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Fluid mechanics research methods

Fluid dynamics research can be divided into the field observations, laboratory simulations, theoretical analysis, numerical calculation the following four aspects:

The field observations of flow phenomena inherent in the nature or existing projects full-size flow phenomena, use of various instruments for systematic observation, which summed up the laws of fluid motion, and in order to predict the evolution of the flow phenomena. Weather observation and forecasting in the past, basically is carried out.

However, the occurrence of flow phenomena at the scene often can not control the occurrence of conditions is almost impossible to repeat, affect the flow phenomena and laws; field observations also spend a lot of material, financial and human. Therefore, the establishment of the laboratory, these phenomena can appear in the control conditions, in order to observe and research.

With such disciplines as physics, chemistry, fluid dynamics can not be separated from the experiment, especially the study of fluid movement phenomena. The experiment shows the movement characteristics and key trends, contribute to the formation of concept, testing the correctness of the theory. Two hundred years, each represents a major advance in the history of fluid mechanics development is inseparable from the experiment.

Model experiments in fluid mechanics plays an important role. Model is mentioned here refers to the guidance, based on theoretical study of scale changes (zoom in or out) in order to arrange the experiment. Some flow phenomena are difficult to * the theory of computing, while others can not do a prototype experiment (the cost is too high or too large). At this time, according to model experimental data obtained from the conversion system of units of a simple algorithm to find the prototype data.

The field observations are often of existing things, the observation of existing projects, and laboratory simulations can not things did not happen the phenomenon (such as waiting for the design engineering, mechanical, etc.) were observed, so that it can improve. Therefore, laboratory simulation is an important method for the study of fluid mechanics. The theoretical analysis is the universal law of fluid motion such as mass conservation, momentum conservation, energy conservation, etc., means of mathematical analysis, the study of fluid movement, explain known phenomena and predict possible outcomes. The theoretical analysis of the steps as follows:

The first is to establish the "mechanical model", that is, for practical fluid mechanics problems, the analysis of the various contradictions and grasp the main aspects of the problem can be simplified set up to reflect the nature of the problem "mechanical model". The most commonly used in fluid mechanics the basic model: continuous media, the Newtonian fluid, an incompressible fluid, ideal fluid flow plane.

Followed by the characteristics of fluid motion, the mathematical language of conservation of mass, momentum, and energy conservation law expressed, resulting in the equation of continuity, momentum and energy equations.

Also, with some contact flow parameters of the relationship (such as the equation of state), or other equation.

These equations together known as the basic fluid mechanics equations. Find the solution of the equations, combined with the specific flow to explain the physical meaning of these solutions and the flow mechanism. Would normally these theoretical results with experimental results were compared to determine the accuracy of the obtained solutions and the scope of application of the mechanical model.

From basic concept to a series of quantitative research in the basic equations are related to deep mathematical problems, the development of fluid mechanics is the development of mathematics. , In turn, through experiments and engineering practice test hydrodynamic theory, but also to test and enrich the mathematical theory, it raises a number of unresolved problems, but also mathematical research, the development of mathematical theory a good topic. The current level of development of mathematics, there are many questions will be difficult from a purely mathematical point of perfect resolved within the next few decades.

Simplify fluid physical properties in fluid mechanics theory, the theoretical model of a particular fluid, reduce the self variables and to reduce the unknown function to simplify the mathematical problem, is successful in a certain range, and to solve many practical problems .

To seize the main factors for a specific area, consider the specific physical properties and movement of specific environmental ignore secondary factors abstraction also simplifies the establishment of a specific mechanical theoretical model, we can overcome the mathematical difficulties, further The study of fluid balance and the nature of sports.

50 years of the 20th century {BANNED} beginning in the rocket engine designed to carry satellites to heaven, with the experimental theory, is to rely on one-dimensional steady flow to introduce and simplify, in order to receive timely guidance hydrodynamic conclusions.

In addition, fluid mechanics often use a variety of small perturbations simplified into linear from the nonlinear differential equations and boundary conditions. Acoustics is a small perturbation method in fluid mechanics and the earliest subjects of substantial achievements. The acoustics of the so-called small perturbations, refers to the sound propagation in the fluid, the fluid state (pressure, density, fluid particle velocity) with the sound is not reached when the difference is very small. The linear water wave theory of thin wing theory due to the simplification and some rough, but they are well used examples of the small perturbation method.

Every reasonable simplifies have the results of the mechanical, but also has its limitations. For example, ignores the changes in density can not discuss the propagation of sound; ignore the viscosity can not discuss the resistance associated with it and some other effects. To master a reasonable simplified approach, the correct interpretation of the law or the conclusions drawn in the simplified, comprehensive and fully understand the scope of application of the simplified model, correctly estimated it brings with the actual deviation is the hydrodynamics of the essence of the theoretical work and experimental work.

The basic equations of fluid dynamics is very complex, especially considering the viscous, if not the computer, can only be calculated on a relatively simple situation or simplified Euler equation or the NS equations. 20 the 1930s to the 1940s, is particularly important for the complex and fluid mechanics problems, had been organized by human use months or even years to do the numerical calculation, such as the cone to do the inviscid flow field around supersonic flight from 1943 The years have been counted in 1947.

Development of mathematics, the continuous advancement of the computer, and hydrodynamics of various calculation methods the invention, many of the original can not solve the theoretical analysis of complex fluid mechanics problems has been to obtain the numerical solution of the possibility of promoting the computational fluid dynamics methods development, and the formation of a computational fluid dynamics.

Since the 1960s, aircraft and other topics related to fluid movement, often using computer numerical simulations, which can complement each other and the physical experiment. Numerical simulation and experimental simulation complement each other, so that the speed of scientific and technological research and engineering design, and cost savings. Numerical methods recently developed very rapidly growing in importance.

To solve fluid mechanics problems, field observations, laboratory simulations, theoretical analysis and numerical aspects are complementary. The experiment requires theoretical guidance, can come to the conclusion of the regular scattered surface contact phenomenon and the experimental data. Conversely, theoretical analysis and numerical calculation should give physical pattern or data according to the * field observations and laboratory simulation to establish the flow of mechanical models and mathematical models; also rely on experiments to test the degree of perfection of these models and patterns . In addition, the actual flows are often exceptionally complex (eg, turbulence), the theoretical analysis and numerical computation will encounter a huge mathematical and computational difficulties, lack of concrete results, only through field observations and laboratory simulation study.

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