Initial Assessment of Space Launch System Transonic Unsteady Pressure Environment

Abstract

A series of wind tunnel tests were conducted at the NASA Langley Research Center Transonic Dynamics Tunnel to assess the transonic buffet environment for the Space Launch System (SLS) launch vehicle. An initial test, conducted in 2012, indicated an elevated buffet environment prompting a second test to provide further insight into the buffet phenomena and assess potential solutions to reduce the response levels of these environments. During the course of the test program, eight variants of the SLS-10000 configuration were examined. The effect of these configuration variants on the coefficient of the root-mean-square fluctuation of pressure about the mean as a function of test condition indicates that the maximum fluctuating pressure levels are extremely sensitive to the geometry of the forward attachment of the solid rocket boosters (SRBs) to the SLS Core. The addition of flow fences or changes to the SRB nose cone geometry can alleviate the unsteady pressure environment. Nomenclature L c = coherence length M = Mach number C p,rms = coefficient of the root-mean-square fluctuation of pressure about the mean = model pitch angle = model roll angle Notice to Readers The predicted performance and certain other features and characteristics of the Space Launch System vehicle are defined by the U.S. Government to be Sensitive But Unclassified (SBU). Therefore, values in plots and figures have been either removed or normalized to arbitrary values.

Sensitivity of Space Launch System Buffet Forcing Functions to Buffet Mitigation Options

“…[6][7][8][9] Efforts to develop BFFs for the SLS configuration have been underway since 2011 and there have been two primary test programs conducted to obtain unsteady buffet pressures. [10][11] Buffet tests in 2012 identified high fluctuating pressure environments on the core and booster downstream of the booster forward attachment near Mach 0.92. Coupled loads analysis revealed that when preliminary BFFs developed from these environments were applied to the vehicle structure, buffet loads were largely the source of exceedances of structural and vibratory limits on the SLS vehicle.…”