 100). Prior to the investigation of drag and heat transfer phenomena, the critical values of the Reynolds number for wake formation (0.55 < Re c < 0.6) and for the onset of vortex shedding (39.5 < Re c < 40) have been identified. The corresponding values of the lift coefficient, drag coefficient, and Strouhal number are also presented. After establishing the limit of the steady flow regime, the influence of the Reynolds number (0.01 ⩽ Re ⩽ 39.5) and Prandtl number ( Pr = 0.72, 1, 10, 50 and 100) on the global flow and heat transfer characteristics have been elucidated. Detailed kinematics of the flow is investigated in terms of the streamline and vorticity profiles and the variation of pressure coefficient in the vicinity of the cylinder. The functional dependence of the individual and total drag coefficients on the Reynolds number is explored. The Nusselt number shows an additional dependence on the Prandtl number. In addition, the isotherm profiles, local Nusselt number ( Nu L ) and average Nusselt number ( Nu) are also presented to analyze the heat transfer characteristic of a semi-circular cylinder in Newtonian media.

O mecanismo de autopropulsão de vórtices oceânicos: uma revisão

Vórtices oceânicos são efetivos transportadores de momentum, massa, calor, de características químicas e biológicas associadas, em geral, com o seu local de origem. Estas feições exercem influência na circulação global, na distribuição de larga escala de massas d'água e na biologia dos oceanos. Esta influência não envolve somente transferência de energia e de propriedades associadas com o local de origem do vórtice, mas também a sua acentuada atuação em processos de mistura. O movimento dos vórtices pelos oceanos é influenciado basicamente por três fatores: a autopropulsão intrínseca à feição, que a impulsiona no sentido oeste; a advecção por correntes externas e a influência de vórtices próximos. Para um melhor entendimento da importância dos vórtices nas largas escalas o seu comportamento isolado deve ser estudado. Este trabalho se concentra no primeiro aspecto, onde a autopropulsão de vórtices isolados é amplamente revisada e discutida. A expressão que permite o cálculo aproximado da velocidade de translação de vórtices isolados é deduzida. As equações básicas (águas rasas, função de Bernoulli e integrada do momentum meridional) necessárias para este desenvolvimento são apresentadas e discutidas, assim como as forças meridionais que atuam sobre estas feições em movimento, onde o formalismo matemático associado a cada uma delas é também revisado. Esta revisão mostra que todos os vórtices isolados são autopropulsionados no sentido oeste, independentemente do hemisfério considerado. Mostra ainda que três forças meridionais atuam sobre os vórtices em movimento: (1) a força β, devida à diferença do parâmetro de Coriolis entre os hemisférios norte e sul do vórtice, (2) a força de Coriolis e a (3) força ambiente, devida à ação do ambienteexterno sobre o vórtice. Diversas análises podem ser feitas com respeito a estas forças e esta revisão também apresenta, como exemplo, uma comparação da força β que atua na situação de vórtices anticiclônicos e ciclônicos, de mesmas características, em trânsito no hemisfério Sul. Conclui-se que a força β do primeiro ésuperior a do segundo. O presente estudo aborda ainda aspectos relacionados com o balanço de forças sobre as partículas em rotação dentro de um vórtice, ondeos balanços gradiente, geostrófico, quase-geostrófico e ciclostrófico são discutidos.

Turbulent Flow at 190 m Height Above London During 2006–2008: A Climatology and the Applicability of Similarity Theory

Flow and turbulence above urban terrain is more complex than above rural terrain, due to the different momentum and heat transfer characteristics that are affected by the presence of buildings (e.g. pressure variations around buildings). The applicability of similarity theory (as developed over rural terrain) is tested using observations of flow from a sonic anemometer located at 190.3 m height in London, U.K. using about 6500 h of data. Turbulence statistics—dimensionless wind speed and temperature, standard deviations and correlation coefficients for momentum and heat transfer—were analysed in three ways. First, turbulence statistics were plotted as a function only of a local stability parameter z/Λ (where Λ is the local Obukhov length and z is the height above ground); the σi/u* values (i = u, v, w) for neutral conditions are 2.3, 1.85 and 1.35 respectively, similar to canonical values. Second, analysis of urban mixed-layer formulations during daytime convective conditions over London was undertaken, showing that atmospheric turbulence at high altitude over large cities might not behave dissimilarly from that over rural terrain. Third, correlation coefficients for heat and momentum were analyzed with respect to local stability. The results give confidence in using the framework of local similarity for turbulence measured over London, and perhaps other cities. However, the following caveats for our data are worth noting: (i) the terrain is reasonably flat, (ii) building heights vary little over a large area, and (iii) the sensor height is above the mean roughness sublayer depth.

Viscoelastic MHD flow boundary layer over a stretching surface with viscous and ohmic dissipations

In this study the momentum and heat transfer characteristics in an incompressible electrically conducting viscoelastic boundary layer fluid flow over a linear stretching sheet are considered. Highly non-linear momentum and thermal boundary layer equations are reduced to set of nonlinear ordinary differential equations by appropriate transformation.

Style Migration and the Cross-Section of Stock Returns

Stocks experiencing sharp changes in their style characteristics present unique opportunities to examine how investors view style information in making their portfolio allocation decisions. We examine the average returns of such stocks - which we call “style migrants” - and the covariation of the returns of style migrants with their new style cohort stocks to provide new insight into the way investors use equity style information. Our results indicate that investors strongly judge a stock by its style. Specifically, we find that stocks experiencing large levels of variability in their book-to-market and momentum characteristics during the prior three years significantly out perform, during the following year, other stocks with more style stability. In addition, these high style risk stocks covary much more with their new style cohorts than do low style risk stocks that have also moved into the same new style category, consistent with investors overreacting to style shifts of high style risk stocks, while exhibiting a “style memory” effect for low style-risk stocks. In further tests, we find some evidence that high style risk stocks exhibit style return reversals, while low style risk stocks exhibit style return continuations. Overall, our paper provides new evidence about investor behavior by demonstrating that some investors appear to overweight style information when allocating their portfolios, especially for certain high style-risk stocks.

Style Migration and the Cross-Section of Average Stock Returns

Stocks experiencing sharp changes in their style characteristics present unique opportunities to examine how investors view style information in making their portfolio allocation decisions. We examine the average returns of such stocks — which we call “style migrants” — and the covariation of the returns of style migrants with same-style stocks to provide new insight into the way investors use equity style information. Our results indicate that investors strongly judge a stock by its style, even when other information indicates that they should not do so. Specifically, we find that stocks experiencing large levels of variability in their size, book-to-market, and momentum characteristics during the prior five years significantly outperform, during the following year, other stocks with more style stability; thus, investors appear to penalize style risk by requiring higher future returns. In addition, these high style risk stocks covary much more with their new style cohorts than other low style risk stocks that have also moved into the same new style category — this is consistent with investors overreacting to style shifts with high style risk stocks, while exhibiting a “style memory” effect for low style-risk stocks. In further tests, we find some evidence that low-skill mutual fund managers tend to exhibit “style-chasing” behavior, and that their trades are correlated with contemporaneous abnormal returns of style migrants — consistent with their trades affecting migrant returns. Overall, our paper provides new evidence about investor behavior by demonstrating that some investors appear to overweight style information when allocating their portfolios, especially for certain high style-risk stocks.

Viscous flow over a shrinking sheet with an arbitrary surface velocity

In this paper, an analytical solution in a closed form for the boundary layer flow over a shrinking sheet is presented when arbitrary velocity distributions are applied on the shrinking sheet. The solutions with seven typical velocity profiles are derived based on a general closed form expression. Such flow is usually not self-similar and the solution can only be implemented when the mass transfer at the wall is prescribed and determined by the moving velocity of the wall. The characteristics of the flows with the typical velocity distributions are discussed and compared with previous similarity solutions. The flow is observed to have quite different behavior from that of the self-similar flow reported in the literature and the results demonstrate distinctive momentum and energy transport characteristics. Some plots of the stream functions are also illustrated to show the difference in flow field between the shrinking sheet and the stretching sheet. An integral approach to solve boundary layer flow over a shrinking or stretching sheet with uncoupled arbitrary surface velocity and wall mass transfer velocity is outlined and the effectiveness of this approach is discussed.

Research of transmission characteristics of single-photon orbital angular momentum

We describe the high order elliptic hermite gaussian beam and the average orbital angular momentum of single-photon, and analyze some situations of the change of orbital angular momentum, briefly by the simulation. Finally, the probability distribution and changes in the probability distribution within the range of space for the single-photon orbital angular momentum are analyzed. The results show that the change magnitude of the single-photons average orbital angular momentum varies with the material when the high order elliptic Hermite-Gaussian beam interacts with mater.

0139 一様流中でのDBDプラズマアクチュエータが与える運動量の特性(OS1-8 噴流,後流および剥離流れ現象の解明と制御,オーガナイズドセッション)

This paper deals with characteristics of momentum added by a DBD Plasma actuator (PA) in uniform flow. The PA on a thin flat plate was located in uniform flow and velocity profiles in wakes of the PA was measured using a hot-wire anemometer. We investigated the momentum in flow filed added by PA, when velocity in the uniform flow was changed and voltage and frequency of input supplied to the PA were constant. As a result, the increase of the momentum is maximum value, when the induced velocity by PA (1.4m/s) is equal to the uniform flow velocity. In this case, the increasing rate of momentum was approximately 50%. On the other hand, if the difference to uniform flow velocity (6.0m/s) was large, the increasing rate of momentum was about 1%.