Design and testing of a composite material for modelling wind turbine blade structures in tropical region.

Abstract

Currently large wind turbine blades have been installed in several offshore and onshore wind farms around the world, particularly in the desert areas of North East Africa where wind turbine blades and nacelles are affected by elevated temperatures. The aim of this study is to investigate the effect of temperature variation on the mechanical behaviour of composite wind turbine blades installed in tropical wind farms. The blades are constructed from unidirectional carbon fibre/epoxy, glass fibre/epoxy and hybrids of these two composite materials. ASTM standards were taken into account when the composite specimens were manufactured for testing purposes. Short Beam Shear (SBS), Dynamic Mechanical Analysis (DMA) and tensile tests were conducted under increasing temperatures to investigate the mechanical behaviour of composite materials when used for structural modelling of wind turbine blades. Experimental findings revealed that the strength and stiffness properties of composite specimens were reduced when temperatures increased. Betz’s element momentum theory and Glauert’s modelling methods were used to investigate the characteristics of composite wind turbine blades measuring 54m and generating 2MW power. Flap-wise loading was taken into account along the length of the wind turbine blades when they were analysed using the Blade Element Momentum (BEM) theory. The wind turbine blades were developed using carbon fibre/epoxy, glass fibre/epoxy, glass-carbon fibre/epoxy and carbon-glass fibre/epoxy composite materials. The tip deflection of the blades was analysed allowing for different flap-wise and thermal loadings. Simulation results indicated that a glass/epoxy blade has the highest and a carbon/epoxy blade the lowest tip deflection. The values for the tip deflections of the blades show minimal change under thermal loading. To study the mechanical behaviour of the blades under thermal loading, an element-wise approach was developed and the failure index for different composite materials was computed. Tsai-Wu failure criterion was employed to determine the failure index of each composite material under thermal and mechanical loadings. Blades failed when the thermal loading was above 40ºC irrespective of the flap-wise loading. This finding was similar to the experimental results mentioned above. Carbon/epoxy showed non-linear behaviour when the test temperature approached 40ºC. Generally, experimental and numerical results are comparable and can be considered valid. To conclude carbon-glass fibre/epoxy composite wind turbine blades are observed to be a better option for tropical wind farms based on experimental and simulation results. Iqoqa Njengamanje sekufakwe ophephela bomoya abakhulu emapulazini amaningi omoya asolwandle nasezweni emhlabeni jikelele, ikakhulukazi ezindaweni eziwugwadule zaseMpumalangantshonalanga Afrika lapho amazinga okushisa aphakeme enomthelela kophephela bomoya nakuzembozo zezihambisiphephela. Inhloso yalolu cwaningo ngukuhlola umthelela wokuguquguquka kwamazinga okushisa endleleni okusebenza ngayo ophephela bomoya abafakwe emapulazini asezindaweni ezishisa kakhulu. Ophephela bakhiwe ngomabhekanxazonke befayibha yekhabhoni/ ephoksi, ifayibha yengilazi/ephoksi, Kucatshangelwe amazinga e-ASTM ngenkathi kwakhiwa amasampula ayindidiyela ngenhloso yokuhlola. Kwenziwe uhlelo lwe-Short Beam Shear (SBS), Dynamic Mechanical Analysis (DMA) nokuhlola kwamathensayili ngaphansi kwamazinga okushisa anyukayo, ukuhlola indlela ezisebenza ngayo izakhi eziyindidiyela uma zisetshenziselwa ukubona ukuthi singama kanjani isakhiwo sophephela bomoya. Imiphumela yokuhlola iveze ukuthi amazinga amandla nokuqina kwamasampula ayindidiyela kwehlile uma kunyuswa amazinga okushisa. Kusetshenziswe injulalwazi ka-Betz yomthamosivinini kanye nezindlela zika-Glauret zesibonelokulinga ukuhlola izimpawu zophephela bomoya abayindidiyela, abanesikalo esingu-54m futhi esiphehla amandla angu-2MW. Kucatshangelwe isisindo sokuthwala uma ophephela bebheke phansi noma phezulu ngokunjalo nobude bophephela bomoya ngenkathi behlaziywa, kusetshenziswa injulalalwazi i-Blade Element Momentum (BEM). Ophephela bomoya benziwe kusetshenziswa izakhi eziyindidiyela zefayibha yekhabhoni/ ephoksi, ifayibha yengilazi/ ephoksi nefayibha yekhabhoni-ngilazi/ ephoksi. Impebezo yezihloko zophephela ihlaziywe kuvunyelwa okuhlukahlukene kwesisindo sokuthwala netemali, uma ophephela bebheke phansi noma phezulu. Imiphumela yokulingisa ikhombise ukuthi uphephela wengilazi/ ephoksi unempebezo yesihloko ephakene kanti uphephela wekhabhoni/ ephoksi unempebezo yesihloko ephansi. Amavelu empebezo yezihloko zophephela akhombisa uguquko olusesilinganisweni esincane, ngaphansi kokulayishwa kwetemali. Ukucwaninga okwenziwa ngophephela okuphathelene nokusebenza kwemishini uma kulayishwe itemali, kwenziwe ngokuqamba indlela evuna i-elementi, kwase kwenziwa uhlelo lokubala ngekhompyutha inkomba kwehluleka yezakhi eziyindidiyela ezihlukahlukene. Kuthathwe indlelakukhetha kuhluleka kaTsai-Wu ukubona inkomba kuhluleka yesakhi ngasinye esiyindidiyela uma kulayishwe itemali nokusebenza ngemishini. Ophephela behlulekile uma umthamo wetemali ungaphezu kuka-40ºC kungakhathaliseki izinga kulayisha elivuna ukubheka phansi noma phezulu kophephela. Okutholakele bekufana nemiphumela yokuhlola ebalulwe ngenhla. Ikhabhoni/ ephoksi ikhombise indlela okwenza ngayo ophephela engaqondile uma amazinga okushisa okuhlola esondela ku-40ºC. Ezimweni eziningi, imiphumela yokulinga neyezibalo iyaqhathaniseka futhi ingase ibhekwe njengekholakalayo. Ukuphetha, ophephela bomoya abayindidiyela yefayibha yekhabhoningilazi/ ephoksi babonakala beyisu elingalunga kahle emapulazini omoya uma kuthathelwa emiphumeleni yokuhlola nokufanisa.