The drag force (Fdrag) exerted by air on a moving car depends on a dimensionless drag coefficient (Carag), the specific volume of air (Vair), the velocity of the car (Var), and the frontal area of the car (Afront). (a) Based on unit considerations alone, obtain an equation for the drag force. Be sure to explicitly demonstrate that the final units are correct. (b) Explain, based on your equation, what happens to the drag force when each variable is changed in isolation. Indicate whether this predicted behaviour matches your intuition in each case. air

The drag force (Fdrag) exerted by air on a moving car depends on a dimensionless drag coefficient (Carag), the specific volume of air (Vair), the velocity of the car (Var), and the frontal area of the car (Afront). (a) Based on unit considerations alone, obtain an equation for the drag force. Be sure to explicitly demonstrate that the final units are correct. (b) Explain, based on your equation, what happens to the drag force when each variable is changed in isolation. Indicate whether this predicted behaviour matches your intuition in each case. air

Elements Of Electromagnetics

7th Edition

ISBN:9780190698614

Author:Sadiku, Matthew N. O.

Publisher:Sadiku, Matthew N. O.

ChapterMA: Math Assessment

Section: Chapter Questions

Problem 1.1MA

See similar textbooks

Similar questions

The drag coefficient in aircraft industry affected by some parameters which are thespeed of plane (v), the plane length (L), the air density (ρ), the air dynamic viscosity(μ), and speed of sound (a). By using dimensional analysis, identify two non-dimensionnumbers in which the drag coefficient is a function of them and explain how these twowill effect on drag coefficient.
The power P generated by a certain windmill design dependson its diameter D , the air density ρ , the wind velocity V , therotation rate Ω , and the number of blades n . ( a ) Write this relationship in dimensionless form. A model windmill, of diameter50 cm, develops 2.7 kW at sea level when V = 40 m/s andwhen rotating at 4800 r/min. ( b ) What power will be developedby a geometrically and dynamically similar prototype, ofdiameter 5 m, in winds of 12 m/s at 2000 m standard altitude?( c ) What is the appropriate rotation rate of the prototype?
The drag of a sonar transducer is to be predicted, based on wind (Air) tunnel test data. The prototype is 1.5 m diameter sphere, is to be towed at 4.3 m/s in seawater. The model is 0.2 m diameter. Take: Air density = 1.2 kg/m, Air dynamic viscosity = 1.81 x 10$ Pa. s, seawater density = 1000 kg/m, seawater dynamic viscosity 1.813x 10 Pa s, If the drag of the model at these test conditions is 9.5 N, estimate the drag of the prototype in (N).
MLT By dimensional analysis, obtain an expression for the drag force (F) on a partially submerged body moving with a relative velocity (u) in a fluid; the other variables being the linear dimension (L), surface roughness (e), fluid density (p), and gravitational acceleration (g).
When a capillary tube of small diameter D is inserted into a container of liquid, the liquid rises to height h inside the tube (Fig.). h is a function of liquid density ? , tube diameter D, gravitational constant g, contact angle ?, and the surface tension ?s of the liquid. (a) Generate a dimensionless relationship for h as a function of the given parameters. (b) Compare your result to the exact analytical equation for h. Are your dimensional analysis results consistent with the exact equation? Discuss.
Mott ." cometer, which we can analyze later in Chap. 7. A small ball of diameter D and density p, falls through a tube of test liquid (p. µ). The fall velocity V is calculated by the time to fall a measured distance. The formula for calculating the viscosity of the fluid is discusses a simple falling-ball vis- (Po – p)gD² 18 V This result is limited by the requirement that the Reynolds number (pVD/u) be less than 1.0. Suppose a steel ball (SG = 7.87) of diameter 2.2 mm falls in SAE 25W oil (SG = 0.88) at 20°C. The measured fall velocity is 8.4 cm/s. (a) What is the viscosity of the oil, in kg/m-s? (b) Is the Reynolds num- ber small enough for a valid estimate?
A prototype automobile is designed for cold weather inDenver, CO ( - 10 ° C, 83 kPa). Its drag force is tobe tested on a one-seventh-scale model in a wind tunnelat 150 mi/h, 20 ° C, and 1 atm. If the model and prototypeare to satisfy dynamic similarity, what prototypevelocity, in mi/h, needs to be matched? Comment onyour result.
The power P generated by a certain windmill design depends upon its diameter D, the air density p, the wind velocity V, the rotation rate 0, and the number of blades n. (a) Write this relationship in dimensionless form. A model windmill, of diameter 50 cm, develops 2.7 kW at sea level when V= 40 m/s and when rotating at 4800 r/min. (b) What power will be developed by a geometrically and dynamically similar prototype, of diameter 5 m, in winds of 12 m/s at 2000 m standard altitude? (c) What is the appropriate rotation rate of the prototype?
P1.20 A baseball, with m = 145 g, is thrown directly upward from the initial position z = 0 and Vo = 45 m/s. The air drag on the ball is CV², as in Prob. 1.19, where C~ 0.0013 N: s*/m". Set up a differential equation for the ball motion, and solve for the instantaneous velocity V(t) and position z(1). Find the maximum height zmax reached by the ball, and compare your results with the classical case of zero air drag.
1. The Stokes-Oseen formula for drag force Fon a sphere of diameter D in a fluid stream of low velocity V, density p, and viscosity u is: 9T F = 3TuDV + 16PD? Is this formula dimensionally homogenous? 2. The efficiency n of a pump is defined as the (dimensionless) ratio of the power required to drive a pump: QAp input power Where Q is the volume rate of flow and Ap is the pressure rise produced by the pump. Suppose that a certain pump develops a pressure of Ibf/in? (1ft = 12 in) when its flow rate is 40 L/s (1L =0.001 m). If the input power is 16hp (1hp = 760 W), what is the efficiency?
Q1: Consider laminar flow over a flat plate. The boundary layer thickness o grows with distance x down the plate and is also a function of free-stream velocity U, fluid viscosity u, and fluid density p. Find the dimensionless parameters for this problem, being sure to rearrange if neessary to agree with the standard dimensionless groups in fluid mechanics. Answer: Q2: The power input P to a centrifugal pump is assumed to be a function of the volume flow Q, impeller diameter D, rotational rate 2, and the density p and viscosity u of the fluid. Rewrite these variables as a dimensionless relationship. Hint: Take 2, p, and D as repeating variables. P e paD? = f( Answer:
(b) A wind-tunnel experiment is performed on a small 1:5 linear-scale model of a car, in order to assess the drag force F on a new full-size car design. A dimensionless "drag coefficient" Ca is defined by C, =- pu'A where A is the maximum cross-sectional area of the car in the flow. With the model car, a force of 3 N was recorded at a flow velocity u of 6 m s. Assuming that flow conditions are comparable (i.e., at the same Reynolds number), calculate the expected drag force for the full-sized car when the flow velocity past it is 31 m s (equivalent to 70 miles per hour). [The density of air p= 1.2 kg m.]