arXiv subjects

N. Ananthkrishnan

Publications and source records attributed to N. Ananthkrishnan.

3 recordsLinked to original sources

arXiv2025

Aerodynamic Design Considerations for Biconic Supersonic Air Intakes Revisited

Traditional design principles for determining the optimal intake ramp or cone angles, for ensuring no flow spillage at the intake cowl under design conditions, and for the form of the terminal shock in the intake duct are revisited. We show that it is preferable to select the ramp or cone angles to be somewhat smaller than that suggested by the Oswatitsch criterion. An offset cowl lip that slightly violates the shock-on-lip condition is found to be beneficial; in fact, an offset cowl can be arranged for conical intakes with no flow spillage at the cowl lip at all. Improvements to the total pressure recovery are seen when the terminal normal shock is replaced by a strong form of the oblique shock for two-dimensional ramp-type intakes, and with a Lambda shock in case of conical intakes. The necessary design modifications are simple and virtually cost-free. These results rewrite the ground rules for the aerodynamic design of supersonic intakes.

physics.flu-dyn↗

arXiv2025

Tradeoffs in Biconic Intake Aerodynamic Design Optimization with Sub-optimal Oswatitsch Solutions

The notion of sub-optimal Oswatitsch solutions is introduced in order to systematically conduct a tradeoff between total pressure recovery (TPR) and intake drag coefficient (CDi) for supersonic intakes. It is shown that the Oswatitsch-optimal TPR for a biconic intake may be enhanced by adding a conical flare which modifies the terminal normal shock into a novel Lambda shock structure. The optimization problem is formulated along the lines of Axiomatic Design Theory with the conical angle pair and the cowl fineness ratio as the two design parameters. Reynolds-averaged Navier-Stokes (RANS) simulations are performed to iteratively arrive at the optimal solutions, with and without an intake length constraint, for a fixed value of the intake mass flow rate. The results are used to generate the Pareto front in the space of the objective functions, which yields the set of solutions between which TPR and Cdi may be traded off for one another. Additionally, an off-Oswatitsch solution, where only the second cone angle is altered from its optimal Oswatitsch value, is obtained and is compared with the sub-optimal Oswatitsch solutions that form the Pareto front.

physics.flu-dyn↗

arXiv2024

Turbojet Module Sizing for Integration with Turbine-Based Combined Cycle Engine

A turbine-based combined cycle (TBCC) vehicle is studied that relies on a scramjet engine for high-speed flight but requires a turbojet module to accelerate it to a high supersonic handover Mach number. The challenge is to scale a given turbojet engine (TJE) core (compressor, burner, turbine) to a particular value of the air mass flow rate such that the desired thrust at the handover point is achieved. To this end, a model for the engine core is integrated with a supersonic intake model that is designed to supply the required mass flow rate, and a nozzle model that is expected to deliver the desired thrust. Both the TJE intake and nozzle are constrained by the design choices made for the DMSJ module, and the TJE core is itself constrained by the volume available from the TBCC vehicle sizing for hypersonic flight. The TJE module is sized by scaling the engine core with matching intake and nozzle designs in an iterative manner until the process converges to a solution with acceptable thrust satisfying all the system constraints. The task turns out to be non-trivial due to the scarcity of steady operating points for the engine core at high speeds, due to possible mismatch between the mass flow rate demanded by the compressor and that delivered by the supersonic intake, and due to the difficulty in adapting a DMSJ-style single-expansion ramp nozzle (SERN) to adequately expand the turbojet exhaust flow.

physics.flu-dyn↗