Nonlinear Aerodynamic Responses of Flight Control Surfaces to Thrust Reverser Jet-Induced Flow Interference

Abstract

Numerical simulations were performed using the RANS (Reynolds-averaged Navier–Stokes) approach to analyze the flow field around an aircraft during the landing rollout phase with thrust reversers deployed. The objective was to characterize the flow structure modifications induced by the reversed jet flow and to assess its impact on the aerodynamic performance of various control surfaces. The results demonstrate that the reverse jet flow introduces significant disturbances to the flow field, substantially altering the aerodynamic load distribution over the airframe and causing a marked reduction in overall lift. High-lift devices are particularly susceptible to these effects: the pressure distributions on both the leading-edge slats and trailing-edge flaps are severely disrupted, resulting in a notable degradation of their lift augmentation capabilities. The rudder retains a generally linear response characteristic, though a slight reduction in effectiveness is observed. In contrast, the elevator exhibits a pronounced asymmetry in control effectiveness, with significantly greater degradation under positive deflection compared to negative deflection. This study elucidates the complex interference mechanisms associated with thrust reverser-induced flows and provides valuable insights for the optimization of thrust reverser system design and the enhancement of flight control strategies during the landing phase. It further delivers the first quantitative evaluation of elevator response asymmetry and accompanying lift degradation caused by reverse jet plumes, supplying design-ready metrics for reverser integration.

1. Introduction

Thrust reversers serve as a critical deceleration system for large civil aircraft, playing an essential role during the landing rollout phase [1,2]. By redirecting the engine exhaust forward to generate reverse thrust, these devices effectively reduce the landing distance [3]. Compared to wheel braking systems, thrust reversers can provide effective braking even on wet or slippery runways, thereby enhancing landing safety under adverse weather conditions [4]. Among various configurations, cascade-type thrust reversers are widely adopted in high-bypass turbofan engines due to their compact structure and high reverse thrust efficiency [5,6].

In aircraft design, thrust reversers are typically developed and supplied independently by engine manufacturers, with a design focus primarily on engine performance. Consequently, limited attention has been given to the aerodynamic interactions between the reverse jet flow and the airframe [7,8,9]. However, during operation, thrust reverser flows can pose significant aerodynamic disturbances to surrounding aircraft components, particularly the control surfaces. These disturbances may alter the flow field around the aircraft, degrade control surface effectiveness, and increase flight control system complexity. In severe cases, such effects may lead to control surface failure, stall, hard landing, or runway excursion incidents [10]. Thus, ensuring aerodynamic compatibility between thrust reversers and control surfaces is a critical consideration in reverser system design.

Traditionally, wind tunnel testing has been employed to assess such compatibility [11,12,13]. However, wind tunnel tests are constrained by model scaling issues and measurement accuracy limitations, in addition to high costs and long development cycles, and there is an urgent need for experimental optimization using advanced simulation methods [14,15]. Moreover, they often fail to capture the full flow field characteristics. With the rapid advancement of computational fluid dynamics (CFD), integrated airframe–engine simulations of reverse flow have become increasingly feasible. Trapp et al. [16] employed CFD to simulate the reverse jet flow during the landing phase of a commercial aircraft and validated their results through wind tunnel experiments. Qian et al. [17] conducted numerical simulations to analyze the disturbed flow field with the reversers deployed. Zhang [18] incorporated CFD into the design process for reverse flow patterns and performed full-aircraft simulations. Hu et al. [19] studied the effects of thrust reverser flow on the rudder and spoilers through both numerical simulations and experimental validation. Although significant efforts have been made in the aerodynamic optimization of thrust reverser systems [20,21,22] and in analyzing their effects on engine inlet flow [23,24,25,26] and wing aerodynamics [27,28], studies addressing the nonlinear aerodynamic responses of flight control surfaces to thrust reverser jet interference remain limited. In-depth investigation of nonlinear phenomena such as flow separation, local stall, and abrupt changes in aerodynamic efficiency that occur on control surfaces under intense reverse jet flows remains insufficient.

To address this gap, the present study investigates a twin-engine commercial aircraft using a fully integrated CFD model that includes both airframe and propulsion systems. The aerodynamic characteristics of the reverse jet flow and its influence on the flow field structure and key control surfaces are systematically analyzed with particular emphasis on nonlinear response mechanisms. Special attention is given to the spatial distribution of reverse flow, its interference mechanisms on high-lift devices, and its effects on rudder and elevator effectiveness. The findings provide theoretical support for optimizing thrust reverser design and refining flight control laws. Compared to earlier investigations that either isolated the nozzle plume or focused on a single lifting surface, the present work contributes in three specific ways: (i) it establishes a non-dimensional linkage between reverse jet momentum and lift system degradation; (ii) it reveals a previously unreported sign-dependent nonlinearity in elevator response to thrust reverser plumes; and (iii) it couples aerodynamic and thermal fields to highlight potential hot-spot formation on high-lift devices. These advances lay a physics-based foundation for subsequent jet angle optimization studies and adaptive control law development.

2. Numerical Method and Case Validation

The flow field was solved using the commercial CFD software STAR-CCM+ 2019 [29]. The governing equations are the three-dimensional compressible RANS equations in Cartesian coordinates, expressed in integral conservation form [30] as Equation (1):

$${\displaystyle \frac{\partial }{\partial t}}\iiint QdV+\iint f\cdot ndS=0$$

(1)

where $V$ is the control volume, $S$ is the surface area of the control volume, $Q$ is the vector of conserved variables, $f$ represents the net flux vector—including both inviscid and viscous fluxes through the surface $S$, and $n$ denotes the unit outward normal vector to the surface.

A fully implicit time integration scheme, known for its numerical stability, was employed for time discretization, while a second-order upwind scheme was adopted for spatial discretization. Considering the strong convection characteristics of the thrust reverser flow field, the $k-\omega SST$ turbulence model [31] was used. This model is well-suited for simulating flows in adverse pressure gradients and separated regions, and includes cross-diffusion terms to ensure accuracy near both the wall and the far field.

The boundary conditions used in the simulation are defined as follows: The outer boundary of the computational domain is a hemispherical far-field, with freestream boundary conditions specifying static temperature, static pressure, Mach number, and flow direction. The ground surface is modeled as a no-slip moving wall with a velocity equal in magnitude and direction to the freestream. The aircraft surfaces—including fuselage, wings, nacelles (inner and outer), horizontal and vertical stabilizers, and high-lift devices—are all defined as no-slip wall boundaries. The engine bypass, core nozzles, and thrust reverser exits are set as stagnation inlet boundaries, where total pressure, total temperature, and flow direction are specified. The flow direction at the thrust reverser exits forms specific angles with respect to the axial, circumferential, and radial directions of the exit boundary. The bypass and core nozzles have flow directions aligned with the boundary normal. The engine inlet is defined as a pressure outlet boundary condition, where static pressure, flow direction, and static temperature are specified at the inlet. The pressure is iteratively adjusted to match the target mass flow rate.

The present simulation represents a maximum-reverse-thrust landing-roll scenario. To ensure reproducibility while respecting confidentiality constraints, the following key non-dimensional parameters are provided: (i) the cascade exits are deflected ≈138° from the engine axis in the polar direction and ≈20° outward in azimuth, typical of current cascade-type thrust reversers; (ii) the nozzle-to-free-stream total-pressure ratio is ≈1.6 and the corresponding total-temperature ratio is ≈1.14; (iii) the reverse jet mass flow rate is about 0.87 times the free-stream mass flux through the exit area, while the fan inlet mass flow rate is ≈4% higher than the jet mass flow, reflecting bypass duct losses.

To verify the reliability of the numerical method, simulations were conducted based on the NAL-AERO-02-01 TPS (Turbine Powered Simulator) wind tunnel model developed by the National Aerospace Laboratory of Japan [32]. The external geometry of the model is shown in Figure 1 and can be generated by rotating the meridional profile 360 degrees about the center axis. Based on the TPS engine configuration, unstructured meshes with scales of 0.9 million, 1.8 million, and 3.6 million elements were generated. The surface mesh corresponding to the 1.8 million case is shown in Figure 2.

The maximum diameter of the TPS model is 0.51163 m, and the selected Case 17 operating conditions are listed in

Table 1. Computational setup of the TPS engine.

Case	$\mathit{M}\mathit{a}$	${\mathit{m}}_{\mathit{t}\mathit{a}\mathit{r}\mathit{g}\mathit{e}\mathit{t}}$	${\mathit{p}}_{0\mathit{f}}/{\mathit{p}}_{0\mathit{\infty }}$	${\mathit{T}}_{0\mathit{f}}/{\mathit{T}}_{0\mathit{\infty }}$	${\mathit{p}}_{0\mathit{c}}/{\mathit{p}}_{0\mathit{\infty }}$	${\mathit{T}}_{0\mathit{c}}/{\mathit{T}}_{0\mathit{\infty }}$
17	0.801	12.68 kg/s	1.43035	1.13299	1.12451	0.60995

where $p_{0f(c)}/p_{0\infty }$ represents the total pressure ratio and $T_{0f(c)}/T_{0\infty }$ represents the total temperature ratio. The total pressure and total temperature can be determined based on these two parameters.

.

Figure 3 presents a comparison between the numerically simulated surface pressure coefficient distribution (ranging from 0.9 to 3.6 million cells) and wind tunnel experimental data (Exp) for the TPS engine model. In the figure, the horizontal axis X denotes the actual axial dimension, and Geo refers to the geometric profile of the engine. As shown, the computed pressure coefficient distributions on the surfaces of the nacelle inlet, outer cowl, and core fairing wall of the 1.8 million-cell case agree well with the experimental results, thereby validating the reliability of the numerical simulation method. Figure 4 shows the iteration–residual convergence curves, indicating good convergence behavior.

3. Effects of Thrust Reverser Flow on Flow Field Structure

3.1. Physical Model and Mesh Generation

The research object is a type of civil aircraft featuring a full-configuration wing–body–tail–nacelle layout in a landing configuration. The aircraft model is symmetrical about the central longitudinal plane, with one engine mounted on each wing. The main components of the configuration include the fuselage, wings, horizontal and vertical stabilizers, nacelles, high-lift devices, and landing gear. Cascade-type thrust reversers are installed at the bypass nozzle exits of the engines to deflect the bypass airflow and generate reverse thrust. The thrust reverser cascades are arranged circumferentially around the engine nacelles. In the modeling process, the structural details of the cascades were simplified by neglecting the internal flow passages. Instead, an equivalent pressure outlet surface with a specified exhaust direction was used to represent the flow deflection effect of the cascade structure [33]. The aircraft and engine physical model is shown in Figure 5.

A hemispherical external flow domain was established around the aircraft, with a radius set to 20 times the aircraft’s length. The bottom surface of the computational domain was defined as the ground plane. A polyhedral unstructured mesh was employed, with local mesh refinement applied in the vicinity of the thrust reverser devices. A total of 15 boundary layer prism layers were generated along wall surfaces, with the height of the first near-wall cell satisfying the $Y^{+}\le 1$ criterion. The overall mesh contained approximately 18 million cells. The mesh distribution in the region near the fuselage and the engine, high-lift devices, rudder, and elevator is shown in Figure 6, Figure 7, Figure 8 and Figure 9.

3.2. Flow Field Characteristics Before and After Thrust Reverser Deployment

Considering that thrust reversers are typically deployed during the landing rollout phase, the freestream Mach number was set to $M{a}_{\infty }=0.2$ $T_{\infty }=288.15 \mathrm{K}$. Taking into account flow losses within the bypass duct, the fan inlet mass flow rate was set slightly higher than the reverse jet exhaust mass flow rate, thereby approximating the actual operating condition of the engine during thrust reversal.

The flow field characteristics differ significantly between the stowed and deployed states of the thrust reverser. As shown in Figure 10, when the thrust reverser is stowed, the airflow smoothly passes along the fuselage surface, with streamlines distributed in an orderly manner. A portion of the flow is captured by the engine inlets, forming a converging bundle of streamlines directed toward the engines. This results in a typical flow tube contraction ahead of the inlet, accompanied by an acceleration trend in the velocity field. Figure 11 illustrates the isosurface distribution of total temperature at 293 K under the stowed condition, representing the spatial structure of the high-temperature core flow exhausted from the engine.

When the thrust reverser is deployed, the flow structure undergoes dramatic changes. Figure 12 presents the velocity streamline distribution of the reverse jet flow, which reveals that the reverse jets are expelled obliquely forward and subsequently impeded by the relative incoming flow, resulting in gradual velocity reduction and eventual downstream flow deflection. This process generates large-scale complex vortex structures around the engine nacelle. Furthermore, the temperature of the reverse jet flow significantly exceeds that of the freestream flow. The total temperature isosurfaces corresponding to the reverse jet flow in Figure 13 provide a clearer representation of the spatial distribution characteristics of the reverse flow field. The reverse jet flow also induces aerodynamic interference effects on various aircraft components. A portion of the flow travels axially along the fuselage surface, with high-temperature reverse jet flow being channeled through the leading-edge slats, thereby creating elevated temperature flow field regions that envelop the main wing. These flows cause disturbances to the boundary layer flow and consequently affect the aircraft’s lift characteristics. Additionally, a portion of the reverse jet flow deflects upward and subsequently flows over the aircraft’s aft section, generating aerodynamic load interference on the elevator and rudder surfaces, which may potentially compromise the aerodynamic performance of these control surfaces.

Figure 14, Figure 15, Figure 16 and Figure 17 provide a more intuitive visualization of the aerodynamic and thermal effects of thrust reverser deployment on the aircraft surface through contours of pressure coefficient and temperature distribution. The unit is Kelvins. When the thrust reversers are stowed, the aircraft exhibits a typical flight-state pressure distribution: a pronounced low-pressure region forms near the leading edge of the wing, with low pressure maintained on the upper surface and relatively higher pressure on the lower surface, thereby generating normal lift through this pressure differential. However, once the thrust reversers are deployed, the low-pressure region on the upper wing surface diminishes. High-pressure zones induced by reverse jet impingement appear near the engine nacelles and wing roots. On the lower surfaces of the wings and flaps, the pressure changes are more intense. The deflected reverse jet forms a negative pressure region downstream, causing a substantial portion of the originally high-pressure area to become low-pressure, which leads to a significant drop in the overall lift coefficient, from 2.95 to 0.84.

In addition, the thermal effects of the thrust reverser flow on the aircraft surface are even more pronounced. Upon deployment, the deflection and diffusion of the reverse flow, along with its interference with the high-temperature core jet, result in continuous high-temperature regions on the wing and high-lift devices. The reverse flow traveling along the fuselage also impinges on the vertical tail, horizontal tail, rudder, and elevator, causing their surface temperatures to rise.

The analysis indicates that the deployment of thrust reversers introduces significant aerodynamic interference to the main components of the aircraft. Due to the strong disturbance and wide spatial diffusion of the reverse jet flow, its influence is not limited to the area surrounding the nacelles but extends to various control surfaces across the airframe. During the landing phase, the aerodynamic performance of critical control surfaces—such as high-lift devices, the rudder, and the elevator—is directly linked to the aircraft’s controllability and flight safety. Therefore, it is essential to further investigate the effects of thrust reverser flow on the aerodynamic characteristics of these typical control surfaces.

4. Effects of Thrust Reverser Flow on the Aerodynamic Performance of Typical Control Surfaces

To comprehensively evaluate the impact of thrust reverser deployment on the performance of typical control surfaces, this section focuses on a comparative analysis of the aerodynamic characteristics of high-lift devices and the variation in control effectiveness of the rudder and elevator under both stowed and deployed conditions.

4.1. Effects of Thrust Reverser Flow on High-Lift Devices

Figure 18, Figure 19, Figure 20 and Figure 21 illustrate the surface pressure coefficient and temperature distribution characteristics of the leading-edge slats before and after thrust reverser deployment. From the pressure coefficient distribution, it can be observed that, after the deployment of the thrust reversers, a localized high-pressure region forms near the inboard section of the slat due to the direct impingement of the reverse jet. Meanwhile, a distinct low-pressure wake region develops on the windward side near the nacelle, where the reverse jet induces a substantial pressure drop. On the leeward side, the vortex structure becomes more complex, characterized by alternating high- and low-pressure regions, which disrupt the original smooth pressure gradient.

In terms of temperature distribution, the high-temperature reverse flow directly impacts the windward surface of the leading-edge slat after deployment, resulting in a surface temperature rise near the nacelle and forming a concentrated high-temperature region. Although the inboard section of the leeward side is less affected by direct impingement, a channel effect between the outboard slat and the wing facilitates the spanwise diffusion of high-temperature flow into the outer region, thereby producing a broader high-temperature area.

The combined effect of these altered pressure and temperature fields significantly weakens the lift-enhancing capability of the leading-edge slats and contributes to the overall reduction in the aircraft’s lift coefficient.

Figure 22 and Figure 23 present a comparison of the pressure coefficient and temperature contours on the lower surface of the flap before and after thrust reverser deployment. When the thrust reversers are stowed, the lower surface of the flap exhibits a typical high-pressure distribution, effectively contributing to lift generation. After deployment, the forward-directed reverse jet induces a low-pressure wake region downstream, causing the pressure on the flap’s lower surface to shift from positive to negative, thereby resulting in a loss of lift.

The temperature distribution changes are even more pronounced. In the stowed condition, the flap surface temperature is close to that of the freestream. However, once the thrust reversers are deployed, the flap is directly impacted by the reverse jet, leading to a surface temperature rise. More significantly, the deflection and diffusion of the reverse flow disturb the high-temperature core jet, causing it to deviate laterally from its original axial direction. This redirected hot flow impinges on the outer sections of the flap’s lower surface, leading to a broader area of elevated temperature, with local maxima reaching up to 450 K. As a result, the flap’s lower surface is subject to intensified thermal loads, and it is necessary to implement appropriate thermal protection and structural reinforcement in the affected regions.

4.2. Effects of Thrust Reverser Flow on the Rudder

As shown in Figure 24, the yawing moment coefficient slightly decreases after the thrust reversers are deployed. However, its variation with rudder deflection angle remains generally consistent with the stowed condition, exhibiting a well-maintained linear relationship. This indicates that the aerodynamic performance of the rudder is not fundamentally altered. Figure 25 shows the pressure coefficient distributions along cross-sections near the fuselage for rudder deflection angles of 20° and 30°, comparing the flow conditions with and without thrust reverser deployment. At a 20° deflection angle, thrust reverser activation leads to a significant reduction in peak pressure on both sides of the rudder, resulting in a smaller pressure differential and a corresponding loss in control effectiveness. At 30°, although a slight increase in peak pressure is observed on the upper surface, a substantial drop on the lower surface still leads to an overall reduction in rudder effectiveness.

Figure 26 and Figure 27 further illustrate the interference mechanism through pressure coefficient contours and streamline distributions. After thrust reverser deployment, a low-pressure jet is deflected upward and flows over the root region of the vertical tail, altering the pressure field around the rudder. This results in a reduced pressure differential across the rudder surfaces, effectively diminishing the rudder’s active area and thus weakening its ability to generate yawing moment.

4.3. Effects of Thrust Reverser Flow on the Elevator

As shown in the pitching moment coefficient curve (Figure 28), the deployment of the thrust reverser results in an overall upward shift in the curve, accompanied by a distinct asymmetry between the positive and negative deflection ranges. In the negative deflection range, the slope of the curve remains relatively unchanged, indicating stable elevator effectiveness. In contrast, in the positive deflection range, the slope of the pitching moment curve gradually decreases with increasing deflection angle after thrust reverser deployment, reflecting a progressive loss of elevator effectiveness.

Figure 29 presents the pressure coefficient distributions along cross-sections near the fuselage for elevator deflection angles of −15° and 15°, comparing the cases with and without thrust reverser deployment. A clear contrast is observed between the two conditions: in the positive deflection case, thrust reverser activation causes a significantly greater loss in pressure differential than in the negative deflection case. This asymmetry originates from the relative positioning between the reverse jet and the elevator. Under positive deflection (elevator deflected downward), the lower surface of the elevator is directly impinged by the low-pressure reverse jet, leading to a pronounced reduction in pressure differential. In the case of negative deflection (elevator deflected upward), the control surface avoids the core region of the reverse jet and thus experiences comparatively weaker disturbance [34,35,36].

Figure 30 and Figure 31, which show pressure coefficient contours and streamline distributions, further illustrate the underlying mechanism. When the elevator is negatively deflected, the reverse jet primarily flows beneath the control surface and has limited influence on the high-pressure region on the upper surface, resulting in a relatively mild disturbance. In contrast, under positive deflection, the elevator’s lower surface lies within the low-pressure wake zone induced by the reverse jet. The direct interaction between the reverse flow and the lower surface eliminates the high-pressure region, leading to a significant reduction in control effectiveness [37,38].

5. Conclusion

A numerical simulation was conducted to investigate the flow field structure before and after thrust reverser deployment during the aircraft landing rollout, as well as the aerodynamic effects of the reverse jet on typical control surfaces. The main conclusions are as follows:

(1)

The deployment of thrust reversers significantly alters the flow field structure. The reverse jet is ejected obliquely forward, then bends downstream under the influence of the incoming flow, forming a complex vortex system. Part of the jet flows axially along the fuselage surface, creating a high-temperature region surrounding the main wing, which results in a sharp reduction in the overall lift coefficient from 2.95 to 0.84. Another portion of the reverse flow rises upward toward the tail, disturbing multiple control surfaces.

(2)

The high-lift devices are most severely affected by the reverse jet. A low-pressure wake region forms near the inboard leading-edge slat where the reverse jet impinges, and vortex structures on the leeward side become disorganized. On the flap’s lower surface, a large region transitions from high pressure to low pressure, severely degrading lift augmentation. Additionally, the direct impact of the reverse jet and its interference with the core jet cause a substantial temperature rise on the surfaces of the high-lift devices, with local temperatures reaching up to 450 K, posing potential risks to structural integrity.

(3)

The rudder maintains an approximately linear yawing moment characteristic, though with a slight effectiveness reduction. The upward-deflected reverse jet induces a disturbed flow field around the root of the vertical tail, reducing the pressure differential across the rudder surfaces. This effect is equivalent to a reduction in the rudder’s effective area, though the loss in control authority remains relatively minor.

(4)

The elevator exhibits a pronounced asymmetric response, with significantly different levels of effectiveness loss under positive and negative deflections. Under negative deflection, elevator effectiveness remains relatively stable. In contrast, positive deflection leads to substantial performance degradation, as the lower surface of the elevator is directly exposed to the low-pressure wake region generated by the reverse jet, experiencing stronger aerodynamic interference.

These findings suggest that the design of thrust reverser systems must fully account for their complex aerodynamic interactions with various aircraft components. In practical engineering applications, the jet angle of the reverser outlet should be optimized to mitigate adverse effects on control surfaces. Additionally, flight control laws should incorporate compensation strategies to account for changes in aerodynamic characteristics induced by the reverse flow, thereby ensuring flight safety and controllability during the landing deceleration phase. Furthermore, the numerical results indicate that limiting the positive angle of attack of the elevator to within 15° during reverse thrust can control the pitch moment slope decay to less than 10%, providing a direct angle reference for flight control law pre-bias and gain scheduling.