Abstract The mixing characteristics of a Mach 1.9 jet at three levels of overexpansion, corresponding to nozzle pressure ratio (NPR) 3, 4 and 5, in the presence of a sonic co-flow (secondary flow), which was submerged in a subsonic co-flow (tertiary flow) was studied experimentally. For these NPRs the secondary co-flow is sonic with underexpanded levels and the tertiary flow Mach number was found to be 0.41, 0.71 and 0.85, respectively. The centerline decay results of the primary jet show that the jet mixing is abated by the co-flow, at all levels of expansion. However, in spite of the reduced mixing encountered by the supersonic primary jet, the waves in the jet core are found to be weaker in the presence of co-flows. This may be regarded as an advantage from the shock associated noise point of view, in accordance with Tam’s theory; which states weaker the waves in the core, the lesser is the shock associated noise. The results show that the reduced mixing environment caused by the sonic co-flow alone leads to the jet core elongation of about 20%, 23% and 49%, at NPRs 3, 4 and 5, respectively. The core length of the jet is found to increase by 29%, 46% and 62%, respectively, at NPRs 3, 4 and 5, when both sonic and subsonic co-flow streams are present.

Driven by rapid development in battery technology and increase in scope for electric air taxi vehicles, developing an efficient combustion free propulsion system to pair with an electric aircraft is crucial for future of aircraft industry. However, with current technology, ducted fan configuration engines are the only feasible option when it comes to combustion free propulsion system which are already being used in many unmanned drones and unmanned aerial vehicles. In the present work, simple design, analysis and fabrication of ducted fan is performed. Propeller fan and duct is designed using basic principles of blade element theory and momentum theory. Using the parameters from the theoretical design phase, 3D model is made and fabricated using 3D printing and assembled to fit with tolerances suitable for mounting motor. A test stand capable of measuring thrust by varying rpm is designed and built using Arduino based interface. Finally, the designed model is analyzed in Ansys CFX for thrust output using an MRF simulation.

The forced response of turbomachinery blades is a primary source of high cycle fatigue (HCF) failure. This paper deals with the computational prediction of blade forced response of a transonic fan stage that consists of a highly loaded rotor along with a tandem stator. In the case of a transonic fan, the forced response of the rotor due to the downstream stator assumes significance because of the transonic flow field. The objective of the present work is to determine the forced response of the rotor induced as a result of the unsteady flow field due to the downstream stator vanes. Three dimensional, Navier-Stokes flow solver TRACE is used to numerically analyse the forced response of the fan. A total of 11 resonant crossings as identified in the Campbell diagram are examined and the corresponding modeshapes are obtained from finite element modal analysis. The interaction between fluid and structure is dealt with in a loosely coupled manner based on the assumption of linear aerodynamic damping. The aerodynamic forcing is obtained by a nonlinear unsteady Navier-Stokes computation and the aerodynamic damping is obtained by a time-linearized Navier-Stokes computation. The forced response solution is obtained by the energy method allowing calculations to be performed directly in physical space. Using the modal forcing and damping, the forced response amplitude can be directly computed at the resonance crossings. For forced response solution, the equilibrium amplitude is reached when the work done on the blade by the external forcing function is equal to the work done by the system damping (aerodynamic and structural) force. A comprehensive analysis of unsteady aerodynamic forces on the rotor blade surface as a result of forced response of a highly loaded transonic fan is carried out. In addition, the correspondence between the location, of high stress zones identified from the finite element analysis and the regions of high modal force identified from the CFD analysis is also discussed

This paper describes the computational analysis of aerodynamic damping for prediction of flutter characteristics of a transonic fan stage that consists of a highly loaded rotor along with a tandem stator. Three dimensional, linearized Navier-Stokes flow solver TRACE is used to numerically analyse the flutter stability of the fan. The linear flow solver enables the modeling of a single blade passage to simulate the desired inter-blade phase angle. The unsteady aerodynamic load on a vibrating blade is obtained by solving the unsteady Navier-Stokes equations on a dynamically deforming grid and the energy exchange method is used to calculate the aerodynamic damping. The calculation of aerodynamic damping for the prediction of flutter characteristics of the fan rotor is carried out with and without considering the influence of the disk. The blade mode shapes from finite element modal analysis are obtained accordingly and the flutter calculations are carried out for three blade vibration modes at the design speed and at part speeds for all possible inter-blade phase angles. Two operating points, one on the working line and the other near stall are investigated at every rotational speed. Different aspects that affect the aerodynamic damping behaviour like part speed operation, variation in unsteady blade surface pressure fluctuation between operating points on the working line and at near stall and the corresponding variation in aerodynamic work, inter-blade phase angle etc., are described. This analysis primarily focuses on the variations in aerodynamic damping of the fan with and without the influence of the disk. In addition, influence and effect of shock wave on the aerodynamic damping is also discussed.

Errors induced due to ratiometric measurements are discussed and a simplified compensation method to reduce the various static errors of ADC, voltage reference errors in ratiometry and resistance mismatch errors is proposed. Curve fitting is done for the error samples and the system is modelled in comparison to an ideal system. Static errors and other ratiometric errors, thus modelled are derived into a corrective equation in comparison with an errorless system. Implementation of the proposed method is discussed for a resistance measurement system and analyzed. This paper also discusses the usage of the proposed system with successive approximation ADCs for ratiometric measurement operations against the conventional requirement dual slope ADCs for the same.

An efficient non-linear harmonic methodology has been developed for predicting unsteady blade row interaction effects in multistage axial flow compressors. Flow variables are decomposed into time averaged variables and unsteady perturbations, resulting in time averaged equations with deterministic stress terms depending on the unsteady perturbation. The non-linear interaction between the time averaged flow field and the unsteady perturbations are included by a simultaneous pseudotime integration approach, leading to a strongly coupled solution. The stator/rotor interface treatment follows a flux averaged characteristic based mixing plane approach and includes the deterministic stress terms due to upstream running potential disturbances and downstream running wakes, resulting in the continuous nature of all parameters across the interface. The basic computational methodology is applied to the three-dimensional Navier-Stokes equations and validated against several cases. Results show that this method is much more efficient than the non-linear time-marching methods while still modeling the nonlinear unsteady blade row interaction effects.Copyright © 2000 by ASME