Simulation of fluid flow and collection efficiency for an SEA multi-element probe

Abstract

Numerical simulations of fluid flow and collection efficiency for a Science Engineering Associates (SEA) multi-element probe are presented. Simulation of the flow field was produced using the Glenn-HT Navier-Stokes solver. Three-dimensional unsteady results were produced and then time averaged for the heat transfer and collection efficiency results. Three grid densities were investigated to enable an assessment of grid dependence. Simulations were completed for free stream velocities ranging from 85-135 m/s, and free stream total pressure of 44.8 and 93.1 kPa (6.5 and 13.5 psia). In addition, the effect of angle of attack and yaw were investigated by including 5 degree deviations from straight for one of the flow conditions. All but one of the cases simulated a probe in isolation (i.e. in a very large domain without any support strut). One case is included which represents a probe mounted on a support strut within a finite sized wind tunnel. Collection efficiencies were generated, using the LEWICE3D code, for four spherical particle sizes, 100, 50, 20, and 5 micron in diameter. It was observed that a reduction in velocity of about 20% occurred, for all cases, as the flow entered the shroud of the probe. The reduction in velocity within the shroud is not indicative of any error in the probe measurement accuracy. Heat transfer results are presented which agree quite well with a correlation for the circular cross section heated elements. Collection efficiency results indicate a reduction in collection efficiency as particle size is reduced. The reduction with particle size is expected, however, the results tended to be lower than the previous results generated for isolated two-dimensional elements. The deviation from the two-dimensional results is more pronounced for the smaller particles and is likely due to the reduced flow within the protective shroud. As particle size increases differences between the two-dimensional and threedimensional results become negligible. Taken as a group, the total collection efficiency of the elements including the effects of the shroud has been shown to be in the range of 0.93 to 0.99 for particles above 20 um. The 3D model has improved the estimated collection efficiency for smaller particles where errors in previous estimates were more significant.

A Thermal Analysis of a Hot-Wire Probe for Icing Applications

“…However, the model over predicts the power by approximately 5.5% at = 135 m/s and = 93.1 kPa. Figure 5 also shows results using heat transfer correlations generated from CFD results 6 . These correlations were generated by maintaining the wire at a constant temperature in the CFD model and calculating the resulting heat transfer.…”

“…Overall, the radiation term was found to be very small in the calculations so the sensitivities of the parameters were not examined in detail. A recent CFD study 6 of the SEA multi-wire probe indicated that the mass flow through the shroud is about 80% of the upstream value based on the projected cross-sectional area of the probe. For calculating the heat-transfer coefficient of the elements, the far field conditions based on the corrected mass flow in the inlet were deemed the most appropriate.…”

“…(14) is used in several calculations presented in this paper. However, as discussed in section II.D, the Reynolds number and property values are calculated using the average conditions in the shroud which are different than the freestream conditions upstream of the probe as indicate by recent CFD calculations 6 . In Eq.…”

“…Since the authors were not aware of a correlation for a half-pipe configuration, a recent CFD study 6 of the SEA multi-wire probe was used to generate a correlation. In the CFD study, the hot-wire elements were fixed at a constant temperature of 140C while the shroud was set to 50C.…”

“…A complementary study further examines the collection efficiency of the SEA multi-wire probe via detailed 3D fluid flow and particle trajectory calculations 6 . Results from those computations are used in this study.…”