Analysis of Applicability of CFD Numerical Studies Applied to Problem When Pump Working as Turbine

The present research depicts an analysis of the implementation of computational fluid dynamics (CFD) in the study of pumps such as turbines and PATs. To highlight the benefits of CFDs for PAT studies, results from both experimental tests have been compared to better understand the reproduction error phenomena. For this, data analysis used in successful models has been applied to determine variables and parameters, and to report a low relative error. The results show that most of the studies focused on fixed speed rotation with some cases of variable speed rotation. Furthermore, there is not enough information in the academic literature for PAT of axial and mixed flows with fixed and variable speed. Finally, turbulence models based on Reynolds average Navier–Stokes (RANS) have been used to simulate PATs with fixed speed rotation in most cases.

Numerical Assessment of Turbulence Effects on Water Entry of a Hemisphere

Water entry of a rigid hemisphere is simulated using the unsteady incompressible Reynolds-Average Navier-Stokes (RANS) equations and volume of fluid (VOF) method, which are implemented in the open-source library OpenFoam. The solver InterDyMFoam is applied and the algorithm PIMPLE which is a combination of PISO (Pressure Implicit with Splitting of Operators) and SIMPLE (Semi-Implicit Method for pressure-Linked Equations) algorithms are used in the simulations. A second-order backward difference scheme is applied for the temporal discretization. A convergence and uncertainty study is performed considering different resolutions and constant Courant number (CFL) using the procedures recommended by ITTC. The comparisons of slamming loads and motions between the CFD simulations are presented using both laminar and turbulence fluid models for the hemisphere entering the water at various speeds. Turbulence is modelled with a Reynolds averaged stress (RAS) k-ω two-equation model. The turbulence effects on the slamming loads will be assessed for the case with different entry velocities.

Efecto del refinamiento de la descripción de la rugosidad en una aproximación 2D para un río de montaña: un caso de estudio

La predicción de niveles de agua en ríos es importante para prevenir pérdidas económicas así como de vidas humanas causadas por inundaciones. Los modelos hidráulicos son comúnmente usados para predecir estos niveles de agua y tomar acciones para mitigar el daño debido a inundaciones. En la presente investigación, se analizó una aproximación 2D para resolver las ecuaciones promediadas en profundidad de Reynolds Average Navier Stokes (RANS), llamado Conveyance Estimation System (CES), para explorar sus capacidades predictivas. Este artículo presenta una ampliación del estudio realizado por Knight et al. (2009). De igual forma, en esta investigación se explora una caracterización más detallada del parámetro de rugosidad y del número de zonas de rugosidad produciendo diversos escenarios. Se evaluó el desempeño de cada escenario mediante diferentes funciones de ajuste usando curvas de descarga para comparación. La investigación muestra que el uso de una adecuada descripción de la rugosidad, como un factor de rugosidad calibrado para toda la sección transversal o un modelo de rugosidad para cantos rodados calibrado para el lecho junto con valores de rugosidad obtenidos en valores sugeridos por el CES para los bancos, produce resultados del modelo óptimos en un río de montaña.

Numerical Comparisons of Heat Transfer From a Single Jet Emanating From a Slot Nozzle Impinging on an Isothermal Plate

Impingement jets are used in different cooling applications where it is required to remove large amounts of heat. Heat transfer in the stagnation point for a single jet impinging on an isothermal plate is investigated with four turbulence models. Two models are RANS (Reynolds Average Navier-Stokes): Transition SST and Transition κ–κl–ω. The other two models are URANS (Unsteady Reynolds Average Navier-Stokes): SAS and DES-SST. This paper explores the best turbulence model for thermal design and cooling purposes. Results are validated with experimental data reported by Gardon & Akfirat. These four turbulence models are available in the commercial CFD software package ANSYS FLUENT 18.1. Special attention is paid to the heat transfer in the impingement region through evaluation of Nusselt number in the stagnation point. Different dimensionless nozzle-to-plate distances are considered in this work (z/b = 14 to z/b = 40), and two different Reynolds numbers are used Re = 11,000 y Re = 22,000. Three turbulence models are within reasonable accuracy (10%) of the experimental data, but some turbulence models have problems with convergence and grid independence, especially the URANS models. Based on these results, the best turbulence model for applications in heating and cooling systems where impingement heat transfer is critical is the Transition κ–κl–ω.

Studi Eksperimental dan Simulasi Numerik Karakteristik Aerodinamika Airfoil NACA 4412

Penelitian ini bertujuan untuk menyelidiki karakteristik aliran di sekitar profil airfoil NACA 4412 dengan eksperimen dan simulasi numerik. Spesimen uji tiga dimensi dari bahan kayu balsa dengan panjang chord 100 mm dan lebar span 200 mm dibuat dalam skala laboratorium untuk keperluan pengujian pada terowongan angin, sedangkan simulasi direalisasikan dengan geometri airfoil dalam bentuk dua dimensi. Sejumlah 810.000 elemen bujursangkar dengan nilai Δy+ hingga 17,2 berhasil dibuat untuk mencapai tingkat keakuratan hasil simulasi keadaan tunak berbasis Reynolds Average Navier Stokes (RANS). Penyelidikan karakteristik aerodinamika dilakukan pada sudut serang (α) antara -5o dan 20o dengan kecepatan udara 10 m/s. Beberapa parameter penting seperti koefisien lift (CL), koefisien drag (CD), rasio lift-drag (L/D), koefisien distribusi tekanan (CP) serta profil aliran udara di sekitar airfoil diselidiki secara seksama. Hasil penelitian menunjukkan bahwa koefisien hambat (CD) dan koefisien angkat (CL) yang diperoleh dengan pendekatan numerik maupun pengujian dalam wind tunnel memiliki kesesuaian dengan data peneliti terdahulu. Seiring dengan peningkatan sudut serang airfoil (α), kedua koefisien tersebut mengalami peningkatan. Penurunan koefisien angkat terjadi secara signifikan pada kondisi stall, yaitu pada saat sudut serang melebihi dari 15°. Perubahan sudut serang berpengaruh terhadap pergeseran titik stagnasi maupun titik ekspansi di daerah leading edge pada permukaan bodi airfoil, yang selanjutnya mempengaruhi karakteristik aerodinamika secara keseluruhan. Semakin besar perbedaan tekanan antara sisi atas dan bawah dari bodi airfoil menghasilkan gaya angkat yang semakin besar.

Hydrodynamic design of an advanced submerged propulsion

A new kind of advanced submerged propulsion is automatically modeled and analyzed based on the hydrodynamic and cavitation performance. A mathematical algorithm is proposed to describe the fusion-duct, which is controlled by several design parameters, including section diameters, section lengths, and inlet shape and aspect ratio. The hydrodynamic performances of 13 cases with different parameter combinations are numerically simulated. The simulation is carried out by solving the Reynolds Average Navier-Stokes equations with STAR-CCM+, and the SST k-ω turbulence model is applied. The curves of rotor thrust and torque, stator thrust and duct resistance, along with efficiency and merit coefficient are obtained as functions of the advance coefficient and are compared for different cases. Meanwhile, the pressure distribution on both sides of the rotor and the flow field of intermediate section are systematically analyzed. To guide future designs, an impact factor is further defined and calculated to quantify the effects of different parameters. The results indicate that the section diameters have the most significant influence on hydrodynamic and cavitation performances.

SIMULASI ALIRAN PADA TURBOSAIL MENGGUNAKAN MODEL RANS - SCALABLE WALL FUNCTION

Turbosail merupakan silinder yang diletakkan di tengah kapal yang berfungsi meningkatkan gaya angkat (lift) kapal sehingga mampu mereduksi penggunaan bahan bakar. Sama seperti cara kerja layar dan turbin, turbosail memanfatkan propulsi angin sebagai sumber energinya. Pada penelitian ini akan disimulasikan sebuah turbosail dengan bentuk bulat telur yang ditambahkan ekor pada bagian belakangnya untuk mengurangi gaya hambat (drag). Untuk mengetahui kinerja turbosail, dilakukan simulasi menggunakan RANS (Reynolds Average Navier Stokes) dengan model simulasi Scalable Wall Function. Geometri dan meshing dibangun dengan software Salome. Perhitungan simulasi dijalankan menggunakan program Code Saturne, sedangkan penyajian grafik menggunakan program Paraview dan Phyton. Hasil simulasi menunjukkan bahwa bentuk bulat telur dan penempatan ekor di bagian belakang turbosail mampu meningkatkan nilai CL dan mereduksi nilai CD. Nilai CL untuk bilangan Reynold 104 adalah 1,45 dan nilai CD sebesar 0,58. sedangkan untuk bilangan Reynold 105 nilai CL adalah 1,47 dan nilai CD adalah 0,71.