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Kanat ucu mesafesinin ve gövde üzeri olukların eksenel pompa içerisindeki akışa etkisinin hesaplamalı akışkan dinamiği analizi ile incelenmesi

Research of tip clearance effects and casing grooves on fluid flow in an axial pump with computational flud dynamics analysis

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  1. Tez No: 978088
  2. Yazar: MEHMET DENİZ PAÇACI
  3. Danışmanlar: PROF. DR. LEVENT ALİ KAVURMACIOĞLU
  4. Tez Türü: Yüksek Lisans
  5. Konular: Makine Mühendisliği, Mechanical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2025
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Lisansüstü Eğitim Enstitüsü
  11. Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Isı-Akışkan Bilim Dalı
  13. Sayfa Sayısı: Belirtilmemiş.

Özet

Bu tez çalışmasında eksenel akışlı bir pompanın kanat ucu mesafesinin ve gövde üzerine açılan olukların pompa performansına etkisi incelendi. Yüksek debi gerektiren sistemlerde çokça tercih edilen eksenel pompaların verimliliğinin arttırılması ve/veya en yüksek seviyede tasarlanması mühendislik açısından büyük önem taşımaktadır. Pompanın kanat ucunda kanat ucu girdapçıklarının (KUG) nasıl oluştuğu ve konumu, bunun performansa etkisi ve bu analizlere dayanarak kanat ve pompa verimini arttırma yolları araştırıldı. Kanat ucu girdapları, basma kanadından emme kanadına doğru, yüksek basınçlı bölgeden düşük basınca doğru gelişen sızıntı akımlarının etkisiyle oluşur ve bu yapı kanat etrafındaki akışı doğrudan etkiler. Belli bir akış hacmi belirlenerek pompa kanatları etrafındaki üç boyutlu, türbülanslı ve sıkıştırılamaz akış, Hesaplamalı Akışkan Dinamiği (HAD) yaklaşımıyla analiz edildi. Ansys Icem CFD yazılımı kullanılarak farklı kanat ucu mesafeleri için çözüm ağı oluşturulmuştur. Tüm çözüm ağları, hegzagonal elemanlar kullanılarak hazırlandı. Çözüm ağları oluşturulurken özellikle sınır tabaka bölgelerinde çözünürlüğe önem verilmiş ve y+ değeri küçük tutulmuştur. Ansys CFX yazılımı kullanılarak analizler yapılmıştır; Ortalama-Reynolds Navier-Stokes denklenmleri çözümlenmiş ve KGA (Kayma Gerilmesi Aktarımı) türbülans modeli seçildi. Eksenel akışlı pompalar üzerine yapılan araştırmalar detaylıca incelendi. Literatürde kanat ucu girdapçıklarının pompa geometrisine ve kanatta oluşan kavitasyona olan etkilerine dair yapılan analizler, gözlemler, tasarım iyileştirme önerileri ele alındı; kanat ucu girdabının karakterizasyonuna yönelik belirlenen metodlar ve katkılar listelendi. Çalışma kapsamında öncelikle çözüm ağı bağımsızlık çalışması yapıldı, çözüm ağı kalitesi, sınır tabaka çözünürlüğü, y+ değeri değerlendirildi ve en iyi çözüm ağı seçildi. Daha sonra, sınır koşullar belirlenerek farklı debi değerlerinde pompa karakteristik eğrileri hazırlandı. Hidrolik verimin en yüksek görüldüğü noktada kanat ucu girdapçıklarının oluşumu incelendi. Kanat ucu girdabı, hücum-firar kanadı doğrultusunda kanadın üç farklı bölgesinde kanat yüzeyine dik yüzeylerde görüntülendi. Bulgular ve sonuçlar, hem görüntülü hem sayısal sonuçlar halinde ortaya kondu. Akış çizgileri ve basınç dağılımları incelendi; basınç farkı, hidrolik güç, mekanik güç, verim ve manometrik basma yüksekliği hesaplandı. Nihayetinde, yapılan analizlere istinaden yapılan gözlemler ve kanat ucu tasarımını parametrik hale getirebilmek için belirlenen öneriler sunuldu.

Özet (Çeviri)

Within the scope of this thesis study, blade tip clearances and casing grooves on an axial flow pump were numerically analyzed and effects of different blade tip clearances and casing grooves on pump performance were investigated by using computational fluid dynamics methods. Axial pumps are widely used in different industries such as marine, energy and different applications and require different installation and maintenance specifications. . Tip clearance distance is the distance between blade and casing which is necessary for thermal expansion and safety; but it creates leakage flow and mechanical losses and it has a significant effect on hydraulic performance and cavitation formation of axial pumps. Tip leakage vortex can be optimized and made parametric using numerical methods. Tip vortex mainly triggered by pressure difference between pressure and suction sides of the blade. High pressure triggers flow separation and results in tip leakage from pressure side to suction side. This reverse flow forms tip leakage vortex on hydraulic machines. Tip leakage vortex can be observed experimentally and numerically. Thus, clearance distance can be optimized. This research focused on different blade tip clearances and casing grooves and how these result in developing tip leakage vortexes. These vortexes have dramatic effects on pressure distribution and overall efficiency of the pump. In this study, tip leakage vortexes have been analyzed under different boundary conditions. It also aimed to get a design solution to minimize the effects of tip leakage flow and optimize performance of the pump. A three dimensional, steady-state, incompressible and turbulent flow around blades was simulated under different boundary conditions. Mesh structures were built in Ansys Icem CFD and simulations were carried out in Ansys CFX softwares. Three different domains have been designed for this investigation: inlet, rotor and outlet. Rotor length has been selected as 180 mm; length of inlet and outlet domains has been selected as 180 mm and 900 mm, respectively. All domains have been designed 90 degree rotational periodic. Structured hexahedral meshes were created for different tip clearances. Mesh quality, boundary layer and resolution around near-wall regions were observed. Low y+ values were targeted to ensure accurate analysis of boundary layer. In addition, mesh independence study was conducted. The final mesh selection was made based on both accuracy and computational cost. Additionally, solution convergence was ensured by monitoring residuals and imbalances. All simulations were considered converged when residuals dropped below 10⁻5. The Reynolds-Averaged Navier-Stokes equations were solved using the Shear Stress Transport turbulence model. Different mass flow rate conditions were identified to generate pump characteristic curves to observe pump head, efficiency and flow rate. The operating point was selected as highest hydraulic efficiency, then, detailed tip leakage flow analysis was conducted. At the inlet, a uniform velocity profile was defined corresponding to specified mass flow rates, while the outlet was set to static pressure. Walls were defined as no-slip and adiabatic. The interface between stationary and rotating domains was treated using a frozen rotor method. Turbulence intensity was set to 5% at the inlet, following standard practices in turbomachinery simulations. The working fluid was considered as water at 25°C, with constant density and viscosity. The static pressure boundary condition was applied at the outlet, while the inlet was defined with a specified mass flow rate. The simulations used a pressure-based solver with its algorithm for pressure-velocity coupling. Detailed post-processing was carried out using CFD-Post. Streamline plots were generated to trace the path of the flow and observe secondary motion patterns near the blade tip. Pressure contours helped identify low-pressure zones associated with vortex formation. Tip leakage vortex structures were visualized at different locations in different constant angular locations along the blade and constant span in tip clearance area. Additionally, vortex structures were evaluated using iso-surfaces of vorticity magnitude. The effect of increasing tip clearance was found to reduce vortex location and shift the vortex core closer to the endwall. These changes resulted in enhanced turbulence and greater mixing losses, which contributed to the overall reduction in pump efficiency. In addition to flow visualization, performance parameters such as pressure drop, hydraulic power, mechanical power, overall efficiency and pump head were calculated and compared. Performance plot is created and tangential velocity contours were checked to identify flow separation and high-vorticity zones near blade tip region. It's been concluded that tip clearance and circumferential grooves significantly affects formation of tip leakage flow. Moreover, a comprehensive literature review on axial-flow pumps was carried out. It was aimed to search the role of blade tip geometry, leakage flow and cavitation effects on overall performance. Studies employing numerical methods were carefully analyzed, and design strategies proposed in the literature were gathered. The findings of this study were compared with existing results, highlighting similarities, differences and potential improvements. In conclusion, this master thesis provides valuable view into effect of blade tip clearance on tip leakage vortex behavior and pump performance. The simulation results not only understanding of flow dynamics but also foundin future geometric optimization of blade tips. Design suggestions were generated from the numerical results to support the development of high-efficiency axial pumps with reduced losses. From both academic and practical perspectives, understanding and controlling tip leakage vortex formation is essential for the designing turbomachinery with high efficiency and reliability. Benefits of this thesis are expected to support CFD-based optimization processes in future and to contribute to the development of design guidelines for blade tip clearance specifications. The findings are especially relevant in applications to minimize energy loss and to keep operational stability, such as in marine applications. These analysis enable improvements in casing design as well as blade design. Blades with several group of casing grooves be also analyzed to reduce tip leakage vortexes. Also, hub treatment to blade geometry can also be analyzed afterwards. Lastly, as a recommendation for future work, unsteady flow phenomena can also be investigated using transient simulations. Blade tip treatment features could also provide insight the understanding of loss mechanisms and guide innovative design solutions.

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