ch 7: Flow Past Immersed Bodies

Calculate the skin friction factor of a turbulent flat-plate flow if the reynolds number is 10^6

0.0037

the reynolds number of a flow over a flat plate is 6250. according to Karman's analysis, the skin friction coefficient is ____. round the answer to four decimal places

0.0092

for a laminar flow, calculate the drag coefficient on one side of a plate if the skin friction coefficient at the trailing edge is 0.0428

0.0856 the drag coefficient is equal to twice the value of the skin friction coefficient at the trailing edge

For commercial automobiles, the theoretical minimum value of drag coefficient C(D) ≈ ____

0.15

A fluid flows over a thin flat plate. the reynolds number of the flow is 2500. calculate the boundary layer thickness at 1m from the leading edge of the plate.

0.1m

the maximum value of the mach number up to which the drag coefficient depends only on the reynolds number is ____.

0.3

the lift force (L) and the drag force (D) experienced by an airfoil of unit area are 500 N and 600 N, respectively. the density of air is 1.2 kg/m^3 and it flows at 5 m/s. if C[L] and C[D] represent the lift coefficient and the drag coefficient, determine the ratio C[L]/C[D]

0.833

Rank the objects a, b, c according to the drag force experienced by them when placed along a creeping flow with a velocity V. Place the object with the highest drag coefficient at the top of the list.

1. a 2. b 3. c

fthe image shows 2 square cylinders and a tube, and the arrow head represents the direction of the flow. Rank the objects according to the drag coefficient. Place the object with the lowest drag coefficient at the top of the list.

1. c 2. b 3. a

how is the drag coefficient of pressure (Cₚ) related with the angle of separation of flow (θ) over a circular object?

Cₚ = 1 - 4sin^2(θ)

calculate the reynolds number if the boundary layer thickness is judged thin such that δ/x = 0.1

Re = 2500

The ratio of the square of the average span of an airfoil to the planform area is called the _____ _____.

aspect ratio

the distance by which an external potential flow is pushed outwards from a flow surface due to decrease in velocity in the boundary layer is called the ____ thickness

displacement

the viscous shearing forces tangential to the body's surface result in _____ drag

friction

identify the true statements about an experimental external flow

in an external flow, the viscous effects are confined to be the boundary layer and wake region. the lift developed by airplane wings is an example of an external flow.

what does the critical reynolds number signify?

it signifies that the flow transfers from laminar to turbulent.

the force which is perpendicular to the drag force which bears the weight of the body is called the _____ force.

lift

the dimensionless shape factor is an important factor in the laminar integral theory. it is the ratio of displacement thickness to the _____.

momentum thickness

identify the devices where the drag force acts as a positive factor

parachute automobile spoilers

Which of the following bodies when placed parallel to an oncoming stream can be assumed to have a negligible interaction between the boundary layer and the outer pressure distribution?

plates airfoils

identify the factors that can delay the transition of reynolds number from laminar to critical

polished wall surface streamlined body

the difference between the high pressure in the front stagnation region on a blunt body and the low pressure in the rear separated region causes a large drag contribution called _____ drag.

pressure

identify the effects over an airfoil when it is stalled

the drag force increases the foil is no longer flyable the lift force drops off

identify the true statements about angle of attack over an airfoil.

the drag force varies with the angle of attack the lift force varies with the angle of attack. (the lift force depends on the angle of attack.)

identify the true statements about the boundary layer analysis.

the reynolds number of a flow can be determined by the boundary layer thickness the velocity profile is partially developed in a boundary layer the boundary layer concept is closely related with the flow analysis of airfoils

identify the effect of maximum lift coefficient on the stall speed of a craft.

the stall speed will be minimum when the lift coefficient is maximum.

what will be the effect of adding high-molecular-weight polymer additive to kerosene which flows through a pipe

the turbulent friction gets reduced

identify the true statements about the flow past the sharp flat plate

the viscous region extends far ahead and to the sides of the plate the broad viscous region indicates a low reynolds number the plate retards the oncoming stream greatly small changes in flow parameters cause large changes the pressure distribution

identify the true statements about forces acting on lifting bodies.

they provide a large force normal to the free stream they provide as little drag as possible

true or false: the viscous effects are highly significant in the boundary layer region.

true

identify the areas where the momentum integral relation can be applied

turbulent flat plate flow laminar flat plate flow

for a positive angle of attack on the upper surface of an airfoil, without a lift. a _____ is formed at the trailing edge.

vortex

identify the objects that can be subjected to external flow analysis

windmill flow over a flat plate airfoil

at the point of separation of the boundary layer, the value of wall shear stress will be _____ N/m^2

zero