INTRODUCTION The MAAT project is a revolutionary concept of transportation presented in works such as the ones of Ilieva et al. [ 1] and Trancossi et al. [ 2]. MAAT stands for Multi-body Advanced Airship for Transport. Due to its high altitude flight conditions, low turbulence intensities are predominant. Thus critical elements of the feeders and cruiser vehicles, such as propulsive systems, will be exposed to late transition and consequently considerable sized laminar flow regions. The design of these components will be strongly conditioned by the predicted flow conditions. This implies that possession of a tool able to calculate transitional flows is of fundamental importance. Prediction of flow separation, drag and even pressure distribution along component surfaces will deeply depend upon whether the flow is laminar or turbulent. Industry reliable turbulence transitional models are a relatively recent development. Previously, designers relied on experimental data and on the first effective transition prediction model, the e N method. Developed simultaneously by Smith et al. [ 3] and Ingen [ 4], this model predicts only natural transition conditions. Later on, with the works of Abu-Ghannam [ 5] and Mayle [ 6], the first empirical correlations for transition onset were created. Using these, the first turbulence transitional models based on empirical correlations were formulated. Some of these works were performed by Cho [ 7] and Suzen [ 8]. The latter models were initially non-locally formulated. This results in a problematic issue for parallel processing of large mesh computational problems. The reason for this is related to the processing nodes need of access to information that may not be in their computational domain. However, with the recent accomplishment of Menter [ 9] and Langtry [ 10], locally formulated empirical correlation turbulence transition models are being developed. Due to the transition process complexity, up until now only empirical models were successfully developed with practical industry application. Besides the linear stability theory based transition onset model, e N , no model attempts to simulate the physics of transition. However, alternatives were formulated that attempt to predict transition onset as well as calculate its development process. Through the award winning paper by Mayle [ 11], a new type of turbulence transitional model was introduced. Although this first model is non-locally formulated, and therefore, not yet easily applicable to industry, it suggests a revolutionary concept for 2013-01-2268 Published 09/17/2013 Copyright © 2013 SAE International doi: 10.4271/2013-01-2268 saeaero.saejournals.org High Altitude Transitional Flow Computation for a Propulsion System Nacelle of MAAT Airship Rui Vizinho Jose C. Pascoa University of Beira Interior Miguel Silvestre ABSTRACT The flow around the nacelles of high altitude airships is very important in order to assess the inlet conditions and losses associated to their propulsion systems. The aerodynamics prediction of low Re number flows is a problem usually associated to the lack of accuracy of most of the turbulence models in everyday use. Herein we present a laminar kinetic energy transitional model that is then applied on the analysis of the flow around an example of the MAAT airship nacelle. The model is also validated using several well known test cases from the literature. Results indicate the effects of accurate transition prediction in the redesign of the nacelle for improvement in efficiency. CITATION: Vizinho, R., Pascoa, J., and Silvestre , M., "High Altitude Transitional Flow Computation for a Propulsion System Nacelle of MAAT Airship," SAE Int. J. Aerosp. 6(2):2013, doi:10.4271/2013-01-2268. ____________________________________ 714 Downloaded from SAE International by Jose Pascoa, Friday, May 27, 2016