Papers by Nathan Hariharan
Standardized Post-Processing and Visualization of Participants’ Simulations of a Rotor in Hover
55th AIAA Aerospace Sciences Meeting, 2017
AIAA Standardized Hover Simulation: Hover Performance Prediction Status and Outstanding Issues
55th AIAA Aerospace Sciences Meeting, 2017
High Order Simulation of Unsteady Compressible Flows over In - teracting Bodies with Overset Grids
In Situ and Post-Processing Volume Rendering with Cinema
ISAV'20 In Situ Infrastructures for Enabling Extreme-Scale Analysis and Visualization, 2020
We present a new batch volume rendering technique which alleviates the time and expertise needed ... more We present a new batch volume rendering technique which alleviates the time and expertise needed by the domain scientist in order to produce quality volume rendered results. This process can be done both in situ and as a post-processing step. The advantage of performing this as an in situ process is that the user is not required to have a priori knowledge of the exact physics and how best to create a transfer function to volume render that physics during the in situ run. For the post-processing use case, the user has the ability to easily examine a wide variety of transfer functions without the tedious work of manually generating each one.
Several high order methodologies are investigated for their ability to capture rotor/wing tip vor... more Several high order methodologies are investigated for their ability to capture rotor/wing tip vortices. The evaluated methodologies include third/fifth/seventh ENO-based constructs, and an entropy-splitting scheme. These schemes are validated against experimental velocity, pressure data for a wing. The ability of the seventh order scheme, in conjunction with overset grids, to capture the wake vortex-structure of a rotor is also demonstrated.
Effects of Grid Interfaces/Quality onWide-Stencil High Order Accurate Simulations of Vortex-wake
This paper focuses upon the use of fifth/seventh order spatially accurate, Essentially Non-Oscill... more This paper focuses upon the use of fifth/seventh order spatially accurate, Essentially Non-Oscillatory (ENO), and weighted ENO (WENO) schemes for capturing vortices while minimizing numerical dissipation. ENO/WENO schemes are not compact, and hence a wide stencil of information is required to construct a high fidelity solution. However, the accuracy of the captured physics of vortex dynamics is affected by the how the solution is constructed near inter-grid interfaces, and the quality of the underlying grids. Recent research at Georgia Tech indicates that grid quality -especially grid stretching plays a crucial role in correctly convecting vortex wake associated with a UH60A rotor-blade in hover, when wide-stencil high order schemes are used. A controlled study of selfconvecting vortex system using high order ENO/WENO schemes in relation to grid interfaces/stretching will provide insights that can be useful for larger hover computations. The objective of this study is to characterize the effects of grid interfaces, and grid quality on the accurate computation of convection of vortices in external and self-induced flow fields, using high order schemes. Results indicate that the computed strength, and convection speed of a system of Lamb’s vortices is strongly affected by grid interfaces, and stretching. Nomenclature |A| = Roe’s dissipation matrix F = flux vector for inviscid fluxes Fv = flux vector for viscous fluxes q = vector of primitive flow variables qL = left hand side flow vector at a given face qR = right hand side flow vector at a given face ∆S = face surface area VF = fluid velocity VG = grid velocity ΩJ = cell volume A(.),E(.), R(.) = Operators τ = time vi = induced velocity Ω = rotor angular velocity R = rotor disk radius Mtip = tip Mach number (for rotor blade) CT = thrust coefficient λ = advance ratio M∞ = freestream Mach number α = angle of attack ξ,η,ζ = structured grid generalized coordinate directions i,j,k = Cartesian directional unit vector 1.0 Introduction The flow field around a rotor, whether in forward flight or hover, is difficult to model due to the presence of strong vorticity. The flow phenomena for a rotor differ from that for a wing-inforward-flight, because of the differing influence of their respective wakes. For a wing in forward flight, the generated tip vortex and the vortex sheet are quickly convected away from the wing, and the influence of the shed wake on the flow field in the vicinity of the wing is small. For an adequate numerical simulation of a wing in forward flight, it is sufficient to capture the generated tip vortex in the vicinity of the wing. In contrast, in the flow field around a rotor, a strong vortex wake system lingers in the vicinity of the rotor. In hover, the wake vortex coils beneath the rotor, and significantly alters the effective angle of attack of the rotor. 47th AIAA Aerospace Sciences Meeting Including The New Horizons Forum and Aerospace Exposition 5 8 January 2009, Orlando, Florida AIAA 2009-48 Copyright © 2009 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. 2 Accurate numerical prediction of rotor-blade aerodynamic parameters such as thrust coefficient and induced torque coefficient requires an accurate modeling of the wake vortex. In forward flight the entire vortex system is swept back leading to strong interactions between the blade-tip vortices and the successive blades, a phenomenon known as the bladevortex interaction (BVI). These blade vortex interactions result in rapid changes in local flow conditions and are a major source of aerodynamic noise and structural vibration. The underlying issue in modeling rotorcraft aerodynamics is the necessity to fully account for the complex vortex system generated by the rotor blades. Researchers in the past two decades have adopted a broad class of methodologies with various levels of complexity to model the vortex system. Until recently this representation was externally input from empirical/analytical models because full Euler/NavierStokes (NS) computations were infeasible. With the enormous advances in computational methodologies and computational power researchers have been adapting Euler/NS techniques for the study of the rotorflowfield. These solvers are particularly useful in analyzing new or complex rotor blades where no experimental data is available. Studies by Srinivasan and Ahmad [1], Strawn and Barth [2], and Duque [3, 4] have used a variety of strategies such as unstructured methodologies, and overset methodologies to tackle this problem. An excellent survey article by McCroskey [5] gives a comprehensive review of modern computational strategies for rotor applications. Such methodologies that solve for the flow field from the basic conservation laws without using additional information (information from analyses such as other numerical formulations, analytical formulations, or experimental observations) are generally referred to as…
First-Principles Physics-Based Rotorcraft Flowfield Simulation Using HPCMP CREATE-AV Helios
Computing in Science & Engineering
Comparison of Computational Fluid Dynamics Hover Predictions on the S-76 Rotor
Journal of Aircraft
Risk-Based Software Development Practices for CREATE Multiphysics HPC Software Applications
Computing in Science & Engineering, 2016
A First Principles Based Method for the Prediction of Loading Over Fixed and Rotary Wing Geometries
First-principles based techniques for the prediction of fixed and rotary wing wake geometry are d... more First-principles based techniques for the prediction of fixed and rotary wing wake geometry are described. It is demonstrated that fifth order accuracy schemes do substantially better than third order spatial accuracy schemes in capturing the details of the vortex core structure. It is demonstrated that the use of embedded grids can further enhance the resolution of the tip vortex, particularly if the boundary conditions and the order of interpolation accuracy are carefully maintained to be fifth order. A hybrid approach where the costly Navier-Stokes analysis is confined to small viscous regions near the blade surface is also described. Sample applications of this method to the vortex wake behind a fixed wing, and the surface pressure distribution over a rotor are presented.
Recent Development on the Conservation Property of Chimera
Int J Comput Fluid Dynamics, 2001
ABSTRACT
A third order upwind scheme for aero-acoustic applications
An implementation of an upwind multidimensional upwind scheme for aeroacoustic phenomena calculat... more An implementation of an upwind multidimensional upwind scheme for aeroacoustic phenomena calculations is presented that is second-order accurate in time and third-order accurate in space. The scheme allows (1) nonuniform mean flows with embedded shock waves, and (2) prescription of such internal or external acoustic sources as plane acoustic waves, monopoles, dipoles, and distributed-body forces. The scheme has built-in numerical
System and Method for Threat Propagation Estimation
A Parametric Study of Planform Effects on Rotor Hover Performance Using a Hybrid Navier Stokes – Free Wake Methodology
High Order Accurate Numerical Convection of Vortices Across Overset Interfaces
43rd AIAA Aerospace Sciences Meeting and Exhibit, 2005
Venting Apparatus and Methods
49th AIAA Aerospace Sciences Meeting including the New Horizons Forum and Aerospace Exposition, 2011
This paper describes the efforts to model vorticity laden flowfields using the CREATE-AV Helios p... more This paper describes the efforts to model vorticity laden flowfields using the CREATE-AV Helios platform. Helios employs a dual-mesh paradigm: near body unstructured grids, and high order accurate off-body Cartesian grids, and information exchange is facilitated by an automated, implicit hole cutting method. Further, an automatic mesh refinement capability is employed to refine regions of intense vorticity. Two different scenarios are considered: (a) the vortical flow field off a high-angle-of-attack aircraft, (b) the helical wake of a model rotor in hover. The ease of use, efficiency, and power of the Helios dualmesh paradigm is demonstrated through high fidelity solutions for the aforementioned unsteady, vortical fields.
CFD-FOIL-A computational environment for study of shape changing airfoils in unsteady flow
HPCMP CREATE (TM) AV Quality Assurance: Lessons Learned by Validating and Supporting Computation-Based Engineering Software
Computing in Science & Engineering, 2015
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Papers by Nathan Hariharan