Projects / Programmes
Modelling of flow and temperature conditions in rotating elements
| Code |
Science |
Field |
Subfield |
| 2.13.02 |
Engineering sciences and technologies |
Process engineering |
Transmissibility in solids and fluids |
| Code |
Science |
Field |
| P240 |
Natural sciences and mathematics |
Gases, fluid dynamics, plasmas |
| Code |
Science |
Field |
| 2.11 |
Engineering and Technology |
Other engineering and technologies |
Computational fluid dynamics CFD, PIV, brake disks, brake drums, cooling, rotational element, dynamometer
Researchers (18)
Organisations (2)
Abstract
A part of Cimos's production are brake disks and drums. A part of production (capacity over 1500000 parts/year ) is in Maribor and the other part is in Kikinda (capacity over 2000000 part/year). Cimos is taking over a part of research and testing activities increasing the added value of their products and increasing the odds to keep their production lines occupied after the car model (brake system) change. Cimos team is capable of performing hardness calculation and simulations. Temperature of brake disks (drums) rises as a result of brake system operation influencing material properties of the material (tensile, friction coefficient, Young module) significantly resulting in brake performance. Dynamometer for brake system tests is delivered, operational and enables testing.
It is beneficial from the cost and response time point of view if it is possible to simulate flow and temperature field in brake system first and perform actual test on promising designs only. Cooling of the brake disc (drum) is significant parameter. Temperature and flow conditions are extremely demanding due to intensive heat generation and un-stationary flow field, making common engineering approach to estimation of transport phenomena by the use of engineering transport coefficients unsuitable. Transport phenomena is clearly un-stationary, turbulent, anisotropic, local dependent, with material properties of solid and fluid dependent on temperature. All mechanism of heat transfer like conduction, convection and radiation are important. The brake system cooling system will be studied numerically by CFD and experimental by modern un-invasive methods like PIV and LDA.
The goal of the project is to develop an algorithm for numerical simulation fluid flow in and around brake disks. Temperature dependence of material properties of the discs will not be neglected. The simulation will be performed at different rotational speeds of disks. Numerical data for flow and temperature field will enable to grade the cooling intensity at different rotational speeds. Specific geometry and surface roughness (sand casting) of internal channels will considered assuming they are similar to the shape of the fan blades but with some discrepancies. Casting anomalies are likely and we will try to study their influence on cooling efficiency since the channel cross-sections are relatively small. We are aware that the circumstances on vehicle defer from the circumstances on dynamometer, but it is easier to achieve repeatability of the results on dynamometer so we will take dynamometer results for comparison. Numerical results will be compared to PIV measurements in the disc outlet and temperatures on the disc to validate the selection of numerical model and the interval of trust. We expect to get in insight view in the cooling process in influential factors by implementing CFD. It is expected to be able to design internal shape of the disc to find an optimum between mechanical properties, cooling efficiency and production feasibility enabling the design of the discs fulfilling customer’s demands at attractive production costs. The model will be used during optimization of blade number and shape. There is an additional advantage that the Cimos is repeating (agreement with the customer) some calculations and simulation on existing brake systems currently in mass production. That fact will enable comparison of numerical and experimental results and confirm suitability and estimate the interval of trust. It will also be possible to compare the results from existing (commercial) packages in modified model and to find the level of agreement. We expect to be able to present the customer the benefits and shortages from different models and maybe adjust some existing models. Additionally it is expected to be able to identify the “hot spots” by direct simulation of heat transfer and experimentally confirm them.
Significance for science
With newly developed numerical model for estimation of cooling efficiency of ventilated brake disc it is possible to estimate the efficiency of the cooling channels in the development stage. This way it is possible to avoid of making expensive and unnecessary disc prototypes and experiments. Because the fluid flow and heat transfer in rotating elements is very complex, it is also very complex to simulate these phenomena virtually. As first we had to know the physics of the problem or the connection between the fluid flow and heat transfer, which we would like to capture in our numerical simulation. Therefore, at first the scientific contribution represents the knowledge and understanding of physics or phenomena inside the ventilated brake disc, especially to incorporate the air expansion inside the cooling channels due to the high temperature of the disc. The ventilated disc pumps the cool air through the cooling channels, where it heats up, due to the difference between the circumferential velocity or pressure. Also we are dealing with strong unsteady turbulent flow, especial around the disc or at the exit of the cooling channels, which we had to describe it with appropriate turbulence model. The intensity of the turbulence is greater on the outside of the cooling channels than inside. However there is a separation of the flow inside of the cooling channel, which we had to simulate it to get good results on heat convection. At this the classical engineering approach with k-? turbulence model gives up. To describe this behaviour it is more appropriate to choose SST turbulence model incorporating low-Re approach of dealing with boundary layer. Because the fluid flow in such rotating elements is very unstable and therefore time dependent, this can be also seen from the convergence of RANS simulations using finer meshes. To describe the fluid flow and heat transfer more accurately it is needed to treat problem as time dependent with advance turbulence models like URANS, LES and other hybrid models. Therefore one scientific contribution can be also found in dealing or threating the described problem of modelling turbulence, not only on the field of ventilated brake disc but also on the field of other rotating elements as radial-axial pumps, ventilators etc. The scientific contribution also represents the experimental work of measuring semi-stationary velocity field on the exit region, as well as inside the cooling channel, using PIV (Particle Image Velocimetry) measurement technique, which is one of the optical methods. The results of this kind of measurement had to be treated adequately to achieve low scatter of the values. The advantage of this PIV method is that you can get the velocity values or velocity field in the observation plane at once not only in one point. The measurement of the velocity field has also been compared with numerical simulations to validate the model and therefore represents a high contribution in this field. The new approach of threating the problem using CFD (Computational Fluid Dynamics) can give the detail description of physics and phenomena inside the rotating elements like brake discs. This approach also represents the contribution to the science on the field of determination the cumulative heat transfer from the ventilated break disc, especially the convection part, because it is more accurate than the old analytical approach using a heat transfer coefficient, which gives up in the determination of the efficiency of the ventilated brake disc.
Significance for the country
This research project with development of the new numerical model and experimental support has the direct as well as indirect impact on the development of Slovenia. Direct impact is visible with support to an automotive industry, especially on the field of ventilated brake disc, because it is possible to determine the cooling efficiency of design ventilated brake disc in the development stage using this newly developed numerical model. One of these companies in Slovenia is Cimos d.d., which is also a co-financer of this project. One part of the Cimos d.d. is focused on the development and testing of new brake discs for a different car manufacturers. This can also have an impact on the new free jobs offered from the company. Direct impact can also be found in the field of optical measurement techniques, like PIV for measuring velocity fields, and their adaptability. Not only on the field of brake disc but also on the wide field of rotating elements like ventilators, pumps etc. This opens the doors not only in automotive companies, but in other industry as well. And the indirect influence is visible in transferring the knowledge not only to students of mechanical engineering in Slovenia but also to the researchers inside the mentioned industries.
Most important scientific results
Annual report
2011,
2012,
2013,
final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Annual report
2011,
2013,
final report,
complete report on dLib.si
