Twenty-First Symposium on Naval Hydrodynamics (1997) / Chapter Skim
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Unsteady Three-Dimensional Cross-Flow Separation Measurements on a Prolate Spheroid Undergoing Time-Dependent Maneuvers
Unsteady Three-Dimensional Cross-Flow Separation Measurements on a Prolate Spheroid Undergoing Time-Dependent Maneuvers
Pages 161-176
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From page 161... ...
Time-dependent separation locations are measured successfully for the first time, as are time-dependent force and moment measurements. Steady and unsteady data are presented for each of these systems for two maneuvers: a 0° to 30°, 0.33 second (t'=11)
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From page 162... ...
gives a brief overview of the steady prolate spheroid literature along with a detailed description of the steady flowfield. The prolate spheroid flowfield at angle of attack is characterized by massive crossflow separation that forms on the tail at low aIlgles of attack and migrates windward and noseward at increasing angles of attack (2~.
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From page 163... ...
The data obtained by DyPPiR experiments will provide data sets upon which to base unsteady models of the separation process in these flows. For example, by having the capability to measure separation location as a function of time, one can potentially develop a model describing that time dependency as a Function of non-dimensional maneuver pitch rate.
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From page 164... ...
from the mathematical analysis, k is the thermal conductivity, l and w describe the sensor size, a is the thermal diffusivity, and ~ is the viscosity. Here, the main purpose of the sensors is not necessarily to measure the absolute magnitude of the wall shear or the skin friction coefficient, but to measure the relative shear distributions through measurements of the film coefficient to locate shear minima and thus separation locations.
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From page 165... ...
This plot is not as informative as the equivalent plots in Me pitchup maneuver due to Me low number of steady data points for these low angles of attack, but a lag in separation formation is still evident. Figure 19 to Figure 21 show direct comparisons between steady circumferential skin friction distributions and unsteady ones for ~c/L=0.729.
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From page 166... ...
In this case, the steady data show both a primary and secondary separation, while the Unsteady distribution shows only a primary separation which is more leeward than the steady primary separation. This shows that in unsteady flows the separation location topology itself can be very different than in an equivalent steady configuration.
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From page 167... ...
While the normal force coefficient increases at greater rates at the higher angles of attack, the pitch moment settles in at a relatively constant slope at around a~10°. 5.4 Unsteady Results The normal force and pitch moments for the pitchup maneuver are shown in Figure 27.
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From page 168... ...
The added mass effect is such that a larger, not smaller, nonnal force should be generated. This is equivalent to the unsteady data leading the steady data, or He added mass resulting in a leading time constant.
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From page 169... ...
Also, added mass effects contribute to lower time lags. Again, more robust systems will allow one to determine not only whether the unsteady aerodynamics lead or lag the steady data, but will also bring out more specific details about He processes involved and point to improved dynamical models.
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From page 170... ...
Hot-film and force and moment measurements were made on Me model in two maneuvers. The hot-film data showed definite lags in the formation and migration of the separation line for the pitchup maneuver, but showed much weaker trends for Me submarine maneuver due to Me much weaker separations at the lower angles of attack.
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From page 171... ...
Simplified flow separation topology for the secondary streamlines in a plane normal to the major axis of an axisymmetric body. S1 and S2 refer to primary and secondary separation locations, respectively, and R1 and R2 refer to prepay and secondary reattachment locations.
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From page 172... ...
Pnmary Separation Figure 8. Steady flow skin friction values superimposed on secondary streamlines from Chesnakas and Simpson 1000.Cf (5)
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From page 173... ...
Constant temperature primary separation locations for various x/L stations sensors as a function of angle of attack for steady flow.
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From page 174... ...
Dashed lines are equivalent steady separation lines, solid lines are instantaneous separation lines. "P" indicates primary separation, while "S" indicates secondary separation.
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From page 175... ...
Figure 21. Comparison of wall shear distribution at xlL=0.729 for steady data and pitchup maneuver at a~29.9°.
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From page 176... ...
Unsteady normal force and pitch moment for pitchup maneuver. Quasi Steady Unsteady / -- A .-0.1 O 5 - 1 - a - -1 ~ ' ~ '\2,,N,-" 2 TO o , 0.5 0.4 0.3 ° 0.2 0.1 ° 0.0 -0.1 no a' 10 15 20 t' Figure 28.
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