Simplified thermo-fluid model of an engine cowling in a small airplane

Abstract

Purpose – The purpose of this study is to developed a simplified thermo-fluid model of an engine cowling in a small airplane. An aircraft engine system is composed of different elements operating at various temperatures and in conjunction with the composite nacelle creates a region with high intensity of heat transfer to be covered by the cooling/ventilation systems. Therefore a thermal analysis, accounting for the complex heat transfer modes, is necessary in order to verify that an adequate cooling is ensured and that temperatures of the nacelle are maintained within the operating limits throughout the whole aircraft's flight. Design/methodology/approach – Simplified numerical simulations of conductive, convective and radiative heat transfer in the engine bay of the small airplane I-23 in a tractor arrangement were performed for different air inlet and outlet configurations and for varying conditions existing in air inlets during the flight. The model is based on the control volume approach for heat and fluid flow as well as for thermal radiation and on k-ɛ turbulence model. Findings – The flow and temperature distributions inside the cowling were determined, and high-temperature spots on the internal side of the nacelle and on other airplane systems located close to the turboprop engine and the exhaust system were found. The thermal radiation was found to play the key role in heat transfer inside the engine bay. The optimal configuration of air inlets and outlets was determined. Practical implications – The obtained results will help in future studies on ventilation and cooling systems and will contribute to the selection of materials for parts of the engine bay and the nacelle as well as in developing solutions for reducing the temperature inside the cowling of the airplane I-23. Originality/value – A complete simplified thermo-fluid model of heat transfer inside the engine bay of the airplane I-23 was developed. Additionally, influence of the thermal radiation on temperature distribution at the nacelle was investigated.

Comparison of 1D and 3D thermal models of the nacelle ventilation system in a small airplane

“…The air and hot exhaust gases were treated as totally transparent and therefore thermal radiation occurred only between the hot and cold surfaces of the engine systems and the nacelle. The firewalls, exhaust pipes, exhaust pipe covers, air ducts and engine systems surfaces (all metallic surfaces) were assumed grey and diffusive and had surface emissivity ε = 0.6 (roughly estimated average value for the polished stainless steel, Łapka et al , 2014) whereas at the internal and external side of the nacelle the emissivity was assumed to be ε i = 0.83 (epoxy resin EPIDIAN E53 reinforced with glass fabric, Łapka et al , 2014) and ε e = 0.9 (white enamel paint, Łapka et al , 2014), respectively.…”

“…The new propulsion requires a completely new design of the nacelle [Figure 1(b)] as well as the engine bay and all engine systems [Figure 1(c)]. There are several papers related to the redevelopment of the airplane I-23, for example, Łapka et al (2014) presented the thermal analysis of the new design of the nacelle and engine bay, Stalewski and Żółtak (2014) performed optimization of the air-intake system and the nacelle shapes, Goetzendorf-Grabowski (2014) analysed design of TP100 engine mount.…”

“…Originally, the mass flow rate of the ventilation air through the nacelle was estimated by considering it as a pipe flow problem. However, for the comparison it was decided to adopt the mass flow values found by the 3D approach (Łapka et al , 2014).…”

“…In the first paper, analyses of five design configurations of the nacelle cooling system were carried out while in the second one the performance of different nacelle ventilations systems under hover and forward flight conditions were investigated. Recently, Łapka et al (2014) analysed heat transfer and fluid flow in the nacelle and inside the engine bay of the small airplane I-23 that had been newly redeveloped and equipped with a turboprop engine under the FP7 EU ESPOSA project (Efficient Systems and Propulsion for Small Aircraft). They proposed a 3D numerical model which includes thermal radiation and performed several sets of simulations for different inlet and outlet configurations.…”

“…Because of the use of a commercial software the 3D model can be quite expensive, but it is applicable for a detailed analysis of any selected case. The 3D model was directly based on the one previously presented by Łapka et al (2014). Here boundary conditions at the engine were better adjusted to reality and the new structure of the nacelle was applied – the cowling was partially made of the solid material and honeycomb structure.…”