Emre Alpman

Frequency-domain prediction of turbofan noise radiation

This paper describes a frequency-domain numerical method for predicting noise radiation from ducted fans, including acoustic treatment and non-uniform background flow effects. The method solves the Euler equations linearized about a mean flow in the frequency domain. A pseudo-time derivative term is added to the frequency-domain equations so that a time marching technique can be employed to drive the acoustic field to steady state explicitly. This approach makes distributed parallel computing more viable for equations of this type and will allow for future use of well-known convergence acceleration techniques, such as multigrid, to obtain the solutions efficiently. Simulations of the JT15D static test inlet are performed including the effects of liners, and the results are compared with experimental data. A generic engine geometry is used for demonstrating further the prediction capability of the code, calculating the attenuation effects of different liner impedances and liner installation locations on the radiated sound fields.

Understanding Ducted Rotor Antitorque and Directional Control Characteristics Part II: Unsteady Simulations

Understanding the dynamic relationship between the antitorque thrust moment and the applied collective pitch angle is crucial, especially for directional control sensitivity analyses. Although there are many studies in the literature on the steady-state behavior of the FANTAIL TM , little is known about the transient response and thrust buildup, which is the primary focus of this paper. Computational fluid dynamics is used for the solutions here because it provides a more complete flowfield prediction, especially in low-power, near edgewise conditions. The flowfield is assumed to be inviscid, and the Euler equations are solved with a blade-element model for the FANTAIL. The main rotor is excluded in this study. Solutions are obtained by modifying the computer code PUMA2 (Parallel Unstructured Maritime Aerodynamics) and using an unstructured grid of 2.8 million cells. The code was run on Beowulf PC clusters. Dynamic fan thrust and moment response to applied collective pitch in hover and forward flight are presented and discussed. Nomenclature Cp = pressure coefficient L = total length of the helicopter N =y awing moment Tfan =f an thrust t = time V = freestream velocity v � =a verage induced velocity y = helicopter spanwise station θ.75 = collective pitch angle

Effectiveness of Advanced Coating Systems for Mitigating Blast Effects on Steel Components

This work aimed to study the effectiveness of an advanced coating material, polyurea, as a blast mitigation tool for steel components. The response of polyurea-coated steel components under blast loads is studied using the explicit LS-DYNA code with appropriate loading time histories supplied by a computational fluid dynamics code developed at the Pennsylvania State University, PUMA2 (Parallel Unstructured Maritime Aerodynamics-2). Results presented from this ongoing research study are related to an application of polyurea onto armor grade steel plates and an examination of resulting failure modes and governing design parameters. Failure modes examined herein consist of fracturing in the polyurea/steel composite structure. Effects of thicknesses and locations of the polyurea on the blast mitigation are also studied. Explanations of selected strain-rate dependent material models for the steel and polyurea are provided. CFD blast simulations using PUMA2 are described and validated. Results obtained from numerical studies completed to date show that bare steel plates undergo severe fracturing and fragmentation under prescribed blast loads while polyurea coated plates are able to sustain prescribed pressures without fully fracturing.

Coupled Flight Dynamics and CFD Analysis of Pilot Workload in Ship Airwakes

This paper describes a recent investigation of the helicopter/ship dynamic interface, in which pilot workload is examined using a novel coupling of flight dynamics and CFD analysis. This fully coupled method uses preexisting flight dynamics and CFD analysis codes, running concurrently; the two codes share data, with the flight dynamics code providing position and loading data and the CFD analysis code providing local velocity data. Results obtained using the fully coupled method are compared to results with no coupling, one-way coupling, where the flight dynamics code uses precalculated airwake solutions, and flight test data. Analysis of the time history and frequency domain results and the CFD solutions shows that the one-way coupling method can predict a level of pilot workload equal to or greater than that of the fully coupled method for the cases simulated. The addition of the rotor downwash to the CFD solution in the fully coupled method shows that vortices in the airwake that have a significant effect in one-way coupling may have either a similar effect or a lessened effect if the vortices are pushed away from the helicopter. I. Background hipboard operation of rotorcraft remains a topic of significant interest to both civilian and military operators, particularly in the launch and recovery regimes where the rotorcraft is in close proximity to the ship and its resultant airwake. Due to the combination of a moving ship deck and an unsteady, highly turbulent ship airwake, pilot workload for a rotorcraft operating in the vicinity of a ship can be very high, as shown in numerous simulation studies.

Separated Turbulent Flow Simulations Using a Reynolds Stress Model and Unstructured Meshes

Numerical simulation of three-dimensional, separated, high Reynolds number turbulent flows is performed using a second-order accurate cell-centered finite volume method on unstructured meshes. The computations include an application of Reynolds Stress Modeling (RSM), which consists of coupling the Reynolds transport equations with the Favre averaged Navier-Stokes Equations. The resulting system of 12 coupled, non-linear partial differential equations is solved using PUMA_RSM which is an in-house an unstructured grid computational fluid dynamics code written in ANSI-C++. Computations are performed on unstructured meshes composed of tetrahedral cells. In order to reduce the CPU time and memory requirements, parallel processing is applied with the MPI (Message Passing Interface) communication standard. The resulting parallel code is run on Beowulf clusters. Results for high Reynolds number flow around a 6:1 prolate spheroid and a sphere are presented and compared with experimental results. In the prolate spheroid case predictions of mean pressure and circumferential locations of cross flow separation points are in good agreement with experiment. The locations of primary and secondary separation points are computed with an error of roughly three degrees. Mean pressure and skin friction predictions for sphere solutions are also in good agreement with the measurements. The computed separation location is very close to the measured one. The distribution of turbulent stresses shows that the turbulent flow around a sphere is highly anisotropic and supports the notion that using anisotropic turbulence models are necessary for three- dimensional separated flows.

UNSTEADY RAH-66 COMANCHE FLOWFIELD SIMULATIONS INCLUDING FAN-IN-FIN

Understanding the dynamic relationship between the antitorque moment thrust and the applied collective pitch angle is crucial especially for directional control sensitivity analyses. Although there are many studies in the literature on the steady state behavior of the FANTAIL TM , little is known about the transient response and thrust build up, which is the primary focus of this paper. Computational fluid dynamics is used for the solutions here, because it provides a more complete flowfield prediction, especially in low-power, near edge-wise conditions. The flowfield is assumed to be inviscid and the Euler equations are solved with a blade element model for the FANTAIL TM . The main rotor is excluded in this study. Solutions are obtained by modifying the computer code PUMA2 (Parallel Unstructured Maritime Aerodynamics), and using an unstructured grid of 2.8 million cells. It was run on the Beowulf clusters COCOA2 and COCOA3. Dynamic fan thrust and moment response to applied collective pitch in hover and forward flight are presented and discussed.

Effect of Selection of Design Parameters on the Optimization of a Horizontal Axis Wind Turbine via Genetic Algorithm

The effect of selecting the twist angle and chord length distributions on the wind turbine blade design was investigated by performing aerodynamic optimization of a two-bladed stall regulated horizontal axis wind turbine. Twist angle and chord length distributions were defined using Bezier curve using 3, 5, 7 and 9 control points uniformly distributed along the span. Optimizations performed using a micro-genetic algorithm with populations composed of 5, 10, 15, 20 individuals showed that, the number of control points clearly affected the outcome of the process; however the effects were different for different population sizes. The results also showed the superiority of micro-genetic algorithm over a standard genetic algorithm, for the selected population sizes. Optimizations were also performed using a macroevolutionary algorithm and the resulting best blade design was compared with that yielded by micro-genetic algorithm.

An unstructured grid Reynolds stress model for separated turbulent flow simulations

Most of the turbulence models in the literature contain simplified assumptions which make them computationally inexpensive but of limited accuracy for the solution of separated turbulent flows. Dramatic improvements in computer processing speed and parallel processing make it possible to use more complete models, such as Reynolds Stress Models, for separated turbulent flow simulations, which is the focus of this work. The Reynolds Stress Model consists of coupling the Reynolds transport equations with the Favre–Reynolds averaged Navier–Stokes equations, which results in a system of 12 coupled non-linear partial differential equations. The solutions are obtained by running the PUMA_RSM computational fluid dynamics code on unstructured meshes. The equations are solved all the way to the wall without using any wall functions. Results for high Reynolds number flow around a 6:1 prolate spheroid and a Bell 214ST fuselage are presented. For the prolate spheroid basic flow features such as cross-flow separation are simulated. Predictions of circumferential locations of cross flow separation points are in good agreement with the experiment. A grid refinement study is performed to improve the computations. The fine mesh solution predicted locations of primary and secondary separation points with errors of roughly 2° and 0°, respectively. Flow simulations around an isolated Bell 214ST helicopter fuselage were also performed. Predicted pressure and drag force correlate well with the wind tunnel data, with a less than 10% deviation from the experiment. Drag predictions also show relative speed of Reynolds Stress Model compared to Large Eddy Simulation to compute time averaged quantities. For numerical solutions parallel processing is applied with the MPI communication standard. The code used in this study is run on Beowulf clusters. The parallel performance of the code PUMA_RSM is analysed and presented.

LARGE EDDY SIMULATION AND AEROACOUSTIC ANALYSIS FOR SIMPLE EXPANSION SILENCER LIKE GEOMETRIES

This study includes compressible large eddy simulations performed for flow predictions inside circular pipes resembling automobile exhaust pipes. Compressible large eddy simulation approach is selected because of its ability to resolve complex turbulent flow fields along with the wave motions present. Three geometries including the pipe alone and the pipes which include simple expansion chambers with circular and elliptical cross-sections are studied. The acoustic performances of the geometries are analyzed by recording the pressure fluctuations at the exit of the pipes. Predictions showed that the presence of a simple expansion chamber can reduce the pressure fluctuations not only by the expansion they provide but also by the wave reflections from the open ends and solid surfaces.Power spectral densities of the pressure fluctuations at the exitsof the pipes showed that the noise improvements by the expansion chambers are more evident at lower frequencies which become more pronounced when an A-weighting procedure was applied.

Havacılıkta Sürdürülebilir Gelişme Göstergeleri

Genel surdurulebilir gelisme indeksi, kendisini belirleyen uc indeksten ozellikle toplumsal surdurulebilir gelisme indeksi dolayisiyla, politik kararlar icin onem tasimaktadir. Eksergoekonomik ve cevresel surdurulebilir gelisme indeksleri ise teknolojik gelisme icin on plana cikmaktadir. Bu calismada, birlesik eksergoekonomik - cevresel indeksi olusturan gostergelerden havacilik sektorunu ilgilendirenler irdelenmistir. Gostergeleri normallestirme ve aritmetik, geometrik birlestirme yontemlerine iliskin gelistirme onerileri sunulmustur. Cok sayidaki benzer eksergoekonomik gostergelerden, havacilik alt sektorlerinin ihtiyaci dogrultusunda temel olanlar uzerinde durulmasi teknolojik iletisim icin kolaylik saglayacaktir. Surdurulebilirlik analizinin uygulanmasi yararli olacak baslica alt sektorler: Ucak govdesi ve ucus; ucak itki sistemleri, ucak yardimci enerji sistemleri, hava meydanlari, hava trafigi kontrolu ve ucak yer hizmetleri, ucak disi hava araclari, askeri havacilik, havacilikta geri donusumdur. Beyaz esya ve binalar icin uygulanmakta olan enerji sertifikasyonuna benzer olarak eksergoekonomik - cevresel gelisme indeksi ve sertifikasyonu, sanayi tesislerine ve havacilik alt sektorlerine, genis bir zaman cercevesi icinde, uygulanmalidir. Calismada ucus sirasinda cevre sartlarinin degisiminin etkisi ve Genisletilmis Ekserji Muhasebesi yontemi hakkinda bilgilere de yer verilmistir