Chapter 1495 Hall Effect

Chapter 1495 Hall Effect

"The first round of tests begins. The incoming Mach number is 1.5, the angle of attack is +5°, the magnetic interaction number is 0.29, and the duration is 100 milliseconds..."

"..."

Chang Haonan's eyes were fixed on the jumping data stream on the main screen, and his voice spread throughout the wind tunnel laboratory through the loudspeaker.

As the command was given, a low roar was heard from outside the wind tunnel, like thunder rolling in the distance. The compressed air passed through the test section at a speed that broke the sound barrier, forming a vaguely visible milky white turbulence on the monitoring screen.

The slender silver body of the Lingxiao-1 modified vehicle emits faint high-frequency vibrations in the high-speed airflow, and the honeycomb-shaped reinforced ceramic insulation tiles covering the surface emit a cold metallic luster under strong light.

"The incoming flow velocity is stable, M1.52, total temperature 530K, and the incoming flow pressure is 5.2kPa."

Li Min quickly reported the reading, her voice trembling slightly due to nervousness.

On the several display screens in front of her, the data streams sent back from nearly a hundred sensors were displayed in real time. The young female engineer's fingers flew on the keyboard, constantly adjusting the acquisition parameters displayed on the large screen in front of her, and the strands of hair on her forehead were soaked with sweat.

At the same time, more than a dozen pairs of eyes in the control room were focused on the front at the same time.

The first set of data appeared quickly: gas conductivity 3.57mho/m, outlet pressure 2.52Mpa, temperature 620K…

These numbers are displayed sequentially on a huge LCD screen and automatically recorded in the experimental database. At the same time, they are simultaneously updated by a dedicated person on a physical recording board at the back of the control room - this is a habit that Chang Haonan insists on keeping. He believes that physical media, such as whiteboards and paper books, are more effective than electronic devices when inspiration is needed.

"No potential difference detected."

Wang Rui, the engineer in charge of monitoring the electrodes, reported with a hint of disappointment. He pushed his glasses up on the bridge of his nose and confirmed the flat waveform on the oscilloscope again.

"As expected." Xing Muchun patted his shoulder to reassure him: "The degree of ionization is too low at this speed. Even the ionization seeds have not been fully activated."

Chang Haonan also added: "Moreover, the conductivity data is better than our expectations, which is a good sign."

While speaking, his eyes never left the screen.

He noticed that the pressure distribution on the third slope of the inlet was highly consistent with the numerical simulation results, which showed that the newly designed shock wave control system was working properly: "Back up the data and prepare for the second round of tests, Mach number 3.0."

His voice was calm as he gave the order, as if he had foreseen the outcome.

The wind tunnel was started for the second time, and after this ignition, the roar became noticeably louder, as if even the gas pipelines began to vibrate slightly.

On the main screen, the stress curve begins to climb but remains within a safe range.

In the monitoring footage, you can clearly see the bow shock wave generated at the leading edge of the inlet, which separates the supersonic airflow like a transparent barrier.

However, compared to before, the surface of the engine is now covered with a faint glow.

"Gas conductivity 9.85mho/m."

This number is 12% higher than theoretical predictions and is very close to producing a measurable Hall current.

"Combustion chamber parameters?" Chang Haonan asked, signaling the operator to zoom in on the real-time infrared image inside the combustion chamber.

"Outlet pressure 2.83M[a, temperature 920K." Li Min answered quickly, her eyes switching rapidly between multiple display screens, "Still no power generation detected, but the plasma luminescence intensity has increased." She pointed to the faint lavender halo visible inside the combustion chamber on the screen.

Xing Muchun walked over to Chang Haonan and said, "The conductivity growth curve is better than we expected. It seems that the newly designed ionized seed atomization system is indeed effective."

Chang Haonan nodded slightly and glanced at the structural stress monitoring data.

The Lingxiao-1 modified aircraft is only a technology verification aircraft used for temporary testing, so the original Lingxiao-1 structure has not been extensively modified. It simply adds two MHD-related structures.

The aspect ratio is nearly 20:1, and there is only one mounting frame on the outside to provide support, which will inevitably affect the structural strength.

Fortunately, the redundancy is high enough and all values ​​are still within the green safety range.

"Prepare for the third round, Mach 4.5." He turned to the entire team, "This time we need to focus on the potential difference and current waveform between the electrodes, and increase the sampling rate to 1kHz."

1000 samples per second may sound very dense, but considering that the entire test process only takes 0.1 seconds, it is equivalent to only 100 data points.

Under lighting at a specific angle, you can see that the surface of the Lingxiao-1 modified fuselage has subtle wavy deformations - this is the piezoelectric actuator actively suppressing structural vibrations.

"The shock wave position is stable, and the air inlet is working normally." Li Min stared at the screen, trying his best to suppress the urge to raise his voice. "The gas conductivity is 21.57 mho/m, which has reached the theoretically predicted MHD activation threshold!"

The control room suddenly became quiet and everyone held their breath.

A 0.1 second test can be completed in the blink of an eye, but the subsequent data collection and analysis process will take some time.

After a few long seconds, the curve representing the potential difference between the electrodes on the main interface of the data acquisition system was still a straight green line.

Only someone with very sharp eyesight could notice that tiny glitches were beginning to appear near the baseline.

Li Min felt that his right hand, which was holding the mouse, had begun to sweat.

"Academician Chang, do you want to arrange an examination after this test?"

This question came out of nowhere, so much so that it felt like a red herring:

"I mean, could it be that the active vibration suppression system had an effect on the results?"

As a result, at this moment, a new green indicator light suddenly lit up, accompanied by a crisp beeping sound.

"The potential difference is detected at both ends of the electrode!" Wang Rui almost jumped up from his seat. His glasses slid to the tip of his nose due to the violent movement, and were pushed back the next moment. "±150V! Inductive current 12.5A."

His voice was a little distorted, but fortunately it was still clear.

A deliberately suppressed cheer broke out in the control room, but Chang Haonan quickly raised his hand to signal for everyone to be quiet:

“Enthalpy extraction rate and power generation efficiency?”

Li Min had already forgotten the question he had just asked, and after quickly calculating, he replied:

“0.08% and 11.6%.” Her eyes lit up. “Although not high, it proves that the principle is feasible!”

Then he pulled up the energy balance chart and said, "Look at this. The MHD channel absorbs about 0.3% of the incoming kinetic energy. This energy loss actually makes the inlet shock wave system more stable."

She didn't say anything more, but it was obvious that this result was highly consistent with Chang Haonan's previous design.

"Continue the test, Mach number 6.0." The latter paused, "But before that, first give the support frame a comprehensive inspection, especially the leading edge fixing point."

Over the next few hours, the team completed four sets of tests at Mach numbers 6.0, 7.5, 9.0 and 10.5.

As the speed increases, the roar of the wind tunnel becomes more and more like the roar of a wild beast, and the temperature in the control room gradually rises due to the equipment running at full capacity.

Technicians had to turn on backup air conditioning, but the cool air was quickly offset by the heat emitted by the electronic equipment.

"Mach number 6.0, gas conductivity 58.34 mho/m... enthalpy extraction rate 0.31%, power generation efficiency 14.2%..." On the display screen, the contour map representing the plasma density has turned bright red.

"Mach number 7.5, gas conductivity 89.72 mho/m... enthalpy extraction rate 0.53%, power generation efficiency 15.7%..." This time it was Xing Muchun who reported the data. He stood behind Li Min, holding a cup of cold strong tea in his hand. "The thrust of the power generation channel reached 147N, which began to have a measurable impact on the overall aerodynamic characteristics."

Everyone was delighted and seemed ready for the final success.

However, something unexpected happened.

When the test reached Mach 9.0, things started to get weird.

"The gas conductivity is 147.65 mho/m, but..." Li Min frowned. She checked the data again and again. "The enthalpy extraction rate is 0.55%, and the power generation efficiency is 14.9%... This is not right. The conductivity is nearly doubled, but the power generation has only increased by less than 5%."

Xing Muchun immediately noticed something unusual: "The power generation efficiency is starting to decline?"

He walked quickly to the main console and pulled up the data comparison chart of the previous tests: "Looking at this trend, after exceeding M7.5, the efficiency growth began to slow down."

Chang Haonan's eyes quickly switched between several sets of data. He noticed some more subtle changes, but it was impossible to summarize them into a pattern based on just one set of data.

He turned to the operator and said, "Continue at Mach 10.5, but monitor relevant safety parameters closely and be prepared to abort the test at any time."

The results of the top speed test were even more puzzling.

On the surveillance footage, it can be seen that several thermal insulation tiles on the surface of the "Lingxiao-1 Modified" began to fall off, and instantly turned into countless shining fragments in the high-speed airflow.

"The gas conductivity has soared to 215.43 mho/m, but the power generation has almost stagnated." Li Min's voice was full of confusion, "...The enthalpy extraction rate is 0.57%, and it is still rising, but the power generation efficiency has dropped sharply to 12.3%."

Xing Muchun shook his head and pulled up the current density distribution diagrams of different cross sections: "The conductivity is almost increasing exponentially, but the power generation is stagnant... There must be some important factor that we haven't considered."

Chang Haonan pondered for a moment, his eyes moving back and forth between the structural monitoring data and the performance curves: "Let's do a few sets of tests at intermediate speeds, Mach numbers 8.0, 8.5, 9.5 and 10.0." He turned to the team, "We need to locate the inflection point of this efficiency decline more accurately."

As more data is accumulated, the abnormal trend becomes more obvious. When the Mach number exceeds 8.5, although the gas conductivity continues to soar, the power generation efficiency and thrust begin to slowly decline. The most puzzling thing is that this decline is not linear, but occurs suddenly in a narrow speed range.

"Damn it, this doesn't fit the theoretical model at all." Wang Rui grabbed his hair, which had become a mess. "According to calculations, the MHD power generation should be proportional to the conductivity and the square of the velocity."

This young engineer has been working with Chang Haonan and Jiang Zonglin since joining the Institute of Mechanics. While he has had a smooth journey, he has also avoided many of the failures that are necessary in the scientific research process.

"I have an idea." Xing Muchun suddenly tapped the table with his fingers. "The diameter of Lingxiao-1 is too small, only 0.5 meters. At this scale, in addition to the axial direction, the radial end effect will also become very obvious."

As he spoke, he stood up and walked to the whiteboard, and drew a simple diagram on it:

“A return path current of half the circuit may be generated, thus interfering with the operation of the MHD generator.”

After the first person proposed the idea, everyone's thinking began to have a direction.

"It makes sense in theory." Chang Haonan was the first to give feedback, "but it's still a little off in terms of quantification..."

Then, there was another moment of silence.

A few minutes later, he finally took action again -

The test log was called up and the electric field line distribution diagram on the longitudinal section of the MHD generator flow channel was quickly drawn on the computer.

When the image was displayed on the big screen, everyone could see it clearly:

The current lines clearly deflect downstream and contract toward the center, forming a spiral twisting pattern.

"Hall effect!" Li Min was the first to capture the key.

"That's right." Chang Haonan walked slowly to the screen and pointed at the twisted field lines. "And it is also affected by the return path current caused by the end effect."

Then he used a laser pen to draw a track on the screen:

"Look here, the current lines are deflected near the wall, which not only reduces the effective power generation area, but also causes the plasma to form a rotating flow in the channel, further reducing the power generation efficiency."