Michael G. List

Investigation of Loss Generation in an Embedded Transonic Fan Stage at Several Gaps Using High Fidelity, Time-Accurate CFD

The Blade-Row Interaction (BRI) rig at the Air Force Research Laboratory (AFRL), Compressor Aero Research Laboratory (CARL), has been simulated at three axial gaps between the highly loaded upstream stator row and the downstream transonic rotor using TURBO. Previous work with the Stage Matching Investigation (SMI) demonstrated a strong dependence of mass flow rate, efficiency, and pressure ratio on the axial spacing between an upstream wake generator and the downstream rotor through the variation of the axial gap. Several loss producing mechanisms were discovered and related to the spacings, referred to as close, mid, and far. In the SMI work, far spacing had the best performance. The BRI experiments were a continuation of the SMI work with the wake generator replaced by a swirler row to turn the flow and a deswirler row to create a wake by diffusion. Results of the BRI experiments showed a performance degradation between mid and far spacing which was not observed in SMI. This trend is seen in the numerical work as well, and the time-averaged data shows that the majority of this performance change occurred in the rotor. An unsteady separation bubble periodically forms and collapses as shocks reflect through the stator passage, creating additional aerodynamic blockage. The shed vortices induced by the unsteady loading and unloading of the stator trailing edge are chopped, with a frequency related to the spacing, by the rotor leading edge and ingested by the rotor. Once ingested the vortices interact in varying degrees with the rotor boundary layer. A treatment of the loss production in the BRI rig is given based on the time-accurate and time-averaged, high-fidelity TURBO results.Copyright

Investigation of Loss Generation in an Embedded Transonic Fan Stage at Several Gaps Using High-Fidelity, Time-Accurate Computational Fluid Dynamics

The blade-row interaction (BRI) rig at the Air Force Research Laboratory, Compressor Aero Research Laboratory, has been simulated at three axial gaps between the highly loaded upstream stator row and the downstream transonic rotor using TURBO. Previous work with the stage matching investigation (SMI) demonstrated a strong dependence of mass flow rate, efficiency, and pressure ratio on the axial spacing between an upstream wake generator and the downstream rotor through the variation of the axial gap. Several loss producing mechanisms were discovered and related to the spacings, referred to as close, mid, and far. In the SMI work, far spacing had the best performance. The BRI experiments were a continuation of the SMI work with the wake generator replaced with a swirler row to turn the flow and a deswirler row to create a wake by diffusion. Results of the BRI experiments showed a performance degradation between mid- and far spacings, which was not observed in SMI. This trend is seen in the numerical work as well, and the time-averaged data show that the majority of this performance change occurred in the rotor. An unsteady separation bubble periodically forms and collapses as shocks reflect through the stator passage, creating additional aerodynamic blockage. The shed vortices induced by the unsteady loading and unloading of the stator trailing edge are chopped, with a frequency related to the spacing, by the rotor leading edge and ingested by the rotor. Once ingested the vortices interact in varying degrees with the rotor boundary layer. A treatment of the loss production in the BRI rig is given based on the time-accurate and time-averaged, high-fidelity TURBO results.

Unsteady, Cooled Turbine Simulation Using a PC-Linux Analysis System

Summary The first stage of the high-pressure turbine (HPT) of the GE90 engine was simulated with a three-dimensional unsteady Navier-Sokes solver, MSU Turbo, which uses source terms to simulate the cooling flows. In addition to the solver, its pre-processor, GUMBO, and a post-processing and visualization tool, Turbomachinery Visual3 (TV3) were run in a Linux environment to carry out the simulation and analysis. The solver was run both with and without cooling. The introduction of cooling flow on the blade surfaces, case, and hub and its effects on both rotor-vane interac-tion as well as the effects on the blades themselves were the principle motivations for this study. The stud-ies of the cooling flow show the large amount of un-steadiness in the turbine and the corresponding hot streak migration phenomenon. This research on the GE90 turbomachinery has also led to a procedure for running unsteady, cooled turbine analysis on commod-ity PC’s running the Linux operating system. Introduction

PyF95++: a templating capability for the Fortran 95/2003 language

This article outlines a framework that was used to create a templating capability in the Fortran 95/2003 language (hereafter simply referenced as Fortran) as well as additional useful features which provide a native feel for integration into the language. Recent comparisons of Fortran with C++ have cited the lack of templating in Fortran as a major deficiency in the language [1]. Templating is a very powerful capability which allows the programmer to easily create and maintain more complex code than would be desirable to do manually. There are some very good C++ resources on templating for those not familiar with the subject [4] and are worth reading to gain a more thorough appreciation for the concept than what will be discussed here.

A fortran unit-testing framework utilizing templating and the PyF95++ toolset

A simple unit testing framework has been developed utilizing a templating capability and Python based preprocessor for Fortran. The implementation of this framework and its use for testing serial and parallel components is discussed. The capability was successfully applied to the development of a Fortran Standard Template Library and associated toolsets.

Implementation of Fourier methods in CFD to analyze distortion transfer and generation through a transonic fan

Implementations of Fourier Methods in CFD to Analyze Distortion Transfer and Generation Through a Transonic Fan Marshall Warren Peterson Department of Mechanical Engineering, BYU Master of Science Inlet flow distortion is a non-uniform total pressure, total temperature, or swirl (flow angularity) condition at an aircraft engine inlet. Inlet distortion is a critical consideration in modern fan and compressor design. This is especially true as the industry continues to increase the efficiency and operating range of air breathing gas turbine engines. The focus of this paper is to evaluate the Computational Fluid Dynamics (CFD) Harmonic Balance (HB) solver in STAR-CCM+ as a reduced order method for capturing inlet distortion as well as the associated distortion transfer and generation. New methods for quantitatively describing and analyzing distortion transfer and generation are investigated. The geometry used is the rotor 4 fan geometry, consisting of one rotor and one stator. The inlet boundary condition is a 90◦ sector total pressure distortion profile with total pressure and swirl held constant. Multiple HB simulations with varying mode combinations and distortion intensities are analyzed and compared against full annulus Unsteady Reynolds Averaged Navier-Stokes (URANS) simulations. Best practices and recommendations for the implementation of the HB solver are given. The pre-existing Society of Automotive Engineers Aerospace Recommended Practice (SAEARP) 1420b descriptors are demonstrated to be inadequate for the purposes of analyzing distortion transfer and generation on a stage-to-stage basis. New implementations of Fourier methods are presented as an alternative to the SAE-ARP 1420b descriptors. These Fourier descriptors are shown to describe distortion transfer and generation to a higher degree of fidelity than the SAE-ARP 1420b descriptors. These new descriptors are demonstrated on the analysis of full annulus URANS and HB simulations. The HB solver is shown to be capable of capturing distortion transfer, generation and performance degradation. Recommendations for the optimal implementation of the HB method are given.

Tool and Process Improvement for High-Fidelity Compressor Simulations

Compressors for modern gas turbine engines are challenging to simulate. Disparate length and time scales exist in an aggressive adverse pressure gradient environment amongst a wide array of physical phenomena requiring refinement in both space and time. The resulting mesh sizes and CPU time required to complete time-accurate simulations have become staggering, though they will only continue to increase as the simulation strategy switches from Unsteady Reynolds-Averaged Navier-Stokes (URANS) to Detached Eddy Simulation (DES) and Large Eddy Simulation (LES). For the complex compressor flows, this transition has long been necessary. In order to more effectively simulate compressor flows, several tool developments have taken place, which result in better process and reduced engineer effort. Utilizing the Air Force Research Laboratory Department of Defense (DoD) Supercomputing Resource Center (AFRL DSRC) at Wright-Patterson AFB, improvements in geometry handling, grid generation methodologies, and solver features have reduced workload while benefiting simulation quality. Available applications such as Doxygen, Python, VTK, and Subversion created a productive collaboration environment suitable for both development and testing.

Full Annulus High Fidelity Fan and Compressor Simulations

Challenge Project C3L supports research efforts to design distortion tolerant fans and accurately predict the inlet conditions to the core compressor of gas turbine engines. The technical approach and computational challenges associated with the Challenge Project are presented. The simulations run have produced critical understanding that allows design and performanceprediction tools to be improved by being based more on flow physics and less on empiricism. Distortion transfer simulations of two multistage fans show the stage-bystage transfer and generation of total pressure and total temperature distortion. Fan response for each stage along the circumference showed the first stage and the middle stage performance trajectories did not follow a typical speedline pattern while the last stage performance closely resembled a typical speedline. Simulations of an Air Force Research Laboratory (AFRL) research compressor are presented to show how aerodynamic blockage varies at off design operating conditions.

HIgh Fidelity Modeling of Blade Row Interaction in a Transonic Compressor

In order to accurately model the physics associated with losses in a transonic compressor, a time-accurate simulation of a transonic compressor rig was developed. Initially phase-lag simulations were conducted to determine required time stepping and grid re nement to capture the blade row interactions. These parameters were used to develop quarter annulus simulations to investigate the physics involved in the rotor bow shock interaction with a highly loaded upstream blade row and its e ect on the compressor. Three di erent axial spacings between the rotor and the upstream blade row have been simulated corresponding to the experimental rig. Details of the unsteady and time-averaged ow eld are presented and described. Among the many ow features resolved in the simulations was a suction side separation bubble in the upstream stator blade row that forms and collapses as a result of di usion and passing pressure waves.

A polymorphic reference counting implementation in Fortran 2003

This paper outlines a revised reference counting programming pattern for derived types in Fortran 2003. It extends the method described by Car [1] to work with polymorphic types (i.e. using the class keyword). This reference counting pattern reduces the possibility of memory leaks by allowing the object itself to manage allocations and deallocations. It follows the pattern found in many modern object oriented languages like Java [2,3] and Python[4,5] and the auto_ptr template class in C++ [6]. The reference counting pattern described here is being used in conjunction with the PyF95++ pre-processor [7,8] and the accompanying Standard Template Library (STL). All the containers in that project are reference counted and employ the original pattern for derived types. Some of the intricacies of working with polymorphic types in Fortran are described as the implementation is discussed.