Only if the spell says so
There are spells that can direct multiple attacks against the same target, but they use different language. Instead of saying to choose a number of targets, such a spell says that it creates a number of attacks (or strikes, or missiles, etc.) and then requires you to choose a target for each attack. Some spells that use this language are magic missile, scorching ray, and eldritch blast. For example, here is the language used for magic missile:
You create three glowing darts of magical force. Each dart hits a creature of your choice that you can see within range. A dart deals 1d4 + 1 force damage to its target. The darts all strike simultaneously, and you can direct them to hit one creature or several.
Note that the spell is worded in such a way that the same number of darts is created regardless of how many distinct targets you choose. The last clause makes it explicit that multiple darts can be directed at the same target, but even the first 2 sentences by themselves are sufficient to establish this.
As for your specific examples:
Neither steel wind strike nor acid splash can attack the same creature twice
The targeting clause for steel wind strike is:
Choose up to five creatures you can see within range. Make a melee spell attack against each target.
You choose the targets first, and then you get to make one attack against each chosen target. If you only choose a single target, you only get to make a single attack. The same logic applies to acid splash: if you target a single creature, then you are not targeting 2 creatures. Acid only splashes each target once.
Any other interpretation leads to absurd results
If you rule that effects like these can choose the same target multiple times in order to stack multiple effects on that target, that would make the Hunter Ranger's Whirlwind Attack infinitely powerful:
You can use your action to make a melee attack against any number of creatures within 5 feet of you, with a separate attack roll for each target.
Just choose to attack the same creature 1000 times. It says any number, right? Even better, choose every creature in range 1000 times and instantly kill them all. Clearly this is not a reasonable ruling. There are certain to be other ridiculous edge cases like this if you allow multiple targeting of the same creature in this way.