Transition Analysis for the HIFiRe-1 Flight Experiment

Abstract

The HIFiRE-1 flight experiment provided a valuable database pertaining to boundary layer transition over a 7-degree half-angle, circular cone model from supersonic to hypersonic Mach numbers, and a range of Reynolds numbers and angles of incidence. This paper reports the initial findings from the ongoing computational analysis pertaining to the measured in-flight transition behavior. Transition during the ascent phase at nearly zero degree angle of attack is dominated by second mode instabilities except in the vicinity of the cone meridian where a roughness element was placed midway along the length of the cone. The first mode instabilities were found to be weak at all trajectory points analyzed from the ascent phase. For times less than approximately 18.5 seconds into the flight, the peak amplification ratio for second mode disturbances is sufficiently small because of the lower Mach numbers at earlier times, so that the transition behavior inferred from the measurements is attributed to an unknown physical mechanism, potentially related to step discontinuities in surface height near the locations of a change in the surface material.

Stability Analysis for HIFiRE Experiments

“…6, wherein the effect of backward facing steps on second mode amplification was computed. It was found that, because the anticipated step locations near the material discontinuities on the model (X = 0.113 m and 0.213 m) were sufficiently farther upstream of the range of amplification for the relevant second mode disturbances, the effect of steps on second mode amplification during the trajectory window of interest was deemed to be secondary.…”

“…Thus, the likely contribution of various non-stationary instability modes to the sensor 1 signal is examined below. Figure 18 compares the computed and experimentally measured frequency spectra at the sensor 1 location (Fig.16) from wind tunnel measurements of Borg et al 18,19 for Re = 8.1x10 6 /m. The quasi-parallel Nfactor (with both streamwise and transverse curvature accounted for) has been computed by integrating along the streamline that passes through the sensor 1 location.…”

HIFiRE-1 and HIFiRE-5 Test Results

“…15 This number is well above the value of N=5.5 observed in wind tunnel tests of HIFiRE-1, 5,10 and higher even than the commonly referenced N=10 presumed for free flight. 36,37 Stability calculations by multiple researchers for 23 Approved for public release; distribution unlimited.…”

“…3,4,5,6,7,8,9,10,11,12,13,14 A companion paper to the current one presented initial N-factor calculations for the HIFiRE-1 BLT flight experiment. 15 Preliminary results from the HIFiRE-1 aerothermal experiments were previously published. 16 This paper presented results from both the BLT and SBLI experiments during ascent and descent.…”

“…The roughness Reynolds number, Re kk of the large diamond trip at TL transition end, was approximately 2200. 15 At t=19 seconds, when smooth-side transition appeared well-behaved and uninfluenced by any trips, Re kk for the worst-case backward facing nose tip step (k=2x10 -4 m at x=0.1 m) was approximately 700. 15 This evidence further indicates that smooth-side transition for t>19 seconds was uninfluenced by the nose tip steps.…”