Chapter V: HET CO 2 Radiation Measurements
5.9 Integrated Measurements
A quantifiable measure of the difference between the experimental and simulated spectra is the ratio of integrated spectra Iexp/Isim. The integrated radiance I is
Figure 5.34: MSL1 condition freestream measurement compared to 6" core flow simulations at different temperatures to study sensitivity andP∞= 3.35 kPa.
Figure 5.35: MSL2 condition freestream measurement compared to 6" core flow simulations at different temperatures to study sensitivity andP∞= 1.66 kPa.
Figure 5.36: 0◦ AOA stagnation point MSL1 condition measurement compared with simulations assuming a reflected shock processed free stream. Shock layer chemistry is modelled with Fridman chemistry.
Figure 5.37: 0◦ AOA stagnation point MSL2 condition measurement compared with simulations assuming a reflected shock processed free stream. Shock layer chemistry is modelled with Fridman chemistry.
calculated by
I =∫
λIλdλ (5.2)
Figure 5.38: 16◦ AOA stagnation point MSL1 condition measurement compared with simulations assuming a free stream processed by a reflected shock. Shock layer chemistry is modelled with Fridman chemistry.
Figure 5.39: 16◦ AOA stagnation point MSL2 condition measurement compared with simulations assuming a free stream processed by a reflected shock. Shock layer chemistry is modelled with Fridman chemistry.
for the integral bounds 3900 to 5350 nm determined by the range measured on the camera. A summary ofIexp/Isim for the different orientations and conditions tested are shown in Table 5.3.
Table 5.3: Summary of ratio of experimental to simulated integrated radiance in different configurations. Representative ray lengths are chosen. The distance∆nbe- tween the body and shock along the normal line-of-sight extracted from simulations is also shown.
ST0_4 MSL1 MSL1 MSL1 MSL2 MSL2 MSL1 MSL2
Orientation 16◦Stag. 16◦Stag. 16◦Lee 0◦Stag. 16◦Stag. 0◦Stag. FS Probe FS Probe
Ray (m) 1.00 1.00 0.25 0.10 1.00 1.00 0.15 0.15
Iexp/Isim 0.95 1.07 1.25 1.35 1.49 2.32 2.51 3.41
∆n(mm) 7.0 3.7 3.0 1.5 3.2 1.1 N/A N/A
The integrated radiance for the shock tube condition without observable absorption in the boundary layer at the model surface, ST0_4, is within 5% of the integrated simulated radiance. This is an optically thick condition at significantly higher temperatures and pressures than the expansion tube conditions.
The normal line-of-sight distance from the wall to the shock ∆n extracted from simulations for the expansion tube conditions and orientations tested are also shown in Table 5.3. For both the MSL1 condition and the MSL2 condition, the discrepancy between experiment and simulation decreases with increasing shock layer thickness
∆n. The differences in the shock layer thickness also correspond to differences in the post-shock temperature and pressure profiles along the line of sight of the rays, however, these effects on the absorption thickness are not included in this qualitative discussion. The largest discrepancy occurs in the freestream probe measurements and the discrepancy is larger for the MSL2 condition than the MSL1 condition.
The initial conditions for the MSL1 and MSL2 conditions vary only in the initial pressure in the accelerator (MSL1: P5= 180 mTorr vs. MSL2: P5= 75 mTorr).
The larger discrepancies observed in the expansion tube conditions is partially due to freestream flow features such as the expansion fan and the wall boundary layer in the line-of-sight not accounted for in the simulations. A summary of the integrated results for simulations that include these features into the freestream flow field are shown in Table 5.4. The expansion fan is modeled as discussed in Section 5.4.3 and the 16◦AOA stagnation point, 1.0 m ray is considered. The projected boundary layer is modeled as discussed in Section 5.5.1 and the lee side, 0.095 m ray is considered.
Accounting for flow features decrease the discrepancy between the experiment and simulation.
The possibility of a reflected shock processed free stream is considered and the integrated ratio of experimental to simulated (1.0 m ray) radiance for 0◦AOA and
Table 5.4: Summary of Iexp/Isim when the expansion fan and tube-wall boundary layer flow features are implemented into the simulations. The 1.0 m ray simulations are used for the expansion fan flow feature comparison. The columns Start and End correspond to the expansion fan implemented into the simulation at the start and end of measurement exposure time. The 0.095 m ray is used for the lee side boundary layer feature comparison.
MSL1 16◦AOA Stag. MSL2 16◦AOA Stag. MSL1 Lee Side Flow Feature No fan Start End No fan Start End No BL 25 mm BL Iexp/Isim 1.07 1.02 0.97 1.49 1.35 1.24 1.40 1.29
16◦AOA stagnation point free stream is summarized in Table 5.5. The simulations assume Fridman chemistry in the shock layer. In the expansion tube, simulations with Fridman chemistry result in a better match in shock standoff distance compared to simulations with Johnston chemistry discussed in Chapter 4. The shock layer simulations using Fridman chemistry decrease the spectral radiance compared to simulations using Johnston chemistry as discussed in Section 5.6.1.
The better match between integrated experimental and simulated radiance in three of the four cases can be attributed to difference in freestream conditions. For the MSL1 16◦ AOA case, the agreement is slightly worse with the Fridman kinetic model than the Johnston model (Iexp/Isim =1.13 vs. Iexp/Isim =1.07).
Table 5.5: Summary of ratio of experimental to simulated integrated radiance for 1.0 m simulation ray length assuming a reflected shock fully processed free stream and Fridman shock layer chemical kinetics. The nominal case assuming perfect gas free stream and Johnston shock layer chemical kinetics is shown for comparison.
MSL1 MSL2 MSL1 MSL2
Model Orientation 0◦ 0◦ 16◦ 16◦
Iexp/Isimreflected shock 1.20 1.21 1.13 1.36 Iexp/Isimnominal 1.35 2.32 1.07 1.49