Surface Roughness Impact on Secondary Flow and Losses in a Turbine Exhaust Casing

Abstract

This paper experimentally addresses the impact of surface roughness on losses and secondary flow in a Turbine Rear Structure (TRS). Experiments were performed in the Chalmers LPT-OGV facility, at an engine representative Reynolds number with a realistic shrouded rotating low-pressure turbine (LPT). Outlet Guide Vanes (OGV) were manufactured to achieve three different surface roughnesses tested at two Reynolds numbers, Re = 235000 and Re = 465000. The experiments were performed at on-design inlet swirl conditions. The inlet and outlet flow of the TRS were measured in 2D planes with a 5-hole probe and 7-hole probe accordingly. The static pressure distributions on the OGVs were measured and boundary layer studies were performed at the OGV midspan on the suction side with a time-resolved total pressure probe. Turbulence decay was measured within the TRS with a single hot-wire. The results showed a surprisingly significant increase in the losses for the high level of surface roughness (25–30 Ra) of the OGVs and Re = 465000. The increased losses were primary revealed as a result of the flow separation on the OGV suction side near the hub. The loss increase was seen but was less substantial for the intermediate roughness case (4–8 Ra). Experimental results presented in this work provide support for the further development of more advanced TRS and data for the validation of new CFD prediction methods for TRS.

Infrared Thermography Investigation of Heat Transfer on Outlet Guide Vanes in a Turbine Rear Structure

“…The low heat transfer from the expanding roll-up vortex increases in effect spanwise with increased φ. This has earlier been observed in [10] ( Figure 7). Local points of high h 2 can be seen near the hub for φ = 0.657; this area is a heavily loaded point with very high acceleration as earlier shown by pressure distribution in [2], (Figure 4.15) and is an area of much interest for future studies.…”

“…It should be noted that the aero surfaces do not relate to any GKN Aerospace product characteristics but were designed solely for the experimental facility. Further details on the design and validation of the facility are provided by Rojo et al [1,2], and by Jonsson et al [10].…”

“…As the variation in T ∞ 1 and T 3 could be kept small between different data sets, the radiative part could be neglected. This reduces Equation (2) to a linear problem which is shown in Equation (10).…”

Detailed Experimental Study of the Flow in a Turbine Rear Structure at Engine-Realistic Flow Conditions

“…This work highlighted the effect of the turbine tip clearan ce on the losses and the importance of an engine realistic LPT stage. Further investigations in a newly established TRS facility at Chalmers University of Technology [7][8][9] were carried out in a rig equipped with a realistic shrouded LPT and operated at engine-realistic flow Reynolds numbers. The design of the new rig is presented by Rojo et al [7].…”

“…Jonsson et al [8] presented the accurate measurements of the heat transfer coefficient on OGVs, which has allowed for the mapping of the laminar-turbulent transition on OGVs for a number of aerodynamic load cases and his work is further extended and compared to CFD in an accompanying paper [10]. Jonsson et al [9] illustrated the impact of surface roughness on secondary flows and pressure losses in a TRS. Both studies [8,9] highlighted the significance of the laminar-turbulent transition on the performance of the TRS.…”