Raimund Almbauer

A New Method to Estimate Diffusion in Stable, Low-Wind Conditions

Abstract Sonic anemometer observations were made 10 m above ground level for a period of 1 yr. From these data, Eulerian autocorrelation functions were computed for the horizontal and vertical wind velocity fluctuations for low wind speeds. Although the autocorrelation function for the vertical velocity component exhibited the well-known exponential form, the function for the horizontal components of the wind vector showed a negative loop for all stability classes at low wind speeds. This result might be an effect of low-frequency meandering of the flow. Observations of the standard deviations of the vertical wind component confirmed the proportionality with the friction velocity, though with a slightly lower constant of proportionality than has been found by other authors. A Lagrangian dispersion model (LDM) with random time steps and a negative intercorrelation parameter ρu,υ for the horizontal wind components was used to take the first of the above-mentioned findings into account. In a simple test case...

Assessment of Waste Heat Recovery From a Heavy-Duty Truck Engine by Means of an ORC Turbogenerator

This paper documents a feasibility study on a waste heat recovery system for heavy-duty truck engines based on an organic Rankine cycle (ORC) turbogenerator. The study addresses many of the challenges of a mobile automotive application: The system must be simple, efficient, relatively small, lightweight, and the working fluid must satisfy the many technical, environmental, and toxicological requirements typical of the automotive sector. The choice of a siloxane as the working fluid allows for the preliminary design of an efficient radial turbine, whose shaft can be lubricated by the working fluid itself. The systems heat exchangers, though more voluminous than desirable, are within acceptable limits. The simulated ORC system would add approximately 9.6 kW at the design point, corresponding to a truck engine power output of 150 kW at 1500 rpm. Future work will be devoted to further system and components optimization by means of simulations, to the study of dynamic operation and control, and will be followed by the design and construction of a laboratory test bench for mini-ORC systems and components.

VALIDATION OF EMISSION FACTORS FOR ROAD VEHICLES BASED ON STREET TUNNEL MEASUREMENTS

The emission behaviour of road vehicles is regularly estimated by the use of emission factors and models. But there is only limited information available about the validity of such factors or models in real world situations. This is because validation requires roadside measurements and these add an additional element of uncertainty in the form of pollutant dispersion behaviour. Tunnel measurements can help to overcome this problem. Road tunnels can be used as big laboratories because the boundary conditions within such tunnels are well known. Such measurements were undertaken in a 10 km long road tunnel in Austria for a period of six weeks during autumn 1998 and another four weeks during spring 1999. An analysis of the data showed that CO emissions derived from the measurements were in good agreement with the emission factors; surprisingly, this was not the case for NOx, especially for NOx emissions from heavy duty vehicles. Due to the fact that the HDV share of the traffic was up to 35% of total traffic volume the effects of unbalanced emission factors were considerable. Differences of up to a factor of 1.6 between measured and calculated emission factors were recorded.

A simple model for the dispersion of pollutants from a road tunnel portal

Abstract The dispersion of pollutants from a roadway tunnel portal is mainly determined by the interaction between the ambient wind and the jet stream from the tunnel portal. In principal, Eulerian microscale models by solving the conservation equations for mass, momentum, and energy, are thus able to simulate effects such as buoyancy etc. properly. However, for engineering applications such models need too much CPU time, and are not easy to handle by non-scientific personnel. Only a few dispersion models, applicable for regulatory purposes, have so far appeared in the literature. These models are either empirical models not always applicable for different sites, or they do not capture important physical effects like buoyancy phenomena. Here, a rather simple model is presented, which takes into account most of the important processes considered to govern the dispersion of a jet stream from portals. These are the exit velocity, the buoyancy, the influence of ambient wind direction fluctuations on the position of the jet stream, and traffic induced turbulence. Although the model contains some heuristic elements, it was successfully tested against tracer experiments taken near a motorway tunnel portal in Austria. The model requires relatively little CPU time. Current limitations of the model include the neglect of terrain, building, and vehicle effects on the dispersion, and the neglect of the horizontal dispersion arising from entrainment of ambient air in the jet stream. The latter could lead to an underestimation of plume spreads for higher wind speeds. The validation of the model will be the focus of future research. The experimental data set is also available for the scientific community.

Evaluation of GRAL for the pollutant dispersion from a city street tunnel portal at depressed level

Abstract A new data set for evaluation of atmospheric dispersion models, designed to treat road tunnel portals, is presented. Further, the performance of GRAL 3.5 (Graz Lagrangian model Version 3.5) using this data is discussed. One main drawback of the model in its current version is that two empirical parameters have to be adjusted for each tunnel site separately in dependence on average traffic volume and construction of the tunnel portal. As the model has been tested for five different tunnel sites by now, which differ significantly in traffic volume, terrain, and construction, model users should be able to choose reasonable values for those empirical parameters for other tunnel sites as well. GRAL has not been tested against field data, where the tunnel air is colder than ambient air. Here, further research is necessary.

Lagrangian dispersion modeling of vehicular emissions from a highway in complex terrain

Abstract Transit traffic through the Austrian Alps is of major concern in government policy. Pollutant burdens resulting from such traffic are discussed widely in Austrian politics and have already led to measures to restrict traffic on transit routes. In the course of an environmental assessment study, comprehensive measurements were performed. These included air quality observations using passive samplers, a differential optical absorption spectroscopy system, a mobile and a fixed air quality monitoring station, and meteorological observations. As was evident from several previous studies, dispersion modeling in such areas of complex terrain and, moreover, with frequent calm wind conditions, is difficult to handle. Further, in the case presented here, different pollutant sources had to be treated simultaneously (e.g., road networks, exhaust chimneys from road tunnels, and road tunnel portals). No appropriate system for modeling all these factors has so far appeared in the literature. A prognostic wind field model coupled with a Lagrangian dispersion model is thus presented here and is designed to treat all these factors. A comparison of the modeling system with results from passive samplers and from a fixed air quality monitoring station proved the ability of the model to provide reasonable figures for concentration distributions along the A10.

Usage and validation of a fluid structure interaction methodology for the study of different suction valve parameters of a hermetic reciprocating compressor

The dynamics of the flatter valves inside a hermetic reciprocating compressor used in household appliances is the most important factor concerning the gas dynamic behaviour of such a compressor. Hence for a good valve design and for a reliable simulation of the compressor the ability to predict the movement of the valves is indispensable. The present paper describes a methodology which allows the prediction of the valve dynamics. For the validation of the methodology the simulation results of the suction valve dynamics have been compared with experimental data obtained out of measurements with a Laser-Doppler-Vibrometer. Furthermore the method has been used for the variation of some suction valve parameters and their influence onto the overall compressor performance has been shown. The whole methodology has been implemented into a commercial available CFD code (FLUENT) as a user defined function (UDF).

Uncertainty and Local Sensitivity Analysis of View Factors for Steady-State Conjugate Heat Transfer Problems

*† This paper is devoted to uncertainties stemming from view factors. The equations for local sensitivity and uncertainty analysis are derived for diffuse-gray thermal radiation cases coupled with conduction and convection. A numerical analysis of the resulting equations is conducted. A simple test case is used to demonstrate the influence of the heat transfer modes on view factor uncertainties.

Fluid Flow in the Oil Pumping System of a Hermetic Compressor

This work deals with the investigation of the oil pumping system in hermetic compressors for refrigeration application. The oil pump which is used for this study consists of two pumping areas: the lower pumping area with a pick-up tube and an eccentric bore, and the upper pumping area with a helical groove. This study focuses on the helical groove in the upper pumping area. To analyse the fluid flow in the helical groove, a numerical approach is introduced. In this approach the Navier-Stokes equations are adapted to the problem and are solved by using the finite volume method. Compared to analytical models, this method is able to obtain the flow field in the cross section of the helical groove at higher resolution. The higher geometrical resolution also enables the analysis of the flow in the small gap between the rotating crankshaft and the stationary wall. The present method is used to quantify different operating parameters on the oil mass flow rate.

On Uncertainty and Local Sensitivity Analysis for Steady-State Conjugate Heat Transfer Problems

The need for simulating real-world behavior of automobiles has led to more and more sophisticated models being added of various physical phenomena for being coupled together. This increases the number of parameters to be set and, consequently, the required knowledge of their relative importance for the solution and the theory behind them. Sensitivity and uncertainty analysis provides the knowledge of parameter importance. In this paper a thermal radiation solver is considered that performs conduction calculations and receives heat transfer coefficient and fluid temperate at a thermal node. The equations of local, discrete, and transient sensitivities for the conjugate heat transfer model solved by the finite difference method are being derived for some parameters. In the past, formulations for the finite element method have been published. This paper builds on the steady-state formulation published previously by the author. A numerical analysis on the stability of the solution matrix is being conducted. From those normalized sensitivity coefficients are calculated dimensionless uncertainty factors. On a simplified example the relative importance of the heat transfer modes at various locations is then investigated by those uncertainty factors and their changes over time.