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Bài tập thủy lực- chương 3

Tham khảo tài liệu 'bài tập thủy lực- chương 3', khoa học tự nhiên, vật lý phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Flow past a blunt body On any object placed in a moving fluid there is a stagnation point on the front of the object where the velocity is zero. This location has a relatively large pressure and divides the flow field into two portions one flowing over the body and one flowing under the body. Dye in water. Photograph by B. R. Munson. 3. Elementary Fluid Dynamics The Bernoulli Equation The Bernoulli equation may be the most used and abused equation in fluid mechanics. As was discussed in the previous chapter there are many situations involving fluids in which the fluid can be considered as stationary. In general however the use of fluids involves motion of some type. In fact a dictionary definition of the word fluid is free to change in form. In this chapter we investigate some typical fluid motions fluid dynamics in an elementary way. To understand the interesting phenomena associated with fluid motion one must consider the fundamental laws that govern the motion of fluid particles. Such considerations include the concepts offorceandaceeleration. We wllldiscuss in some detail the use of Newton s second law F ma as it is applied to fluid particle motion that is ideal in some sense. We will obtain the ceLebrated Bemouliieurationaddapply it to various flows. Although this equation is one of the oldest in fluid mechanics and the assumptions involved in its derivation are numerous it can be effectively used to predict and analyze a variety of flow situations. However if the equation is applied without proper respect for its restrictions serious errors can arise. Indeed the Bernoulli equation is appropriately called the most used and the most abused equation in fluid mechanics. A thorough understanding of the elementary approach to fluid dynamics involved in this chapter will be useful on its own. It also provides a good foundation for the material in the following chapters where some of the present restrictions are removed and more nearly exact results are presented. .