Statör kanatçıklarına açılan kanallardan tahliye olan havanın kanatçığın firar kenarı yüzeyine etkisinin araştırılması
Investigation of the effect of the air, which is released from the holes drilled on stator vanes, on the vane trailing edge surface
Yazar: TEVFİK CANER ÜNAL
Danışman: PROF. DR. ALİM RÜSTEM ASLAN
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Uçak ve Uzay Mühendisliği Ana Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Havacılık Mühendisliği = Aeronautical Engineering ; Uçak Mühendisliği = Aircraft Engineering

Özet:
Havacılığın devamlı gelişmesi ve hava taşımacılığının artarak önem kazanmasıyla, günümüzde uçaklar en çok kullanılan ulaşım araçlarından biri haline gelmiştir. Yolcu ve kargo taşımacılığı yapan ticari havayolları da ekonomik nedenlerle genelde 9-12 km gibi yüksek irtifalarda uçuşlarını gerçekleştirmektedirler. Ancak bu yüksekliklerde hava sıcaklığı -56,5 °C'lere kadar düştüğünden bu irtifadaki uçuşların uçağın kontrol yüzeylerinde, kanatlarında ve turbo-jet, turbo-fan veya turbo-prop motorların ilk kademelerinde buzlanmaya neden olabildiği görülmektedir.
Uçağın kontrol yüzeylerindeki ve kanatlarındaki buzlanmayı önlemek için uçuşlardan önce bu yüzeylere buz önleyici kimyasal sıvılar püskürtülmektedir. Ayrıca farklı uçaklarda kanatlarda buzlanmayı önleyici kapakçıklar gibi farklı sistemler de bulunmaktadır.
Motorda oluşan buzlanma, eksenel kompresörün ilk kademesinde statör kanatçıklarında görülmekte ve motor performansını olumsuz yönde etkilemektedir. Bunu önlemek için statör kanatçıklarına kanallar açılmıştır ve motorun ileri kademelerinden alınan sıcak hava buralardan tahliye edilerek statör kanatçıklarının firar kenarlarındaki buzlanma önlenmektedir. 
Ancak  kanal ağızlarındaki keskin kenarlarda oluşan gerilme yoğunluğu buralarda çatlak oluşumu ve ilerlemesi ihtimalini ortaya çıkarmaktadır. Bu noktalarda yapısal iyileştirme yaparak  mukavemeti artırmak için kanal ağızlarındaki keskin kenarlarda pah kırma işlemi yapılmaktadır.
Uçak parçalarının üretiminin ve belirli küçük ölçülerde pah kırma işleminin çok hassas olmasından dolayı ufak hatalar bile büyük sorunlara veya performans farklılıklarına yol açmaktadır. Üretimdeki hatalar ve yetersizliklerden ötürü de pah kırma işleminde istenilen ölçü tam yakalanamamakta, hatta tolerans dışına çıkabilmektedir. Bu sebeple tasarlanacak, üretilecek veya tasarımında değişiklik yapılacak her parçanın çok dikkatli bir şekilde testlere tabi tutulması ve uçaklarda kullanılmadan önce, ilgili parçanın görevini doğru bir şekilde yerine getirdiğinden emin olmak gerekmektedir.
Bu yüksek lisans tez çalışması kapsamında farklı pah yarıçaplarına sahip kanal ağızlarından tahliye olan havanın kanatçığın firar kenarı yüzeyine olan etkisi bilgisayar programlarıyla simule edilerek ve deneysel olarak araştırılmış ve karşılaştırılmıştır.
Çalışmanın sonunda sayısal ve deneysel analizlerin genel olarak aynı sonuçta birleştiği, ancak birebir örtüşmediği görülmüştür. Farklılıkların sebebinin sayısal analizlerin kusursuz geometriler üzerinde, deneysel analizlerin ise üretimdeki hatalar ve yetersizlikler nedeniyle kusurlu modeller üzerinde yapılmış olduğu anlaşılmıştır. Sonuç olarak söz konusu deliklerde pah kırılmasının ve üretimdeki hataların deliklerden çıkan jetin kanatçık firar kenarı yüzeyine temasını olumsuz yönde etkilediği tespit edilmiştir.

Abstract:
Due to continuous development of the aviation and increasing importance of the air transportation, nowadays, aircrafts have become one of the most widely used means of transportation. Passenger and cargo airlines perform their commercial flights at high altitudes around 9-12 km because of the economic reasons. However, since the air temperature decreases down to -56,5 °C at these altitudes, it is seen that flying at these altitudes can cause icing on the aircraft control surfaces, wings and early stages of the turbo-jet, turbo-fan or turbo-prop engines.
To prevent the icing on the aircraft control surfaces and the wings, some anti-icing chemical liquids are sprayed to related surfaces before every flight. In addition, to prevent icing on the wings for several aircrafts, some alternative systems are available like anti-icing valves. 
The icing formed in the engine is seen on the stator vanes of the first stage axial compressor and affects the engine performance in a negative way. To avoid this, holes are drilled on the stator vanes and hot air taken from forward engine stages is released from these holes to prevent icing on the trailing edges of the stator vanes.
However, the stress intensity, which accumulates on the sharp edges of the holes,  increases the possibility of crack formation and propogation. In order to strenghten these points as a structural improvement, chamfering of the hole sharp edges is performed.
Since the production of aircraft parts and edge chamfering process in certain small radius are very precise, even small errors can lead to big problems and performance differences. Also, the desired chamfer size cannot be reached and even sometimes it can be out of tolerance due to errors and inefficiencies during production. Therefore, parts to be designed, manufactured or modified must be subject to careful tests before installing on the aircraft and it is necessary to make sure that related parts fulfill their function properly.
Within this thesis, investigation, computational and experimental simulations were done to see the effect of the air, which is released from the holes that have different chamfer radiuses, on the trailing edge surface of the stator vanes. After that results of computational and experimental analysis were compared.
For computational analysis, geometries were prepared according to real stator vane models and other experimental setup to have the oppurtunity to compare the results in similar conditions as much as possible. Then, meshing of the whole geometry was generated and analysis were performed with appropriate boundary conditions and solution methods by using commercial CFD programmes.
For experimental analysis, experimental setup was made ready, calibrations of the required tools were done, room temperature made constant and setup was run for a determined same duration for every single case. 
Computational analysis can be divided into two groups. The first one is the real analysis that considers the actual working conditions of the engine and the second one is the computational analyis of the experimental study based on similarity conditions. So, for  the computational analysis, two pre-determined different actual working conditions of the engine were selected and considering them, thermo-physical properties of the flows were calculated. Afterwards, based on the related references, three similarity paramaters were decided as velocity ratio, mass flux ratio and momentum  ratio and analysis were made for two groups, three different chamfer radiuses, three similarity parameters and two turbulence approach including k-ε and LES.
As a result of computational analysis, mass flux ratio was selected as the similarity parameter to calculate flow properties which were used in experimental analysis since it gave the most similar results to the real cases. 
For experimental analysis, success criteriaof the anti icing jet was determined as the wet area that anti icing flow contacted the trailing edge surface of the stator vane. To evaluate and make this are visible, at first, trailing edge of the stator vane was painted and then paint thinner was atomized and sprayed from the holes drilled on stator vane.
Consequently, following results were obtained as a result of both analysis:
It is seen in the computational analysis results that the area jet flow contacted the surface of stator vane decreases with the increase in the radius of the chamfer. The surface contact area of jet flow is bigger for the stator vanes that have holes with smaller chamfer radius.
The chamfer radius does not affect much the surface contact of jet flow at the holes located in the upper part of the stator vane due to the twisted aerofoil of stator vane.
The effect of the jet velocity differences to the surface contact of jet flow increase with the increase in the chamfer radius and jet velocity is inversely proportional with the surface area jet flow contacted.
As a result of experimental analysis, as expected, stator vane that has the biggest chamfer radius had the least succesful performance in terms of surface contact area. However, the most succesful performance belongs to stator vane that had  the medium sized chamfer radius instead of the smallest chamfer radius. The reasons behind this are the deficiencies in manufactaring of the holes and errors in dimensioning during chamfering process.
Computational and  experimental analysis concurred on a final result in general, however it cannot be said that all results agreed one by one. The reasons behind this is that computational analysis were made using ideal stator vane geometry with perfect holes, but experimental analysis were made using imperfect stator vane geometry that has out of tolerance chamfer radiueses due to the errors and deficiencies during manufacturing process. 
In final words, it was detected that chamfering of the hole edges and errors in production affects negatively the stator vane contact surface area of jet flow.  To prevent this negative effect and to get the desired anti-icing efficiency, smaller chamfer radius must be preferred, manufacturing quality must be improved and chamfering process must be more precise.
If it is desired to expand the research on this subject, stator vane surface contact area of jet flow can be investigated  based on the flow properties inside the boundary layer. Additionally,  effect of aerofoil twist on contact surface area of jet flow and effect of the change of anti-icing holes' coordinates on stator vane can be investigated and opitmum hole positions can be detected.