Fluids project
m-hfsain
ENGR 3553 MECHANICS OF FLUIDS SPRING 2015
Prof. Peter Cavallo [email protected]
SEMESTER PROJECT – PART 3
WIND TUNNEL POWER REQUIREMENTS
Figure 1 illustrates the wind tunnel we are considering in greater detail. As the air passes
through the system and over the model, various losses are encountered, which must be overcome
by the work input provided by the fan. In this segment of the project you are to consider all
major and minor losses depicted in Figure 1 to develop a model for predicting the velocity
obtained in the test section as a function of the fan power input. Eventually this will be cast in
nondimensional terms.
Inlet segment
Test section segment
Diffuser segment
Exit segment
inlet V
W
exit V
Figure 1. Nominal open circuit wind tunnel with major and minor losses.
Relevant data is provided in Table 1. Be sure to include these in your analysis. You have four
(4) pipe segments to consider for major losses, and various minor losses as depicted and
summarized in the figure and table. Assume the same surface roughness height throughout the
system. For the sake of simplicity you may consider the velocity at the start of each segment
when computing the major and minor losses. Be sure to consider hydraulic diameter for any
non-circular segments.
Table 1. Tunnel losses and physical dimensions.
Dimensions (ft) Losses KL
Inlet height 9 Diffuser section height 3 Inlet entrance 1.0
Inlet width 10 Diffuser section width 4 Inlet contraction 0.2
Inlet length 10 Diffuser section length 30 Diffuser expansion 0.1
Test section height 3 Exit section diameter 6 Fan losses 1.5
Test section width 4 Exit section length 12 Exit 1.0
Test section length 8 (Only exit section is circular) Surface roughness =0.0005 ft
NOTES:
1) This is a Class II problem and as such it is strongly recommended that you set up a spreadsheet to perform the calculations. You will need to iterate (i.e. guess) on values for
volumetric flow rate through the system until this value is consistent with other
parameters. You should set up your spreadsheet with all relevant formulas, including
Equation (8.35b) of the text, to update the entire system with just a few inputs.
2) Hint: rearrange the extended Bernoulli equation so all terms are on one side. Iterate on Q until the condition that all head additions/losses sum to zero is met to within some
tolerance (within 0.1 ft, e.g.). 3) The fan power and volumetric flow rate are inputs. The inlet and exit velocities are
unknown but nonzero.
4) Assume standard sea level properties for air in all calculations: 3 3
2.38 10 slug ft
,
2 3
7.66 10 lbf ft
, 7 2
3.74 10 seclbf ft
5) As a sanity check, for a fan power of 80 hp, you should obtain a volumetric flow rate of about 1700 ft
3 /sec, producing a velocity of nearly 142 ft/sec in the test section.