Aerodynamic Optimization of a Two-Part Variable Inlet Guide Vane in a Highly Loaded Low Pressure Compressor

Kurzfassung

Continuous reduction of fuel consumption for a wide range of operating conditions leads to a high efficiency demand for all engine parts of modern jet engines and especially the compressor. To meet these requirements a two-part Variable Inlet Guide Vane (VIGV), composed of a fixed strut and a variable flap, can be used. Besides the aerodynamic aspects, the VIGV strut is a substantial part for the structural integrity of the compressor. The aerodynamic design optimization of such a VIGV, located upstream of the first rotor of a 2.5 stage low pressure compressor, under the conditions of three different operating points is presented in this paper. In a previous study the shape of the axial gap between strut and flap was optimized without changing the envelope of both parts [1]. The new design tool SplitBlade, developed at the DLR, enables the creation of an axial gap and has been integrated in the design process of the in-house optimization tool AutoOpti. The target of the optimization was to decrease the total pressure loss coefficients for all three operating points. The design optimization presented in this paper is more complex by allowing the VIGV blade geometry to change. The basic dimensions of the VIGV such as the axial chord and the maximum profile thickness are still frozen. In total, 88 parameters are free to change in the optimization process. Additionally to the main target of loss reduction, the circumferential outflow angles are restricted to maintain the deflection of the blade and therewith the required rotor inflow conditions to ensure the operability of the entire compressor in the whole working range. The final result is a two-part VIGV with an axial gap, which is optimized in terms of total pressure losses in three operating points. Compared to a reference geometry without an axial gap, the losses are almost equal at nominal speed, and about one to two percentage points higher in the two part speed operating points.