This presentation gives a brief account of different uses of CFD in locomotive with mention of certain case studies. I have collected data from different sources and compiled it in this ppt. In no case i intent to own it. All credits rests with original authors.
14. Locomotive Design Process & CFD
(Cont’d)
speed, power,
tractive force
Initial Requirements
Design of main frame
Sub assemblies design
Prototyping
Testing & Evaluation
23. References
CFD simulation of train aerodynamics: train-
induced wind conditions at an underground
railroad passenger platform by Adelya
Khayrullina, Bert Blocken, Wendy Janssen
Jochem Straathof
The flow around high speed trains by Chris
Baker
http://www.circuitstoday.com/working-of-
maglev-trains
Editor's Notes
Bismillah ir Rehman nir Raheem.
Gentlemen you all are familiar with the term CFD, courtesy to our first introductory lecture on the subject. And if you are asked where it is used you would also tell about the fields where CFD has contributed to a great extent in solving a number of problems whether it be an aircraft design problem, turbo machinery design, automobiles sector, power generation industry or sports or medical profession. CFD is helping to achieve efficiency, economy and safety. Building up on the same point ,Today I will show you how CFD is being applied in locomotive industry and what are advance research areas which are being explored with the help of this computational tool.
During the course of this presentation I will give a brief overview of the journey that locomotive industry has gone through and How a current locomotive design process is followed then we will see how CFD interacts with this process
Before we embark on a journey to see CFD in locomotive I would like you to imagine yourself sitting in a 1870 train and then compare it with the picture of a journey on a TGV. Well train journey indeed became more fast, more economical and more comfortable. At that time someone have to shove coal into steam engine to keep it running and to apply brakes someone have to run over the car to rotate a wheel to apply brakes. But with all these inadequacies trains transformed our world in 19th century. They brought industrial revolution, they transformed the way we use to travel, they transformed the way we moved goods at that time. But if we see locomotive industry today, do we expect same promise from this industry. Do we see train travel to keep transforming our world. To get to answer we have to see a number of factors that will govern our future world.
You might be able to identify one difference between steam engine and today’s diesel-electric driven train History of the modern trains spans the range of last two hundred years of modern human civilization, who in that time used this incredible discovery to drastically change industry, human expansion, and the way we travel on daily basis. From the first time steam train rolled over the railways of industrial England in early 1800s to the modern times when bullet trains carry thousands of passengers with incredible speeds and freight train carry substantial amount of worlds goods, trains enabled us to develop our civilization with unexpected consequences that nobody expected. Distant lands become almost instantly reachable (3000 miles journey from New York to California was cut down from one or two months to few days!), industrial manufacture could be powered with infinite amount of raw materials and outgoing transport of finished goods, and sudden fast travel (far before first airplanes were discovered) caused the need of implementing standardized time zones across entire world.
We call them Megatrends of future. These are the game-changing forces that will shape the world in the future. These macro forces will present both challenges and opportunities as they transform the way society and markets function. One of these mega trends is urbanization. By 2050 around 75% of world population will live in urban areas. This will present an enormous burden on our present cities infrastructure and specially transportation.
The other mega trend is climate change. Although its effects are complex but one thing is sure that there will be an increase in the frequency and intensity of extreme weather events. To limit the increase in average global temperature to within 2%, emission of green house gases will have to be cut by 50% by 2050. Thus more stringent regulations on emissions will affect the transportation. A more greener and eco friendlier modes of transportation will be preferred. Can you tell why I have shown a picture of aircraft emissions. Check this out.
You can see Air travel on one extreme and rail travel on other extreme.
Other trends include use of efficient and alternate energy resources and exponential technological advancements.
Now lets rephrase the question asked in first slide. Can we have another locomotive revolution. Well answer is yes but for that Trains have to be designed keeping in view these megatrends of future. Trains must incorporate eco-friendly technologies faster than any other mode of transport can do. They need to be faster and economical. They must be designed for extreme weathers. These stringent requirements can be met by more optimized and diverse designs.
CFD comes into play here…. in designs..in optimization and in verifications and validations of these technologies. Lets see a typical locomotive design process. The philosophy in locomotive design is a bit different from that of an airplane design.
Here weight is a desired quantity. Because it is necessary to generate a tractive force. Tractive force is the force which generates motion between a body and a tangential surface through the action of friction. In locomotive design it would be force with which locomotive can pull its rail cars on track. Thus weight is desired to increase this force but On the other side maximum weight limit comes from axle load which the track can bear. Based upon this weight and tractive force requirements a power generation mechanism is selected.
Earlier steam engines were used to move the axle. The first steam run locomotive was built in 1804 in england. Later a series of changes were introduced in steam locomotive engines. And the top speed steam locomotive could achieve was around 200km/h.
By mid of 20th century electric locomotives came in .and they replaced the steam engines because of efficiency concerns. but For electric locomotives overhead electricity lines have to be in place.
And very soon trend changed to diesel-electric engines. Which used diesel to produce electricity on board and electric motors were used to run the axle.
Now when this tractive mechanism is finalized. Maximum speed and weight of a locomotive are fixed. CLICK Based upon these inputs main frame and axle are designed. The design process progress with sub assemblies design. This includes design of bogie truck and wheels and placement of subassemblies on main frame. and at last step testing and evaluation of prototype is done. Now CFD has entered in process almost in every phase. From initial design to sub assembly design to test and evaluation. Lets see how
Aerodynamic drag is a major contributor to locomotive power requirements, other than climbing resistance (gravity), frictional resistance. And at higher speeds it can account for 90% of tractive force. Earlier designs made use of instrumented cars and wind tunnel test to predict the aerodynamic drag. But with CFD now flow analysis around a fast moving train helps in optimizing different configurations. This analysis has changed the train shape and also optimized the inter-rail gaps.
Another area where CFD is helping in designs of locomotive train is cross wind speeds and tip over velocity calculations. In this photo you can see derailment of rail cars under cross wind. This incident happened in 2006 in canada and several other such incidents have led to an engineering solution. CFD helped in building a data base for tipping moment calculation and With the help of sensory and this data base a computer algorithm was written to restrict maximum speed in such conditions.
In high-speed trains, due to limitations of other types of brakes which depend upon frictional methods, aerodynamic brake has become an important braking method.
High speed trains passing through tunnel or under ground subways accompany with it strong expansion and compression waves which can cause dangerous wind conditions. CFD methods are being applied in design of tunnels and limiting the speeds a train can pass through an underground stations. One such example is the analysis of wind conditions in underground station performed for dutch railways in 2015. It employed CFD large eddy simulations for different configurations to study the associated wind effects.
Magnetic levitation based trains have achieved velocities as high as 500km/h. The propulsion of these trains does not depend upon friction based tractive force instead they are propelled by magnetic force. There is a cushion of air between the guiding rails and rail car. Although friction force is absent but aerodynamic force is still present and CFD is getting the results for these advanced technologies as well.
CFD can not only help in design of advanced technologies but it can also help in optimizing different configurations. CFD can also help achieve efficiency and comfort. Studies to make rail travel safer and comfortable can also employ this tool. And if wee see future mega trends growing computational power will also enable CFD to provide the answers for future challenges that our transportation system faces.
I thank you all for your patience listening. Now if you have any questions I will be glad to answer.
