University of Maiduguri Faculty of Engineering Seminar Series Volume 6, december 2015 Seminar Series Volume 6, 2015 Page 58 IMPINGEMENT JET COOLING OF GAS TURBINE COMBUSTOR WALL OF HEAT FLUX IMPOSED HOT - SIDE: CONJUGATE HEAT TRANSFER INVESTIGATIONS USING COMPUTATIONAL FLUID DYNAMIC * El-jummah A. M. 1 , Abubakar A. B. 2 , Andrews G. E. 3 and Staggs J. E. J. 3 1 Department of Mechanical Engineering, University of Maiduguri - Nigeria 2 Department of Mechanical Engineering, Ramat Polytechnic Maiduguri - Nigeria 3 Energy Research Institute, University of Leeds, LS2 9JT, UK * al-jummah@hotmail.com; +2348037803678 Abstract Conjugate Heat Transfer (CHT) computational fluid dynamic (CFD) investigations were carried out for 10 × 10 array of gas turbine (GT) impingement cooling jet holes. The grid model geometries are for variable diameter D at constant impingement pitch X and gap Z, which shows that X/D and Z/D ratios are also varied, but Z/D variation is not a significant factor as Z is held constant. Computations were conducted for the same mass flux G of 1.076 kg/sm 2 using a cooling air temperature of 288 K and a fixed heat flux of 47.5 kW/m 2 imposed at the hot face of the target wall or combustor liner. The main objective is to computationally investigate the influence of the heat flux, which is typical of that used in a GT combustion chamber transition duct and is equivalent to a heat transfer coefficient (HTC) of 100 W/m 2 K. Experimentally, 775 K hot gas stream was used to heat the hot side target wall and was conducted using a Nimonic-75 wall material similar to that used in the CFD. The predicted surface average HTC h and percentage pressure loss ΔP were shown to agree well with the experimental work. The CFD prediction also shows that surface average Nusselt number reduced from 52.9 to 37.8 at the impingement point as D increases and as X/D decreases. The result also shows that thermal variations occurred along the length of the wall material and its thickness, which indicates that the wall hot gas stream hence the heat flux also varies. Also predicted is the dependence of pressure loss on flow-maldistribution. Keywords: Conjugate heat transfer, predictions, impingement jet, heat flux, Nimonic-75 material, heat transfer coefficient, pressure loss, thermal variation, flow-maldistribution. 1.0 Introduction Advances in gas turbine (GT) thermal efficiency for future enhancement in power generation rely on improved wall cooling of the GT combustor and turbine blades, as GT combustion temperatures deteriorates the metal materials of the component parts (Arthur and Dilip, 2010). To achieve high temperature operation of the GT components, the combined use of effective cooling techniques with sufficient thermal resistance material walls is important and impingement jet cooling of Figure 1 is shown to be one of the most effective cooling technologies (Andrews and Hussain, 1984, Huitenga and Norster, 2014). The important design flat wall geometrical variables are shown in Figure 2a and are the dimensionless pitch to diameter X/D, gap to diameter Z/D and length to diameter L/D ratios, as well as the dimensional hole density n (m -2 ) or number of holes N in the direction of the cross-flow in the impingement gap (El-jummah et al., 2014a, b).