There is a lot of mention of tourism, but I also see another important point: Ukrainians taking up jobs in, or migrating to the EU.
From the Wikipedia page on Ukrainians in Poland:
1.2 million Ukrainian citizens worked legally in Poland in 2016. 1.7 million short-term work registrations were issued to them in 2017 (an eightfold increase compared to 2013). Ukrainian workers stay in Poland on average 3-4 months.
The number of permanent residence permits increased from 5,375 in 2010 to 33,624 (14 September 2018), while the number of temporary residence permits increased from 7,415 to 132,099 over the same time period.
There is also the sizeable Ukrainian population that lives or works in Russia, plus all those who fled during the war. As of February 2018, 1.7 million had sought refuge in Russia, many ending up taking permanent residence there. In total, there is just shy of 6 million Ukrainians in Russia of all reasons, up from 2 million in 2010. Not only have those numbers increased, but direct flights and border crossings have been shut down in the wake of the conflict. This will also help push up the passenger numbers.
As for tourism, it is the same story we see many other places. Overcrowding of traditional holiday venues because of the influx of Chinese and Indians, while terrorism and unrest has shut down resorts in Turkey and North Africa. Inevitably, prices go up and the cheaper tourists are pushed towards developing venues. The entire tourist thing could collapse from one year to the next if North Africa and Turkey stabilize.