Wind lidars reveal turbulence transport mechanism in the wake of a tree

Solitary trees are natural land surface elements, found in almost all climates, yet their influence on the surrounding air flow is poorly known. Here we use state-of-the-art, laser-based, remote sensing instruments to study the turbulent wind field in the near-wake region of a mature, open-grown oak tree. Our measurements provide for the first time a full picture of the mixing layer of high turbulence that surrounds the mean wind speed deficit. In this layer, we validate the eddy-viscosity hypothesis, a fundamental theory used in modelling the wind conditions. Using the mixing-length hypothesis we find that for this tree the corresponding turbulence length scale in that layer can be approximated by one, height-independent value. Further, the laser-based scanning technology used here was able to accurately reveal three-dimensional turbulent and spatially varying atmospheric flows over a large plane, without seeding or intruding the atmospheric flow. This capability points to a new and more exact way of exploring the complex earth-atmosphere interactions.

Simple Formulas to Predict Center and Mean Temperatures and Total Heat Transfer in Regular Configurations With Surface Temperature Under Small- and Large-Time Conditions

Simple formulas for the prediction of three important thermal quantities, the center temperature, the mean temperature, and the total heat transfer in regular configurations (large plane wall, long cylinder, and sphere) cooled/heated with prescribed uniform surface temperature during “small time,” are addressed in the present paper. Two immediate engineering applications deal with quenching of metals and sterilization of canned food. The simple formulas emanate from the truncated one term series of the supplementary infinite series at small time. The small time subregion has been traditionally characterized in the heat conduction literature by the dimensionless time or Fourier number τ< 0.24 in the large plane wall, τ< 0.21 in the long cylinder, and τ< 0.19 in the sphere. Excellent agreement between the obtained simple formulas and the traditional solutions (namely the exact, analytical infinite series for “all time”) are attained for the center temperature, mean temperature, and total heat transfer in the large plane wall, long cylinder, and sphere.

Semi-analytical unsteady heat conduction in large plane walls with heat convection exchange

Purpose The purpose of this study is to address one-dimensional, unsteady heat conduction in a large plane wall exchanging heat convection with a nearby fluid under “small time” conditions. Design/methodology/approach The Transversal Method of Lines (TMOL) was used to reformulate the unsteady, one-dimensional heat conduction equation in the space coordinate and time into a transformed “quasi-steady”, one-dimensional heat conduction equation in the space coordinate housing the time as an embedded parameter. The resulting ordinary differential equation of second order with heat convection boundary conditions is solved analytically with the method of undetermined coefficients. Findings Semi-analytical TMOL dimensionless temperature profiles of compact form with/without regressed terms are obtained for the whole spectrum of Biot number (0 < Bi < ∞) in the “small time” sub-domain. In addition, a new “large time” sub-domain is redefined, that is, setting a smaller critical dimensionless time or critical Fourier number τcr = 0.18. Originality/value The computed dimensionless center, surface and mean temperature profiles in the large plane wall accounting for all Biot number (0 < Bi < ∞) in the “small time” sub-domain τ < τcr = 0.18 exhibit excellent quality while carrying reasonable relative errors for engineering applications. The exemplary level of accuracy indicates that the traditional evaluation of the center, surface and mean temperatures with the standard infinite series retaining a large number of terms is no longer necessary.

Research on Optimization of Graphical Scheme for Large Plane Cross Signs

In order to find a practical graphical layout of the plane cross sign and the corresponding intersection road information expression method, and effectively solve the multi-attribute information transmission problem of intersecting roads, the drivers’ eye movement characteristics and the visual response time was analyzed when recognizing the signs with different graphic scheme designs and intersecting road information expressions. The tests were divided into static test and dynamic test by using SMT ETG 2W and Tobbi X20-30 eye trackers. The study found that under the condition of three road name information, comparing the graphical layout with both the intersecting road number and road name and the graphical layout which expressed none information of intersecting road for the large plane cross signs, it is equivalent to the addition of two pieces of information. And the conclusion for six road name information is more obvious.