Drag Reduction Through Changes in Cabin Geometry and Trailer Gap of Heavy-Duty Trucks

Reduction of aerodynamic drag of heavy-duty trucks can significantly save fuel costs and US dependence on the imported oil. Reduction of aerodynamic drag by 30% can result in fuel cost savings in billions of dollars every year. Aerodynamic drag of truck depends on the frontal cross-sectional area and the speed of the vehicle. In addition, the gap between the cabin and the trailer significantly affect the drag of the truck. This paper investigates how changes in the cabin geometry and the trailer gap can reduce the aerodynamic drag using numerical simulations. The numerical simulations were carried out using Computational Fluid Dynamics (CFD) software, CFX-5.5, from AEA Technologies (now owned by ANSYS). Effects of vehicle speed, cabin geometry, and trailer gap on the aerodynamic drag were investigated.

Analytical Study of Natural Convection in a Cavity With Volumetric Heat Generation

A semi-analytical method for natural convection in a two dimensional rectangular enclosure, with uniform volumetric heat generation, having insulated horizontal boundaries, and isothermal vertical boundaries, has been studied here. In this method, the governing equations for natural convection, have been solved under the assumption that for a cavity with small aspect ratio, the flow in the central region of the cavity is only in the vertical direction. It is found that for the cavities with small aspect ratio, the temperature in central region of the cavity is nearly constant along the horizontal direction. However, there is a uniform temperature gradient in the vertical direction, which can be related to the maximum temperature in conduction. The velocity profiles and temperature profiles obtained in the present work, are compared with the numerical simulations by Fluent and a fair agreement is found between these results.

A Transient Simulation of Heated Soil Vapor Extraction System

Soil remediation process by heated soil vapor extraction system has drawn considerably attention for the last few years. The areas around chemical companies or waste disposal sites have been seriously contaminated from the chemicals and other polluting materials that are disposed off. Our present study is concentrated on modeling one transient Heated Soil Vapor Extraction System and predicting the time required for effective remediation. The process developed by Advanced Remedial Technology, consists of a heating source pipe and the extraction well embedded in the soil. The number of heat source pipes and the extraction wells depends on the type of soil, the type of pollutants, moisture content of the soil and the size of the area to be cleaned. The heat source heats the soil, which is transported in the interior part of the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then driven out of the soil by the extraction well. The extraction well consists of the blower which would suck the vaporized gases out of the system. A three-dimensional meshed geometry was developed using gambit. Different boundary conditions were used for heating and suction well and for other boundaries. Concentrations of different chemicals were collected from the actual site and this data was used as an initial condition. The analysis uses the species transport and discrete phase modeling to predict the time required to clean the soil under specific conditions. This analysis could be used for predicting the changes of chemical concentrations in the soil during the remediation process. This will give us more insight to the physical phenomena and serve as a numerical predictive tool for more efficient process.

Turbulence at Free Surface in Hydraulic Jumps

In the context of recent work by Brocchini & Peregrine [1,2], this paper aims to document free surface profiles, and turbulence length scales in hydraulic jumps with Froude numbers between 1.98 and 4.82. Although information on bubble size, frequency and velocities in hydraulic jumps is available in the literature, there is not much data on the features of the free surface, or on mixing layer thickness. In the present case, measurements at the free surface have been realized with two miniature resistive wire gauges each comprising two parallel 50 micron diameter wires with a separation of 1mm. These instruments were calibrated dynamically over a range of frequencies up to 20 Hz. Furthermore optical probes were used to measure properties of the air phase within the jump, including void fractions (up to 98%). The present results extend the range of Froude numbers for which two-phase measurements in hydraulic jumps are available, and, in most respects, confirm earlier results obtained with different experimental techniques. Length scales at the free surface are deduced from cross-correlation analysis of wire gauge measurements, and are compared with similar data obtained from images of the surface.

Gravimetric Calibration of Critical Flow Venturi Nozzles

The Metering Research Facility (MRF) was commissioned in 1995/1996 at Southwest Research Institute for research on, and calibration of natural gas flow meters. A key commissioning activity was the calibration of critical flow Venturi (sonic) nozzles by a gravimetric proving process flowing nitrogen or natural gas at different pressures. This paper concerns the calibration of the four sonic nozzles installed in the MRF Low Pressure Loop (LPL). Recently, a new project prompted a review of the relations used to calculate sonic nozzle discharge coefficient in the LPL data acquisition computer code. New calibrations of the LPL sonic nozzles were performed flowing natural gas over a lower range of pressure than used in the original commissioning tests. The combination of new and old gravimetric calibration data are shown to agree well with correlations published by Arnberg and Ishibashi (2001) and by Ishibashi and Takamoto (2001) for laminar, transitional and turbulent boundary layer flow in critical flow Venturi nozzles.

Hot-Film Measurement of Natural Convection in Liquid Gallium With and Without Magnetic Fields

The velocity and temperature fields induced by natural convection in liquid gallium were measured. Measurements were taken with and without an external magnetic field applied to the liquid gallium. The velocity field was measured with a hot-film anemometer and the temperature field with a thermocouple. The hot film was calibrated over a narrow range of temperatures in a rotating turntable filled with liquid gallium. The external magnetic field damped both the velocity and temperature fields compared to similar conditions when no external magnetic field was present. The experimental results compared reasonably well with previous numerical predictions.

Simulation of Air Entrapment by a Plunging Liquid Jet of Finite Length

The impingement of a finite length round water jet on a large pool of water was simulated numerically using a 3D Eulerian-Lagrangian Marker and Micro-Cell (ELMMC) method. The method allowed simulation of the initial impact of the jet on the pool surface, the deformation of the pool surface by the falling jet, and, under certain conditions, the entrapment of an air bubble as the pool closes in on the jet. The conditions considered were for ratios of jet length to radius (h/r) in the range of 4 to 25 and jet Froude number in the range of 16 to 74. The results agreed with previous experimental observations by Oguz et al. (J. Fluid Mech., 294, 1995) in terms of entrapped air volume and the possible geometries of entrapped bubbles (viz., toroidal or spheroidal). The simulation results also allowed for a detailed study of effects difficult to discern experimentally, such as vorticity generation and differences in entrapped air volume between toroidal and spheroidal bubbles.

Rotor Boundary Layer Response to an Impinging Wake

This paper presents results of an experimental investigation on the response of a rotor boundary layer to an impinging Inlet Guide Vane (IGV) wake. High resolution two-dimensional Particle Image Velocimetry (PIV) measurements are conducted in a refractive index matched facility that provides an unobstructed view of the entire flow field. Data obtained at four different rotor phases, as the wake is chopped and passes by the rotor blade, allows us to examine the response of the rotor boundary layer to the mean flow and turbulence associated with the impinging wake. We focus on the suction side boundary layer in regions with adverse pressure gradients, from mid chord to the trailing edge. The phase-averaged velocity profiles are used for calculating the momentum and displacement thicknesses of the boundary layer, and for estimating the pressure gradients along the wall. Distributions of Reynolds stresses are also provided. The phase-averaged velocity profiles in the rotor boundary layer vary significantly with phase. During wake impingement the boundary layer becomes significantly thinner and more stable compared to other phases at the same location. Analysis of the possible causes for this trend suggests that the dominant contributors are unsteady, phase-dependent variation in pressure gradients along the wall.

Wavelet Cross-Correlation Analysis of the Unsteady Signals of the Flow in the Open Sump

The wavelet cross-correlation method was used to analyze the unsteady signals of the flow of the model open pump sump, which include pressure signal, vibration signal and acoustic signal. The continuous wavelet transform was done first to find the signal distribution at various periods and at any time, then the wavelet cross-correlation was used to find the relationship between the signals taken two a two. Through comparing the result of wavelet cross-correlation and the result of classic cross-correlation, one can find the correlation scale of any two unsteady signals (pressure-vibration, pressure-noise, and vibration-noise). The signal on the correlation scale was reconstruct and its characteristics were obtained using classical signal analysis method same as the structural similarity of a arbitrary two signals.

Enhancement of Heat Transfer to an Air Jet Impinging on a Flat Plate

An experimental investigation of the impinging jet cooling from a heated flat plate has been carried out for several Reynolds numbers (Re) and nozzle to plate distances. The present results indicate that the maximum heat transfer occurs from the heated plate at stagnation point and decreases with radial distances for all cases. The maximum value of the stagnation as well as average Nusselt number is found to occur at separation distance, H/D = 6.0 for Re = 55000. An attempt is also made to study effects of nozzle exit configuration on the heat transfer using a sharp edged orifice for same set of Reynolds numbers and nozzle to plate distance. The stagnation Nusselt numbers of sharp orifice jets are found to be enhanced by around 16–21.4% in comparison to that of square edged orifice. However, the enhancement in the average Nusselt number of sharp orifice is found to be in the range of 7–18.9% as compared to the square edged orifice. The maximum enhancement of 18.9% in average Nu is achieved for Re = 55 000 at H/D = 6. Two separate correlations in terms of Nuo, Re, H/D for both square and sharp edged orifice are obtained which will be useful for designing impinging cooling system.