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Mechanical design for an elliptical shaped nozzle exposed for thermal and pressure loads
2007 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

This thesis aims to describe a new design of low signature nozzles offering better accuracy against pressure and thermal loads. Low signature nozzles are used in, for example, military aircraft to lower the signature, defined as the contrast to the background. The work begins with a theoretical part and continues with a practical part where simulations in ANSYS are done. The goal and purpose of this thesis work are to give an understanding of the behaviour of circular and elliptical outlets and find a way to make the structure stronger when needed without increasing the weight. The theoretical part gives a mathematical understanding of the problem that is necessary for the simulations, conducted in the following practical part. Chapter 3 focuses on the program and model. Different methods and element types were tried and three elements were eventually used in the program. Two are shell elements used for structural forces and one is a thermal element. To solve the thermal load, a layered element was used. Several evaluations were done to confirm that the program was correct. These evaluations showed that the model here is not sensitive to the number of elements used in the simulation. Three different analyses were done, all with an elastic model. The different loads used are a pressure load, a thermal load and a combination of both loads. All simulations were done with a circular and an elliptical geometry. From the simulations, the conclusions can be divided in two groups, depending on the geometry. When a circular geometry is exposed to pressure, the stresses become of a membrane kind, and when the load is thermal, the stresses are of a bending kind. To lower the membrane stresses is an increased thickness the solution. For the bending stresses the thermal gradient, ΔT, should be lowered. An increased ΔT increases the stresses, but not the thickness. When the thicknesses increase, ΔT remains the same, which can be related to how the load is applied. The elliptical geometry has mainly bending stresses for both loads: to lower the stresses the solution is the same as for the circular geometry. These conclusions are useful when the thickness is uniform. When the thickness varies and the load is pressure an increased thickness is still the solution. For a thermal load, the conclusion about ΔT remains true. The result gives only the stress level, the position is the weakest point in the structure. The highest stress level is found in the thinnest part of the structure.

Place, publisher, year, edition, pages
Keyword [en]
Technology, tryck, termiska laster
Keyword [sv]
URN: urn:nbn:se:ltu:diva-54202ISRN: LTU-EX--07/159--SELocal ID: b2c02fc0-4dfb-4de9-9186-a8c623fdab47OAI: diva2:1027582
Subject / course
Student thesis, at least 30 credits
Educational program
Mechanical Engineering, master's level
Validerat; 20101217 (root)Available from: 2016-10-04 Created: 2016-10-04Bibliographically approved

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