Philip C. E. Jorgenson

Mixed Phase Modeling in GlennICE with Application to Engine Icing

A capability for modeling ice crystals and mixed phase icing has been added to GlennICE. Modifications have been made to the particle trajectory algorithm and energy balance to model this behavior. This capability has been added as part of a larger effort to model ice crystal ingestion in aircraft engines. Comparisons have been made to four mixed phase ice accretions performed in the Cox icing tunnel in order to calibrate an ice erosion model. A sample ice ingestion case was performed using the Energy Efficient Engine (E 3 ) model in order to illustrate current capabilities. Engine performance characteristics were supplied using the Numerical Propulsion System Simulation (NPSS) model for this test case.

Robust and simple non-reflecting boundary conditions for the space-time conservation element and solution element method

This paper reports on a significant advance in the area of non-reflecting boundary conditions for unsteady flow computations. Sets of new non-reflecting boundary conditions for ID Euler problems are developed without using any characteristics-based techniques. These conditions are much simpler than those commonly reported in the CFD literature, yet so robust that they are applicable to subsonic, transonic and supersonic flows even in the presence of discontinuities. The paper details the theoretical underpinning of the boundary conditions, and explains their unique robustness and accuracy, in terms of the conservation of space-time fluxes. Some numerical results for an extended Sods shock-tube problem, illustrating the effectiveness of the boundary condi* Senior Research Scientist, e-mail: vvscc@noboo.lerc.nasa.gov ^Member, AIAA; e-mail: fshiman@trout.lerc.nasa.gov ^Member, AIAA; e-mail: fsloh@nasp03.lerc.nasa.gov § Member, AIAA, and Research Associate, e-mail: wangxy@rintintin.colorado.edu ^Member, AIAA, and Senior Engineer, e-mail: styu@lerc.nasa.gov II Member, AIAA, and Aerospace Engineer, e-mail: jorgenson@lerc.nasa.gov Copyright ©1997 American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental Purposes. All other rights are reserved by the copyright owner. tions, are included, together with the simple Fortran computer program with which they were obtained. Since the properties of the numerical boundary conditions are closely linked to the previously developed interior schemes, a summary of the interior schemes is also provided.

Computing Axisymmetric Jet Screech Tones using Unstructured Grids

The space-time conservation element and solution element (CE/SE) method is used to solve the conservation law form of the compressible axisymmetric Navier-Stokes equations. The equations are time marched to predict the unsteady flow and the near-field screech tone noise issuing from an underexpanded circular jet. The CE/SE method uses an unstructured grid based data structure. The unstructured grids for these calculations are generated based on the method of Delaunay triangulation. The purpose of this paper is to show that an acoustics solution with a feedback loop can be obtained using truly unstructured grid technology. Numerical results are presented for two different nozzle geometries. The first is considered to have a thin nozzle lip and the second has a thick nozzle lip. Comparisons with available experimental data are shown for flows corresponding to several different jet Mach numbers. Generally good agreement is obtained in terms of flow physics, screech tone frequency, and sound pressure level.

The CE/SE Method for Navier-Stokes Equations Using Unstructured Meshes for Flows at All Speeds

In this paper, we report an extension of the Space-Time Conservation Element and Solution Element (CE/SE) Method for solving the Navier-Stokes equations. Numerical algorithms for both structured and unstructured meshes are developed. To calculate the viscous flux terms, a ‘midpoint rule’ is used. In the setting of space-time flux conservation, a new and unified boundary-condition treatment for solid wall is introduced. The Navier Stokes solvers retain all favorable features of the original CE/SE method for the Euler equations, including high fidelity resolution of unsteady flows, easy implementation of nonreflective boundary conditions, and simplicity of computational logic. In addition, numerical results show that the present Navier-Stokes solvers can be used for high-speed flows as well as low-Mach-number flows without preconditioning. The present Navier Stokes solvers are efficient, accurate, and very robust for flows at all speeds.

Engine Icing Modeling and Simulation (Part I): Ice Crystal Accretion on Compression System Components and Modeling its Effects on Engine Performance

ABSTRACT During the past two decades the occurrence of ice accretionwithin commercial high bypass aircraft turbine engines undercertain operating conditions has been reported. Numerousengine anomalies have taken place at high altitudes that wereattributed to ice crystal ingestion such as degraded engineperformance, engine roll back, compressor surge and stall,and even flameout of the combustor. As ice crystals areingested into the engine and low pressure compressionsystem, the air temperature increases and a portion of the icemelts allowing the ice-water mixture to stick to the metalsurfaces of the engine core. The focus of this paper is onestimating the effects of ice accretion on the low pressurecompressor, and quantifying its effects on the engine systemthroughout a notional flight trajectory. In this paper it wasnecessary to initially assume a temperature range in whichengine icing would occur. This provided a mechanism tolocate potential component icing sites and allow thecomputational tools to add blockages due to ice accretion in aparametric fashion. Ultimately the location and level ofblockage due to icing would be provided by an ice accretioncode. To proceed, an engine system modeling code and amean line compressor flow analysis code were utilized tocalculate the flow conditions in the fan-core and low pressurecompressor and to identify potential locations within thecompressor where ice may accrete. Note that there is abaseline value of aerodynamic blockage due to low velocityair near the compressor inner and outer walls and bladesurfaces (boundary layer blockage). There is also a blockagedue to the blade metal thickness. In this study, the “additionalblockage” refers to blockage due to the accretion of ice on themetal surfaces. Once the potential locations of ice accretionare identified, the levels of additional blockage due toaccretion were parametrically varied to estimate the effectson the low pressure compressor blade row performanceoperating within the engine system environment. This studyincludes detailed analysis of compressor and engineperformance during cruise and descent operating conditionsat several altitudes within the notional flight trajectory. Thepurpose of this effort is to develop the codes to provide apredictive capability to forecast the onset of engine icingevents, such that they could help in the avoidance of theseevents.It has been reported that ice crystal accretion in gas turbineengines is dependent on the amount of mixed phaseconditions (liquid and solid) that exist. In addition, theproblem of ice accretion is highly multi-disciplinary, since itinvolves heat transfer from the air to the compressor metalsurfaces. The first phase of this study focuses on addressingthe thermodynamic cycle through the engine system code andthe mean line flow analysis through the compressor through aflight trajectory. The second phase of this study focuses on

Prediction of Sound Waves Propagating Through a Nozzle Without/With a Shock Wave Using the Space-Time CE/SE Method

AbstractThe benchmark problems in Category l(InternalPropagation) of the third Computational Aeroacous-tics (CAA) Workshop sponsored by NASA GlennResearch Center are solved using the space-timeconservation element and solution element (CE/SE)method. The first problem addresses the propaga-tion of sound waves through a nearly choked tran-sonic nozzle. The second one concerns shock-soundinteraction in a supersonic nozzle. A quasi 1-DCE/SE Euler solver for a nonuniform mesh is de-veloped and employed to solve both problems. Nu-merical solutions are compared with the analyticalsolution for both problems. It is demonstrated thatthe CE/SE method is capable of soMng aeroacous-tic problems with/without shock waves in a simpleway. Furthermore, the simple non-reflecting bound-ary condition used in the CE/SE method which isnot. based on the characteristic theory works verywell.1. IntroductionThe method of space-time conservation elementand solution element (abbreviated as the CE/SEmethod) is an innovative numerical method for solv-ing conservation laws. It is different in both con-cept and methodology from the well-established tra-ditional methods such as the finite difference, finitevolume, finite element and spectral methods. It isdesigned from a physicists perspective to overcomeseveral key limitations of the traditional numericalmethods.Simplicity, generality and accuracy are weightedin the development of this method while the funda:mental requirements are satisfied by the scheme. Its

Modeling Commercial Turbofan Engine Icing Risk with Ice Crystal Ingestion

The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that have been attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, and one or more of the following: loss of thrust control (roll back), compressor surge or stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the increase in air temperature causes a portion of the ice crystals to melt. It is hypothesized that this allows the ice-water mixture to cover the metal surfaces of the compressor stationary components which leads to ice accretion through evaporative cooling. Ice accretion causes a blockage which subsequently results in the deterioration in performance of the compressor and engine. The focus of this research is to apply an engine icing computational tool to simulate the flow through a turbofan engine and assess the risk of ice accretion. The tool is comprised of an engine system thermodynamic cycle code, a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor flow path, without modeling the actual ice accretion. A commercial turbofan engine which has previously experienced icing events during operation in a high altitude ice crystal environment has been tested in the Propulsion Systems Laboratory (PSL) altitude test facility at NASA Glenn Research Center. The PSL has the capability to produce a continuous ice cloud which are ingested by the engine during operation over a range of altitude conditions. The PSL test results confirmed that there was ice accretion in the engine due to ice crystal ingestion, at the same simulated altitude operating conditions as experienced previously in flight. The computational tool was utilized to help guide a portion of the PSL testing, and was used to predict ice accretion could also occur at significantly lower altitudes. The predictions were qualitatively verified by subsequent testing of the engine in the PSL. The PSL test has helped to calibrate the engine icing computational tool to assess the risk of ice accretion. The results from the computer simulation identified prevalent trends in wet bulb temperature, ice particle melt ratio, and engine inlet temperature as a function of altitude for predicting engine icing risk due to ice crystal ingestion.

A Model to Assess the Risk of Ice Accretion due to Ice Crystal Ingestion in a Turbofan Engine and its Effects on Performance

4The occurrence of ice accretion within commercial high bypass aircraft turbine engines has been reported under certain atmospheric conditions. Engine anomalies have taken place at high altitudes that were attributed to ice crystal ingestion, partially melting, and ice accretion on the compression system components. The result was degraded engine performance, engine roll back, compressor surge and stall, and flameout of the combustor. As ice crystals are ingested into the fan and low pressure compression system, the air temperature increases and a portion of the ice crystals melt. This allows the ice-water mixture to stick to the metal surfaces of the compressor components. The resulting accretion causes a blockage on stationary components such as the stator vanes, and subsequently results in the deterioration in performance of the compressor and engine. The main focus of this research is the development of a computational tool that can estimate whether there is a risk of ice accretion by tracking key parameters through the compression system blade rows at all engine operating points within the flight trajectory. The tool has an engine system thermodynamic cycle code, coupled with a compressor flow analysis code, and an ice particle melt code that has the capability of determining the rate of sublimation, melting, and evaporation through the compressor blade rows. Assumptions are made to predict the complex physics involved in engine icing. Specifically, the code does not directly estimate ice accretion and does not have models for particle breakup, or erosion. Two key parameters have been suggested as conditions that must be met at the same location for ice accretion to occur: the local wet-bulb temperature to be near freezing and below, and the minimum local melt ratio must be above 10%. These parameters were deduced from analyzing normalized laboratory icing test data. These two parameters are the criteria that are used to determine whether ice accretion due to ice crystals is possible in an engine, and are used to identify the specific blade row where it could occur. Once the possibility of accretion is determined from these parameters, the degree of blockage due to ice accretion on the local stator vane can be estimated from an empirical model of ice growth rate and time spent at that operating point in the flight trajectory. The computational tool can be used to assess specific turbine engines to their susceptibility to ice accretion in an ice crystal environment.

Computation of Feedback Aeroacoustic System by the CE/SE Method

It is well known that due to vortex shedding in high speed flow over cutouts, cavities, and gaps, intense noise may be generated. Strong tonal oscillations occur in a feedback cycle in which the vortices shed from the upstream edge of the cavity convect downstream and impinge on the cavity lip, generating acoustic waves that propagate upstream to excite new vortices. Numerical simulation of such a complicated process requires a scheme that can : (a) resolve acoustic waves with low dispersion and numerical dissipation, (b) handle nonlinear and discontinuous waves (e.g. shocks), and (c) have an effective (near field) non-reflecting boundary condition (NRBC). The new space time conservation element and solution element method, or CE/SE for short, is a numerical method that meets the above requirements [1–4]. A detailed description of the 2-D CE/SE Euler scheme can be found in [1, 2], only a brief sketch is given here.

Engine Icing Modeling and Simulation (Part 2): Performance Simulation of Engine Rollback Phenomena

Abstract Ice buildup in the compressor section of a commercial aircraft gas turbine engine can cause a number of engine failures. One of these failure modes is known as engine rollback: an uncommanded decrease in thrust accompanied by a decrease in fan speed and an increase in turbine temperature. This paper describes the development of a model which simulates the system level impact of engine icing using the Commercial Modular Aero-Propulsion System Simulation 40k (C-MAPSS40k). When an ice blockage is added to C-MAPSS40k, the control system responds in a manner similar to that of an actual engine, and, in cases with severe blockage, an engine rollback is observed. Using this capability to simulate engine rollback, a proof-of-concept detection scheme is developed and tested using only typical engine sensors. This paper concludes that the engine control system’s limit protection is the proximate cause of iced engine rollback and that the controller can detect the buildup of ice particles in the compressor section. This work serves as a feasibility study for continued research into the detection and mitigation of engine rollback using the propulsion control system.