Turbine design optimizations using high fidelity CFD
Başlık çevirisi mevcut değil.
- Tez No: 401726
- Danışmanlar: PROF. DR. REZA S. ABHARI, PROF. DR. PATRICK JENNY
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2014
- Dil: İngilizce
- Üniversite: Eidgenössische Technische Hochschule Zürich (ETH)
- Enstitü: Yurtdışı Enstitü
- Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 246
Özet
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Özet (Çeviri)
Temperature distribution downstream of the combustor exhibits nonuniformities both in radial and circumferential directions. When the relatively hot gases termed as hot streaks migrate downstream they alter both the aerodynamics of the turbine and increase the incident heat load on the HP turbine along their flow path. This study numerically investigates the interaction of the hot streaks with the turbine aerodynamics using an unsteady particle tracking tool in conjunction with the unsteady RANS simulations. The necessary numerical tools required have been developed and the capabilities of the existing tools have been extended enabling more accurate and faster numerical predictions. Regarding the accuracy the solver's capability in modeling the diffusion processes is greatly improved through the development of novel techniques. The k-ω turbulence model enabled to impose the highly turbulent flow field downstream of the combustor which greatly affects the mixing behavior within the turbine. A cell Reynolds and local CFL number scaled, anisotropic artificial dissipation algorithm is proposed for the Ni-Lax Wendroff scheme to improve the accuracy at the very high aspect ratio cells used at the wall in RANS simulations. The new artificial dissipation scheme showed a superior accuracy in resolving the boundary layers compared to the similar central 2nd order schemes present in the literature and resulted in a more accurate prediction of the secondary flows especially of the tip leakage vortex. A further improvement is also observed in the studies with the temperature non-uniformities present at the turbine inlet. Regarding the speed the solver is GPU accelerated which enabled to complete unsteady, one-and-a-half stage turbine simulations within 24 hours. In the numerical study the inlet boundary conditions are taken from the experiments that are conducted in the axial research turbine facility“LISA”at ETH Zurich. Two different hot streak shapes have been considered. With its relatively high circumferential temperature gradients the circular hot streak models the temperature distribution downstream of the can-annular combustors. For the second study a non-axisymmetric hot streak shape has been considered which has reduced circumferential temperature gradients at midspan and has different spanwise extents impinging on the opposite sides of the stator. With these properties it models the temperature distribution downstream of the more recent full annular combustor designs. The numerical results have been validated in different aspects with the time resolved measurements conducted. Flow physics behind the observed hot streak migration patterns is in detail discussed revealing the effect of the stator aerodynamics, non-axisymmetric endwall profiling and also the hot streak induced secondary flows. The unsteady particle tracking studies revealed the increase in the radial transport within the rotor blade in presence of hot streaks. As the underlying mechanism in the rise in the radial transport, the effect of the hot streak induced secondary flows on the rotor blade heat load is investigated. The hot streak induced secondary flows in the case of the circular hot streak led to about 0.25 % rise in the adiabatic wall temperature level at the rotor pressure side that would correspond to about 5 K rise in the real engine conditions. On the other hand, the temperature level at the rotor suction side was completely insensitive to the presence of the secondary flows induced by the hot streaks. The particle tracking studies also showed a considerable effect of the stator aerodynamics on the hot streak migration. Accordingly, the main hot streak convection to the rotor blade tip originates from the region close to the stator suction side at the inlet plane. Also the non-axisymmetric endwalls affect the hot streak migration. They reduce the circumferential non-uniformity in the hot streak convection to the rotor blade tip. Parallel to the migration pattern observed, adaptations in the hot streak's circumferential orientation at the turbine inlet have been conducted by taking the combustor framework into account for the applicability of the considered temperature boundary conditions in real engines. For the circular hot streak the fuel injector – stator clocking has been considered. Due to its relatively high circumferential temperature gradients clocking the circular hot streak even by 10% of the stator pitch towards the stator's pressure side led to considerable reductions in the rotor blade tip adiabatic wall temperature levels that would correspond up to 24 K in realistic engine conditions.For the non-axisymmetric hot streak shape the effect of impinging the spanwise larger edge of the hot streak on the opposite sides of the stator blade on the rotor blade heat load is evaluated. The alignment of the hot streak's spanwise larger extent to stator's pressure side reduced the adiabatic wall temperature levels both at the rotor midspan and also at the tip region reaching values up to 10 K in realistic engine conditions. Controlling the penetration of the dilution air on the liner the circumferential temperature distribution at the endwalls can be modified according to the observed turbine aerodynamics. This method is proposed as a more practical approach to be used in modern full-annular combustors as opposed to the fuel injector – stator clocking which puts serious constraints both on the turbine and combustor design.
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