The jet propulsion exhaust nozzle system is an integral part of an airbreathing gas turbine engine and critical to its overall performance. Challenges associated with the design and manufacturing of an exhaust nozzle increases with the cruise speed of the aircraft. The exhaust nozzle system for a supersonic cruise aircraft mandates additional features such as variable throat and exit area, jet noise suppression, and reverse thrust. In the past, in order to address this challenge, an ejector nozzle with clamshells was designed and fabricated. The experimental investigation and computation of the nozzle at low subsonic conditions showed the presence of a recirculation zone at the inner surface of the clamshells. The present work summarizes the computational simulation of the ejector nozzle with clamshells at flight conditions. Similar recirculation zones were predicted at the inner surface of the clamshells. Initiatives were taken to improve the ejector performance by the elimination of the recirculation zone. The current nozzle design was modified by the application of chevrons on the nozzle throat. A preliminary design and computational analysis of the ejector nozzle with clamshells and chevrons was carried out. Two design cases with different number of chevrons were implemented and their computational analysis was successfully carried out. It was observed that the nozzle flow features were improved because of enhanced mixing and the recirculation zone was decreased in its extent.

Industrial and aeroderivative gas turbines use exhaust systems for flow diffusion and pressure recovery. These processes result in a three-dimensional, unsteady, turbulent, and complex flow in the exhaust diffusers. The downstream balance-of-plant systems such as heat recovery steam generators or selective catalytic systems require, in general, a steady, uniform flow out of the exhaust system. Aeroderivative gas turbines for power generation application have a wide operational envelope. Even though the exhaust systems are designed for 70% load to 110% load, its performance is significantly altered at low power operations. Application of gas turbines at low power can increase exhaust diffuser vibrations because of diffuser flow separations and wakes from the last stage of the power turbine. Aerodynamic excitations which result in excessive structural vibration can cause the units to trip and the power plant to stop, resulting in customer revenue loss. The primary motivation for this research is to investigate an aerodynamic mechanism to ensure reliable operation of the exhaust system by identifying the regimes where aerodynamic instabilities can occur. In-house and university supported initiative to predict unsteady aerodynamics at low power conditions shows the presence of turbulent and time dependent flow. The frequency spectrum results are discussed for low power and high power gas turbine operating conditions. The numerical predictions are in good agreement with test results.

For gas turbines (GTs) with free power turbines (FPTs), the capacity or flow parameter matching is of prime importance. Accurately matched capacity enables the GT to run at its optimum condition. This ensures maximum component efficiencies and optimum shaft speeds within mechanical limits. This paper presents the challenges, uncertainties, and opportunities associated with an accurate matching of a generic two-shaft aeroderivative high pressure (HP)-low pressure (LP) gas generator with the FPT. Additionally, generic performance trends, uncertainty quantification, and results from the verification program are also discussed. These results are necessary to ensure that the final FPT capacity is within the allowable range, and hence, the product meets the performance guarantees. The sensitivity of FPT capacity to various design variables such as the vane throat area, vane trailing edge size, and manufacturing tolerance is presented. In addition, issues that may arise due to not meeting the target capacity are also discussed. To conclude, in addition to design, analysis, and statistical studies, a system-of-systems approach is mandatory to meet the allowed variation in the FPT capacity and hence the desired GT performance.

A new supersonic ejector nozzle with clamshell doors is proposed as a noise suppression jet engine exhaust system. A design table driven, parametric nozzle geometry was designed. The experimental and numerical studies of its flow field were carried out. Cases with and without clamshells were considered and their mean velocity flow fields were compared. The experimental investigation involved the testing of the nozzle in a wind tunnel and the measurements were taken using a seven-hole probe, mounted on an automated 2-axis traverse instrument. Various flow visualization techniques such as the fluorescent oil flow, surface sediment traces, smoke wand and surface tuft were also implemented to capture the flow physics on the inside of the clamshells. Numerical simulations were performed using the commercially available finite volume-based computational fluid dynamic code FLUENT. The computational results are in good agreement with the experimental measurements at different axial locations downstream of the nozzle throat. A zone of flow separation and recirculation is captured at the inner surface of the clamshells in both the experimental investigation and numerical computation.

For gas turbines with free power turbines, the capacity or flow parameter matching is of prime importance. Accurately matched capacity enables the gas turbine to run at its optimum conditions. This ensures maximum component efficiencies, and optimum shaft speeds within mechanical limits. This paper presents the challenges, uncertainties, and opportunities associated with an accurate matching of a generic two-shaft aeroderivative HP-LP gas generator with the free power turbine. Additionally, generic performance trends, uncertainty quantification, and results from the verification program are also discussed. These results are necessary to ensure that the final free power turbine capacity is within the allowable range and hence the product meets the performance guarantees. The sensitivity of free power turbine capacity to various design variables such as the vane throat area, vane trailing edge size, and manufacturing tolerance is presented. In addition, issues that may arise due to not meeting the target capacity are also discussed. To conclude, in addition to design, analysis, and statistical studies, a system-of-systems approach is mandatory to meet the allowed variation in the free power turbine capacity and hence the desired gas turbine performance.