45 



60 



>40 



20 



-ST 



-AROESTy.BERGER (1975) 



I I 



©-(STRAZISAR (1975) 



^Ol2 



ft 



-0.4 



-0.6 



SEP 



FIGURE 20. Effect of overheat on Falkner-Skan separa- 

 tion parameter. 



Experimental model 



NACA 632-015 profile 

 Maximum thickness = 1.175" 

 L = 9.213" 



1" electric 

 4^ heater 



.jBOO_ 



J0_ 



^1 00 

 12750 



_4»00 

 _»5(I0. 

 _6.100 



_4750 



7»0 



3" electric 

 " heater 



Maximum output of each 

 heater is 600 watts 



?^o Q09 9S_£-^ 



approximate procedure showed that despite the 

 large changes in profile shown in Figure 19, the 

 value of e at separation did not change very much 

 with heating (Figure 20) . This was confirmed as 

 also shown on Figure 20 by exact calculations of 

 Strazisar (1975) using Lowell's (1974) program. 

 The question of the length retardation of separa- 

 tion on a real configuration nevertheless remained 

 an open one. 



Experiment 



This experiment was also performed in the CWRU Low 

 Turbulence Water Tunnel described in Section 4 

 using a specially designed two-dimensional model 

 having an NACA 632-015 profile. The model (Fig- 

 ure 21) is designed as part of the upper wall of 

 the test section of the water tunnel. The boundary 

 layer developing on the upper wall of the nozzle 

 is removed through a scoop with the bleed rate 

 adjusted so that the stagnation streamline is 

 straight and steady. Rod heaters (Figure 22) are 

 provided over the length of boundary layer develop- 

 ment. The tests were conducted at rather low unit 

 Reynolds numbers so as to promote laminar flow 

 in the separation region and to minimize the power 

 needed for large temperature differences. The 

 electric heaters distributed through the plate 

 provide wall temperatures of the order of 60°F 



FIGURE 22. Location of rod heaters in experimental 

 model . 



above the free-stream fluid temperature in the 

 region of separation. Wall temperature distribu- 

 tions are shown in Figure 23. 



The separation behavior was determined by com- 

 binations of the following indicators: 1) indi- 

 cation of separation by visual observations of a 

 dye stream injected along the surface through static 

 pressure holes, 2) location of separation indicated 

 by the static pressure distribution along the plate, 

 and 3) use of hot film anemometry to measure bound- 

 ary layer velocity profiles. 



As with many water flow facilities, results are 

 dependent on the state of cleanliness of the 

 experimental equipment. In particular, the veloc- 

 ity profiles were affected by the condition of 

 the airfoil surface and the screens in the settling 

 chamber. Even when the screens and airfoil surface 

 were relatively clean, there was some scatter in 

 the level of the boiindary layer shape parameter 

 as evidenced by the results for the unheated air- 

 foil. The effects of heating on shape factor 

 displayed consistent trends that were generally 

 independent of facility condition. The experi- 

 mental setup, procedures and measurement systems 

 are described in detail by Timbo and Prahl (1977) . 



X Pressure tap 



(taps run down centerllne of model) 



Model 



FIGURE 21. Model as mounted in water tunnel. 



140- 

 T.-F 



HEATER VOLTAGE 

 8S. 

 70, 

 55 



J. 



L 



FIGURE 23. Surface temperature distributions. Too = 70''f. 



