Drag measurements on a laminar flow body of revolution

Abstract

LOW-SPEED wind-tunnel drag force measurements were taken on a laminar flow body of revolution free of support interference. This body was tested at zero incidence in the NASA Langley 13 in. Magnetic Suspension and Balance System (MSBS). The primary objective of these tests was to determine the drag force measuring capabilities of the 13 in. MSBS. The drag force calibrations and wind-on repeatability data let us assess these capabilities. Other studies included the effects of fixing transition and surface flow visualizations using both liquid crystals and oil flow. In addition, the drag coefficient data from this study are compared with data from another source. Contents Background Support interference is a serious problem in testing models in wind tunnels.1'2 Using a Magnetic Suspension and Balance System (MSBS)3 is the only way to eliminate completely support interference. With the elimination of the support, not only will the flow distortion produced by the sting be eliminated, but many other advantages will accrue, such as 1) elimination of model modifications to accomodate the sting, 2) ease of model movement for dynamic testing, 3) fast, efficient testing at any attitude, and 4) improvement in productivity due to elimination of stings and struts. Since the late 1970's, in-house activity with MSBS's has steadily increased at NASA Langley. Most of the effort has been aimed at improving the 13 in. MSBS by using a digital control system and an optical position sensing system. However, in 1984 this MSBS was combined with a small low-speed (M < 0.5) wind tunnel, and in 1986 a program was initiated to obtain drag data on various axisymmetric shapes at zero incidence. The results reported here are part of this program. Description of Model The profile of the laminar flow body (see Fig. 3) was generated from an eight-parameter class of rounded-nose, tailboom bodies described in Ref. 4. This class of bodies was developed to verify a method of shaping axisymmetric bodies to produce minimum drag in incompressible, nonseparating flow at zero incidence. The model used in this study is 12 in. long with a fineness ratio of 7.5. Drag Force Characteristics and Repeatability of Data A drag force calibration was performed with a full-scale load of 242.5 gf. The data was fitted with a second-order polynomial. The rms of the errors between the applied loads and the calculated loads from the polynomial equation is 0.27 gf or 0.1197o of the full-scale calibration load.