No abstract

The objective of this investigation was to develop a dimensionless model for predicting the onset of cavitation in torque converters applicable to general converter designs. Dimensional analysis was applied to test results from a matrix of torque converters that ranged from populations comprised of strict geometric similitude to those with more relaxed similarities onto inclusion of all the torque converters tested. Stator torque thresholds at the onset of cavitation for the stall operating condition were experimentally determined with a dynamometer test cell using nearfield acoustical measurements. Cavitation torques, design parameters, and operating conditions were resolved into a set of dimensionless quantities for use in the development of dimensionless empirical models. A systematic relaxation of the fundamental principle of dimensional analysis, geometric similitude, was undertaken to present empirical models applicable to torque converter designs of increasingly diverse design parameters. A stepwise linear regression technique coupled with response surface methodology was utilized to produce an empirical model capable of predicting stator torque at the onset of cavitation with less than 7% error for general automotive torque converter designs.

Hydrogen as a carbon-free fuel is commonly expected to play a major role in future energy supply, e.g., as an admixture gas in natural gas grids. Which impacts on residential and commercial gas appliances can be expected due to the significantly different physical and chemical properties of hydrogen-enriched natural gas? This paper analyses and discusses blends of hydrogen and natural gas from the perspective of combustion science. The admixture of hydrogen into natural gas changes the properties of the fuel gas. Depending on the combustion system, burner design and other boundary conditions, these changes may cause higher combustion temperatures and laminar combustion velocities, while changing flame positions and shapes are also to be expected. For appliances that are designed for natural gas, these effects may cause risk of flashback, reduced operational safety, material deterioration, higher nitrogen oxides emissions (NOx), and efficiency losses. Theoretical considerations and first measurements indicate that the effects of hydrogen admixture on combustion temperatures and the laminar combustion velocities are often largely mitigated by a shift towards higher air excess ratios in the absence of combustion control systems, but also that common combustion control technologies may be unable to react properly to the presence of hydrogen in the fuel.

Dimensional analysis has been applied to automotive torque converters to understand the response of performance to changes in torque, size, working fluid, or operating temperature. The objective of this investigation was to develop a suitable dimensional analysis for estimating the effect of exact geometric scaling of a particular torque converter design on the onset of cavitation. Torque converter operating thresholds for cavitation were determined experimentally with a dynamometer test cell at the stall operating condition using nearfield acoustical measurements. Dimensionless quantities based upon either speed or torque at the onset of cavitation and flow properties (e.g., pressures and temperature dependent fluid properties) were developed and compared. The proposed dimensionless stator torque quantity was found to be the most appropriate scaling law for extrapolating cavitation thresholds to multiple diameters. A power product model was fit on dimensionless stator torque data to create a model capable of predicting cavitation thresholds. Comparison of the model to test data taken over a range of operating points showed an error of 3.7%. This is the first paper of a two-part paper. In Part II, application of dimensional analysis will be expanded from torque converters with exact geometric similitude to those of more general design.

This article describes some of the computational fluid dynamics (CFD) work being done on three-element torque converters using a commercially available package CFX TASCflow. The article details some of the work done to validate CFD results and gives examples of ways in which CFD is used in the torque-converter design process. Based on the validation study, it is shown that CFD can be used as a design and analysis tool to make decisions about design direction. Use of CFD in torque converters is a developing field. Thus, more work needs to be done before the requirement of hardware to validate designs can be fully eliminated. This article demonstrates the confidence level in torque converter CFD and demonstrates how it can be used to assist torqueconverter design today. Analyzing fluid flow within a torque converter using computational fluid dynamics (CFD) is a developing field. The close coupling of the elements in a torque converter and the fact that it is a closed-loop turbomachine give rise to complicated flows within a torque converter. The flow is threedimensional, and secondary flows are present. To improve the The authors thank Don Maddock, manager of the Advanced Torque Converter Group at GM Powertrain, for his support and direction. Appreciation also goes to Professor Ronald Flack at the Department of Mechanical and Aerospace Engineering of the University of Virginia and his students for their work on LDV measurements inside the torque converter. Likewise, thanks to Dr. Budugar Lakshminarayana at the Center for Gas Turbine and Power, Department of Aerospace Engineering, at The Pennsylvania State University and his students for their work with aerodynamic probe measurements inside the torque converter.Address correspondence to Jean Schweitzer, Advanced Power Transfer, GM Powertrain, MC 481-700-718, P.O. Box 935, Ypsilanti, MI 48197-0935, USA. E-mail: jean.m.schweitzer@gm.com performance of a torque converter, it is necessary to understand the flow of fluid within it. CFD can simulate this flow and thus can be used as an analysis and design tool. This article presents a comparison of CFD results with laser Doppler velocimetry (LDV) data, probe data, and dynamometer data. Velocity profiles at various locations in a torque converter are compared with LDV data, and pressure profiles are compared with probe data. A comparison of the standard performance parameters of a set of converters with dynamometer data is presented.Some of the applications of CFD in torque converter design and study are also presented. It has been used in element design, torus design, and cavitation study. CFD analysis results have also been used to optimize designs before fabricating experimental hardware. GRID DEFINITIONIn the pump and the turbine, one blade-centered H-grid block was constructed as shown in Figure 1a and b. Block-structured, boundary-fitted, nonorthogonal grids were constructed using the grid generator CFX Turbogrid (AEA Technology, 2000a). The grid elements inside the blade were blocked off and the grid lines were con...