F.R.Haferkorn Fachhochschule Dortmund/ University of Applied Sciences

Transcription

1 Vehicle surface geometry optimisation F.R.Haferkorn Fachhochschule Dortmund/ University of Applied Sciences Abstract Providing sustainable mobility and reducing energy and air pollution in traffic is an important task for our society. An interdisciplinary team of computer scientists, engineers and designers at the Fachhochschule Dortmund used software tools, the inhouse data network and a data base (as a base for a future expert system) to collect and assess the surface geometry and cw values of vehicle prototypes. Vehicles were viewed as structures of cw and finite surface elements out of a prototype kit. Data sources were literature, results of measuring scale prototypes in wind tunnel and field experiments, and of flow simulations (CAD preprocessor I-deasand flow simulator FLUENT). Our protoyping kit method supports recombining, assessing and optimizing transit systems for the following indicators: - The transit impulse follows attractivity (velocity /just-in-time reliability) and transit costs (transportation units / motive performanc / energy consumption) - The motive performance required is a function of velocity and the cw value, optimized by a favourable design of the vehicle surface. As an application of our prototype kit and the indicators a study compared the high speed maglev system HYPERMAG with the ICE, the Transrapid, the Airbus and the Concorde. The aim in this interdisciplinary project was to acquire and provide experience for services - cooperation in research and development, - consulting, studies and workshops, - instruction and training.

2 1 Introduction Computers in Railways VII Providing sustainable mobility and reducing energy and air pollution in traffic is an important challenge for our society. Many different solutions to achieve both aims have been discussed. The solutions vary from new technologies e.g. exhaust catalysators in automobiles to political measures e.g. ecological taxes and traffic prohitions in smog situations. 2 The AeroRail prototyping kit One way to save energy and to reduce exhaust emissions and noise is aerodynamic shaping of vehicles and airplanes. As society demands a high mobility and fast transportation media, aerodynamics and aerodynamical shaping are becoming more important. So an interdisciplinary team of computer scientists, engineers and designers at the Fachhochschule Dortmund (university of applied sciences) used software tools, the inhouse data network and a data base (as a base for a future expert system) to collect and assess the surface geometry and cw values of vehicle prototypes. We are currently developing the modular software tool AeroRail. This tool, itself a kit, will enable us to combine surface elements from the database to make vehicle prototypes, to modify their shape using CAD modules and to simulate their flow behaviour with CAE modules. Aerorail's elements are office communication, picture processing, animation and graphical presentation and the CAD/CAE systems I-deas and FLUENT to model the surfaces of vehicles, to create the FEM volume nets and to simulate the air flow. An important player in the game is the data processing centre, taking care of the inhouse data network, the prototype data base and the future expert system. Input data for the AeroRail kit is literature [1-7], the results of our wind tunnel, and hopefully results of planned field experiments. All these results are normalised by the flow simulation tool. We found that only some minor differences between measuring results and simulation results had to be adjusted. 3 A picture series While the influence of different surface mikrostructures still has to be examined, the data base already includes the values of some shapes, standard rotational surfaces and real freeforms. 5 pictures from the AeroRail data base show turbulence values k of 2 different surfaces,,,ice-head" and,,ice-car" in different combinations forming the test models TM-4,-2n,-2,-5, and -3. Please observe that turbulence areas change in size and location to give valuable hints to developers where a surface should be optimized in the sense of a generic freeform. The fuzzy assessments,,better" or,,worse" refer to the usual cw values and to our invention dd, the Dortmund Direct Coefficient. In an animation we can show the pictures morph from any state to the neighbours, left hand the short vehicles, right hand the long ones, and from 5.74e-10 N via 4.84, 3.04, 2.66 down to 1.74e-10 N, for TM-4, -2n, -5, -2 and -3 according to their dd values.

3 Computers in Railways Figure 1: Test model TM-4, a cylindric/prismatic can shape, less suitable configuration. The turbulence range was 99.9 to 531

4 654 Computers in Railways VII Figure 2: Test model TM-2n, a shortened ICE end car running at negative velocity with can end forward, is considerably better. The turbulence range was 31 to 463

5 Computers in Railways VII 655 Figure 3: Test model TM-2 of same shape but running the ICE front end forward, shows improved turbulence figures. The turbulence range was 99.7 to 182

6 656 Computers in Railways VII Figure 4: Test model TM-5, an ICE end car of real length and a combination of TM-2 and TM-4, increased turbulence due to it's increased length. The turbulence range was 99.6 to 178 mw.

7 Computers in Railways VII 657 Figure 5: Test model TM-3, a very short ICE train combined of TM-2 and TM-2n, proved the best solution with turbulence range 99.7 to 87.8

8 4 The Dortmund Direct Coefficient dd Computers in Railways VII The AeroRail prototyping kit includes an assessment value dd (,,Dortmund Direct") based on a new theory of vehicle flow resistance force Fw. dd is more precise and practicable yet compatible to the commonly used cw value. Indded, cw is dimensionless and for large surface protoypes it is nearly constant. However for low scale prototypes, e.g. 1:20 in our wind tunnel models and 1:23.5 in test models TM-2 to TM-5, cw strongly depends on velocity. This makes it difficult to infer values for large scale prototypes from results with low scale ones. The reason is that in the formula cw=fw/(ap/2*v^2) velocity v and diameter d of the profile area A=d^2 both are treated with exponent 2, which is necessary to obtain the dimension of a force for (Ap/2*v^2) and to keep cw dimensionless. Introducing the coefficient dd we follow another way. Assessing the results of flow simulations we found that in the formula dd=fw/re^c the dimensionless Reynolds number Re=v*d/v is not raised to the square potence 2, but to an exponent c between 1.75 and As a mean value of our results on TM-2 and TM-3 we found c= Indeed dd is not dimensionless as are both cw and Re, but like Fw it has the dimension of a force, dd's advantage of cw is that it is constant in a wide velocity range and even for prototypes of any scale, if you find the result precise enough for practise. So it will do to measure the resistance force Fw for one velocity and to calculate the dd value once for any scale. If desired it is no problem to calculate the cw from a given dd. In literature we had to infer the resistance force Fw from a given cw and from estimated - because not given - A and v. In literature on Airbus and Concorde we did not even find cw values, and instead of the performance P there was specified a force. To find dd we take forces as an input to our formula dd =Fw/Re^c. So dd and cw arecompatible. Parameters of dd and data in the AeroRail kit are the shapes of vehicles' front and rear and the portion of gaps, T=G/d, forming the pressure fraction ddp and all being subject to interference, and the roughness of surface e*a - A=l/d is the dimensionless length of the vehicle - forming the viscous fraction ddv of dd. 5 Assessing indicators Vehicles are viewed as linear combinations of dd and finite surface elements from a prototyping kit. They can quickly be recombined to assess system variants and to optimize systems. Our method supports optimizing and assessment of transit systems for the following indicators: The transit impulse I (in tkm/h or pass.kmth) follows attractivity and transit costs and determines the amount of transportation units required due to their capacity and velocity. The decisive quality for attractivity in passenger transit is velocity. In freight transit it is the just-in-time reliability of the schedule.

9 Computers in Railways VII Transit costs follow the amount of transportation units (staff costs), the motive performance required (operating costs and depreciation), and the energy consumed (external or environmental costs). The motive performance required is a function of, in addition to velocity, the dd value which can be optimized by a favourable design of the vehicle surface. 6 Application examples To demonstrate the efficiency of our software tool Aerorail even in the sector of transsonic velocities we analysed the surface of the Active HYPERMAG which is a high speed maglev system. In a study it was compared with the ICE, the Transrapid, the Airbus and Concorde. This maglev system is supposed to hover in elevated or submarine tubes at the velocity of the Concorde (2500 km/h). A journey from South Africa via the EU, Japan and the USA to Argentina in a HYPERMAG train would take just 4*4.2=16.8 hours. Because of speed HYPERMAG is more favourable than ICE and TRANSRAPID, whereas Airbus and Concorde have the advantage on short routes overseas, e.g. between Europe and the USA and between South Africa and South America, against that the HYPERMAG is faster and less expensive than the airplanes on the single overland sections of the route from South Africa to Argentina. Shipping express and valuable goods in a,,main run" over distances of 600 kms and as for attractivity and costs the container railcar CargoSprinter of Deutsche Bahn proved superior to the transport by lorries. As reliability of schedule seems to be the main indicator of attractivity in goods transport, the advantage of rail transport can be extended by improving vehicle surfaces for lower resistance to air flow, especially on routes along the sea shore with strong head winds and low gradients. FLUENT and I-deas are such mighty elements in our kit, that we have not yet used all the features included. Measuring not only the resistance force Fw in the running direction z of the rail vehicle, but also the lateral component Fx and the vertical component Fy - even all three momentum components can be obtained - it will be possible to analyse the effect of lateral wind and wheelset spoilers on the stability of trains. Conclusions The AeroRail kit and the computer aided methods included offer the following advanages: - a short working time and a reduction of costs for the optimisation of vehicle surfaces because of starting with the parameters of standard surfaces and then modelling and testing generic freeform surfaces,

10 Computers in Railways 111 _ quick assessing to show the effects of optimised vehicle surfaces resulting in a reduced resistance to air flow, energy consumption, motive performance required, operating costs etc.. As a university of applied sciences, the aim of our interdisciplinary project was to acquire and provide experience for these services: cooperation in research and development, consulting and training for users who wish to buy our system, to use it in their own firm and to do their work themselves, working by order of users who just are interested to have one special problem solved, persuading public and politics (lobbyism) to notice which system advances rail transit has of it's competitors and which it could have, if it was promoted in a fair way. Our students, the regional administration and industry are interested to cooperate. References [IJBuchheim, R. Expertensystem zur Unterstiitzung der Aerodynamikoptimierung von Fahrzeugen. GMD-StudienNr. 160, 1989 [2] Hucho, W.-H. (Hrsg.): Aerodynamik des Automobils, Eine Briicke von der Stromungsmechanik zur Fahrzeugtechnik, 3. Auflage, Springer 1999 [3] Kuchemann, D : The Aerodynamic Design ofaircraft, Pergamon 1985 [4] Mackrodt, P -A, Pfizenmaier, E.: Aerodynamik und Aeroakustik fur Hochgeschwindigkeitszuge, Physik in unserer Zeit, IS.Jahrgang, S , 1987 [5] Peters, J.L.: Aerodynamische Gestaltung von Schienenfahrzeugen fur den Schnellverkehr, ART, Band 40, S.28-35, 1985 [6] Becker, H.-J.: Concorde, Motorbuch 1991 [7] Morgenstern, K., Plath, D Airbus A330/A340, Die groflen Europaer, Motorbuch 1996