International audienc

Launch vehicles experience extreme acoustic loads during liftoff driven by the interaction of rocket plumes and plume-generated acoustic waves with ground structures. Currently employed predictive capabilities to model the complex turbulent plume physics are too dissipative to accurately resolve the propagation of acoustic waves throughout the launch environment. Higher fidelity liftoff acoustic analysis tools to design mitigation measures are critically needed to optimize launch pads for the Space Launch System and commercial launch vehicles. To this end, a new coupled two-field simulation capability has been developed to enable accurate prediction of liftoff acoustic physics. Established unstructured computational fluid dynamics algorithms are used for simulation of acoustic generation physics and a high-order-accurate discontinuous Galerkin nonlinear Euler solver is employed to accurately propagate acoustic waves across large distances. An innovative hybrid computational fluid dynamics/ computational aeroacoustics coupling method is used to transmit the computational fluid dynamics-predicted acoustic field to the computational aeroacoustics domain for accurate propagation throughout the launch environment. Implementation of the coupling procedure is described in detail, and results are presented that demonstrate the accuracy of the capability for aeroacoustics predictions. Additionally, the merits of the approach are evaluated for acoustic propagation using a notional Space Launch System environment in which rocket plumes are represented by transient acoustic sources.

This paper presents development efforts at the NASA Marshall Space flight Center to establish a hybrid computational fluid dynamics and computational aero-acoustics (CFD/CAA) simulation system for launch vehicle liftoff acoustics environment analysis. Acoustic prediction engineering tools based on empirical jet acoustic strength and directivity models or scaled historical measurements are of limited value in efforts to proactively design and optimize launch vehicles and launch facility configurations for liftoff acoustics. CFD based modeling approaches are now able to capture the important details of vehicle specific plume flow environment, identify the noise generation sources, and allow assessment of the influence of launch pad geometric details and sound mitigation measures such as water injection. However, CFD methodologies are numerically too dissipative to accurately capture the propagation of the acoustic waves in the large CFD models. The hybrid CFD/CAA approach combines the high-fidelity CFD analysis capable of identifying the acoustic sources with a fast and efficient boundary element method (BEM) that accurately propagates the acoustic field from the source locations. The BEM approach was chosen for its ability to properly account for reflections and scattering of acoustic waves from launch pad structures. The paper will present an overview of the technology components of the CFD/CAA framework and discuss plans for demonstration and validation against test data.

This paper presents the development effort to establish modeling capabilities for launch vehicle liftoff acoustics and ignition transient environment predictions. Peak acoustic loads experienced by the launch vehicle occur during liftoff with strong interaction between the vehicle and the launch facility. Acoustic prediction engineering tools based on empirical models are of limited value in efforts to proactively design and optimize launch vehicles and launch facility configurations for liftoff acoustics. Modeling approaches are needed that capture the important details of the plume flow environment including the ignition transient, identify the noise generation sources and allow assessment of the effects of launch pad geometric details and acoustic mitigation measures such as water injection. This paper will present a status of the CFD tools developed by the Marshall Space Flight Center (MSFC) Fluid Dynamics Branch featuring relevant advanced multi-physics modeling capabilities and related efforts to establish a hybrid acoustic environment modeling capability combining CFD with a Boundary Element Method (BEM) acoustic field propagation model.The CFD analysis software program utilized at the MSFC Fluid Dynamics Branch is Loci/CHEM. Loci is a highly scalable computational framework with automatic parallelization for computational field simulations [1,2]. Loci was developed at Mississippi State University by Dr. Ed Luke. Loci/CHEM is a density-based Navier-Stokes solver [3] implemented in the Loci framework with the following features:Generalized unstructured grids RANS, URANS, DES, Hybrid RANS/LES turbulence modeling Eulerian multiphase models for particulates and droplets Lagrangian multiphase models for particulates and droplets with particle vaporization, condensation, combustion Real fluids EOS for cryogenic injection and combustion analysis Non-gray radiation transport models (particle and gas phase radiation) Solution adaptive mesh refinement with various error estimators available Mesh deformation for fluid-structure deformation and fuel burn-back surface Overset moving body with prescribed motion and 6-DOF Body Collision 6-DOF modeling Loci/CHEM has been extensively verified using the Method of Manufactured Solutions (MMS) Technique. The numerical algorithms are verified to be 2 nd order space and 2 nd order time accurate, but do not feature low dispersion and low dissipation algorithms at this point of development. Production simulations are routinely executed with up to 300M mesh cells on more than 3000 processors on the NASA NAS Pleiades supercomputer. The advances in CFD simulation capability and fidelity in the Fluid Dynamics Branch at MSFC have resulted in CFD modeling of complete launch vehicles with multiple plumes interacting with detailed launch pad geometric models ( Figure 1). These analyses have become invaluable in defining liftoff environments for Shuttle and future NASA heavy lift launch vehicle designs. Simulations with these tools are capable of capturing the sources of acoustic waves o...

The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleed-through, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion.