Chapter 1687 Dual Variable Cycle Engine

"Academician Liu, President Qin, please look here." Song Fu pointed to the cloud map. "This is the flow field we reconstructed by combining the pressure sensor array."

"After the mode switch command was issued, during the first half of the period when the first-stage fan was locked and the mode selector valve began to operate, all core engine parameters, including speed, temperature, pressure, and flow, fluctuated within the normal envelope, indicating that there were no issues with the basic control logic and mechanism operation itself."

The cursor moved forward with the movement of his hand, and finally focused on the mode select valve (MSV) and the flow channel area behind it.

"The key turning point occurs when the mode selector valve opening θ reaches about 72%, which corresponds to an angle of about 13 degrees."

As Song Fu explained, the color blocks on the cloud map representing the airflow velocity changed. Near the entrance of the second duct, a low-speed recirculation area represented by dark blue appeared, which was quite eye-catching on the warm-toned map.

"At this point, the airflow from the first duct began to enter the second duct on a large scale. However, at the inlet of the second duct, a significant recirculation zone formed due to the drastic change in duct geometry and the abrupt turn in airflow direction. This recirculation zone caused significant mixing losses, corresponding to the sudden drop in intake efficiency we initially monitored."

The picture continued to evolve, and the value of the opening θ steadily increased under Song Fu's control.

"As the valve opening continues to increase, the situation worsens. When θ reaches 83%, more of the airflow from the first duct is forced into the second duct. However, due to the increased valve opening, the effective flow path through the valve changes from the designed convergent flow path to a complex shape that first expands and then contracts. This shape is not friendly to high-speed airflow, and the airflow's acceleration ability is severely weakened, causing the flow rate to decrease rather than increase..."

Song Fu switched to a real-time curve chart:

"Until θ=94%, the throat Mach number has dropped below 1, and the second outer duct is almost completely blocked. Our turbojet operating mode is set to start above M=1.8, so it is obviously impossible to switch normally in this situation."

"Therefore, when the mode selector valve is further opened to 100%, that is, the maximum 18 degrees, the airflow that had been introduced into the second outer duct is forced back to the first outer duct, resulting in insufficient intake air in the turbojet mode and the onset of surge."

After the introduction, he turned back to the two big men in the office.

But for some reason, I felt that the air pressure around me seemed a little low.

So he added:

"Thankfully, President Qin's judgment was quite accurate, and the intervention order was issued promptly and decisively. This allowed Unit 04 to avoid substantial damage from the core engine surge, thus protecting the precious prototype..."

These words were obviously meant to save face, but Qin Xiaoming waved his hand, indicating that Song Fu did not need to emphasize this part, and then directly concluded to Liu Yongquan:

"Mr. Liu, based on this 'blockage-backflow' mechanism, our current response strategy remains to prioritize reliable switching between medium- and low-bypass-ratio turbofans, allowing the aircraft to operate in the two most commonly used flight modes, subsonic cruise and supersonic cruise. On this basis, we will gradually adjust the matching relationship between the mode selector valve and the three flow passages, and collect as much data as possible during the switching process to turbojet mode."

As he spoke, he called up a project file on the computer in front of him and turned the screen to show it to Liu Yongquan.

"At the same time, we are also continuously collecting data on the boundary of switching to turbojet mode, trying to widen the safety margin by optimizing the control logic and fine-tuning the MSV action curve. See."

He pointed to a set of comparative data in the document:

"Through iterative optimization, the critical opening that triggers blockage of the second outer duct has been increased from 68% in the initial design to 94% in this test. The fluctuation range of engine operating parameters has also been significantly improved, proving that this general direction should be correct."

Although it seemed like he was announcing good news, when he said this, Qin Xiaoming's brows were locked in a habitual frown, and his voice lowered a bit:

"However, to completely avoid blockage and backflow in this last 6% opening range, I'm afraid it can't be solved by simply optimizing control parameters or modifying local flow channel shapes."

He scratched his head, revealing a rather distressed expression:

"My personal assessment is that the root of the problem may lie in the structural design of the variable geometry splitter ring itself... Its inherent geometric constraints and flow channel matching create bottlenecks when faced with such extreme flow regime transitions. It may require... more fundamental optimization, or even a redesign."

After these words were spoken, a brief silence fell in the office.

Qin Xiaoming, Song Fu and others could not hide the disappointment and pressure on their faces.

As the team mainly responsible for solving the problem, they have fallen at the same threshold many times in a row. You can imagine how they feel as they see the deadline approaching.

However, to their surprise, Liu Yongquan on the sofa not only did not show any anxiety or dissatisfaction, but a hint of...relaxation slowly emerged on his serious face.

"Yes," Liu Yongquan said calmly, even with a hint of approval. "Your description of the problem phenomenon is very clear. The fact that you were able to pinpoint such a complex transient flow problem to the core issue of 'blockage and backflow' in such a short time demonstrates the capabilities of your team and the value of your work..."

This affirmation made the others a little surprised, and their anxiety became even worse.

This doesn't seem like the right attitude to take towards a critical bottleneck issue.

Qin Xiaoming even went on to explain:

"General Liu, although the turbojet mode switch hasn't been successful yet, as I just reported, the switch between the two turbofan modes is already very mature and reliable. Based on the current situation, even if the turbojet mode cannot be activated temporarily, we can fully ensure that the Project 50 prototype in Shengjing will complete its maiden flight and major subsonic/supersonic envelope test flights as planned..."

Liu Yongquan didn't listen any further, but took out a thickly bound technical document from the briefcase at his feet.

The document cover does not have any fancy titles, only a simple project number and the word "Top Secret".

He stood up and handed the heavy document to Qin Xiaoming:

"check it out."

Qin Xiaoming took the document with suspicion and opened the first page.

What comes into view is a brand new three-dimensional structure diagram of the variable geometry diverter ring.

Just one glance and his breath stopped.

"This...this is..."

The more Qin Xiaoming looked, the more frightened he became.

This is completely different from the plan that the entire team has painstakingly designed and iterated countless times over the past year.

Although the idea is to enhance the adaptability of the flow channel and optimize the aerodynamic performance at extreme openings, the specific implementation path and detailed design are much bolder and more thorough than before, almost a subversive reconstruction of the original configuration!

Major adjustments have been made to the articulation method of the main blades and sub-blades, the motion trajectory of the spatial linkage mechanism, and even some load-bearing structures.

Qin Xiaoming suddenly looked up at Liu Yongquan, his eyes filled with shock and some instinctive doubts.

Such a major change is extremely risky and the cycle is difficult to predict.

He opened his mouth and was about to raise a question, but his eyes subconsciously swept to the designer's signature column at the bottom of the design document's first page.

The name that ranked first instantly made him swallow back all the questions and worries that were on the tip of his tongue.

Chang Haonan.

Seeing Qin Xiaoming's expression change instantly and then return to calmness and understanding, Liu Yongquan's smile deepened.

He walked to the window and said slowly:

"I came here this time at the request of Academician Chang... The root cause of the current problems facing the WS-25 is indeed the incompatibility of the diverter ring structure itself with extreme flow state transitions. This proposal, based on the latest theoretical breakthroughs, has fundamentally optimized the diverter ring structure. The goal is to solve all mode switching problems in one go, especially the flow field stability problem when switching to turbojet mode."

Qin Xiaoming opened his mouth several times in succession: "But...this..."

"I'll explain the specific principles to you later..." Liu Yongquan's voice suddenly stopped. "Ahem... maybe Academician Chang will have to come and explain it in detail... But anyway, the core components of the new design are already in emergency production and are expected to be delivered to Fucheng in three days."

Qin Xiaoming's eyes lit up. "Understood! I'll immediately adjust the subsequent testing schedule for Prototype 03, prioritizing the replacement and testing of the new diverter ring assembly! Ensure the results are verified as soon as possible!"

"Yeah." Liu Yongquan nodded, expressing satisfaction with Qin Xiaoming's reaction speed.

But then he added, his tone meaningful, "Don't forget to notify the comrades in charge of engine interfaces and flight control at Shengfei Group's Project 50, and have them send their core team over to participate in subsequent test planning and data analysis."

Qin Xiaoming had just picked up the phone to arrange work, but his fingers paused on the keys when he heard the words.

He looked at Liu Yongquan with a hint of doubt in his eyes, which then quickly turned into realization.

"One step at a time..." Qin Xiaoming repeated in a low voice, completely understanding what the other party had meant.

It is not only necessary to solve the problems of the WS-25 engine itself, but also to optimize and verify the engine and aircraft as a whole system, pursuing the overall best, rather than just breakthroughs in some individual indicators.

"I'll contact Sheng Fei immediately!"