Session: 01-05: Inlets, Nozzles, Mixers and Nacelles I

Submission Number: 175918

Control of Asymmetric Separation and Thrust Deflection in a Serpentine Convergent–Divergent Nozzle With a Curved Divergent Section 

The serpentine convergent–divergent (CD) nozzle provides the essential characteristics of high stealth and wide operating range required for future fighter aircraft. However, under overexpanded conditions, it tends to experience asymmetric flow separation and thrust deflection, which severely degrade performance and stability. To achieve controllable separation modes and thrust deflection, this study proposes a serpentine CD nozzle with a curved divergent section and develops an asymmetric separation control method based on the characteristic position of the separation point.

The results indicate that, under a fixed nozzle pressure ratio (NPR), regardless of variations in the divergent-curve design parameters, when symmetric separation occurs, the vertical distance of the upper and lower separation points from the throat wall and their corresponding static pressures remain nearly constant. Based on this feature, the separation mode can be effectively regulated by forcing the divergent curve to pass through a specified control point (x_c, y_c). Further analysis reveals that, for each NPR, there exists a critical distance D_crit (the distance between the control point and the nozzle exit): when D > D_crit, the flow becomes asymmetric; when D ≤ D_crit, the flow remains nearly symmetric, the thrust vector angle approaches zero, and thrust deflection is effectively suppressed. The critical distance exhibits a non-monotonic variation with NPR: as NPR decreases, D_crit first increases and then decreases when NPR drops below 1.8. This trend is closely related to the transition of internal shock structures within the nozzle.

At an NPR of 2.0, the influence of divergent-section length L on the critical distance was further examined. The results show that, as L decreases, the influence of upstream flow non-uniformity becomes stronger, and to maintain symmetric separation, the control point must be placed closer to the exit. Accordingly, a quantitative model describing the relationship between the critical distance and the divergent-section length was established: D_crit = D_sym - A * exp[-k * (L - L_c)], where L_c is the characteristic length required to eliminate the upstream non-uniform effect, and Dsym represents the maximum symmetric separation position under uniform conditions.When L ≥ L_c, D_crit approaches D_sym; when L < L_c, D_crit decreases exponentially with L.

The findings reveal the interaction mechanisms among y_c, D_crit, NPR, and divergent-section length, and propose an empirical model applicable to separation suppression and thrust deflection control. This work provides valuable reference for the stability-oriented design of stealth propulsion systems in next-generation aircraft.

Presenting Author: mingxin Wang Northwestern Polytechnical University

Presenting Author Biography: I am a Ph.D. Candidate at Northwestern Polytechnical University, focusing on aero-engine exhaust systems. My research involves the design of serpentine nozzles and flow control technologies, with extensive experience in analyzing their aerodynamic performance.

Authors:

mingxin Wang Northwestern Polytechnical University
Li Zhou Northwestern Polytechnical University
Zhanxue Wang Northwestern Polytechnical University