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1

Fluid particle

A relatively small mass of the fluid, containing a large number of molecules that will provide a meaningful statistical averages

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2

Kutta Condition

For a given airfoil at a given angle of attack, the circulation around the airfoil is such that the flow leaves the trailing edge smoothly.

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3

Streakline

a line connecting fluid particles that has passed from the same point (Eularian)

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4

Streamline

imaginary lines, which are tangent to flow direction at a given instant of time

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5

Pathline

a trajectory traced out by a fluid particle moving in a flow field (Lagrangian)

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6

Reynolds number

a dimensionless number used in fluid mechanics to indicate whether fluid flow past a body or in a duct is steady or turbulent.

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7

Kutta-Joukowski Theorem

the lift per unit length of a spinning cylinder is equal to the density (r) of the air times the strength of the rotation (G) times the velocity (V) of the air.

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8

dynamic similarity

all forces in the model flow scale by a constant factor to corresponding forces in the prototype flow

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9

Stagnation point

a point in a flow field where the local velocity of the fluid is zero

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10

Boundary layer thickness

the distance normal to the wall to a point where the flow velocity has essentially reached the 'asymptotic' velocity

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11

Separation

reduced lift and increased pressure drag, caused by the pressure differential between the front and rear surfaces of the object

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12

Wall shear stress

expresses the force per unit area exerted by a solid boundary on a fluid in motion (and vice-versa) in a direction on the local tangent plane.

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13

𝛁×𝑽

Curl

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14

𝛁∙𝑽

Divergence

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15

Dividing streamline

The part of the flow that separates the recirculating flow and the flow through the central region of the duct

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16

Elementary flow

a collection of basic flows from which it is possible to construct more complex flows by superposition.

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17

Buckingham Pi Theorem

Dimensional analysis is used to formulate a physical phenomenon as a relation between a set of nondimensional (unitless) groups

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18

No-slip condition

assumes that at a solid boundary, the fluid will have zero velocity relative to the boundary

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19

Circulation

the line integral of velocity around a closed curve in the flow

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20

Vorticity

a region in a fluid in which the flow revolves around an axis line

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21

Magnus effect

fluid pressure decreases at points where the speed of the fluid increases

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22

d’Alembert’s Paradox

Body immersed in Fluid, There is no net drag, There is no net lift

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23

Eularian

\n Fixed in the flow field and you \n observe the variation of properties at the point \n (spatial description)

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24

Lagrangian

Identified fluid particles are followed in \n The course of time

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25

Source/sink

fluid moves radially inward/outward towards a point known as sink, and fluid disappear at sink/source at a constant rate.

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26

Doublet

a result of construction of a flow field using the superposition of a source and a sink that are placed very close to each other

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27

Mean free path

The average distance a molecule travels before it collides with another molecule

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28

Continuum

Fluid (gas or liquid) is continuously distributed along the region of interest.

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29

Wake

the region of disturbed flow (often turbulent) downstream of a solid body moving through a fluid, caused by the flow of the fluid around the body.

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