空氣動(dòng)力學(xué)中的動(dòng)名詞解釋

1、Aerodynamics: some nouns1Chapter 1Types of flow:Uniform FlowSteady FlowUnsteady FlowContinuum Versus Free Molecule FlowInviscid Flow: p = 0Viscous Flow: u # 0Incompressible Flow: p =constCompressible Flow: p constSubsonic if Ma 1Gradient of a Scalar Field:The gradient of p, p, at given point in spac

2、e is defined as a vector such that:1. Its magnitude is maximum rate of change of p per unit length of the coordinate space at the given point.2. Its direction is that of maximum rate of change of p at the given point.Divergence of a Vector Field:The time rate of change of the volume will , in genera

3、l , a moving fluid element of fixed mass, per unit volume of that element, is equal to the divergence of V,denoted by V dVx dVy NV V = + +-dx dy dzCurl of a Vector Field:o)is equal to one-half of the curl of V,where the curl of V is denotedbyVXV.Vx V =d dx Vx+Vx V =d dx Vx+Mass Flow:The mass flow th

4、rough A is the mass crossing A per second. Let m denote mass flow.p(Vndt)Am = = pVnABody forces:Gravity, electromagnetic forces, or any other forces which act atdistance on the fluid inside V.Surface forces:Pressure and shear stress acting on the control surface 5.The prefect gas equation of state:3

5、P=p RTChapter 2Pathlines :We trace the path of element A as it moves downstream form point, as given by the dished line. Such a path is defined as the pathline for element A.Streamlines:A streamline is a curve whose tangent at any point is in the direction of the velocity at that point.The differenc

6、e between streamlines and pathlines:In general , streamlines are different from pathlines. You can visualize a pathlines as a time-exposure photograph of a fluid element, whereas a streamline pattern is like a single frame of a motion picture of the flow. In an unsteady flow, the streamline pattern

7、changes; hence, each frame of the motion picture is different.However ,for the case of steady flow, the magnitude and direction of the velocity vectors at all points are fixed, invariant with time. Hence, the pathlines for different fluid elements going through the same . moreover , the pathlines an

8、d streamlines are identical . therefore, in steady flow, there is on distinction between pathlines and streamlines; they are the same curves in space.z/urjSufence SAUVorticity:4We define a new quantity, vorticity , which is simply twice the angular velocity.g 三 2g)g = VIn a velocity field, the curl

9、of the velocity is equal to the vorticity.The above leads to two important definitions:If V x V#0 at every point in a flow ,the flow is called rotational. This implies that the fluid elements have a finite angular velocity.If V x V=0 at every point in a flow, the flow is called irrotational.This imp

10、lies that the fluid elements have no angular velocity; rather,their motion through space is a pure translation.Circulation:The circulation is simply the negative of the line integral of velocity around a closed curve in the flow.r 三 一 3 V - ds*4 *4 - v=M Ll=- IvrVelocity Function:舛 1舛 舛* =況商 Vz=wCha

11、pter 3Bornoullis EquationFor incompressible 、inviscid、steady、rotational flow with no body forces.1 7p + - pV2 = const along a streamlineFor incompressible、inviscid、steady、irrotational flow with no body forces.1 7p + -pV2 = const throughout the flowQuasi-one-dimensional continuity equationFor compres

12、sible flowPiAM = p2A2V2For incompressible flowAV = A2V2Pitot-static probeTotal pressure felt hereStatic pressure/ felt hereTotal pressure felt here16Pi +5pVi = p0Static dynamictotalPressure pressure pressureCondition on velocity for incompressible flowv v = oGoverning equation for irrotational, inco

13、mpressible flow :Laplaces equationv24)= o。2中 ,2中 k砂=Uniform flowA uniform flow is a physically possible incompressible flow and that it is irrotational.In Cartesian coordinates4 = VooX中=VgyIn cylindrical coordinates巾=VqoFCOSGW = Vg rsin0Source flowIn a incompressible flow where all the streamlines a

14、re straight linesemanating from a central point 0. Such a flow is called a source flow.In cylindrical coordinates2ttt4)=京 nrDoublet flowThere is a special, degenerate case of a source-sink pair that leads to a singularity called a doublet.In cylindrical coordinatesk三ZAk cos0 d)=2tt rk si n0 xb =* 2tt rVortex flowConsider a flow where all the streamlines are concentric circles about a given point, as sketched in Figure 3.31. Moreover, let the velocity along any given circular s