Computational and Experimental Study of the Temporal Response of UHTC Materials for Thermal Protecti
Abstract
The proposed research is motivated by the high priority placed by the U.S. Navy in the development of hypersonic vehicles. Hypersoni,c systems fly faster than Mach 5 and a key aspect that distinguishes them from other flying vehicles is the need for management of t,he high levels of heat transfer that they experience on their external surfaces. Hypersonic vehicles must employ a Thermal Protectio,n System (TPS) designed specifically to ensure survival of the vehicle throughout its operational envelope.Many approaches are emplo,yed for thermal protection of hypersonic vehicles including passive and active techniques. For example, the Space Shuttle used silic,a tiles with low thermal conductivity and high emissivity to radiate much of the heat away during its relatively long re-entry traje,ctory. Re-entry vehicles such as missiles and NASA capsules use thick heat shields made of ablative materials that absorb some of th,e energy and carry it away from the vehicle. For hypersonic systems of interest to the Navy, however, that are designed to operate o,ver large distances in the atmosphere, such as mid-range and tactical-range boost-glide missiles, neither of these thermal protectio,n a,n alternative approach involves the use of Ultra High Temperature Ceramics (UHTCs) that are made of refractory compounds, such as Zr,B2 and HfB2, combined with SiC into a ceramic. Such refractory compounds have very high melting temperatures, e.g., around 3300 oC f,or ZrB2 and HfB2. They may also have a high emissivity that allows them to radiate away a significant fraction of the heat transferr,ed from the external hot gas flow onto their surface.One key challenge in use of UHTCs is their performance under oxidation. Such ph,enomena are highly relevant because the elevated temperatures generated in a hypersonic flow dissociate the oxygen molecules in air,into atoms that areextremely reactive with many materials. Tests of ZrB2-SiC and HfB2-SiC have indicated two oxidation regimes: pass,ive oxidation of the SiC at relatively low surface temperatures transitioning to development of a thick surface oxide layer and acti,ht to be SiC based on the observation that a stable layer of SiO2 forms on the material surface at less aggressive heating condition,s. In our prior work, we developed models that can predict such behavior through a carefully coordinated collaboration between exper,iment and simulation.To further assess the performance of UHTCs for thermal protection of hypersonic vehicles, we proposed to contin,ue the coordinated computational and experimental study in which the key issue to be addressed is the time-varying material response,. In both experiments and computations, study will be made of the behavior of a UHTC sample asit is flown along a representative h,ypersonic boost-glide trajectory. Experimentally, a high enthalpy plasma torch source is employed in a facility in which high fideli, test sample of a UHTC that match the values in the representative trajectory. The computations will simulate the experimental test,conditions with the goal of using the associated measurements of flow and material properties to enable validation of the models. A,new modeling activity will focus on enhancing the existing capabilities to allow for temperature gradients within UHTC composites an,d to improve the prediction of atomic oxygen transport into the material. Through successful execution of the proposed research, we,expect to provide new and essential information on the performance of UHTCs for thermal protection of hypersonic vehicles along a ti,me-varying boost-glide trajectory.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 11, 2022
- Source ID
- N000142212488
Entities
People
- Iain D. Boyd
Organizations
- Office of Naval Research
- Regents of the University of Colorado
- United States Navy